Turbo Duo recap distorted audio and no left channel on headphone jack

PapaSmurf · 11/30/2017, 11:07 PM

Hello everyone. I've had a Duo since it came out and have been reading that I need to recap it. Well, I took it apart and sure enough there were leaky caps.

I ordered then SMD/SMT kit from console5 and started recapping a few days ago. First, I recapped the headphone jack audio area, tested it and all was well. Then I recapped the through hole caps and SMD caps above the heatsinks. Everything was fine.

Then I recapped several more SMD caps (marked by red dots in the pic below) and I lost the left channel on the headphone jack. The sound from the RCA got a bit quiet and slightly distorted, but both channels are working.

I checked to see if I used the right value caps and they are, but I will check again.

Does anyone have any idea of what went wrong and how to test/diagnose the cause of this problem?

ginoscope · 11/30/2017, 11:54 PM

I would just finish capping the entire board. I had a similar issue when I recapped a duo and the solution was to wash the board. I used soap and water and just let it dry really good for a day or 2. Leaking caps can leave fluid on the board that can cause shorts.

MobiusStripTech · 12/01/2017, 01:23 PM

When recapping Duos it's better to just get all of the caps off and then clean the hell out of the entire board before putting the new caps on. Also make sure you get all the old solder off.

PapaSmurf · 12/01/2017, 08:25 PM

Thank for the replies and suggestions.

A little more detail:

I removed the old solder with flux & solder wick. There were only three leaked caps on the entire board and the damage was minimal. I activated the flux at a low temp to help get rid of the corrosion. Then I cleaned up the areas with IPA. The areas I worked on were spotless before I recapped.

When I turn on the Duo with a game that plays music immediately (JJ & Jeff,) the sound plays fine for the first second. Then it gets quieter and slightly distorted. I haven't recapped the CDROM area yet; I'd like to figure out what's wrong here first.

Maybe the leads on one or more of the tiny caps are bridged with solder. I'll check to see if they are shorted and get back. I don't like the idea of started all over, and putting more stress on the PCB. But I will if necessary. Any other ideas or suggestions?

MobiusStripTech · 12/02/2017, 01:33 AM

Don't assume that the only areas with electrolytic fluid are the areas where you saw leaks. Assume the entire board is coated in fluid. You need to clean the top and bottom. Scrub everything down. The fluid gets under everything. Op amps tend to have fluid hidden under them. You aren't describing anything that hasn't been seen before. The best thing you can do is pull all the caps. Clean everything, not just the spots where caps were leaking, and when every nook and cranny is cleaned, then put new caps on.

If you still have issues at that point, it's time to start tracing. Going cap by cap on a duo is just a waste of your time. I get the thought process, but you are going to need to replace all of the caps regardless, so just replace them all and then test.

PapaSmurf · 12/05/2017, 10:46 PM

I've taken your advice and began cleaning the PCB a few days ago. Some of the flux I used could be causing shorts here and there. Plus, when I opened up my Duo for the first time in 25 years, I noticed that it was caked in flux. Various parts were masked off and it looked like it had been reworked by hand.

Lots of IPA and q-tips later, I'm almost done. I'll retest the board in a few days to see if the sound problems clear up. If not, I'll get some new caps and start again.

PapaSmurf · 12/13/2017, 09:29 PM

I haven't had much time to work on the Duo until the past couple of days. But I've cleaned it completely and switched out a couple of caps that that weren't on perfectly. But the was no change; the distortion is still there. The distortion problem seems unrelated to the missing left headphone jack, because it sounds distorted through both the AV and headphone jack.

In regards to the missing left channel on the headphone jack:
I removed the volume knob to clean it, but I haven't put it back in. The sound is now at full volume out of the headphone jack. But still no left channel audio. I then removed C671 and cleaned up because it looked a little dodgy. But I didn't replace the capacitor. When I fired up the Duo, the left channel on the headphone jack started working, but the right was gone! WTF? I expected either both channels gone, or the right channel to still be working. I'll remove three other caps next to the volume knob and replace them soon.

The sound distortion problem affects all audio. It's not specific to the PSG, ADPCM, or CD audio. It seems that the louder the sound is, the worse the distortion. Lower frequencies are seem like they are more prone to cause distortion. Here is a video I made with some examples of the sound distortion:

wayback.vimeo.com/247244642

Nodoka75 · 12/14/2017, 04:08 AM

Hi from France

Right channel sound goes through C671 towards the phone jack, so no C671 = no Right sound.

