Pioneer RT-707 Capacitor Upgrade and Service
- Thread starter Trevor White
- Start date
Trevor White
Classic not Plastic
Cheers mate. Hope you get some value from it.
Trevor White
Classic not Plastic
OK everyone, now we move on to the Control Assembly, RWG-070. This board on my machine is actually an RWG-087-B, some more small variations on the theme.
This board is important in that it controls the various solenoids that control the brakes and the pinch roller tension etc.
Here is the Control Board mounted in the frame, from the top.
And again before I remove it from the machine. I have already removed the 4 self tapper screws that secure the mounting bracket/heat sink.
After gently lifting the board out you can get to it properly. To do this you do need to unbundle the wiring loom a bit, remove the fibreglass protective sheath and also one cable tie in my case.
Before removing the board from the bracket you need to undo the clamps from the two transistors and GENTLY pry them away from the bracket.
Once separated from the bracket you can remove the four screws securing the circuit board and carefully lift the bracket out of the way. Then the old thermal paste can be carefully cleaned off of both the bracket and the backs of the transistors. Be sure to carefully retain the two Mica shims that go between the bracket and the transistors.
Here is the board with its original complement of caps.
And now with a nice new set of Nichicons.
I have gone up at least one grade in voltage spec for these caps. Other than the 22uF C408, which is now 400V. Thanks to GPS16 for pointing out that this cap is critical to the life and health of the Solenoids, so I just went BIG. I have used Nichicon FG caps for the smaller values, but the big axial ones are VX series, and the 22uF 400V is a CA series.
Here is one of the transistors, remounted with new thermal paste and it's Mica shim.
And finally, securely remounted with the wiring loom back in place, and protected by it's fibreglass sheath. Do not forget to re-use that sheath, this alloy heat sink can get quite HOT.
And after hooking everything up, the old girl works still! Outstanding.
The caps used on the Control Assembly board were: (in no particular order)
1 x Nichicon FG 3.3uF 100V: http://www.mouser.com/ProductDetail/Nichicon/UFG2A3R3MDM
1 x Nichicon CA 22uF 400V: http://www.mouser.com/ProductDetail/Nichicon/UCA2G220MHD
1 x Nichicon FG 33uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H330MPM
1 x Nichicon FG 100uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H101MPM
1 x Nichicon VX 470uF 50V: http://www.mouser.com/ProductDetail/Nichicon/TVX1H471MCD
1 x Nichicon VX 1000uF 100V: http://www.mouser.com/ProductDetail/Nichicon/TVX2A102MDD
And here are the measured values of the old electrolytics:
3.3uF 50V - 3.96
22uF 35V - 28
33uF 35V - 40
100uF 35V - 119
470uF 35V - 578
1000uF 63V - 1119
That's it for today.
Cheers.
This board is important in that it controls the various solenoids that control the brakes and the pinch roller tension etc.
Here is the Control Board mounted in the frame, from the top.
And again before I remove it from the machine. I have already removed the 4 self tapper screws that secure the mounting bracket/heat sink.
After gently lifting the board out you can get to it properly. To do this you do need to unbundle the wiring loom a bit, remove the fibreglass protective sheath and also one cable tie in my case.
Before removing the board from the bracket you need to undo the clamps from the two transistors and GENTLY pry them away from the bracket.
Once separated from the bracket you can remove the four screws securing the circuit board and carefully lift the bracket out of the way. Then the old thermal paste can be carefully cleaned off of both the bracket and the backs of the transistors. Be sure to carefully retain the two Mica shims that go between the bracket and the transistors.
Here is the board with its original complement of caps.
And now with a nice new set of Nichicons.
I have gone up at least one grade in voltage spec for these caps. Other than the 22uF C408, which is now 400V. Thanks to GPS16 for pointing out that this cap is critical to the life and health of the Solenoids, so I just went BIG. I have used Nichicon FG caps for the smaller values, but the big axial ones are VX series, and the 22uF 400V is a CA series.
Here is one of the transistors, remounted with new thermal paste and it's Mica shim.
And finally, securely remounted with the wiring loom back in place, and protected by it's fibreglass sheath. Do not forget to re-use that sheath, this alloy heat sink can get quite HOT.
And after hooking everything up, the old girl works still! Outstanding.
The caps used on the Control Assembly board were: (in no particular order)
1 x Nichicon FG 3.3uF 100V: http://www.mouser.com/ProductDetail/Nichicon/UFG2A3R3MDM
1 x Nichicon CA 22uF 400V: http://www.mouser.com/ProductDetail/Nichicon/UCA2G220MHD
1 x Nichicon FG 33uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H330MPM
1 x Nichicon FG 100uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H101MPM
1 x Nichicon VX 470uF 50V: http://www.mouser.com/ProductDetail/Nichicon/TVX1H471MCD
1 x Nichicon VX 1000uF 100V: http://www.mouser.com/ProductDetail/Nichicon/TVX2A102MDD
And here are the measured values of the old electrolytics:
3.3uF 50V - 3.96
22uF 35V - 28
33uF 35V - 40
100uF 35V - 119
470uF 35V - 578
1000uF 63V - 1119
That's it for today.
