Ohgoshjosh I wonder if you found any instances of the polarity that is displayed on the board being incorrect. I found several caps (three I think) in the power protection board that appeared to be installed with the polarity reversed. The cap displayed the negative terminal installed in the positive marking on the board. This unit worked perfectly prior to disassembly, the only problem were a number of burned out lamps. I saw someone on this forum who said that you should be careful of faulty silk screening. You have now finished this process and would appreciate your advice. Thanks.
SX-3700 Recap/Restore Thread
- Thread starter ohgoshjosh
- Start date
ohgoshjosh
New Member
I didn’t personally find any that were incorrectly screened on my board, however, I only worked on a very small section of the board, and I was careful to put the caps in the same way they came out. However, I did find that the board diagram included with the service manual was not always 100% correct. Some of the test pins appeared in the wrong place, or I couldn’t find them on the board at all.
Thanks. I replaced all of the caps excluding the ceramics. I did replace the 103 ceramic near the 8200uf which was melted into one of these large caps. Strangely, when I tested it after removing it came back normal including the ESR. I found a couple of small 0.47uf caps that appeared to be reversed. I am plugging it into my DBT today and then, on its own if all goes well. Thanks again for your help and advice.
Just and update. I completed the rebuild and everything works as it should. It took time but I think replacing all the caps has resulted in a much cooler running amp and I think upping the large 8200uf to 10,000 was probably worth it. Just a note to anyone else who has one of these and is considering a complete refurbishment. My brother's stereo was built in November 1980. I downloaded the service manual and all of the forks put out by Pioneer to try to understand how this thing was put together. The circuit and board diagrams included in the Service Manual were helpful. However on my unit there was a problem. On page 15 of the manual is an overview of the way in which the stereo is laid out. On the bottom left of that diagram is a picture of the FL assembly, AWV-012 which drives the left power indicator display. You will see three silver caps on the left side of the board. This is where the problem lies. If you look at the silk screening for these caps, all show the negative polarity of these three caps facing the front of the unit. In reality, the cap closes to the left side of the unit is correct. Negative is to the front of the unit. The other two appear at first glance to be installed backwards if you follow the plus - negative signs on the board. The silk screening is incorrect. I noticed this on recheck of my installs because of the photos I took of the board before I disassembled it. These were the only two like this.
I don't know if this applies to any other unit of this type manufactured before or after November of 1980. Pioneer may have caught the mistake and changed the subsequent boards. I hope this may help.
I don't know if this applies to any other unit of this type manufactured before or after November of 1980. Pioneer may have caught the mistake and changed the subsequent boards. I hope this may help.
After reassembly and the amp working well for a few hours, I moved it and lost the right channel. I opened it up and did the tap test to see if I have loosened any of the solder joints but all seemed well, but still no sound or, very faint sound. I happened to touch the right tape switch on the front of the unit and the channel came back on. Wiggling it turned the channel off and on. I pulled the bottom cover and looked a the solder connections. This switch is soldered directly to the board but the front and back pins are not, they just sort of float in two holes that appear to align it. One back solder joint was loose, I could see it moving back and forth with movement of the tape switch. Heated it up and added some new solder. The channel is now working. Why this tape switch has anything to do with the right channel is a mystery at the moment; a look at the schematic may help. Anyway just thought that it may help someone else who may be repairing one of these old beasts.
oldgearhog
Active Member
Nice job ohgoshjosh and rt253, I'll reference this when I do my own SX-3700 that's on my bench. Actually on a shelf next to the bench under a couple of others.
Good luck oldgearhog with your SX-3700. My brothers unit is now back in his garage (jeeez) and not in the living room but that is where he enjoys listening to it. You may have much more experience than I did, I overhaul old radios so this project was a little different for me. I photographed the entire unit as I took it to pieces to recap it, and all of it was recapped. It runs much cooler now. If you need a new set of lamps I found that "David Wojnarowski <dwojo69@msn.com was excellent to deal with and the lamp holders and LEDs he provided fit and worked well. The old lamp sockets were just a brittle as a potato chips.
