Pioneer SA-9800 hum after Recap (Help!)

Jerry.S

New Member
I'm fairly new to this whole thing but took the dive and recapped my SA-9800. I used M.T.F.'s most recent threads for the parts lists. Everything went great and powered up fine, relay after 6 or 7 sec., and played music with a dead quiet backround noise. I was so happy. It was still sitting on the workbench a few days later when I came back to work on it some more. I turned it on and there is now a loud buzzing sound or hum that is coming from both channels equally and registers one bar on the indicator. It does not increase with volume.
I've replaced almost everything on the P.S. board except for the two sk34's. So i'm kinda stuck not knowing what to do now. Any help would be much appreciated.
 
See people?

The widely touted "re-capping" doesn't cure all ills.
Sorry, but it's the truth.
With hundreds of individual parts in a certain electronic set, it's difficult to impossible for even a knowledgeable tech to "diagnose" an issue over the internet.
Add to that fact that improper servicing might have been performed - and you've now got something non-standard as a problem to address.
Were these "caps" properly installed?
Was a wire pinched accidentally during the procedure?
The list goes on.... christ only knows now.

But nevertheless, the hoardes of online geeks and wannabes will create an endless thread to chip in and help the needy.. at times being no more than "the blind leading the blind".

With all due respect - online cries for help after a DIY f**kup don't have to be.
The old time-tested and proven "take it to a shop" way of doing things seemed to have almost dissapeared, in favor of "cheap DIY fixes" led on by internet blabber - "it ain't rocket science, you can do it".

Put the good ole service shops out of business slowly but surely by internet blabbering - then they cry they can't find a decent one anymore.

I'm sure this post will get "flack" from some - and ya know what?
I don't give a crap.
I won't mince words.
 
When doing the recap did you run the set after each board was completed; for the same amount of time. Was this latest completion, the final process for the recap work?

Specialone53: I know you know your stuff! (And) I know you have a slight point but this Forum is for helping each other and you have helped many others. What's up? I'm having a beer and enjoying the evening. I'd love to share one with you.
 
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See people?

The widely touted "re-capping" doesn't cure all ills.
Sorry, but it's the truth.
With hundreds of individual parts in a certain electronic set, it's difficult to impossible for even a knowledgeable tech to "diagnose" an issue over the internet.
Add to that fact that improper servicing might have been performed - and you've now got something non-standard as a problem to address.
Were these "caps" properly installed?
Was a wire pinched accidentally during the procedure?
The list goes on.... christ only knows now.

But nevertheless, the hoardes of online geeks and wannabes will create an endless thread to chip in and help the needy.. at times being no more than "the blind leading the blind".

With all due respect - online cries for help after a DIY f**kup don't have to be.
The old time-tested and proven "take it to a shop" way of doing things seemed to have almost dissapeared, in favor of "cheap DIY fixes" led on by internet blabber - "it ain't rocket science, you can do it".

Put the good ole service shops out of business slowly but surely by internet blabbering - then they cry they can't find a decent one anymore.

I'm sure this post will get "flack" from some - and ya know what?
I don't give a crap.
I won't mince words.

:thmbsp:
Before doing a recap, it's best to listen to the AUT. I put it through its paces on the Scope & distortion analyzer to see what's going on.
True, a recap doesn't cure all. It just adds to the possibility of a failure. Now you have to retrace your work before further troubleshooting.
Just a possibility. Most recaps are successful or easily rectified.
I like to do a section at a time. Then check the results. No obvious issue like hum or buzz, proceed to the next section. Time consuming yes, but better than having a failure after everything is put back together and now having to go through the entire set.
 
It may reside in the pre amp area. were the signals run close because both channels are showing the buzz. Check for any visual clues like reversed components, blown caps. You may have installed a slightly lower voltage cap in the wrong place.
 
I haven't seen a SINGLE regulated voltage's voltage reading to confirm that the power supply regulators are doing their jobs...

Until THAT is done, this is just hot air.