Cheers.
evoroadster
Active Member
Once I finish with the rehab of my B77 2 track high speed I will be tackling my RT-707. These posts will be invaluable during the rebuild.
phantomrebel
Serial Tapist
Yes, it's rare to get such detailed information and fine pictures with a rebuild. Great job Trevor, thanks for taking the time to document everything!
Trevor White
Classic not Plastic
A nice surprise in the post yesterday 
This pair of tapes set me back a Kings Ransom (well almost). What I have here is the default Multi Frequency calibration tape- 21T204 that has tones recorded at 0dB and -10dB, which provides a near equivalent of the old Pioneer STD-154. I also bought a 4 frequency tape which provides 4 frequencies recorded with much longer duration than on the Multi Frequency tape.
The only possible issue I have come up against is that these tapes are recorded with a fluxivity of 250 nWb/m, whereas I now suspect that the original Pioneer STD-154 was actually 200 nWb/m. I have been able to learn though that the difference would be effectively less that 2dB in the calibration, so not really worth worrying about.
The 4 frequency tape was in the catalog as being recorded at 250 nWb/m and -10db. If you look closely at the label on the 4 frequency tape (Nr 233-673-382-126) you will see that the label actually says that this tape was recorded at 80 nWb/m and 0dB. When I first saw this I was in a panic, thinking that I had spent a fortune on a tape that did not match it's catalog description. Despite e-mails to MRL, who did not provide an adequate explanation at all, just a statement that all 7.5ips tapes are recorded at -10dB to avoid high frequency saturation.
I have now learned from elsewhere that a 250 nWb/m recording at -10db is exactly equivalent to an 80 nWb/m tape recorded at 0db. I was unaware of the relationship between the fluxivity level and the effective dB level. So despite my early concerns I think this tape should be fine.
I continue learning every day.
I will now attach long leaders to both ends of the test tapes and keep them wound 'tails out'.
Cheers for now.
This pair of tapes set me back a Kings Ransom (well almost). What I have here is the default Multi Frequency calibration tape- 21T204 that has tones recorded at 0dB and -10dB, which provides a near equivalent of the old Pioneer STD-154. I also bought a 4 frequency tape which provides 4 frequencies recorded with much longer duration than on the Multi Frequency tape.
The only possible issue I have come up against is that these tapes are recorded with a fluxivity of 250 nWb/m, whereas I now suspect that the original Pioneer STD-154 was actually 200 nWb/m. I have been able to learn though that the difference would be effectively less that 2dB in the calibration, so not really worth worrying about.
The 4 frequency tape was in the catalog as being recorded at 250 nWb/m and -10db. If you look closely at the label on the 4 frequency tape (Nr 233-673-382-126) you will see that the label actually says that this tape was recorded at 80 nWb/m and 0dB. When I first saw this I was in a panic, thinking that I had spent a fortune on a tape that did not match it's catalog description. Despite e-mails to MRL, who did not provide an adequate explanation at all, just a statement that all 7.5ips tapes are recorded at -10dB to avoid high frequency saturation.
I have now learned from elsewhere that a 250 nWb/m recording at -10db is exactly equivalent to an 80 nWb/m tape recorded at 0db. I was unaware of the relationship between the fluxivity level and the effective dB level. So despite my early concerns I think this tape should be fine.
I continue learning every day.
I will now attach long leaders to both ends of the test tapes and keep them wound 'tails out'.
Cheers for now.
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Hi Trevor,
I can't remember where I came across the info but I am sure I did. The 200nWb/m is the Std Tape level. The 250nWb/m is for the High Output formulations ie LH.
I still used the 250nWb/m tape and had to make a small deviation as the manuals for a Revox specify a 257nWb/m. So we all have to make compromises. I set my references so that the meter needle and the scale were just next to each other (allowing for parallax errors) and not OVER each other. It was the only way to keep the setting lower and repeatable.
It sounds silly to spend that much on a calibrated level and then set it ISH but the reference tape has still been used to set matching levels for each channel, verify the frequency response and most important of all set the Azimuth spot on!!!
For the speed I have been happy with the FG frequency setting. This is usually in the manual somewhere. So far this has brought the speed to within the spec. So as long as it is consistent then fine. On the C270 and A700 it is quartz locked anyway and can't be moved. The B77 needs to be checked but it is easy to do and again so far has not drifted much anyway. I feel if there is a marked shift then something is on it's way out and will need to be replaced (the pot seems to be favourite). (I always put in the extra U!!! Me English!!!)
Remember to leave the tapes OFF the machine until it has been demagnetised. If you do not have one then leave them in their wrapping until you do. If they go past anything which is magnetised there is a good chance that they will be partially erased AND RUINED.