Watch for the polarity of the capacitors as laid on the board and schematics in the driver board for the power meters, two are incorrect, at least for my November 1980 unit. I replaced the 8200 uf caps in the power supply with 10,000 uf and all of the caps to higher voltages where I could get them. The dial cord is bugger to get back on correctly. Maybe its just me. The controls in the front are soldered directly to the board and the joints are a problem, I lost a channel for a while until I just happened to bump the tape lever and the channel came back on. I removed and re-seated all of the power transistors on the heat sink. It is not an easy unit to work on but again perhaps it is just me. There is a considerable amount of disassembly, especially the front to get to the switches, lamps and boards to recap. I bagged and labelled all of the parts as I removed them because, well, I tend to misplace things. It helped. No leftover pieces. The unit look great with all the colors of the display and lamps and sounds great as well. I gained about 5 watts per channel after recapping. I think i will look for another on for myself at some point. Fantastic sound with my turntable. Good luck.
Watch for the polarity of the capacitors as laid on the board and schematics in the driver board for the power meters, two are incorrect, at least for my November 1980 unit. I replaced the 8200 uf caps in the power supply with 10,000 uf and all of the caps to higher voltages where I could get them. The dial cord is bugger to get back on correctly. Maybe its just me. The controls in the front are soldered directly to the board and the joints are a problem, I lost a channel for a while until I just happened to bump the tape lever and the channel came back on. I removed and re-seated all of the power transistors on the heat sink. It is not an easy unit to work on but again perhaps it is just me. There is a considerable amount of disassembly, especially the front to get to the switches, lamps and boards to recap. I bagged and labelled all of the parts as I removed them because, well, I tend to misplace things. It helped. No leftover pieces. The unit look great with all the colors of the display and lamps and sounds great as well. I gained about 5 watts per channel after recapping. I think i will look for another on for myself at some point. Fantastic sound with my turntable. Good luck.
oldgearhog
Active Member
Thanks rt253 that's good info. I've also used egg cartons for holding things but usually for thing that go back together right after I take them apart. I've done the baggy thing too, but even then I lost a couple of tiny screws that were holding a Marantz front panel together. More "do like i say, not like i do" sage advice i guess.
Greetings,
Not sure anyone is still looking at this however I need HELP.
SX-3700 was working. Recapped the power board and new relay.
Relay was not engaging. Looked at the protection Trannies and Q21, Q23, and Q24 were bad. Q22 was good. The recap kit had a c2690 that replaced the c1384 Q25.
Now the replay chatters, i.e keeps turning off and on quickly. Will not stop
Cannot get Voltage readings to see what is going on.
Please advise.
Not sure anyone is still looking at this however I need HELP.
SX-3700 was working. Recapped the power board and new relay.
Relay was not engaging. Looked at the protection Trannies and Q21, Q23, and Q24 were bad. Q22 was good. The recap kit had a c2690 that replaced the c1384 Q25.
Now the replay chatters, i.e keeps turning off and on quickly. Will not stop
Cannot get Voltage readings to see what is going on.
Please advise.
Greetings
Very happy you responded.
I have have scope.
I did replace the relay.
Let me give you the details.
3700 was not working when I got it.
I have a working unit I got around the same time.
I ended replacing bad main power trans. All 4.
Still did not work.
Replaced A resister that I noticed was burnt. R332 330 onm.
Then found q16 and q14 were bad. Did this by starting to remove and check because voltage readings were all over the place.
Unit worked after this. Left it on for a day and no issue.
I had previously bought the $99 restore kit so started the cap replacement.
Tuner/AF assy first. GWB 160. Unit still worked fine.
Next the power amp. GWM 159
In this part there was a few trannies I replaced.
Q25 C1384 with c2690
Q17 D880 with c2073
Q18 B834 with A940
Note: When I removed a component, whether a cap or tranny I would check the old one and new one with an ESR meter.