If the regulated supply is running flat out (as in shorted or railed) everything will appear to work, all the while the hum is riding on in...
Basically, THAT is the purpose of the regulated supplies.
 
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It may reside in the pre amp area. were the signals run close because both channels are showing the buzz. Check for any visual clues like reversed components, blown caps. You may have installed a slightly lower voltage cap in the wrong place.

Thanks for your time. I guess I should have said a little more about what i'd done. All parts lists from Markthefixer related threads after extensive reading. All parts were ordered new from Mouser. I did one board at a time and double and triple checked each part and solder joint. I powered up and played music after every board was completed and no prob's. Again, after I had essentially finished the recap and listened to music for about an hour after having done current and bias adjusts, powered down for the evening. When I was going to put the cover back on and take it to its new home in my listening room I turned it on just to have a final quick listen before taking it downstairs and to my shock and surprise it had a loud hum evenly in both channels.
 
I haven't seen a SINGLE regulated voltage's voltage reading to confirm that the power supply regulators are doing their jobs...

Until THAT is done, this is just hot air.

If the regulated supply is running flat out (as in shorted or railed) everything will appear to work, all the while the hum is riding on in...
Basically, THAT is the purpose of the regulated supplies.

I just cut and pasted from a previous thread but these are my voltages
pins 1&2: -51.6, should be -52v, regulated
pins 3&4: +68.5, should be +52v, regulated
pins 5&6: +32.8, should be +32v, regulated
pin 7: +18.8, should be +18v, regulated, provides power for display circuit
pin 8: 0v, ground
pin 9: raw, -54.5, unregulated
pins 10&11: -32.2, should be -32v, regulated
pin 12: raw, +51.7, unregulated
pin 13: raw, +71.4, unregulated
pin 14: 0v, ground
pin 15: raw, -73.8, unregulated
pin 16: +6.1vac
pin 17: +55.9vac
pin 18: +55.9vac
pin 30: +56.7
pin 31: +56.7

Hope this helps.
 
See people?

The widely touted "re-capping" doesn't cure all ills.
Sorry, but it's the truth.
With hundreds of individual parts in a certain electronic set, it's difficult to impossible for even a knowledgeable tech to "diagnose" an issue over the internet.
Add to that fact that improper servicing might have been performed - and you've now got something non-standard as a problem to address.
Were these "caps" properly installed?
Was a wire pinched accidentally during the procedure?
The list goes on.... christ only knows now.

But nevertheless, the hoardes of online geeks and wannabes will create an endless thread to chip in and help the needy.. at times being no more than "the blind leading the blind".

With all due respect - online cries for help after a DIY f**kup don't have to be.
The old time-tested and proven "take it to a shop" way of doing things seemed to have almost dissapeared, in favor of "cheap DIY fixes" led on by internet blabber - "it ain't rocket science, you can do it".

Put the good ole service shops out of business slowly but surely by internet blabbering - then they cry they can't find a decent one anymore.

I'm sure this post will get "flack" from some - and ya know what?

You bet your ass you will.

I don't give a crap.
I won't mince words.

Neither will I.

What are you, a service shop?

At 40 bucks an hour minimum shop rate, not many of these units would stay out of the dump. And they work even MORE poorly when crushed by a bulldozer.

Bitching about service shops cuts both ways. Products that are NOT MADE OR EXPECTED to live long, that the standards they operate on will be obsolete before their capacitors age out of specification.

Manufacturers that gamble that MOST of their units will be out of service before the tortured cheap capacitors in their switching power supplies give up the ghost and hurt their reputation by dying in noticeable droves.

Or that the integration of functions, components and physical layout even lend themselves to repair, with NLA chips and parts literally the size of a grain of sand.

Looking at the number of Audiophiles scattered across the USA, even if we ALL exclusively patronized the shop closest to us, we would be the odd anomaly walking in the door. We could NEVER keep them in business - there's just not enough of us.

AS far as internet refurbishing and diagnosis, what the HELL have I been doing the last NINE YEARS HERE??? IMAGINING IT????