There are plenty of opinions on this and other forums concerning this issue. I see it as "Insurance". A worthy expense and "worth it's weight in gold" when required. In this case though you may not know it is required until it is too late.
Keep us all posted we are all looking forward to your own "Cheshire Cat" moment when you have heard this beast "Sing"!!
Cheers.
GPS16
I can't remember where I came across the info but I am sure I did. The 200nWb/m is the Std Tape level. The 250nWb/m is for the High Output formulations ie LH.
I still used the 250nWb/m tape and had to make a small deviation as the manuals for a Revox specify a 257nWb/m. So we all have to make compromises. I set my references so that the meter needle and the scale were just next to each other (allowing for parallax errors) and not OVER each other. It was the only way to keep the setting lower and repeatable.
It sounds silly to spend that much on a calibrated level and then set it ISH but the reference tape has still been used to set matching levels for each channel, verify the frequency response and most important of all set the Azimuth spot on!!!
For the speed I have been happy with the FG frequency setting. This is usually in the manual somewhere. So far this has brought the speed to within the spec. So as long as it is consistent then fine. On the C270 and A700 it is quartz locked anyway and can't be moved. The B77 needs to be checked but it is easy to do and again so far has not drifted much anyway. I feel if there is a marked shift then something is on it's way out and will need to be replaced (the pot seems to be favourite). (I always put in the extra U!!! Me English!!!)
Remember to leave the tapes OFF the machine until it has been demagnetised. If you do not have one then leave them in their wrapping until you do. If they go past anything which is magnetised there is a good chance that they will be partially erased AND RUINED.
There are plenty of opinions on this and other forums concerning this issue. I see it as "Insurance". A worthy expense and "worth it's weight in gold" when required. In this case though you may not know it is required until it is too late.
Keep us all posted we are all looking forward to your own "Cheshire Cat" moment when you have heard this beast "Sing"!!
Cheers.
GPS16
Trevor White
Classic not Plastic
So, it has been quite wet and stormy here this afternoon which gave me a good reason to stay inside and have a go at another board in the machine.
This time the Function Switch Assembly RWS-052.
Here you can see the front of the machine with everything still in place.
To release this board you need to undo the two small screws holding down the direction switch assembly, and move it gently out of the way. Then there are 6 screws holding the Switch Assembly. 5 from the front and one long one around the side. You can see here that I have released the screws and very carefully removed the buttons. The buttons do pull off, but require some effort, just be careful. My machine already had a couple of dodgy buttons so I have already sourced some replacements which I will fit at the end of this job.
Then you can very carefully ease the switch assembly out of the machine. You will need to release two of the cable loom clamps to give you enough slack in the wiring. There is not a lot of slack here, but with care you can get the board just free of the machine to allow access to it.
Here is the board showing the original two caps. There is a .01uF ceramic and a 1000uF 35V electrolytic.
And here we are after replacing the two caps. I used a WIMA film cap to replace the little ceramic and a big Nichicon FG 1000uF 63V.
BEWARE, the legs of the original electrolytic were bent over hard on the foil side. I had a lot of trouble de-soldering the damned thing. Even when I was sure I had removed all the solder I still managed to damage the foil pads on the back of the board. Some careful repair was then in order before soldering in the new Nichicon. Everything went well though and I had no issues with bad joints or anything.
Whilst the board was accessible like this I also took the chance to properly clean the switches with Deoxit D5 and afterwards to re-lubricate the switch interlock mechanism which has a metal slide that is operated by the stop button and also by the auto-shutoff relay.
You can then carefully reverse the removal procedure. Once the assembly is back in place and screwed down don't forget to re-clamp the wiring loom with the wrap around clamps. Also, once the loom is all back in place, double check that the Molex connector from the Capstan Motor has not moved or been dislodged.
The caps used on the Function Switch Assembly board were:
1 x WIMA .01uF 100V: http://mouser.com/ProductDetail/WIMA/MKS2D021001A00JSSD
1 x Nichicon FG 1000uF 63V: http://www.mouser.com/ProductDetail/Nichicon/UFG1J102MHM
The measured values of the old caps were:
.01uF Ceramic - .016
1000uF 35V - 1089 (This cap was showing signs of bulging slightly at the bottom)
So that's it for this one, a bit awkward, but not too bad.
Cheers.
This time the Function Switch Assembly RWS-052.
Here you can see the front of the machine with everything still in place.
To release this board you need to undo the two small screws holding down the direction switch assembly, and move it gently out of the way. Then there are 6 screws holding the Switch Assembly. 5 from the front and one long one around the side. You can see here that I have released the screws and very carefully removed the buttons. The buttons do pull off, but require some effort, just be careful. My machine already had a couple of dodgy buttons so I have already sourced some replacements which I will fit at the end of this job.