Well the c1384. Q25. In the protection circuit was bad.
Interesting since the relay was engaging before I started on this board.
Once I was done with this board the relay engaged and disengaged and would not engage again.
I started taking readings and accidently touched the collector and emitor and the relay engaged.
So I removed the trannies in power protrction cicuit one at a time, including q25.
Well q22 was bad. Q21 was good. Q25 was still good. Q24 and q23 were bad.
Replaced them and that was when the relay started its dance.
FYI. I think that the power protect never worked because q25 was acting like a diode and the others came up as bad on the EAR.
I pulled a reading off of r121 560 ohm and the zeinor diode d20 and the voltage is going from 16mv to 35mv and back done. Thus the relay dance.
I pulled the diode and resistor and the are fine. Left them out and tested at q24's collector and the voltage is still fluctuating.
I hope I have given enough details.
The Oscope Is an old Tektronix ADS 410A I have had for a few years but never used.
A friend bid a lot and this was part of it.
Thanks in advance!
Very happy you responded.
I have have scope.
I did replace the relay.
Let me give you the details.
3700 was not working when I got it.
I have a working unit I got around the same time.
I ended replacing bad main power trans. All 4.
Still did not work.
Replaced A resister that I noticed was burnt. R332 330 onm.
Then found q16 and q14 were bad. Did this by starting to remove and check because voltage readings were all over the place.
Unit worked after this. Left it on for a day and no issue.
I had previously bought the $99 restore kit so started the cap replacement.
Tuner/AF assy first. GWB 160. Unit still worked fine.
Next the power amp. GWM 159
In this part there was a few trannies I replaced.
Q25 C1384 with c2690
Q17 D880 with c2073
Q18 B834 with A940
Note: When I removed a component, whether a cap or tranny I would check the old one and new one with an ESR meter.
Well the c1384. Q25. In the protection circuit was bad.
Interesting since the relay was engaging before I started on this board.
Once I was done with this board the relay engaged and disengaged and would not engage again.
I started taking readings and accidently touched the collector and emitor and the relay engaged.
So I removed the trannies in power protrction cicuit one at a time, including q25.
Well q22 was bad. Q21 was good. Q25 was still good. Q24 and q23 were bad.
Replaced them and that was when the relay started its dance.
FYI. I think that the power protect never worked because q25 was acting like a diode and the others came up as bad on the EAR.
I pulled a reading off of r121 560 ohm and the zeinor diode d20 and the voltage is going from 16mv to 35mv and back done. Thus the relay dance.
I pulled the diode and resistor and the are fine. Left them out and tested at q24's collector and the voltage is still fluctuating.
I hope I have given enough details.
The Oscope Is an old Tektronix ADS 410A I have had for a few years but never used.
A friend bid a lot and this was part of it.
Thanks in advance!
Sounds like you've done good work, and testing. Nice.
I'll go check the schematic tonight (I'm not familiar with the 3700, but I do own one) and see what I can figure out related to your issue.
My 3700 is at my mothers house, but I could still go over, open it up and compare if we need to.
I'll go check the schematic tonight (I'm not familiar with the 3700, but I do own one) and see what I can figure out related to your issue.
My 3700 is at my mothers house, but I could still go over, open it up and compare if we need to.
Well sir. I put the resister and q25 back in and it works like a champ.
I have no clue.
I pulled and checked q21 thru q25 (protection circuit) to make sure they were still ok and they are.
Amazing. The relay does engage almost instantly, no delay. Not sure if that's an issue.
However voltages look fine.
Thanks for all you help and effort.
I have no clue.
I pulled and checked q21 thru q25 (protection circuit) to make sure they were still ok and they are.
Amazing. The relay does engage almost instantly, no delay. Not sure if that's an issue.
However voltages look fine.
Thanks for all you help and effort.
That's great. I also keep all the OEM parts and if I can't get something right, the old parts might just do the trick.
Enjoy.
