PCE Duo - No Sound *solved*

HuMan · 10/06/2016, 03:39 AM

System: PC Engine Duo (black)
Symptom: No sound, before and after cap kit

When I first got this Duo, it was sold as working (HuCards and CDs), working video, non-working audio on both HuCards and CDs. I opened it and found a partial cap kit applied, somewhat sloppily. There wasn't much capacitor damage, just one ripped trace on one of the big leaded caps behind the 7805s.

I applied a near-full cap kit (can't easily reach the two 100uF 16v leaded caps above the BA6290A). I used a cap kit and instructions from Console5. The video quality improved back to what PC Engines are known for, HuCards and CDs still work, still no audio on either of them.

So in a way, nothing changed after the cap kit, so the audio issue is being caused by something else... Or via/trace corrosion which I hope not. When I have some more time for soldering I'll check the op amps and volume IC. Anything else I should check?

YoshiKnuckles · 10/06/2016, 10:03 AM

Have you tried cranking your set's volume up to max, or plugging in headphones with them at max to see if you get anything at all out of it?

Basically you want to find out of the system is producing audio from it's chipset or not.

If it is producing audio than you have an amplification issue, and should start checking all of the Op Amps and the M51131L.

You want to get the card sound working, then try to get the CD sound working.

For the CD section, start with the DAC to see if it is outputting anything. Not exactly easy to do though as it is on the bottom of the board.

Hopefully that helps a bit.

HuMan · 10/06/2016, 12:12 PM

No sound from either the AV port or the headphone jack. Completely silent.

I'll check all the Op Amps and the M51131L. For checking traces, does anyone know the general layout of the sound? Where does it start and go through on its way to the AV port and headphone jack?

YoshiKnuckles · 10/06/2016, 12:43 PM

For the card sound, you want to check the Hu6280. It's the CPU of the console, and the sound starts here. The pins are rather small though so be careful not to short them out.

https://console5.com/wiki/Hu6280

Pins 17 and 18 of the 6280 output the sound. It's easiest to check this with an oscilloscope, as a multimeter isn't going to show you if the signal is there or not. Also check the 5V audio rail on pin 19 and the audio GND on pin 20. All you really need to do is see if it is producing a waveform or not.

Keith Courage · 10/06/2016, 03:29 PM

most likely your problem is the op amp closest to the AV Jack. Not that the amp is bad though. you should remove the amp and clean underneath it really well. I like to use rubbing alcohol and a toothbrush. then reinstall the amp.

I would say almost 85% of every Duo that I change the capacitors on needs this done now.

most of the voltages from the amp should read about 3.8 volts. the power input should be 7 volts.

another issue with this area is even after cleaning sometimes the ground trace is no good. So you might need to run a new wire or capacitor lead to get a good ground.

if all the traces to the amp seem fine then it's probably a bad op amp and you need to replace it.

HuMan · 10/06/2016, 07:10 PM

I could certainly buy some 4558 op amps but my only source is china and that would take a month. I only have time for this Duo this week... Hopefully it's just a bad trace.

Where is this op amp exactly? Is it near where the DC jack board is? Or is it near the 100uF, 4.7uF smd caps and headphone jack?

YoshiKnuckles · 10/06/2016, 08:01 PM

There is an op amp right by the A/V jack. I believe that's the one he is talking about. It's next to a couple of caps and some inductors.

China? Please. They stock 4558 op amps on Mouser and Digikey.

Within a minute of searching:
http://www.mouser.com/Semiconductors/Amplifier-ICs/_/N-4frvm?Keyword=4558&FS=True

Like $0.50 each + shipping. Not sure of the exact one to get though.

Keith Courage · 10/06/2016, 09:49 PM

get a reading of the voltages on the pins for the amp right by the AV Jack and post them here.

HuMan · 10/06/2016, 10:52 PM

IC506 or IC507? They both look like op amps to me and they are "near the AV jack".

I tested pin 8 on both of them, they are 3.11v. Ground seems to be working on both as well. If I could find a place to attach the alligator clips on my logic probe, I could try using that too.

Also, I don't live in the US, shipping isn't cheap from either mouser or digikey.

EDIT: I put a fresh battery in my volt meter. The 4 op amps and the volume control chip are 3.3v. I've poked around and in general, this area of the board is of a low voltage. The AC adapter voltage is 9.4v, 7805 regulators input is 8.1v, output is 5.03v, it goes down lower as the power passes through various passive components. The op amps and volume chip only get 3.3v. What is going on here?