Then you can very carefully ease the switch assembly out of the machine. You will need to release two of the cable loom clamps to give you enough slack in the wiring. There is not a lot of slack here, but with care you can get the board just free of the machine to allow access to it.
Here is the board showing the original two caps. There is a .01uF ceramic and a 1000uF 35V electrolytic.
And here we are after replacing the two caps. I used a WIMA film cap to replace the little ceramic and a big Nichicon FG 1000uF 63V.
BEWARE, the legs of the original electrolytic were bent over hard on the foil side. I had a lot of trouble de-soldering the damned thing. Even when I was sure I had removed all the solder I still managed to damage the foil pads on the back of the board. Some careful repair was then in order before soldering in the new Nichicon. Everything went well though and I had no issues with bad joints or anything.
Whilst the board was accessible like this I also took the chance to properly clean the switches with Deoxit D5 and afterwards to re-lubricate the switch interlock mechanism which has a metal slide that is operated by the stop button and also by the auto-shutoff relay.
You can then carefully reverse the removal procedure. Once the assembly is back in place and screwed down don't forget to re-clamp the wiring loom with the wrap around clamps. Also, once the loom is all back in place, double check that the Molex connector from the Capstan Motor has not moved or been dislodged.
The caps used on the Function Switch Assembly board were:
1 x WIMA .01uF 100V: http://mouser.com/ProductDetail/WIMA/MKS2D021001A00JSSD
1 x Nichicon FG 1000uF 63V: http://www.mouser.com/ProductDetail/Nichicon/UFG1J102MHM
The measured values of the old caps were:
.01uF Ceramic - .016
1000uF 35V - 1089 (This cap was showing signs of bulging slightly at the bottom)
So that's it for this one, a bit awkward, but not too bad.
Cheers.
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Trevor White
Classic not Plastic
Thank for that mate.
Yes, I have a lovely old Ferrograph Defluxer that I have had since I bought my first Sony in the 1970's. It still works well and gets regular use! Absolutely mandatory bit of kit in my view.
Needless to say I keep ALL tapes well away from this fellow when in use.
I also did not think twice about purchasing the test tapes. I have spent a small fortune on the RT-707 itself and some test gear, without the calibration tapes it would not be worth the effort.
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Trevor White
Classic not Plastic
Hi All,
So, in getting ready for the next step on this machine, the Mic Amplifier Assembly (RWF-065), I powered up the machine today and ran a long RCA cable from my work table to the normal inputs for the RT-707 on my Luxman amp. My intention was to listen to the 'Hiss' that this machine has, as my intention in re-capping the RWF-065 board was to also replace the sometimes noisy Hitachi transistors.
Now, once hooked up I listened through headphones with the volume well up. Initially I forgot to switch from 'Tape' to 'Source' and to my amazement in the background I could hear local AM radio stations!!! One in particular that transmits on 1323kHz. I was amazed, I can't say that I have ever noticed this before. If I switched to 'Source' then all I got was hiss, no sign of the RF interference. But back on 'Tape' (no tape loaded on the machine by the way) I could clearly make out the AM radio transmission. Admittedly I had to have the volume up pretty high, but once I had heard this I could pick it up at lower more normal volumes as well.
What on earth could be picking up AM radio frequencies in the machine??? Could it be something I have done so far? Or could it be the heads picking up the RF?
The machine is completely undressed at the moment with none of it's metal skin in place, it is completely open. So I imagine that some normal RF shielding provided by the metal case would be missing.
None the less, I am concerned that something is wrong. Can any of you offer any suggestion as to what may be going on?
Cheers.
EDIT: OK, so this may be a storm in a tea cup. I went to the trouble of redressing the machine. Screwed on all of its metal case parts. I then moved the machine back to it's normal location in my cabinets along with all my other stereo gear. It was then connected via short cables etc.
After that the RF interference was virtually undetectable. Now that I knew what I was listening for I could barely make out a bit of bass from the music at my Luxman's maximum volume. This would be why I had never noticed this before. It's interesting to note that the RF interference only showed up when in 'Tape' mode, I could not hear it when in 'Source'. Very strange.
Anyway, now I have to dismantle it all again.
So, in getting ready for the next step on this machine, the Mic Amplifier Assembly (RWF-065), I powered up the machine today and ran a long RCA cable from my work table to the normal inputs for the RT-707 on my Luxman amp. My intention was to listen to the 'Hiss' that this machine has, as my intention in re-capping the RWF-065 board was to also replace the sometimes noisy Hitachi transistors.
Now, once hooked up I listened through headphones with the volume well up. Initially I forgot to switch from 'Tape' to 'Source' and to my amazement in the background I could hear local AM radio stations!!! One in particular that transmits on 1323kHz. I was amazed, I can't say that I have ever noticed this before. If I switched to 'Source' then all I got was hiss, no sign of the RF interference. But back on 'Tape' (no tape loaded on the machine by the way) I could clearly make out the AM radio transmission. Admittedly I had to have the volume up pretty high, but once I had heard this I could pick it up at lower more normal volumes as well.