IF I notched my test probe for just every internet fix I did on here, there wouldn't be enough room.

AND IF I said what my first inclination was, well, I would be destroying my reputation as a tolerant gentleman.
No less when I suggest what to avoid when going through certain doorways.

mods: sorry in advance, and I won't be piqued if you find it necessary to edit this post...
 
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I'm fairly new to this whole thing but took the dive and recapped my SA-9800. I used M.T.F.'s most recent threads for the parts lists. Everything went great and powered up fine, relay after 6 or 7 sec., and played music with a dead quiet backround noise. I was so happy. It was still sitting on the workbench a few days later when I came back to work on it some more. I turned it on and there is now a loud buzzing sound or hum that is coming from both channels equally and registers one bar on the indicator. It does not increase with volume.
I've replaced almost everything on the P.S. board except for the two sk34's. So i'm kinda stuck not knowing what to do now. Any help would be much appreciated.

Does the music come through, and can it be controlled by the volume control?

New caps can cause weak transistors to give up the ghost.

OK, I just saw your voltages, the +52 is up at +68.

Check ALL the screws you put in and also look for pinched wires.

Sometimes there should be just ONE shorter screw somewhere, and a longer one shorts something out in that position.

edit- closer reading makes me think the screws hadn't gone in yet, thus it was the turn on shock...
Q1 and Q3 were new? replacements done at the same time? newe ones that came out, what are their condition?

Read and post the q1, q3 voltages CAREFULLY, the D5 is OK, since it is used to set the +/- 32v and -52v
the unknown is Q5, THAT one doesn't look like it can be replaced by a current source.
This portion of this supply has always been a question mark in my mind, as in "WHAT were they THINKING????????"

You might want to check q1 and q3 out of circuit for shorts. The fet shouldn't have been stressed, also be sure the correct polarity transistors are in q1 and q3 - it's a sziklai pair rather than a darlington pair.
 
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Does the music come through, and can it be controlled by the volume control?

New caps can cause weak transistors to give up the ghost.

OK, I just saw your voltages, the +52 is up at +68.

Check ALL the screws you put in and also look for pinched wires.

Sometimes there should be just ONE shorter screw somewhere, and a longer one shorts something out in that position.

Read and post the q1, q3 voltages CAREFULLY, the D5 is OK, since it is used to set the +/- 32v and -52v
the unknown is Q5, THAT one doesn't look like it can be replaced by a current source.
This portion of the supply has always been a question mark in my mind.

You might want to check q1 and q3 out of circuit for shorts. The fet shouldn't have been stressed, also be sure the correct polarity transistors are in q1 and q3 - it's a silazaki pair rather than a darlington pair.

Thanks so much for your time and patience.
And don't let those others tell you that your not doing something worthwhile. Preserving as much history as possible, is how I see it. I could have just bought a brand new surround theater system and saved myself a lot of time. But I appreciate quality items and care about sound quality. As well as being a bit nostalgic for the "old school iron". Which is why I'm trying to bring this one back to life and have some fun at the same time.

As for Q1 and Q3: replaced with +100 4a 30w 863-MJE15032G npn to-220
-100 4a 30w 863-MJE15033G pnp to-220

The board was pretty bad on the backside and I had to scrape new foil in order to make the connection.

Shots of before and after.
 

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See people?

The widely touted "re-capping" doesn't cure all ills.
Sorry, but it's the truth.
With hundreds of individual parts in a certain electronic set, it's difficult to impossible for even a knowledgeable tech to "diagnose" an issue over the internet.
Add to that fact that improper servicing might have been performed - and you've now got something non-standard as a problem to address.
Were these "caps" properly installed?
Was a wire pinched accidentally during the procedure?
The list goes on.... christ only knows now.

But nevertheless, the hoardes of online geeks and wannabes will create an endless thread to chip in and help the needy.. at times being no more than "the blind leading the blind".

