Pioneer RT-707 service & rebuild

[Trevor White]

Yes i know that thread. To reitterate, the 1845 is under spec on current handling. There is absolutely no confusion there. maybe someone checked that the current in the relevant circuit regions is sufficiently low but i tend to not assume anything. The 50mA of the 1845 is likely enough but personally i wouldnt use an under spec current handling part unless i considered the circuits carefully. And i will not spend the time do analyze the circut while there are many good options for small signal amplification. I mentioned only a couple. This is not an area we are short on options for.

Personally i only buy from trusted sources for transistors and that usually doesnt include the usual auction site.

Thanks for that mate.

Looking at the specs on your suggestions, the KSC1815 and KSA1015 I am certainly much more comfortable with them. As you say, using a part that is clearly under-spec'd looks iffy to say the least. Based on your comments and my own reading that I have done today I have now ordered a batch of both the KSC1815Y and KSA1015Y from Mouser. I should have them in a week or so, when I will also do as you suggested and check their reported hFE specs and use those that are close to one another.

Additionally, those supposedly original Hitachi parts on the auction sites will likely be just as old as the ones in my machine anyway, even if they are NOS.

Thanks again,
Trevor

 

[smurfer77]

Yeah, I think it's really wise to source new trustworthy parts that you can obtain for the foreseeable future.

... check their reported hFE specs and use those that are close to one another.

About the hFE measurement I wouldn't worry too much about matching (although that certainly wont hurt, but if I recall correctly these are not use in sensitive 'differential' application here). What I meant was that it would be nice to measure and use KSC1815Y on the higher end of the gain for that Y class 120-240 hFE range (e.g. maybe >200), since the original was >250. A bit under will be fine, but maybe you don't want to use hFE = 120.

Cheers
David

 

[Trevor White]

Yes, I understand David. Thanks very much for your tips. I have also read somewhere that this is not a 'differential' circuit.

I will do as you suggest though and choose those at the higher end of their scale, whatever they turn out to be. I ordered 20 of each, which should hopefully give me a reasonable selection.

All the best,
Trevor

 

[Trevor White]

David, one other question if I can.

When you do the sort of re-capping work described in this thread, what size (wattage) and type of soldering iron do you use? I have a two, one never seems quite hot enough to adequately flow the solder (10-13w), and has a sharp pointed tip. The other is hotter (Weller SP-40-D 40w), flows the solder really well with a broader chisel tip (3mm), but I am concerned about heating the components.

What do you use?

Cheers,
Trevor.

 

[smurfer77]

David, one other question if I can.

When you do the sort of re-capping work described in this thread, what size (wattage) and type of soldering iron do you use? I have a two, one never seems quite hot enough to adequately flow the solder (10-13w), and has a sharp pointed tip. The other is hotter (Weller SP-40-D 40w), flows the solder really well with a broader chisel tip (3mm), but I am concerned about heating the components.

What do you use?

Cheers,
Trevor.

I am no expert, but I use a high power soldering iron with temperature control feedback (I set a temperature, and it adjusts power to make the tip that temperature). It has interchangable tips. I use a 1.5mm tip for most work but other tips are necessary if you are in this game for long. 3mm is probably a bit big for some of the work on the RT707, although a skilled person could make it work. 10W is on the low side. 40W is even not that high (enough for recapping PCBs, but you may struggle with ground connections to chassis and speaker terminal etc etc). The thing is that higher power doesn't mean you components get hotter, if you use proper technique. A powerful iron enables touching the bits and making them hot quickly, and for a short period of time; with a low power iron you may end up having to make a component quite warm over a longer period of time to get the solder flowing.

I think my iron is capable of upto 110W.... just a 'cheapie' x-tronic model. There are plenty of sites on proper soldering technique... worth a read before we mess up PCBs .

Trevoer, it sounds like you are starting on a big adventure with the 707. I suggest starting a new thread of your own, and drop a link to it here and I will follow it and help out as much as possible. Others will also be more likely to chime in if you make a thread... and share some pics

 

[Trevor White]

Thanks for that David, much appreciated. I think I will invest in a temperature controlled soldering station as well, a worthwhile investment for this project, and not that expensive.

And yes, I am about to embark on a complete re-cap of my 707, much like you did, but I will also be replacing those rather noisy Hitachi signal transistors. Once I get going I think I may do as you suggest, take lots of photos and start a thread. I will still have to wait some time for my stock of parts to arrive from Mouser, but in the meantime I can school up and practice on some old circuit boards. As you say, the last thing I want to do is mess any of the PCB's up. One good thing about the 707 circuit boards though is that the lands around the holes for the components are a reasonable size, good for my ageing eyes

All the best,
Trevor

 

[smurfer77]

Thanks for that David, much appreciated. I think I will invest in a temperature controlled soldering station as well, a worthwhile investment for this project, and not that expensive.