What on earth could be picking up AM radio frequencies in the machine??? Could it be something I have done so far? Or could it be the heads picking up the RF?
The machine is completely undressed at the moment with none of it's metal skin in place, it is completely open. So I imagine that some normal RF shielding provided by the metal case would be missing.
None the less, I am concerned that something is wrong. Can any of you offer any suggestion as to what may be going on?
Cheers.
EDIT: OK, so this may be a storm in a tea cup. I went to the trouble of redressing the machine. Screwed on all of its metal case parts. I then moved the machine back to it's normal location in my cabinets along with all my other stereo gear. It was then connected via short cables etc.
After that the RF interference was virtually undetectable. Now that I knew what I was listening for I could barely make out a bit of bass from the music at my Luxman's maximum volume. This would be why I had never noticed this before. It's interesting to note that the RF interference only showed up when in 'Tape' mode, I could not hear it when in 'Source'. Very strange.
Anyway, now I have to dismantle it all again.
Last edited:
Hi Trevor,
at this stage in the game I would not worry too much. This will only be a problem when all the covers are back in place. There are quite a few High Gain amplifiers in there, the head amp being one of them. If you had long leads in place you will have made an antenna of sorts (screened or not). You then have in place an RF pickup, any PN junction along the way could demodulate it. How far away are you from the nearest AM Transmitter? I can see Winter Hill from my bedroom window during the winter months when there are no leaves on the trees. That services the whole of the Northwest of the UK and is 250kW. The loop aerial on older portable TVs had no problems whatsoever.
So until all screws are back in place to give proper grounding and all covers are in place to give proper shielding I would keep "The Muppets" in mind and sing along with "Phenomenon - do doooo de do do!!!"
GPS16
at this stage in the game I would not worry too much. This will only be a problem when all the covers are back in place. There are quite a few High Gain amplifiers in there, the head amp being one of them. If you had long leads in place you will have made an antenna of sorts (screened or not). You then have in place an RF pickup, any PN junction along the way could demodulate it. How far away are you from the nearest AM Transmitter? I can see Winter Hill from my bedroom window during the winter months when there are no leaves on the trees. That services the whole of the Northwest of the UK and is 250kW. The loop aerial on older portable TVs had no problems whatsoever.
So until all screws are back in place to give proper grounding and all covers are in place to give proper shielding I would keep "The Muppets" in mind and sing along with "Phenomenon - do doooo de do do!!!"
GPS16
Trevor White
Classic not Plastic
Thanks mate, but after a bit of experimenting I have actually been able to fix the issue. The 707 no longer doubles as an AM receiver
Even when on my work table with all of its metal panels off, I have managed to get it perfectly quiet (other than a little 50Hz mains supply hum). All I did was run a ground wire across the room from the common ground post on my Luxman to the chassis ground on the 707. Viola! all fixed. Phew, what a relief.
Cheers.
Trevor White
Classic not Plastic
Hi All, here we go with another update.
This time I tackled the Microphone Amplifier Board (RWF-065). This board contains the Mic and Line input pot's. My intention was to re-cap and also replace the old Hitachi transistors in an attempt to reduce 'Hiss'.
Here is the RWF-065 board in situ at the bottom of the machine.
In order to remove this board from the machine you need to first snip a couple of nylon ties that are securing the wiring loom. Doing so will give enough slack (just) to be able to free the board from the machine to give access to the underside (foil side) as well as the component side.
Then there are two small screws on the face of the machine. I have removed them already here.
Once removed you can gently release some of the wiring loom and carefully ease the board out of the machine frame. After which it should look like this.
The board can then be turned over fairly easily to access the foil side.
Here is the board again but with all the caps replaced. I have used WIMA film caps for all the ceramic caps as well as the two 1uF electrolytics that I also replaced with WIMA film caps. You can see them at the bottom of this picture between the two fat Nichicon UFG's. I use Nichicon UFG's for most of the other electrolytics, except for the two original Orange caps which were specified by Pioneer as 'Low Leakage'. Now I don't pretend to completely understand the difference here between say the Nichicon UFG and UKL (Low Leakage) equivalents, but I chose to use the UKL versions where Pioneer had used those Orange caps originally. You can see them at the top right hand side of the circuit board.
Like Smurfer77 I also used a couple of Murata Ceramics to replace the smallest value (15pF) caps. They are the little blue drops seen here.
And here we are with the Hitachi transistors replaced as well.