YoshiKnuckles · 10/07/2016, 08:25 AM

I'd assume he means IC506.

Pin8 should be around 7-8V, not 3V That's the +V input for the Op Amp. That would be part of the reason you have no sound I'd guess. You'll have to figure out why you're not getting 7V on those.

Likely a dead passive, transistor, missing ground or dead via is my guess. I'd start with tracing the +rail back from one of the op amps to see where it is created. Notes and drawing your own schematic might help.

HuMan · 10/07/2016, 01:26 PM

7 - 8v? Yeah there's a significant drop going on here. The voltage from the 7805s is 5v, so I guess there are passive components that amp the voltage up to 8v between the 7805s and the op amps/volume IC. I will investigate that area and determine where the voltage drops are occurring.

Would anyone happen to know what kind of transistors are used on a PC Engine Duo? The tiny ones with no markings on them. I get the feeling there may be one or two dead ones. Last night I checked one near the 7805s and op amps and I think its output was 4v, that doesn't sound right. The PC Engine Duo doesn't use 3.3v for anything, right? Is it just 5v and up to 8v?

Keith Courage · 10/07/2016, 02:00 PM

all of the pins on the op amp should be about 3.5 volts except for the ground pin obviously and then the Power Pin which should be 7 volts.

the amp that I have been talking about is the one to the right of the AV Jack.

you should also double check that the amps on the bottom of the board have these readings as well.

if the amps are not getting these voltages then the problem is most likely old capacitor goop underneath one or more of the amps causing shorts or that there are bad traces to one or more of the capacitors that you replaced.

HuMan · 10/07/2016, 02:44 PM

All 4 op amps and the volume IC read about 3.3v. One of the op amps under the board looks like its been reflowed in the past. Other than that, all 5 of those chips look okay.

When I was replacing all the capacitors, there was one big trace between a couple leaded caps that was gone, I jumpered that trace while putting the new caps in. I didn't see any other damage.

Any ideas which of the big caps behind the 7805s are used for the op amps?

Keith Courage · 10/07/2016, 10:27 PM

Okay, lets try to narrow this down then. What's the voltage on each one of these caps circled in red? https://postimg.cc/image/c41vw27ah/

Also, can you by chance hear some audio if you crank up your TV really high?

HuMan · 10/08/2016, 01:27 AM

Cap near volume wheel - 1.3v
Caps to left of AV jack op amp - 1.3v
Caps to right - 1.89v (3rd one from top is 1.5v)
Cap near super cap - 0.05v

The Duo outputs dead silence at normal level. If I put the speakers to max, there's just humming. I actually use a 3 piece stereo system rather than the TV speakers.

The 22uF 16v cap near the super cap is probably the culprit. Do you know what it's connected to?

EDIT: I noticed that 22uF 16v cap sits right above the one 4558 op amp under the board. I think the negative side of the cap goes through to the underside next to the 4558 (on its right in the picture). That via seems to be corroded, no continuity through it. I take it this is what you meant by op amps being ravaged by caps? I'll try removing that op amp, cleaning underneath and resoldering it.

Keith Courage · 10/08/2016, 01:49 AM

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 · 10/08/2016, 03:23 AM

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 · 10/08/2016, 03:38 AM

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.cc/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 · 10/08/2016, 03:53 AM

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 · 10/08/2016, 03:59 AM

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 · 10/08/2016, 04:29 AM

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

cloudd · 10/08/2016, 12:05 PM

oops wrong thread

HuMan · 10/08/2016, 02:45 PM

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 · 10/08/2016, 03:44 PM

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 · 10/08/2016, 03:53 PM

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 · 10/08/2016, 07:13 PM

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 · 10/08/2016, 07:43 PM

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 · 10/08/2016, 07:50 PM

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 · 10/08/2016, 08:51 PM

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 · 10/08/2016, 11:16 PM

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

HuMan · 10/08/2016, 11:22 PM

I bought one of these and installed it myself. It went very well, not a single ripped solder pad.

https://console5.com/store/nec-turbo-duo-pc-engine-duo-smd-cap-kit.html

YoshiKnuckles · 10/09/2016, 10:31 AM

HuMan, you can still get to those caps. It's just a bit tricky.