I picked up a sx-3700 recently. It works ok but needs some TLC. Just like most of these... I'm looking for a Complete Rebuild List. Caps, Transistors ETC. I could go through the Service Manual and figure it out but was hoping someone could save me some time. Also, other than the SA726 transitors, are there others that are known to have reliability issues? If someone could share a rebuild kit list, I would be very appreciative!
Trodder
Member
Did you ever figure out what the lead spacing is? Also, do you recall if it is a 2 pin or 3 pin cap? I thought all of these were 2 pin, but looking at the back of the board it looks like a 3 pin. The schematic leads me to believe it is a 2 pin however. I just want to be sure I get the right thing. I want to order replacements right away, but might be a bit before I can pull them.
It's not uncommon for the board to have an extra hole, and can often be utilized when spacing isn't quite right.
But also, those pads on the board are usually huge, and I'll drill a hole where I need it if it makes the install easier.
Trodder
Member
So these power caps are 3 pin as I suspected, but it looks as if only 2 pins are used? So we only need a 2 pin cap correct? I’m having a hard time finding a good replacement even for a 2 pin. The two pins are 15mm spacing and between each pair it is 10mm lead spacing in case anyone else needs that info. 30mm diameter and 50 maybe 52mm tall.
Attachments
Trodder
Member
Okay… I think I have a bit to add here. Bare with me, but hopefully this is useful/helpful to others.
First, make sure the unit is not plugged in. Anything you do is at your own risk. Anything I mention is for entertainment purposes only. I am not an expert.
First let’s talk caps. These are 3 pin from factory, a 2 pin axial leads is what you need because you will not find one with proper spacing with snap-in style. 8200uf has very limited options if any, so I went with Nichicon 10,000uf 50v FWM.
Part#s
Nichicon Part# UFW1H103MRD
Digikey.com Part# 493-3183-ND
Link to part: https://www.digikey.com/en/products/detail/nichicon/UFW1H103MRD/1965205
Now here is the pins you have to desolder:
Now once you desolated them, there is glue securing the power filter caps to the board. You can try a little heat from a heat gun or a pick or something to score around the base and as you start pulling it away you will statt to see the glue stretch. Be careful not to pull so hard that you bend the board and break the board or solder joints.
Do not go any higher than 10kuf caps. I’m a little nervous going this high as it is, but others have had good success, so I went for it.
Now the 3 T10 style blade bulbs are a nightmare if you try to remove the plastic holders. Really you don’t even need to but I’m an idiot and removed one and it broke. So the other two I removed the acrylic bar by removing these two screws:
Then I very carefully used pliers to remove the old bulbs:
Now what to replace them with… well, I replaced the blade bulbs and LEDs even though the bulbs were fine. A couple of the LEDs were fine. I order them on eBay from this guy:
But here is the big reveal…. Those stupid plastic sockets for the T10s… you cannot find replacements and if you do they are probably just as old and dry rotted. So in order a bunch of different ones on eBay and found just ONE that works well and is a nice tight fit. In fact you will need to use soapy water or petroleum jelly or whatver to squeeze the socket in WITHOUT the bulb installed. This is what I used:
uxcell 10 Pcs T10 Wedge Base Light Car Instrument Panel Dash Board Socket Universal https://a.co/d/dBYScYC
Once the socket is installed then you can install the led or standard bulb. The bulb will sit exactly the same as the original socket. This will continue in my next post as I am limited to 10 attachments.
First, make sure the unit is not plugged in. Anything you do is at your own risk. Anything I mention is for entertainment purposes only. I am not an expert.
First let’s talk caps. These are 3 pin from factory, a 2 pin axial leads is what you need because you will not find one with proper spacing with snap-in style. 8200uf has very limited options if any, so I went with Nichicon 10,000uf 50v FWM.
Part#s
Nichicon Part# UFW1H103MRD
Digikey.com Part# 493-3183-ND
Link to part: https://www.digikey.com/en/products/detail/nichicon/UFW1H103MRD/1965205
Now here is the pins you have to desolder:
Now once you desolated them, there is glue securing the power filter caps to the board. You can try a little heat from a heat gun or a pick or something to score around the base and as you start pulling it away you will statt to see the glue stretch. Be careful not to pull so hard that you bend the board and break the board or solder joints.