What to use as replacements for the 2SC1344 and 2SA672 is a bit of a headache. Many other audio forum threads suggest using Fairchild KSC1845F for the 2SC1344 and its complement the KSA992F for the 2SA672. I had discussed this issue with Smurfer77 who pointed out, rightly so, that the specs of these two do not really match the old Hitachi's all that well, particularly in regard to their current handling and hFe specs, where the KSC1845F was probably OK for the 2SC1344, but the hFe of the KSA992F was WAY above that of the old 2SA672. Smurfer suggested using Fairchild KSC1815Y and it's complement KSA1015Y. These two more closely match the current specs of the originals. However, I could not find a single instance of anyone using this combination in place of these Hitachi's. But I was able to find examples where people had used the KSC1845F and KSA992F pairing, with success. The KSC1845F and KSA992F are both specifically described as "Audio Frequency Low-Noise Amplifier", whereas the KSC1815Y and KSA1015Y are described as "Audio Frequency Amplifier and High Frequency OSC". It was pointed out to me by a technician on another forum that the specs of the transistors do not necessarily imply that in any given circuit they will be driven to those levels, and that current loadings are entirely dependent on the circuit itself. Not having the skill to determine these things for myself I elected to use the parts that others had already used with success. So although I did purchase a number of KSC1815Y and KSA1015Y in the end I used KSC1845F and KSA992F. EDIT: 27th October 2017 - See below for notes regarding changes to these choices.
After testing these there was no doubt that noise levels (in Source mode) were well down on what they had been. Although there was still some hiss, as there always will be, overall it was a lot quieter. Even when raising the Line In levels (with the Mic Levels at zero) there was definitely less noise. So, hopefully these will do the job nicely. There are other 2SC1344 and 2SA672's on the Playback Amplifier board and I will replace them as well when I get to them.
Finally here are the removed components.
The caps and transistors used on the Mic Amplifier Assembly board were:
2 x Murata 15pF 100V - http://www.mouser.com/ProductDetail/Murata-Electronics/RDE5C2A150J0P1H03B
2 x WIMA 68pF 1kV - http://www.mouser.com/ProductDetail/WIMA/FKP2O100681D00JSSD
4 x WIMA 100pF 100V - http://www.mouser.com/ProductDetail/WIMA/FKP2D001001D00JSSD
2 x Nichicon KL 10uF 25V - http://www.mouser.com/ProductDetail/Nichicon/UKL1E100KDDANA
2 x WIMA 1uF 1kV - http://www.mouser.com/ProductDetail/WIMA/FKP2O100681D00JSSD
4 x Nichicon FG 4.7uF 50V - http://mouser.com/ProductDetail/Nichicon/UFG1H4R7MDM
2 x Nichicon FG 47uF 25V - http://mouser.com/ProductDetail/Nichicon/UFG1E470MEM
2 x Nichicon FG 33uF 50V - http://www.mouser.com/ProductDetail/Nichicon/UFG1H330MPM
2 x Nichicon FG 100uF 35V - http://mouser.com/ProductDetail/Nichicon/UFG1V101MPM
6 x KSC1845F NPN Transistor - http://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/KSC1845FTA
2 x KSA992F PNP Transistor - http://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/KSA992FTA
And here are the measured values of the old electrolytics etc:
15pF Ceramic - .015, .016
68pF Ceramic - .065, .065
100pF Ceramic - .100, .102, .104, .102
10uF 16V LL - 11.43, 11.61
1uF 50V - 1.400, 1.298
4.7uF 35V - 5.97, 5.90, 5.72, 5.42
47uF 10V - 67, 68
33uF 16V - 42, 40
100uF 25V 105, 100
2SC1344 (hFE) - 321, 304, 332, 345, 298, 318
2SA672 (hFE) - 114, 106
That's it for this one
EDIT: 27th October 2017 - After running into feedback/oscillation noise issues I elected to change out the KSC1845F and KSA992F transistors. Read about the problem and the rectifications from post #76 onwards: Pioneer RT-707 Capacitor Upgrade and Service
This time I tackled the Microphone Amplifier Board (RWF-065). This board contains the Mic and Line input pot's. My intention was to re-cap and also replace the old Hitachi transistors in an attempt to reduce 'Hiss'.
Here is the RWF-065 board in situ at the bottom of the machine.
In order to remove this board from the machine you need to first snip a couple of nylon ties that are securing the wiring loom. Doing so will give enough slack (just) to be able to free the board from the machine to give access to the underside (foil side) as well as the component side.
Then there are two small screws on the face of the machine. I have removed them already here.
Once removed you can gently release some of the wiring loom and carefully ease the board out of the machine frame. After which it should look like this.
The board can then be turned over fairly easily to access the foil side.
Here is the board again but with all the caps replaced. I have used WIMA film caps for all the ceramic caps as well as the two 1uF electrolytics that I also replaced with WIMA film caps. You can see them at the bottom of this picture between the two fat Nichicon UFG's. I use Nichicon UFG's for most of the other electrolytics, except for the two original Orange caps which were specified by Pioneer as 'Low Leakage'. Now I don't pretend to completely understand the difference here between say the Nichicon UFG and UKL (Low Leakage) equivalents, but I chose to use the UKL versions where Pioneer had used those Orange caps originally. You can see them at the top right hand side of the circuit board.