With all due respect - online cries for help after a DIY f**kup don't have to be.
The old time-tested and proven "take it to a shop" way of doing things seemed to have almost dissapeared, in favor of "cheap DIY fixes" led on by internet blabber - "it ain't rocket science, you can do it".

Put the good ole service shops out of business slowly but surely by internet blabbering - then they cry they can't find a decent one anymore.

I'm sure this post will get "flack" from some - and ya know what?
I don't give a crap.
I won't mince words.
Whoa! Kind of a broad brush there, partner! I did not notice ANY "due respect." Remote troubleshooting is something I have done here since the first day I joined in 2005, very successfully. It just takes a bit longer, and shotgun work has no valid application to it.

I can link to countless complicated remote repairs successfully completed here at AK. All of them were assisted by knowledgeable AK "online geeks," and taking not a penny from repair shops. In fact there has been alot of AK cleanup of "work" perpetrated by said "repair shops." In fact, I have NEVER seen a crappy ECG sub installed by anyone but a "repair shop tech." Personally, I have been a repair shop tech, and have been working on this gear since it was new, and I am a software and hardware design engineer with 35+ years of experience, with quite a few patents to my name.

Before you start slapping the faces of people you don't know, and have never met, I suggest you step back and take a very deep breath, or prepare to take a vacation. Contribute something positive, express yourself less like an ass hat, or take a freaking hike. "No attitude" means "no attitude." LOSE YOURS! Go "not giving a crap" and "not mincing words" elsewhere. We don't need you.

You have been warned.

Rich P
 
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To the OP, I don't have much time for remote troubleshooting these days. Mark has volunteered to step up to help. He has done exceptionally well at it here for many years. You are in good, patient hands. When you are done, please show your gratitude by a contribution to the forum.

I will contribute this...please get yourself some eye protection and do NOT operate this piece without it until repairs have been completed and this piece has been adequately burned in. The inferrence I am drawing from your description is that the piece worked before you started, and what you describe was likely caused "by your work." It happens to the very best of us. In such case, the most likely cause is a solder bridge, a polarized cap installed backwards, a pinched or broken wire, or the like. You may have lost a rectifier.

There are tricks to the trade. Mark has alluded to some, like doing a piece at a time, and verifying that you did not break something in the process. If you did break something, it is then easier to find it. The reason is that a solder bridge or backward cap can be almost impossible to find, depending on where it is.

If the unit did not work before you started, it was wrong to try to fix it by a recap. A recap is a procedure that is only to be done after a complete repair, and is intended to aim for longevity. It is NOT a repair activity.

In any case, you have what "is." That is what you will need to work with. Be patient. Don't get frustrated or in a hurry. Do a very careful and comprehensive visual inspection. Pick a voice and listen to that one pretty much exclusively. Do exactly what you are told, and come back with the requested readings and results. Don't force anything. Don't jump ahead. Do not keep the unit powered up any longer than you must to obtain the requested readings. WEAR YOUR EYE PROTECTION!

My suggestion is to let Mark lead you through some measurements without power applied, before going on to powered readings. If serious damage has not been done by now, it certainly seems to be looming. If you replaced the main filter caps, the inrush to initially charge those could have been too much for your old rectifiers. Verify the rectifiers first. Your speaker protection does not appear to be kicking in. That is an important clue. It is also a warning that you should not work with any speakers you want to keep connected to the unit. Use load resistors, or work without speakers attached, at least until you have determined that it is safe to hook them up. Load resistors are not expensive, it will just take time to wait for them to come in, and you may then need an o'scope, instead of your ears. The output drivers in this unit are special. If they can be saved, do so.

The hum you describe will likely resolve to silence in short order. Then the failure path will be easier to find, but you may wind up with some pretty extensive repairs to do. You may need to let a knowledgeable tech take it from here, or somewhere down the road. Mark will help you know if/when that is the case. Let me say this again...WEAR YOUR EYE PROTECTION!

Good luck. I'll be watching, and will contribute as I may be able.

Rich P
 
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See people?