And yes, I am about to embark on a complete re-cap of my 707, much like you did, but I will also be replacing those rather noisy Hitachi signal transistors. Once I get going I think I may do as you suggest, take lots of photos and start a thread. I will still have to wait some time for my stock of parts to arrive from Mouser, but in the meantime I can school up and practice on some old circuit boards. As you say, the last thing I want to do is mess any of the PCB's up. One good thing about the 707 circuit boards though is that the lands around the holes for the components are a reasonable size, good for my ageing eyes

All the best,
Trevor

Trevor, do take care though as I did ruin a couple of eyeholes, the traces are rather thin & flimsy from memory. So I just got some more KSC1815 and they also turned out to be around hFE = 215. The KSA1015 turned out to be hFE = 300, which will probably be okay although it's a bit high.

 

[Trevor White]

Trevor, do take care though as I did ruin a couple of eyeholes, the traces are rather thin & flimsy from memory. So I just got some more KSC1815 and they also turned out to be around hFE = 215. The KSA1015 turned out to be hFE = 300, which will probably be okay although it's a bit high.

Thanks for the tip David.

I think I have already come across the issue of the thin traces. When I initially got my 707 the Left Line In RCA plug on the back had a bad joint. When I desoldered the pin the trace around the hole came off completely! I had to clean some laquer off of the the trace further along and then solder to that. Fortunately it worked OK and seems solid. None the less, it is a concern and I will just have to be as careful as I can.

As for the transistors it's just a fact of life that we have little choice. Without a direct replacement for either the 2SC1344 or 2SA672 we have to use whatever is closest. I came across another thread where someone had used the 2SC1815 and 2SA1015 as replacements with success. http://www.tapeheads.net/showthread.php?t=42045 See post #4. I think the 2SA1015 and 2SC1815 are Toshiba transistors and which I think the KSA1015 and KSC1815 are replacements for?


Cheers, and thanks again,
Trevor

 

[GPS16]

Hi Trevor,

I use a 50W Weller Iron. It is temp controlled. As a tip, when removing components in bulk attempt to get the habit of doing one leg per component. This helps to keep the time spent on one joint and component to a minimum. If possible, as the removed component will be discarded, cut off the legs with nippers. The joints can then be treated as single items with tweezers and put up less of a fight.

A decent solder sucker is worth it's weight in gold too!!

If a dull joint does not melt quickly, don't persist. Leave it to cool and go elsewhere. Reflow it with fresh solder to allow the fresh flux to work, leave it to cool and go elsewhere. It will then be able to be removed much easier without too much temperature stress on the PCB.

These are all tips to keep the tracks and pad bonding sound on the PCBs. For this task the components are secondary!!!

Hope this helps.

GPS16

 

[Trevor White]

Hi Trevor,

I use a 50W Weller Iron. It is temp controlled. As a tip, when removing components in bulk attempt to get the habit of doing one leg per component. This helps to keep the time spent on one joint and component to a minimum. If possible, as the removed component will be discarded, cut off the legs with nippers. The joints can then be treated as single items with tweezers and put up less of a fight.

A decent solder sucker is worth it's weight in gold too!!

If a dull joint does not melt quickly, don't persist. Leave it to cool and go elsewhere. Reflow it with fresh solder to allow the fresh flux to work, leave it to cool and go elsewhere. It will then be able to be removed much easier without too much temperature stress on the PCB.

These are all tips to keep the tracks and pad bonding sound on the PCBs. For this task the components are secondary!!!

Hope this helps.

GPS16

Thanks very much for the tips mate.

I have recently got myself a new 48W temperature controlled iron, which after a little practice is clearly better than the 'uncontrolled' versions.
I have a solder sucker, but have also had a lot of success with Goot solder wick. That stuff is magic in it's ability to remove the solder quickly and leave a bright shiny pad on the PCB ready for replacing the component.

My first batch of caps and transistors has arrived from Mouser today. Still another package to arrive, so I'm almost ready to start.

All the Best,
Trevor

 

[GPS16]

Hi Trevor,

your welcome!!

Be slow steady and methodical. With the Electrolytics, make sure you know which way round they were in the PCB before removal. Schematics can have errors!!! In my experience what came off the PCB wins!!!