Like Smurfer77 I also used a couple of Murata Ceramics to replace the smallest value (15pF) caps. They are the little blue drops seen here.
And here we are with the Hitachi transistors replaced as well.
What to use as replacements for the 2SC1344 and 2SA672 is a bit of a headache. Many other audio forum threads suggest using Fairchild KSC1845F for the 2SC1344 and its complement the KSA992F for the 2SA672. I had discussed this issue with Smurfer77 who pointed out, rightly so, that the specs of these two do not really match the old Hitachi's all that well, particularly in regard to their current handling and hFe specs, where the KSC1845F was probably OK for the 2SC1344, but the hFe of the KSA992F was WAY above that of the old 2SA672. Smurfer suggested using Fairchild KSC1815Y and it's complement KSA1015Y. These two more closely match the current specs of the originals. However, I could not find a single instance of anyone using this combination in place of these Hitachi's. But I was able to find examples where people had used the KSC1845F and KSA992F pairing, with success. The KSC1845F and KSA992F are both specifically described as "Audio Frequency Low-Noise Amplifier", whereas the KSC1815Y and KSA1015Y are described as "Audio Frequency Amplifier and High Frequency OSC". It was pointed out to me by a technician on another forum that the specs of the transistors do not necessarily imply that in any given circuit they will be driven to those levels, and that current loadings are entirely dependent on the circuit itself. Not having the skill to determine these things for myself I elected to use the parts that others had already used with success. So although I did purchase a number of KSC1815Y and KSA1015Y in the end I used KSC1845F and KSA992F. EDIT: 27th October 2017 - See below for notes regarding changes to these choices.
After testing these there was no doubt that noise levels (in Source mode) were well down on what they had been. Although there was still some hiss, as there always will be, overall it was a lot quieter. Even when raising the Line In levels (with the Mic Levels at zero) there was definitely less noise. So, hopefully these will do the job nicely. There are other 2SC1344 and 2SA672's on the Playback Amplifier board and I will replace them as well when I get to them.
Finally here are the removed components.
The caps and transistors used on the Mic Amplifier Assembly board were:
2 x Murata 15pF 100V - http://www.mouser.com/ProductDetail/Murata-Electronics/RDE5C2A150J0P1H03B
2 x WIMA 68pF 1kV - http://www.mouser.com/ProductDetail/WIMA/FKP2O100681D00JSSD
4 x WIMA 100pF 100V - http://www.mouser.com/ProductDetail/WIMA/FKP2D001001D00JSSD
2 x Nichicon KL 10uF 25V - http://www.mouser.com/ProductDetail/Nichicon/UKL1E100KDDANA
2 x WIMA 1uF 1kV - http://www.mouser.com/ProductDetail/WIMA/FKP2O100681D00JSSD
4 x Nichicon FG 4.7uF 50V - http://mouser.com/ProductDetail/Nichicon/UFG1H4R7MDM
2 x Nichicon FG 47uF 25V - http://mouser.com/ProductDetail/Nichicon/UFG1E470MEM
2 x Nichicon FG 33uF 50V - http://www.mouser.com/ProductDetail/Nichicon/UFG1H330MPM
2 x Nichicon FG 100uF 35V - http://mouser.com/ProductDetail/Nichicon/UFG1V101MPM
6 x KSC1845F NPN Transistor - http://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/KSC1845FTA
2 x KSA992F PNP Transistor - http://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/KSA992FTA
And here are the measured values of the old electrolytics etc:
15pF Ceramic - .015, .016
68pF Ceramic - .065, .065
100pF Ceramic - .100, .102, .104, .102
10uF 16V LL - 11.43, 11.61
1uF 50V - 1.400, 1.298
4.7uF 35V - 5.97, 5.90, 5.72, 5.42
47uF 10V - 67, 68
33uF 16V - 42, 40
100uF 25V 105, 100
2SC1344 (hFE) - 321, 304, 332, 345, 298, 318
2SA672 (hFE) - 114, 106
That's it for this one
EDIT: 27th October 2017 - After running into feedback/oscillation noise issues I elected to change out the KSC1845F and KSA992F transistors. Read about the problem and the rectifications from post #76 onwards: Pioneer RT-707 Capacitor Upgrade and Service
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Trevor White
Classic not Plastic
In the post above I described using Nichicon UKL Low Leakage caps to replace the little Orange caps that Pioneer had originally spec'd as "Low Leakage".
It occurred to me that the Servo Amplifier board that I had already done also had some of those little Orange caps. So I actually went back and removed the Nichicon UFG's that I had used for them on that board and replaced them with their equivalent KL versions.
I don't know if this is important or not, but I will now edit the post for the Servo Amplifier to reflect that change.
It occurred to me that the Servo Amplifier board that I had already done also had some of those little Orange caps. So I actually went back and removed the Nichicon UFG's that I had used for them on that board and replaced them with their equivalent KL versions.