The widely touted "re-capping" doesn't cure all ills.
Sorry, but it's the truth.
With hundreds of individual parts in a certain electronic set, it's difficult to impossible for even a knowledgeable tech to "diagnose" an issue over the internet.
Add to that fact that improper servicing might have been performed - and you've now got something non-standard as a problem to address.
Were these "caps" properly installed?
Was a wire pinched accidentally during the procedure?
The list goes on.... christ only knows now.

But nevertheless, the hoardes of online geeks and wannabes will create an endless thread to chip in and help the needy.. at times being no more than "the blind leading the blind".

With all due respect - online cries for help after a DIY f**kup don't have to be.
The old time-tested and proven "take it to a shop" way of doing things seemed to have almost dissapeared, in favor of "cheap DIY fixes" led on by internet blabber - "it ain't rocket science, you can do it".

Put the good ole service shops out of business slowly but surely by internet blabbering - then they cry they can't find a decent one anymore.

I'm sure this post will get "flack" from some - and ya know what?
I don't give a crap.
I won't mince words.
Moderator post:

This site is about enjoying audio, sharing information, helping others. For many it is a hobby; for some it is a place to communicate and learn or teach. It is "All audio and no Attitude". I am not sure what it is for you but your attitude shown in this post needs to change. If you do not have anything positive to contribute to a thread, post somewhere else where you can assist. There are many knowledgeable techs on AK who are a blessing to the community and provide first class assistance to those who are willing to "give it a go" and learn.
 
To the OP, I don't have much time for remote troubleshooting these days. Mark has volunteered to step up to help. He has done exceptionally well at it here for many years. You are in good, patient hands. When you are done, please show your gratitude by a contribution to the forum.

I will contribute this...please get yourself some eye protection and do NOT operate this piece without it until repairs have been completed and this piece has been adequately burned in. The inferrence I am drawing from your description is that the piece worked before you started, and what you describe was likely caused "by your work." It happens to the very best of us. In such case, the most likely cause is a solder bridge, a polarized cap installed backwards, a pinched or broken wire, or the like. You may have lost a rectifier.

There are tricks to the trade. Mark has alluded to some, like doing a piece at a time, and verifying that you did not break something in the process. If you did break something, it is then easier to find it. The reason is that a solder bridge or backward cap can be almost impossible to find, depending on where it is.

If the unit did not work before you started, it was wrong to try to fix it by a recap. A recap is a procedure that is only to be done after a complete repair, and is intended to aim for longevity. It is NOT a repair activity.

In any case, you have what "is." That is what you will need to work with. Be patient. Don't get frustrated or in a hurry. Do a very careful and comprehensive visual inspection. Pick a voice and listen to that one pretty much exclusively. Do exactly what you are told, and come back with the requested readings and results. Don't force anything. Don't jump ahead. Do not keep the unit powered up any longer than you must to obtain the requested readings. WEAR YOUR EYE PROTECTION!

My suggestion is to let Mark lead you through some measurements without power applied, before going on to powered readings. If serious damage has not been done by now, it certainly seems to be looming. If you replaced the main filter caps, the inrush to initially charge those could have been too much for your old rectifiers. Verify the rectifiers first. Your speaker protection does not appear to be kicking in. That is an important clue. It is also a warning that you should not work with any speakers you want to keep connected to the unit. Use load resistors, or work without speakers attached, at least until you have determined that it is safe to hook them up. Load resistors are not expensive, it will just take time to wait for them to come in, and you may then need an o'scope, instead of your ears. The output drivers in this unit are special. If they can be saved, do so.

The hum you describe will likely resolve to silence in short order. Then the failure path will be easier to find, but you may wind up with some pretty extensive repairs to do. You may need to let a knowledgeable tech take it from here, or somewhere down the road. Mark will help you know if/when that is the case. Let me say this again...WEAR YOUR EYE PROTECTION!

Good luck. I'll be watching, and will contribute as I may be able.

Rich P

Thanks for the insight, much appreciated.
 
