C-200 preamp, starting to >POP<

[davstev]

Hi all,

I have an Accuphase c-200 that works really well. Lately, it's started popping. If I leave it on with no music playing, every once in awhile (I'd say, an average of every half hour or so), it'll just emit a single >POP< sound. Somewhere between a thump and a pop. Problem seems to be slowly getting worse.

I think something must be starting to go. I know it's not my amp, because I put a different preamp in, and no popping.

Is anyone familiar with the preamp enough to know what might be starting to go? Where to start investigating- transistors, caps? It's all original parts inside. I know it's due for a recap, but if I wanted to try to locate the problem specifically, where to start looking, and how to test? I have a DMM, I can solder.

Thanks for your ideas.

David

 

[transmaster]

Is this a Kenwood C2 pre-amp? The C-200 seems to be a car stereo. If it is a C2 here is the service manual.

http://www.manualscenter.com/manuals/kenwood/basicc2-service-manual.html

 

[davstev]

Is this a Kenwood C2 pre-amp? The C-200 seems to be a car stereo. If it is a C2 here is the service manual.

http://www.manualscenter.com/manuals/kenwood/basicc2-service-manual.html

Hi transmaster. No, it's the well-regarded C-200 preamp by Accuphase. Sorry, I should have specified accuphase.

https://www.hifiengine.com/manual_library/accuphase/c-200.shtml

It won't be hard to get my hands on the schematic for it, but more than that, I'm wondering if anyone knows of any particularly fault-prone areas of the preamp that could lead to this popping. I'm not expert at troubleshooting this kind of thing, and I'd probably just recap the whole thing rather than pay a tech to try to locate the source of the problem. However, even a recap might not cure it, if it is a transistor issue or something.

 

[ManyMoonsAudio]

It is most likely, a transistor issue if it is popping. If it does it in all modes, not just phono, and in one channel, you have it isolated to the line stage.

 

[Blue Shadow]

You mentioned recap...all I can do is offer a picture thead from the web of the work getting done. This one isn't easy. Hope you get it working right again.

In case you decide to go all in:
http://www.tapeheads.net/showthread.php?t=31825

 

[davstev]

You mentioned recap...all I can do is offer a picture thead from the web of the work getting done. This one isn't easy. Hope you get it working right again.

In case you decide to go all in:
http://www.tapeheads.net/showthread.php?t=31825

I like the pics- the C-200 in the wild. I've seen your thread before. I might need to get there someday. At least the boards are easy to extract....

 

[Blue Shadow]

yes, that is PS, he used to be here but now owns tapeheads and well, moved on.

 

[davstev]

It is most likely, a transistor issue if it is popping. If it does it in all modes, not just phono, and in one channel, you have it isolated to the line stage.

It pops in both channels. I know this because I see both LED meters on my power amp bump up equally when it pop/thumps. And it is happening when in line stage mode. But i wouldn't be surprised if it happened in phono too, I just haven't been listening to vinyl of late. Could test this by hooking it up.

With this being the case- both channels and in line stage, if not both- is there a logic to where a faulty transistor might be? (I'm no wizard with schematics, btw.) Somewhere in the output section?

many thanks.

 

[transmaster]

OK I saw the Accuphase C-200. Don’t know much about Kenwood Audio gear, I do have considerable knowledge about Kenwood’s excellent amateur radio equipment. I have numerous sources for service manuals for ham radios and most of these sites have audio service manuals as well.

Here is a part of my Kenwood equipment.

1986 Kenwood TS-440S-AT (automatic antenna tuner) HF transceiver 10-160 meters.

 

[davstev]

OK I saw the Accuphase C-200. Don’t know much about Kenwood Audio gear, I do have considerable knowledge about Kenwood’s excellent amateur radio equipment. I have numerous sources for service manuals for ham radios and most of these sites have audio service manuals as well.

Here is a part of my Kenwood equipment.

1986 Kenwood TS-440S-AT (automatic antenna tuner) HF transceiver 10-160 meters.
View attachment 1169601

View attachment 1169602

No trouble getting my hands on an Accuphase c-200 schematic, really. I hope you enjoy your radio, sir....

 

[transmaster]

Here is a suggestion for you. There is a nifty vintage piece of test equipment called the Sencore “cricket”. It is a great transistor tester. What it does is in circuit testing of transistors. I have the larger Sencore TR-139B which also does in circuit testing. What the cricket does is it gives you a simple Yes-No decision on a transistor. To test it in detail you still need to pull it but the cricket, and my 139B has never been wrong when a suspected transistor is pulled and checked out fully. There are always a bunch of these on eBay. These Sencore transistor testers are particularly good with vintage transistors, and my 139B is primo on pestilential Germanium transistors.

 

[davstev]

Here is a suggestion for you. There is a nifty vintage piece of test equipment called the Sencore “cricket”. It is a great transistor tester. What it does is in circuit testing of transistors. I have the larger Sencore TR-139B which also does in circuit testing. What the cricket does is it gives you a simple Yes-No decision on a transistor. To test it in detail you still need to pull it but the cricket, and my 139B has never been wrong when a suspected transistor is pulled and checked out fully. There are always a bunch of these on eBay. These Sencore transistor testers are particularly good with vintage transistors, and my 139B is primo on pestilential Germanium transistors.

View attachment 1169625

This looks fantastic.Thanks for the suggestion, I'll investigate!

 

[transmaster]

In addition a capacitor ESR tester will give you the information you need to checkout your capacitors in circuit. The best Capacitor tester, for the money, for modern electronic circuits is the Peak Atlas ESR-70. I also have a Heathkit C3 condensor test for higher voltage vacuum tube rigs it leak tests to 450 Volts.

With a good DMM, the Cricket, and the ESR-70 you are pretty much covered for DXing modern audio gear. If you need more then this send it to a qualified tech.

 

[transmaster]

I should have mentioned those of you who need calibrated testing equipment Peak can calibrate these instruments, with the necessary certification documents.

 

[transmaster]

My next Altas instrument is the LCR-45
https://www.peakelec.co.uk/acatalog/lcr45.html

Here is a accurate instrument that fits in a shirt pocket and gives you everything thing you need to test out your latest speaker find at the thift store or garage sale.

 

[ManyMoonsAudio]

If both channels are popping, then you can point blame at the supply.

 

[davstev]

If both channels are popping, then you can point blame at the supply.

Thanks, I also suspected this.

 

[avionic]

Check for cracked solder connections on the PS pass transistors.