For the distortion, make sure the PCB is properly cleaned before placing new caps. If distortion remains, maybe the cap leak went under one of the opamps. Don't forget via's continuity, including through hole components. I had a DUO without Left sound until I resoldered the chokes just before AV port.

SiberianSpForces · 12/15/2017, 08:23 AM

Could it be a polarity issue? Maybe check to see if the polarity on the cap matches up on the board?

PapaSmurf · 12/15/2017, 09:11 AM

Hi everyone. Here's a quick update.

Last night I looked at he entire PCB for trace damage, but couldn't find any. I guess I got lucky that the board was caked in flux at the factory and the flux frosting protected the PCB from the leaky caps. Anyway, the board is pristine now, at least the parts that aren't covered by components.

I checked several vias and continuity is good. But that could still be a problem. As for polarity, they are correctly oriented. It's harder to make that mistake when using SMT/SMD caps.

Also last night, I removed C670, C674, C675, and C884. I found unflowed solder paste underneath...............

It must have spread underneath the caps when I was cleaning with IPA. Luckily I didn't use paste and hot air for all of the caps because I didn't like the results. But I'll be taking all of the caps off and looking for problems underneath. Starting with C678 and C679, because I might have used solder paste on those.

One way or another, I'm determined to get my Duo fixed. More to come soon.

gtsamour · 12/17/2017, 07:00 AM

I had a kind of similar problem with my PCE DUO, the sound was fine before the recap (no leaks anywhere) but thought I would do the recap anyway so I got an SMD kit from console5.
Did the recap and after a while I noticed that after the console warm up, there was some kind of audio problem.
Even if nothing was playing there was something in the background. Something like when you touch a microphone sounds like.... coming and going... I imagined that it had to be a small solder blob somewhere that after console warm up it expanded and made contact.

I couldn't see anything wrong while inspecting.... so i took the whole board out and immersed it in isopropyl alcohol for a while. Thought it could be a small solder blob somewhere making contact. I gently rubbed with a brush while the board was immersed both sides.
Let it dry in the oven at 45C and placed everything back together.

That solved it.

Whatever it is in your case, it has to be on the upper left corner area of the board.

PapaSmurf · 12/17/2017, 03:39 PM

gtasamour,

Thanks for the suggestion. Did the IPA bath remove the serial number from the board? Also, how long did you leave in the alcohol bath?

Today I doused the upper right area with 91% IPA and let it sit about five minutes, soaked it again and gently scrubbed it both front and back. Then rinsed the area with more IPA.

I'm waiting on some 100uf 16v caps to come in the mail. I'll test again after those are installed.

gtsamour · 12/18/2017, 10:20 AM

Yes it did, the serial is printed with ink.

More time can't harm, just let it soak for a couple of hours to make sure the board (or the part of it that you want) is clean.
Since I have an abundance of ISP, i even changed it a couple of times to make sure all this yellow orange goo has been removed from the whole board.

Here's mine, as you can see its squeaky clean.

_{https://i1169.photobucket.com/albums/r502/gtsamour/DSC_0013.jpg

https://i1169.photobucket.com/albums/r502/gtsamour/DSC_0005_2.jpg}

Psycho Punch · 12/18/2017, 11:38 AM

Hey, what did you do with the CDROM drive gears? Did you just clean it off or did you apply any lubricant later?

gtsamour · 12/18/2017, 12:41 PM

Quote from: guestHey, what did you do with the CDROM drive gears? Did you just clean it off or did you apply any lubricant later?

I cleaned it as good as possible with cotton swabs and ISP and then applied Tamiya boron nitrite lubricant.

PapaSmurf · 12/22/2017, 10:48 PM

I made some progress today.

I woke up early and finished recapping the left side of the board this morning. The sound cleared up! Perfect sound through the AV out and both channels on the headphones are now working.

The headphones are loud because I took off the volume knob to clean it. There is also clipping on the HP jack. I'm not sure if it's that the super-cheap Radio Shack headphones I'm using can't handle the loudness or because there is volume knob is missing. Probably the latter. I'll reattach the volume knob and see if the clipping disappears. BTW, does anyone know a source for new volume knobs?

I just finished recapping the SMD caps in the CDROM area (previously I had only done the 3.3uf 50v one.) So the Duo is now 100% recapped. I'll test out the CD function tomorrow morning.

Here's the patient before I finished recapping today:

gtsamour · 12/23/2017, 01:23 AM

Good job !!!!! Anything is possible but I think its going to be hard to find the exact nob and replace it.
I don't remember about the DUO but on the CDROM2 unit, the sound signal on the headphone jack is indeed high when turned all the way up.... it causes distortion, not like static but more like a loud bass.