Do not go any higher than 10kuf caps. I’m a little nervous going this high as it is, but others have had good success, so I went for it.
Now the 3 T10 style blade bulbs are a nightmare if you try to remove the plastic holders. Really you don’t even need to but I’m an idiot and removed one and it broke. So the other two I removed the acrylic bar by removing these two screws:
Then I very carefully used pliers to remove the old bulbs:
Now what to replace them with… well, I replaced the blade bulbs and LEDs even though the bulbs were fine. A couple of the LEDs were fine. I order them on eBay from this guy:
LED LAMP KIT/SX-3700 SX-3800 SX-3900 SX-820 /WARM WHITE -DIAL-RECEIVER /Pioneer | eBay
Find many great new & used options and get the best deals for LED LAMP KIT/SX-3700 SX-3800 SX-3900 SX-820 /WARM WHITE -DIAL-RECEIVER /Pioneer at the best online prices at eBay! Free shipping for many products!
www.ebay.com
But here is the big reveal…. Those stupid plastic sockets for the T10s… you cannot find replacements and if you do they are probably just as old and dry rotted. So in order a bunch of different ones on eBay and found just ONE that works well and is a nice tight fit. In fact you will need to use soapy water or petroleum jelly or whatver to squeeze the socket in WITHOUT the bulb installed. This is what I used:
uxcell 10 Pcs T10 Wedge Base Light Car Instrument Panel Dash Board Socket Universal https://a.co/d/dBYScYC
Once the socket is installed then you can install the led or standard bulb. The bulb will sit exactly the same as the original socket. This will continue in my next post as I am limited to 10 attachments.
Trodder
Member
Here you can see the stick and the new socket with the bulb in it:
Now for the new socket and the LEDs I used 5/64” diameter heat shrink. I got it from a kit I bought at Harbor Freight. Perfect fit for all of this: https://www.harborfreight.com/127-piece-heat-shrink-tubing-set-67524.html
Now for the LEDs, I did not capture any pics. I don’t know why… I should have. Sorry. What I did for these however is fairly simple. These little black brackets they live in have just a touch of glue to hold the old bulbs in. Gently pull them out the back to remove them. To do that you just need to remove the whole black frame in the front behind the faceplate. Seems daunting, but it’s not bad at all.
Here is all the screw and nut locations as well as the clip at the headphone jack that needs to be removed. Just remove them all. For screwed there is 2 different styles, one corse and one fine thread. I think the fine thread ones are the one that attach the switch boards to the plate. The course attach the plate to the frame…. I think…. Just pay attention when you take them out.
Now once you start gently pulling the LEDs out of the back of the little black plastic holder just clip the VERY end right behind the old bulb so you have more wire to use to splice the new LEDs on. You will find the end of these wires will fall off once you put soldering iron on them… don’t worry… it’s just the bulb leads that you cut. Anyway… once you cut them slide the heat shrink tube on and slide as far away from the cut ends as you can because those wires heat fast! Now solder the new LEDs on and slide the 5/64” heat shrink tubes and shrink em!! Now…. The new LEDs that you got from the kit will be tight in the black plastic holder, enough to cause the heat shrinking they came in to possibly peel back a little (not a big deal) but not tight enough to keep them in place. Just use a glue gun and put a dab where the old glue was to help hold it in place. Now put it all back together. It’s a little bit of pain to get the screws for the boards back in because the boards push back in and move around. Plus the power switch is not secured to anything so that’s a pain… just make sure you start EVERY SCREW before you tighten ANY SCREW! Otherwise you will make it harder on yourself than it needs to be. MAKE SURE YOI LOOK FOR ANY WIRES THAT WILL GET PINCHED BEFORE YOU TIGHTEN the screws down!! Look from backside, front side, underneath, peak in the little holes in the front where the push button switches stick out, etc.