As for Q1 and Q3: replaced with +100 4a 30w 863-MJE15032G npn to-220
-100 4a 30w 863-MJE15033G pnp to-220

I was speaking of q1 and q3 power pass elements, there are the sziklai pair's opposite polarity drivers of q3 (2sa733 > ), q4(2sa904 > ) to consider.

If you really used a 863-MJE15033G pnp to-220 in place of a low power high gain 2sa733 pnp in Q3, I'd like to know WHO recommended that. :nono:

edit - the pictures don't agree... they seem closer to my parts list below.
Q11 and Q12 are the only TO-220 transistors provided for on that board.

my old parts list :
awr-194 q1 2sc1735 pwr pass + 100v .5a .8w 512-KSC2690AYS to-126 30 to 300 hfe 130mhz to-92
awr-194 q2 2sc1735 pwr pass - 100v .5a .8w 512-KSC2690AYS to-126 30 to 300 hfe 130mhz to-92
awr-194 q3 2sa733 pwr sziklai + 50v 0.15a 0.25w 512-KSA1013YBU to-92L 40-700hfe 180mhz to-92
awr-194 q4 2sa904 pwr sziklai - 90v 0.05a 0.2w 512-KSA1013YBU to-92L 250hfe 150mhz to-92*c
awr-194 q5 2sk34 leave alone, unobtanium
awr-194 q6 2sk34 leave alone, unobtanium
awr-194 q7 2sc1914 fb ampl + 90v 0.05a 0.2w 512-KSC1845FTA (ln)to-92 250hfe 150mhz to-92*c
awr-194 q8 2sa904 fb ampl - 90v 0.05a 0.2w 512-KSA992FBU (ln)to-92 250hfe 150mhz to-92*c
awr-194 q9 2sc945 lv err amp + 50v 0.1a 0.25w 512-KSC2383YTA to-92L 600hfe 250mhz to-92
awr-194 q10 2sa733 lv err amp - 50v 0.15a 0.25w 512-KSA1013YBU to-92L 40-700hfe 180mhz to-92
awr-194 q11 2sd712 lv pass + 100 4a 30w 863-MJE15032G npn to-220 55to300hfe 8mhz to-220
awr-194 q12 2sb682 lv pass - 100 4a 30w 863-MJE15033G pnp to-220 55to300hfe 8mhz to-220
awr-194 d1 sib01-02 power 200 1a 512-1n4004
awr-194 d2 sib01-02 power 200 1a 512-1n4004
awr-194 d3 sib01-02 power 200 1a 512-1n4004
awr-194 d4 sib01-02 power 200 1a 512-1n4004
awr-194 d5 xz-060 main zener 6v zener 0.5w 512-1n5233b
awr-194 d6 1s2473 fast 100v 0.1a 512-1n4148
awr-194 d7 1s2473 fast 100v 0.1a 512-1n4148
awr-194 d8 10E2 power 400v 1a 512-1n4004
awr-194 d9 10E2 power 400v 1a 512-1n4004
awr-194 d10 mz-177 shunt reg 17v zener 0.5w 512-1N5247B

But it looks like you need some 2sk34's which are getting rare, because they are 50v parts

You can TRY a general jfet (maybe a j113 or similar) and see if that works in the supply. It is a 35v part and still is common.

I understand that being in Taiwan makes parts procurement a bit more difficult.
 
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Sorry, my bad it was Q11, Q12 that has has +100 4a 30w 863-MJE15032G npn to-220
-100 4a 30w 863-MJE15033G pnp to-220.

Yup, that was the same parts list I used.