PapaSmurf · 12/23/2017, 08:01 PM

Quote from: gtsamour on 12/23/2017, 01:23 AMGood job !!!!! Anything is possible but I think its going to be hard to find the exact nob and replace it.
I don't remember about the DUO but on the CDROM2 unit, the sound signal on the headphone jack is indeed high when turned all the way up.... it causes distortion, not like static but more like a loud bass.

Thanks. I'm really glad it's working this well.

It would be nice if someone could sell me the volume knob from a dead Duo board. I found a new one online with the same dimensions and pin spacing. It shouldn't be hard to retrofit it, provided that they are the same specs. Does anyone know the pin out and the max resistance value for the Duo's volume pot ?

I reinstalled the volume pot and it's definitely messed up. It sort of works, but the lowest setting is still loud. I noticed that, if I press down on the knob, the volume decreases a lot. There's more physical resistance than there should be when you turn the knob. I'm sure flux migrated into the pot when I was cleaning the board. I've soaked it in IPA several times and it helped a little. I'm going to remove it and soak it in IPA overnight, then test the resistance with a multimeter.

Other than that, it's working perfectly. And luckily I didn't have to adjust any trim pots for the CD!

NichlasEk · 12/25/2017, 04:07 AM

The volume pot is a carbon film pot. That carbone trace dosent always fare well in IPA as it dissolves it. (I have screwd up once ore twice that way) The volume pot for the game geat seems similar. Etim sells the four legged version http://etim.net.au/shop/shop.php?crn=206&rn=516&action=show_detail. All other i have found are three legs but works as well if you link the grounds. Might not be the right value but might just work?

PapaSmurf · 12/25/2017, 10:17 AM

Quote from: NichlasEk on 12/25/2017, 04:07 AMThe volume pot is a carbon film pot. That carbone trace dosent always fare well in IPA as it dissolves it. (I have screwd up once ore twice that way) The volume pot for the game geat seems similar. Etim sells the four legged version http://etim.net.au/shop/shop.php?crn=206&rn=516&action=show_detail. All other i have found are three legs but works as well if you link the grounds. Might not be the right value but might just work?

You're right. I vaguely remember cleaning my SNES controllers and removing the carbon from the rubber pads.

I tested it out again and it's working much better now. One of the channels is louder than the other, and gently pressing the knob brings the volume on that channel back down. I think this is a dual-gang pot; one for each channel. A three pin single gang pot wouldn't work.

This pot looks like it will fit http://www.alps.com/prod/info/E/HTML/Potentiometer/RotaryPotentiometers/RKJ1/RK10J12R0A0B.html. I ordered one, so in a few days I'll report the results.

The Game Gear pot looks like it's through-hole and the dial is a bit thick. But it might work. I'll keep it in mind.

Oh yeah, Happy/Merry Christmas everyone!

Nodoka75 · 12/25/2017, 06:01 PM

Yep, it is a stereo pot on our dear DUO ^^

Right, on Game Gear the volume pot is a through-hole model.

Keith Courage · 12/27/2017, 11:23 PM

The original gameboy pot works as a replacement. https://www.ebay.com/itm/2PCS-Replacement-Volume-Switch-Repair-Parts-For-Gameboy-Color-GBC-Motherboard/182562243778?hash=item2a818ec4c2:g:8rgAAOSwBahVFAjn

gamegear pot is not compatible with a DUO. Even though it has 5 pins the pin order is different. However a game gear pot will work to replace the volume dial for a Turboexpress/Pc engine GT.

PapaSmurf · 12/31/2017, 03:12 PM

Quote from: Keith Courage on 12/27/2017, 11:23 PMThe original gameboy pot works as a replacement. https://www.ebay.com/itm/2PCS-Replacement-Volume-Switch-Repair-Parts-For-Gameboy-Color-GBC-Motherboard/182562243778?hash=item2a818ec4c2:g:8rgAAOSwBahVFAjn

gamegear pot is not compatible with a DUO. Even though it has 5 pins the pin order is different. However a game gear pot will work to replace the volume dial for a Turboexpress/Pc engine GT.

I soldered the Alps pot to my Duo today and it works, but I don't like the curve it has. Only a few degrees turn and it gets loud, then the rest of the way increases the volume a little. Also, the legs should be one or two millimeters longer so the wheel will protrude more.

Old and new pots:

KC, thanks for the suggestion. I ordered that pot today and I'll try it out when it gets here from China. The GBC pot is 2mm larger in diameter than the original Duo. So that might help out if the legs don't quite reach.