Before you button everything back up you have seen the old foam on the faceplate fell apart. I just replaced with 1/4” X 1/4” from Amazon also:
Yotache Foam Tape 3 Strips 1/4 Inch Wide X 1/4 Inch Thick, Weather Stripping for Doors and Window High Density Foam Seal Tape Sliding Door Weather Strip, Total 30 Feet Long (3 X 10 Ft Each) https://a.co/d/j90AtR5
Now clean the face plate and use a soft bristle paint brush to wipe the whole dual face clean before reassembly. Of course clean the inside using compressed air and or a vacuum carefully. I still need to do that myself.
One additional tip…. Look all over for any solder breaks. I found one on the under side… take your time looking and fix them before you close it up.
If anyone has any questions let me know. If you need a pic of anything else let me know, I might have one. The only thing I didn’t get pics of is the LEDs for the push button switches. Sorry guys…. Should have gotten them
Now for the new socket and the LEDs I used 5/64” diameter heat shrink. I got it from a kit I bought at Harbor Freight. Perfect fit for all of this: https://www.harborfreight.com/127-piece-heat-shrink-tubing-set-67524.html
Now for the LEDs, I did not capture any pics. I don’t know why… I should have. Sorry. What I did for these however is fairly simple. These little black brackets they live in have just a touch of glue to hold the old bulbs in. Gently pull them out the back to remove them. To do that you just need to remove the whole black frame in the front behind the faceplate. Seems daunting, but it’s not bad at all.
Here is all the screw and nut locations as well as the clip at the headphone jack that needs to be removed. Just remove them all. For screwed there is 2 different styles, one corse and one fine thread. I think the fine thread ones are the one that attach the switch boards to the plate. The course attach the plate to the frame…. I think…. Just pay attention when you take them out.
Now once you start gently pulling the LEDs out of the back of the little black plastic holder just clip the VERY end right behind the old bulb so you have more wire to use to splice the new LEDs on. You will find the end of these wires will fall off once you put soldering iron on them… don’t worry… it’s just the bulb leads that you cut. Anyway… once you cut them slide the heat shrink tube on and slide as far away from the cut ends as you can because those wires heat fast! Now solder the new LEDs on and slide the 5/64” heat shrink tubes and shrink em!! Now…. The new LEDs that you got from the kit will be tight in the black plastic holder, enough to cause the heat shrinking they came in to possibly peel back a little (not a big deal) but not tight enough to keep them in place. Just use a glue gun and put a dab where the old glue was to help hold it in place. Now put it all back together. It’s a little bit of pain to get the screws for the boards back in because the boards push back in and move around. Plus the power switch is not secured to anything so that’s a pain… just make sure you start EVERY SCREW before you tighten ANY SCREW! Otherwise you will make it harder on yourself than it needs to be. MAKE SURE YOI LOOK FOR ANY WIRES THAT WILL GET PINCHED BEFORE YOU TIGHTEN the screws down!! Look from backside, front side, underneath, peak in the little holes in the front where the push button switches stick out, etc.
Before you button everything back up you have seen the old foam on the faceplate fell apart. I just replaced with 1/4” X 1/4” from Amazon also:
Yotache Foam Tape 3 Strips 1/4 Inch Wide X 1/4 Inch Thick, Weather Stripping for Doors and Window High Density Foam Seal Tape Sliding Door Weather Strip, Total 30 Feet Long (3 X 10 Ft Each) https://a.co/d/j90AtR5
Now clean the face plate and use a soft bristle paint brush to wipe the whole dual face clean before reassembly. Of course clean the inside using compressed air and or a vacuum carefully. I still need to do that myself.
One additional tip…. Look all over for any solder breaks. I found one on the under side… take your time looking and fix them before you close it up.
If anyone has any questions let me know. If you need a pic of anything else let me know, I might have one. The only thing I didn’t get pics of is the LEDs for the push button switches. Sorry guys…. Should have gotten them
