2x Turbo Duo's completely Recapped - same problem low sound!

[cloudd]

I have repaired 2 x Turbo Duo's with sound issues.


Turbo Duo 1:
I did the full cap replacement because this unit's cd-rom was faulty. After opening the unit it was clear that the audio caps were leaking. I changed all of the caps on the pcb. Now the sound was great but I had graphic font errors (example the copyright text under games title screen showed up which scrambled characters). This was very odd. I left the unit on the floor for a month.

I turned it on a month later and the graphic glitches were gone but now the audio was popping and it lasted about 2 min and disappeared. There appeared to be no audio after that. I tried re-soldering all caps again. Now I can hear the audio only when the volume it turned up max on my stereo on both hucard and cd-rom games.


Turbo Duo 2:
I cleaned the 2nd  PCB really good and it seem to work great with all caps replaced for about 5-10 minutes and then the sound started popping and after about 2-5 min of the popping there seemed to be no audio. I turned my stereo up to max and I can faintly hear it play the audio  now.


Seems like I am having the same problem on both Turbo Duo's. Does anyone know what this could be or where I could look for the problem example which capacitor or at the opamp or can I solder to pads somewhere else on the PCB. I have been looking all over the PCB and the op amp. no luck yet.

Does anyone have any ideas or suggestions?

*Update I have noticed popping on both Turbo Duos now* 

Thanks

[Keith Courage]

Do you have a multi meter? There could be some caps that are not getting the correct voltage due to bad traces from old cap damage. You would then need to bridge a wire or old cap lead to repair the connection. Also, check that there is no old cap fluid underneath the 4558 op amps. This can cause shorts in voltage as well. The two 4558 op amps that generally have this issue is the one closest to the AV jack and then the one on the underside of the okim5205 chip. I make it a point to remove these op amps, clean, and then reinstall on every duo cap change I perform.

[turbokon]

You can try washing the boards.

[Vimtoman]

Both Kieth Courage and Turbokan are both correct in sourcing the problem audio. It's what i have done in the past.
Multiple cleans and removing IC's and cleaning underneath them is needed.

Tracking faults are more obvious due to corrosion but always check via continuity.

The audio is split into two sources. The CD and chip so check if it's background music on or the sound effects as that would tell you which IC's are letting you down.

[BlueBMW]

What is your cleaning method?

It sounds extreme, but I wash the boards in a dishwasher to get all the leaked fluid out from under chips and out from vias.  I have fixed many many many boards that had recaps but still had problems with a good wash.

Otherwise yes, you're going to have to trace through the circuits until you find the offending connection/chip/via causing your trouble.

[cloudd]

1. How exactly would I go about checking via continuity is there a video or can you explain it?

2. Where is the sound output found on the board before it enters the amplification  portion of the circuit (op amp?) of the sound happens? Can someone provide a picture?

3. Is there a way to jump the output sound that is NOT amplified into a new alternative circuit (separately created) eliminating the cleanup of the leaky acid and boosted the sound. if so can anyone suggest a circuit spam and how I would attach it to the output?

4. Does anyone have a schematic of the amplification circuit drawn out that they would share so I could easily trace back through the circuit?

Really appreciate the help everyone. I thought it shaping all the caps in a very clean organized precise manner would fix the issue. Its really touch and go because of the leaky caps...

[BlueBMW]

This particular post may be of use to you:

http://www.pcenginefx.com/forums/index.php?topic=17498.msg365761#msg365761

[ginoscope]

I had the same exact issue as the OP after I recapped my friends turbo duo.  It would play fine for 5 minutes and then the sound would go out.  I gave the board a really good wash as suggested on here and it has been just fine ever since.  Plays cd and cards with no sound issues at all.

[YoshiKnuckles]

I had one of these earlier this year that had a few corroded vias causing the issues.

The console got worse after I washed it. It went from having intermittent sound, to having extremely weak sound. A few of the vias were disconnected internally from corrosion. Was a bit of a nightmare to troubleshoot as my first Duo repair. =) Here's some of what I learned:

If you can't find any obvious faults, start checking the op amps. 4558.(Google it for a pinout) Check the voltage on the (+) voltage rail(I think like 8 or 9 volts or something?) and - Voltage rail(ground)on each. The main ones of interest are by the A/V jack, headphone jack and on the back of the board in the same region near the A/V jack. Also check the inputs and the outputs of the op amps for signals. DC readings should be fine for all of these measurements.

The other chip of interest with volume issues is the M51131L. It's in a ZIF package I believe. It controls the audio levels in the consoles. Here's the datasheet:

https://console5.com/techwiki/images/8/82/M51131L.pdf

I ended up fixing the one I was working on by jumping ground to an op amp, restoring the card sound to proper levels. I then found the CD had issues, and I jumped a 5V rail to the M51131L's Pin 8, restoring proper sound levels to the CD section of the Duo. The fix for yours will likely be different based on where the electrolyte leaked on your console. Check out the other thread linked here too. I wish I had that when I was working on that PC Engine Duo.

[cloudd]

When people say wash what do you mean exactly? wash with what? remove all caps and wash? Leave everything on the board and wash?

[Keith Courage]

They are talking about putting the board in a dishwasher. I have never done this myself since I do not have a dishwasher but others have with mixed results. Sometimes problems are fixed and other times not.

[Steveodogbiscuit]

Sorry to hijack thread, but how would somebody go about removing the Mitsubishi sound balancer chip and the amp chips? The legs look corroded on my PC engine and the sound is terrible. I have a hot air gun, but is there a recommended temperature level? Is that even the right way to do it.


Thanks in advance

[YoshiKnuckles]

The op amps should come off with even a cheap ebay hot air station quite easily. (Talking 858D quality.)

Just set it to around 300 and play around with it. There is no go to temperature for soldering. It's all done by feel. Solder doesn't melt well? Turn up the heat. Flux may prove extremely useful. Different boards require different amounts of heat. The TG-16 and PC Engine boards I've seen heat up quickly though.

For the M51131L, you're best desoldering that with a desoldering gun.

However, I would suggest checking stuff such as the electrolytic capacitors before going after the Op Amps and IC.

[Keith Courage]

I just use a basic soldering iron to remove the op amps. Just heat up four pins on one side while lightly prying up with a screw driver.

[Steveodogbiscuit]

I've changed all of the capacitors in the sound area. I have cleaned the pads with a wick and then rubbing alcohol, then applied new flux and soldered SMD capacitors on. They didn't work (in the sense that the sound level was scratchy and low), and I thought maybe one of the SMD capacitors was not sitting right, so I replaced them all with through hole so I could see they were definitely connected visually.

If the little 8 pin amps aren't working, are they stock parts? Unfortunately my cheap Chinese multimeters test leads fell apart, so I bought a fluke one, but that's at least 3 weeks away.

Thanks for help so far