These are cracking machines and well worth the time and effort!!!

As Smurfer did, give us plenty of updates and I am sure any difficulties will get sorted.

Cheers.

GPS16

 

[Trevor White]

Hi Trevor,

your welcome!!

Be slow steady and methodical. With the Electrolytics, make sure you know which way round they were in the PCB before removal. Schematics can have errors!!! In my experience what came off the PCB wins!!!

These are cracking machines and well worth the time and effort!!!

As Smurfer did, give us plenty of updates and I am sure any difficulties will get sorted.

Cheers.

GPS16

Cheers mate,

Once I get going I think I will start a new thread, with pictures, much like Smurfer did. His thread was my inspiration, so I'm keen now to have a go. But as you say, slow and steady win's the day!

Trevor

 

[Trevor White]

Hi Trevor,

your welcome!!

As Smurfer did, give us plenty of updates and I am sure any difficulties will get sorted.

Cheers.

GPS16

One other thing if I may. Over a few posts on this and the previous page of this thread Smurfer and I discussed the replacement of the old Hitachi signal transistors 2SC1344 and 2SA672 which the RT-707 uses. In your experience have you ever had cause to replace these, and if so, what substitutes did you use. It seems to us that the most likely candidates are from Fairchild, the KSC1815 and KSA1015. Unfortunately it seems that none of the suggested substitutes are an exact match for the old Hitachi's, so it's a matter of finding something close that will work correctly in their roles on the Mic and line In board (RWF065) and the Playback Amp board (RWF069). I have seen a lot of threads around suggesting the KSC1845 and KSA992, but it seems that these have either current limitations or their hFe is well above the original Hitachi's.

I just wondered if you had ever done anything with these transistors.

Cheers mate,
Trevor

 

[GPS16]

Hi Trevor,

I was lucky enough to never need to. I am an Electronic Engineer and my work is Maintenance/Repair of Deposition/Etch Tools in a wafer fab. So, transistor trouble are the sorts of faults which would slap me in the face. I never has noise on Line and the Hiss with the Mic Level control fully up never seemed to change either (keep that control to zero unless you are using a Mike as it introduces hiss to all recordings if you don't). So I can't really give any advice on them. I would try and keep the hfe in the right ball park as if this too high then the circuit can burst into oscillation. Not a good idea as you then hurl RMS power (pure Sine Wave) straight to the tweeters. It may not be heard until the sound of a strangled chicken alerts you to the tweeters demise!!!

The only problems I had were switch issues which I kept on top of during use. The Bias/Eq switches along with the Left/Right Rec switches need to ne kept clean. The speed switch is generally moved about often enough to keep itself clean. The Bias/Eq switches affect the recorded signals directly. The Rec Left/Right can effect recordings as the Erase Heads are routed through these. Bad connections here varies the load on the Bias Osc and therefore the Bias itself.

As I am sure you have read elsewhere, the plug/socket on the servo PCB (the lead to the capstan motor) also needs to be kept clean. The FG feedback signal is on 2 pins which if dirty will give speed problems.

Cheers.

GPS16

 

[Trevor White]

That's great GPS, many thanks for your comments.

Yes, I'm very aware of the issues with the switches. I purchased this machine only a couple of months ago. It was intended to supplant my venerable old Sony TC-377 which I bought new in 1974. The Sony still works, and quite well for it's age, but I wanted something more robust that I could rebuild and the RT-707 was so highly thought of that I managed to get myself one. It was an Australian delivered machine and had spent it's time in tropical Queensland, but had been in storage for a very long time. The heads were badly tarnished, but in excellent physical condition, and the whole machine needed a lot of mechanical TLC. But once thoroughly cleaned and lubed, with the heads polished, it came back to life and made recordings that were better at 3.75ips than my Sony could make at 7.5ips. Very impressive.

So far I have replaced the VU meters as the red printing had faded so that it was almost illegible. I also got a replacement Capstan Motor as the original was noisy and the capstan shaft was quite corroded! After replacing the Capstan Motor the speed was nice and smooth and accurate, and to boot the motor was quiet and the capstan shaft like new.

I had trouble with many of the switches, particularly the Source/Tape and Bias/EQ and the Record switches. In fact they were all very flakey. However a good wash with some Deoxit D5 and plenty of exercise seemed to fix them up nicely.

No doubt many of the troubles I have had could be due to the high humidity that the machine had lived and been stored in. There was certainly a lot of evidence of moisture tarnishing and corrosion. But thankfully all the PCB's looked very good, other than being dirty.

