PCE Duo - No Sound *solved*

[Keith Courage]

now you are on the right track. Of all those caps that you mentioned with lower voltage they should all be around 3.5 volts when working correctly.the amp that you have picture there should definitely be removed, clean the board really well, and then reattached the amp. also, you might need to repair some of the traces going to the amp itself because  they can be damaged from the leaking through of the 22uf cap up above.

taking care of the problems in this one area might fix all of your issues since the shorting out from the corrosion under that amp can cause the voltage drops in all the other areas.

[HuMan]

I pulled the crusty 4558, it was definitely nasty under there. I cleaned up the pad and found two corroded vias, incidentally they were for the 22uF 16v cap. I patched those and resoldered the crusty op amp. I don't have any in SMD form factor, just DIP, waiting on some SMD 4558s in the mail...

The 22uF 16v cap is now 1.5v. Every other cap you mentioned is at the same voltage, as are the op amps (3.2v). Sound output is still silent. I did notice left channel HuCard audio on the headphone jack is very faint, but present. Right channel seems dead. CD audio seems dead entirely.

Would a faulty 4558 continue to cause problems? Such as the low voltage and the missing right channel?





On an unrelated note, I noticed some other capacitor-looking parts on the board. Shouldn't these be replaced too? While I'm at it, a number of the big chips have that white stuff on the pins. I figured it was just flux from the factory soldering, but if it's not I'll try to clean it off.

[Keith Courage]

Your 2nd pic is still the area needing work. I bet the traces to the 22uf cap are messed up. Also a possibility is the ground via just to the right of the op amp.

I circled in blue the ground via which I normally repair by bridging a cap lead through it and then soldering on each side. https://postimg.org/image/ytytbgskp/

Lines in red are places to make sure you have 3.5V-3.8V going. This is how I repair any bad traces getting to the 22uf uf cap. They can all be wired together if any of the traces under the op amp are bad but usually running just one of those lines can fix the issue. You might also need to run one of these lines directly to the 22uf cap itself if the cap pad was all corroded.

Typically when the op amp is bad voltages read too high around 4.5 or 5V.

No one ever bothers with the caps in your 3rd pic since they are SMD caps.

[HuMan]

Before I soldered the op amp back on, I checked for continuity on all 8 op amp pads. They were all good except for the two vias I patched. In your example picture, pins 3 and 5 are indeed making contact with the trace below the silkscreened "1", only problem is all three of those points show 1.6v. I already patched the corroded ground via, the patch wire for it can be seen in pic 1, it's the one going from cap - to that trace just above. It's as close a fix as I can manage.

As of right now, the voltage is still low on all of the caps you previously mentioned.

[Keith Courage]

Is the solder point that I marked below the 14053B chip putting out 3.8V? Also, is it me or is there old cap goop inside the via for that trace? Might just be the camera angle.

How about the 22uf cap on the other side? Does that have 3.8V? The pad for the cap lead looks extremely corroded in the pic.

The problem for this area needs to be fixed for the other voltages to be corrected.

[HuMan]

Unfortunately, the voltage is 1.6v at both the trace below the 14053B and the 22uF cap.

[cloudd]

oops wrong thread

[HuMan]

Found another corroded via, this time at the cap below the volume wheel.




It's tough to see from here, but it's the lone trace ending in a via to the left of "C676". That trace is supposed to be connecting a 4.7uF cap to R675 and further down the board.

I will continue to look for corroded vias at this point, it seems to be the most glaring ailment with this Duo.

[Keith Courage]

all of the 22uf capacitors that I circled on that picture for you should all be running at 3.8 volts. There is definitely a bad trace or a short in a via somewhere that is killing the voltage.

also, the main larger trace that's sending the power to all of the op amps should be 7 volts so that's another thing to diagnose as well.

[HuMan]

Well, I used my better judgement and wired C671 positive to R677, doing that brought back the right channel on the headphone jack. Both channels are audible, but are very faint and only apply to HuCard sound. CD sound is still out to lunch. AV port audio is also missing.

In your experience, what usually causes a voltage drop? Just broken traces and shorting? Last I recall, a complete shorting to ground would result in almost no voltage on the caps. Nearly half the correct voltage might be something else.

In PM you mentioned temporarily connectin op amp pins 3 or 5 to a nearby 4.3v source, all that did was cut the voltages in half again. 3.3v on the op amps became 1.5v, 1.6v on the caps became 0.5v.

[cloudd]

HuMan you didn't replace all of your caps? I think this is related to at least some of your problems. When I cut my caps off (i replaced all of them), there were at least 3 bad ones with leaking acid/corrosion underneath of them. All of these 3 caps looked completely normal until I removed them.

[Keith Courage]

Old cap goop in vias or corroded pads/traces all cause voltage drops.

Unfortunately its very difficult trying to pin point the problem area without having the board in front of me. From the trouble shooting we have done it sounds like there could be multiple issues and not just one bad connection.

[crispytreat]

I am facing similar issues with 2 duos. Is continuity checking enough? Can I have continuity and still have a voltage drop?  Should a check continuity first and the also measure voltage?

[HuMan]

I did replace all of the caps, or nearly all. There's a pair of 100uF leaded caps in the CD-ROM area that I can't desolder because there's a big chip underneath them.

Ok so just continue searching for corroded vias and traces. When I was installing the cap kit, I was careful to clean the pads and reflow them with fresh solder before soldering the new cap on. I also didn't cut them off, I heated one side, lifted it a bit, then the other, back and forth until the cap was freed.

I will also check that 7v line feeding the op amps, just had a bunch of other stuff to do today. Maybe I will be able to do more troubleshooting on Sunday.

crispytreat, I would suggest doing voltage and continuity tests, that has helped me a lot in diagnosing my Duo.

[cloudd]

HuMan you replaced the caps with the same type of surface mount caps as the originals?