The chip should be a SIP package and you should be able to stand it up, remove the tape and get to the capacitors. Then just put the tape back and bend the chip back down after you replace the caps.

HuMan · 10/09/2016, 02:43 PM

I don't want to risk breaking the pins on that SIP IC. I could desolder it but, really, what difference would 2 leaded caps make?

In other news, I also took the time to recap my white PC Engine, hopefully it'll keep going for another 30 years (almost 30, PCE turns 30 next year).

Keith Courage · 10/09/2016, 04:17 PM

you can change those two capacitors from up above but you honestly don't need to. Those two capacitors have nothing to do with the audio issues you are having.

HuMan · 10/09/2016, 04:48 PM

Good news everyone! I believe I have found the source of the voltage drop - by accident.

R306. When I was checking voltages, I accidentally touched R306 to that nearby power cap, which effectively bypassed that resistor. Doing that brought the audio back nice and loud. Both the AV port and the headphone jack, I only tested with a HuCard game.

Someone with a working Duo, please check the resistance of R306, I'd like to replace it. Also wattage if possible, most of mine are 1/4w, not sure if that's acceptable. I have a few bigger ones though.

EDIT: Yes, I also replaced those two 100uF 16v caps under the SIP package chip. The entire Console5 cap kit has now been applied.

mickcris · 10/09/2016, 05:39 PM

What is the code on the resistor. It's kind of blurry so can't make it out. You would need to remove it to measure so it's easier to just match it up with the value on it. It also looks to be at least 1206 size which would be 1/4 watt

i forgot i had one half pulled apart. it says 202 on it so it is a 2k ohm resistor. also the size is 1210 so its a 1/2 or 1/4 watt resistor.

HuMan · 10/09/2016, 05:50 PM

It's got "202" written on it. I did try to get a resistance value but it doesn't stay consistent. I don't have any smd resistors, or at least probably not correct ones.

mickcris · 10/09/2016, 05:51 PM

Quote from: HuMan on 10/09/2016, 05:50 PMIt's got "202" written on it. I did try to get a resistance value but it doesn't stay consistent. I don't have any smd resistors, or at least probably not correct ones.

i edited my post above. its a 2k ohm 1/4 or 1/2 watt resistor.

edit:
the first site i looked at said 1210 was 1/2 watt but most others say 1/4 watt. better to use a 1/2 watt just to be safe though.

HuMan · 10/09/2016, 07:09 PM

Ok, compared to my previous fixes, this one kinda sucks, but I don't have anything close to "2k ohm 1/2w resistor", I'll have to buy that at a later time. I have 2k resistors but they're 1/8w. For now, I stuck a 600 ohm resistor in there - I won't play the Duo much for now until then. It's bad but the sound finally works now. AV port, headphone jack, HuCard and CDs, it all works.

I also did one more voltage check. The caps are at 3v, op amps are at 6.2v. Still a bit low, will probably be improved further with a correct resistor.

For posterity: Fixes made were patching corroded vias at the 22uF 16v cap near the super cap, at the 4.7uF cap at the volume wheel and lastly the 2k ohm resistor near a 330uF cap under the board.

(pretend you can hear Bomberman 94 playing triumphantly)

Thanks everyone for helping to resurrect my Duo!

mickcris · 10/09/2016, 07:11 PM

It's a 2k ohm not 20k ohm.

HuMan · 10/09/2016, 07:22 PM

... *sigh*, at least it's just text I get stuff wrong in. I'd like to hope that never happened with my Duo.

Still, YAY I got my Duo working!! Thank you to everyone who pitched in to help with the repair!

NecroPhile · 10/10/2016, 10:36 AM

Well done!

It's always nice to hear when someone gets a system back to playin'.

crispytreat · 10/10/2016, 10:30 PM

This thread was a great help to me as well. I was finally able to get my Duo up and running with full audio, HuCard and CD. My issue was related to the transistor that is near pin 1 of IC505. It appears it is supposed to convert the 12V to 8V but one leg was only outputting 1.6V so I assume it was bad.

I just jumped from the good leg and everything started working after cleaning up a few vias.

I need help with sourcing a replacement part for that transistor. I am not the electronically inclined, so if someone could help that would be greatly appreciated.

I am not sure if it is ok to ask this here or if I should start a new thread.

Thanks