As Smurfer said when he started out on his rebuild, I wanted to refurbish this machine because it is in such good condition, and works and sounds very good, despite it's age. I look forward to slowly and carefully replacing all those aging capacitors, and seeing what I can make of this wonderful old piece of engineering.

Best Regards,
Trevor

 

[GPS16]

Hi Trevor,

as another tip, with the machine powered off. Hold in the stop button and repeatedly press the Rec button. There are a couple of interlock switches on it which affect the wired control logic. It is one of the switches which gets missed. It solved problems with both Smurfer77 and Burgerman's machines.

Glad you could get hold of a capstan motor that was on good condition. You will now have cleaned up one of the speed trouble spots when you fitted the replacement motor. The FG pins will now have been cleaned!!!

I have quite a library of tapes done on my 707. They hold up nicely when played on a Revox A700. The RT707 is a real dark horse!!

Do you have faulty transistors or is replacement part of your refurb? Personally, if there are no problems I would leave them alone. Change the Electrolytics (not the big ones for the motors) and then take things from there.

Keep us posted. It is always nice to witness another resurrection of one of these wonderful beasts!!!

Cheers.

GPS16

 

[Trevor White]

Hi Trevor,

as another tip, with the machine powered off. Hold in the stop button and repeatedly press the Rec button. There are a couple of interlock switches on it which affect the wired control logic. It is one of the switches which gets missed. It solved problems with both Smurfer77 and Burgerman's machines.

Glad you could get hold of a capstan motor that was on good condition. You will now have cleaned up one of the speed trouble spots when you fitted the replacement motor. The FG pins will now have been cleaned!!!

I have quite a library of tapes done on my 707. They hold up nicely when played on a Revox A700. The RT707 is a real dark horse!!

Do you have faulty transistors or is replacement part of your refurb? Personally, if there are no problems I would leave them alone. Change the Electrolytics (not the big ones for the motors) and then take things from there.

Keep us posted. It is always nice to witness another resurrection of one of these wonderful beasts!!!

Cheers.

GPS16

Excellent, thanks for the tip re the Record button. I have not as yet encountered any problems there, but I have given all of those big switches a dose of Deoxit D5.

As for the transistors, the machine does produce some hiss (with the Mic level controls at zero). It seems unbalanced, louder to the right than left. From my reading these old Hitachi transistors can be notorious for becoming noisy, and many threads where people have replaced them have resolved that issue.

My only issue at the moment is trying to get in touch with the people at MRL so that I can order a reference calibration tape. I have sent multiple e-mails and had no replies at all?

Cheers,
Trevor

 

[GPS16]

Hi Trevor,

see if google can get things closer to home. I got mine from the UK, I did not go directly to MRL. As the one I was after was not the norm for studios, I had to wait a while for it!!!

For the transistors, if you have hiss on one channel then fair enough. I would still await the electrolytic spree before going for the transistors. See how you go.

Cheers.

GPS16

 

[Trevor White]

Good idea about the transistors. I shall work through all the capacitors first and then see how it behaves.

A question about the caps if I may. On the Head Amplifier (RWF070) and the Mic Amplifier (RWF065) there are a few 10uF caps specifically listed by Pioneer as "Low Leakage". Also on the Servo Amplifier (RWG076) are some 2.2uF and 4.7uF caps specified as "Low Leakage". Accordingly I got myself some Nichicon UKL series caps in the appropriate values (but with upgraded voltage specs). I also have some Nichicon UFG (Fine Gold) caps in the same sizes. I reckon when Smurfer did his rebuild he used the Nichicon UFG versions, rather than specific "Low Leakage" types.

Does it matter? Should I stick with the "Low Leakage" types where indicated, or replace everything with the same style of cap ie: Nichicon UFG's (Fine Gold).

Cheers mate,
Trevor

 

[GPS16]

Hi Trevor,

I have just had a look through the manual I have and don't see any reference to a "Low Leakage" specification. Where did you get this?

I can see that there use in circuits where there are high value resistances and low currents would make their use preferable. Head Amp (low-level), Mic Amp(low level) and Servo (averaging) are all included here.

The low leakage may have been more of an issue 30 years ago. You will probably find that todays components have a much better spec in the first place. If it was specified by Pioneer, then take it into account by all means. Check for the lowest leakage spec and see what components are available now. For lower values of electrolytics. see if there are Polypropylene version which have the same footprint and dimensions are available. They will trounce electrolytics for leakage specs!!!

As a rule of thumb, I have tended to go for the 105 deg, low ESR types first.

Hope this helps.

Cheers.

GPS16