I don't know if this is important or not, but I will now edit the post for the Servo Amplifier to reflect that change.
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rojoknox
Well-Known Member
Greetings from RojoLand!
The board appears to have carbon-film 5% resistors, which shouldn't be too bad. I wonder if any further noise quieting can be gleaned by substituting 1% metal-film resistors in at least the first, lowest-level stages. If the originals were carbon-composition I'd have no hesitation changing them all out, but here there may not be enough return on the parts and time investment. Just a thought.
Take care,
—
J. E. Knox "The Victor Freak"
The board appears to have carbon-film 5% resistors, which shouldn't be too bad. I wonder if any further noise quieting can be gleaned by substituting 1% metal-film resistors in at least the first, lowest-level stages. If the originals were carbon-composition I'd have no hesitation changing them all out, but here there may not be enough return on the parts and time investment. Just a thought.
Take care,
—
J. E. Knox "The Victor Freak"
Trevor White
Classic not Plastic
Hmmm, interesting.
I'll give that some consideration. Thanks!
EDIT: Actually, having thought about this. With audio circuits like this would these resistors ever see a DC signal? Would it not all be AC. In this case, how much do resistors, carbon film/metal film or otherwise contribute to circuit noise?
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Hi Trevor,
there is always "DC" in these circuits as they will be biased to half conduction to superimpose the Audio AC upon it. The caps you are replacing are keeping the DC biasing confined, if they are in the audio path.
The resistors will add a certain amount of noise but as Rojoknox has stated previously, this will chiefly be the composite type. Also the noise from the resistors also seems to be a function of resistance. In low level transistor circuitry there are not enough "High" resistances to give a problem. In Valve circuits this becomes more dominant as resistors in the Meg range are more evident.
Personally I would leave resistors alone unless they are showing signs of stress. If they are near their dissipation spec then they may be discoloured and be drifting up in resistance.
Cheers.
GPS16
there is always "DC" in these circuits as they will be biased to half conduction to superimpose the Audio AC upon it. The caps you are replacing are keeping the DC biasing confined, if they are in the audio path.
The resistors will add a certain amount of noise but as Rojoknox has stated previously, this will chiefly be the composite type. Also the noise from the resistors also seems to be a function of resistance. In low level transistor circuitry there are not enough "High" resistances to give a problem. In Valve circuits this becomes more dominant as resistors in the Meg range are more evident.
Personally I would leave resistors alone unless they are showing signs of stress. If they are near their dissipation spec then they may be discoloured and be drifting up in resistance.
Cheers.
GPS16
Trevor White
Classic not Plastic
Excellent mate, thank you for your reply. I continue to learn daily. All the resistors look fine, no sign of discolouration or stress that I can see, so I think I will leave them alone, as you suggest.
I am about to start looking at the final piece of the puzzle, the Playback Amplifier and Head Amplifier boards. On the Playback Amp Smurfer replaced the VR's with some Bourns 25 turn devices, but I am having trouble isolating on Mouser just what I would need. The circuit diagrams call for 10KOhm, 22KOhm and 33KOhm devices which they call 'Semi-Fixed'. The 10K and 22K are available, but 33K seems an odd size and the Bourns seem to only be available in 30K and 40K sizes. How critical would the maximum resistance value be?
Thanks again mate,
Trevor
Hi Trevor,
the VR are either variable resistances (wiper to one end) to vary gain in the feedback loop or Potential Dividers. As long as you pick the closest value to the spec, you will be fine. If the wiper is shorted to one end then the final resistance is what is of importance not the initial value. For the Divider, the load on the previous stage is what matters. The difference between a 30k and a 33k is not mission critical in this application. It is setting levels only and there are no time constants present where a resistance change would shift the frequency.
Picking the Closest Value will be fine. When you order the pots, make sure you get a proper "Tweaker" at the same time!!! Having a small screw driver slip off a slotted screw head into powered circuits is NOT a good idea!!!! A proper tweaker will have one end which goes completely over the screw head so it will not slip off.
You doing a grand job!!!
GPS16
the VR are either variable resistances (wiper to one end) to vary gain in the feedback loop or Potential Dividers. As long as you pick the closest value to the spec, you will be fine. If the wiper is shorted to one end then the final resistance is what is of importance not the initial value. For the Divider, the load on the previous stage is what matters. The difference between a 30k and a 33k is not mission critical in this application. It is setting levels only and there are no time constants present where a resistance change would shift the frequency.
Picking the Closest Value will be fine. When you order the pots, make sure you get a proper "Tweaker" at the same time!!! Having a small screw driver slip off a slotted screw head into powered circuits is NOT a good idea!!!! A proper tweaker will have one end which goes completely over the screw head so it will not slip off.
You doing a grand job!!!
GPS16
Trevor White
Classic not Plastic
Thanks very much GPS, much appreciated.
Good tip about one of those 'tweakers'
Good tip about one of those 'tweakers'