Plus I also did:

Protection Board
awm-163 Q1 2SC945A Replace with 512-KSC2383OTA
awm-163 Q2 2SC945A Replace with 512-KSC2383OTA
awm-163 Q3 2SC1885 Replace with 512-KSC2690AYS to-126

Amp Left
gwh-129 Q7 2SA912 TO-92L Replace with 512-KSA1220AYS TO-126
gwh-129 Q9 2SA726S Replace with 512-KSA992FBU
gwh-129 Q11 2SC1885 TO-92L Replace with 512-KSC2690AYS TO-126

Amp Right
gwh-130 Q8 2SA912 TO-92L Replace with 512-KSA1220AYS TO-126
gwh-130 Q10 2SA726S Replace with 512-KSA992FBU
gwh-130 Q12 2SC1885 TO-92L Replace with 512-KSC2690AYS TO-126

Also maybe something or not, Pustelniakr posted: 'If you replaced the main filter caps, the inrush to initially charge those could have been too much for your old rectifiers. Verify the rectifiers first.'
I did replace those with: Main caps (x4):667-ECE-T1KA153FA (Panasonic THA Series 15,000uf 80v) But if this indeed is the culprit would the relay still turn on? and would I still be able to listen to music albeit with back round hum? Because it does, and I can.
 
A bit more background:

I bought the unit a few years ago from an avid enthusiast who said that it was originally bought and owned by his brother back in 1980. Since then it was handed down and I could tell that it had had some work done to it. It worked fine for about a year until it started to develop a bump in the left channel only. By this I mean when cold no problem, but after about 15 min. of listening to music and normal operating temp achieved every minute or so the left channel would spike on the indicator sometimes 3/4 to full and i'd get a pop through the speakers and headphones alike. 'It wasn't a huge concern' I thought, as this would only happen about once every listening session.(guess I was wrong) Until it started to happen every other minute regardless of volume level and put it into protection one time. At that point I knew it had to be fixed and didn't turn it on again.

Then the total recap + transistors, and resistors, and diodes, and I must have done it right because she powered up fine and played for a good hour without any problems or "bumps". So I figured problem solved. But it still crept back in and now am faced with this plus the 'hum issue'.

Am I wrong to assume that the source of this pop is from something on the left amp board that I didn't replace?

I have only replaced:
Amp Left
gwh-129 Q7 2SA912 TO-92L Replace with 512-KSA1220AYS TO-126
gwh-129 Q9 2SA726S Replace with 512-KSA992FBU
gwh-129 Q11 2SC1885 TO-92L Replace with 512-KSC2690AYS TO-126
gwh-129 vr1 330k multi offset 652-3296P-1-204LF
gwh-129 vr3 100 single idle 70 652-3386H-1-101LF
gwh-129 vr5 47k single idle 56 652-3386H-1-503LF
gwh-129 c1 2.2uf 50v ceanl 2.2 50 647-UKL1H2R2MDDANA
gwh-129 c11 47uf 63v cea 47 100 647-UPW2A470MPD1TD
gwh-129 c13 47uf 63v cea 47 100 647-UPW2A470MPD1TD

Could this 'pop' have done something to create the 'hum' or are these two things probably unrelated? (I know this is prob difficult to answer)

Regards, Jerry
 
d1 - d4 on that board can be replaced with 512-1n4004 (the 1n4004 diode, even radio shack has them) 1 amp 400v

the other high power diodes are robust but it is a possibility - but for hum to happen on BOTH channels it would be an unlikely double failure.

Thus measure the DC voltage across EACH of the big new cap's terminals, and then the AC voltage (same measuring place) across as well. IF the AC voltage reads impossibly higher than the DC, insert a 0.1uf cap with 100+ volt rating in series with the meter lead and retake the readings...

Rich was speaking generally and from some of the general things he said, he hadn't stringently analyzed your whole thread for clues. A single failure of the +52v regulated supply allowing +68.5v through, would be highly likely to be your failure, and we must fix that before looking further into the unit for hum.

edit - pop vs hum. hum first then we look into pop when the regulated supplies are all behaving. the pop could have been from many things. There are some transistors that bake themselves in the amp and open solder joints. but answer is: very probably unrelated hum to pop.

that's all for tonight in this thread, it's late and there are more threads to try to cover...

to do:
test q1, q3 and the resistors around them, and find a jfet, industry part number "J113" locally for q5.
 
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