PCE Duo/TurboDuo wiring schematic?

[DeshDildo]

I have an odd sound issue on my PC Engine Duo and was wondering if anyone had ever stumbled on or home made a schematic for a Duo sound circuit?

I recently got a PCE Duo that had no sound with obvious cap issues (a couple had broken loose from the board even).  I replaced all capacitors and cleaned the board and repaired 2 pads that were damaged by running jumpers.  When I first started the unit there was a bit of scratching that went away after about 15 seconds.  I thought eh... maybe because the caps were new and had no charge there was distortion for a minute.  After that it was fine.  I even played it multiple times throughout the night an hour or two apart with no issues.  The next day when I fired it up I had that damn distortion again.  I double checked my work and even reflowed a couple suspect solder joints.  This did nothing.  I still have that scratching for the first 15-30 seconds on a cold start.  I have the issues on both left and right channels and while playing CD's or Hu's.  I even replaced all the caps (basically one by one as a test) in that whole back area of the board thinking I may have damaged one during installation.  I have prodded the board while running with a plastic pick and can't make the problem start or disappear by doing this.

Anyways, my next option is to start tracing the parts of the circuit back that I can see and start installing a jumper with an A/V connector until I go past what I assume is a faulty connection somewhere.  Before I started this, I thought I would see if anyone happened to have a schematic as I haven't been able to find anything on the inter webs.

This problem is livable but I want it to be perfect dammit and my frustration level is getting higher.

[turbokon]

Sounds like dirty opt amps.  Try unsoldering the opt amp near the cluster of bad audio caps and clean the board and via's underneath the opt amp and clean the opt amp.

[BlueBMW]

This will sound crazy...

You probably need to wash the board.  As in dishwasher.   Remove the super cap, throw that sucker in the dishwasher with just a bit of detergent.  Set it on the light cycle and turn OFF heated dry.   When its done, turn your oven on to the lowest temperature (180 or 200 or whatever)  once heated, turn the oven off and put your board in there.  Let it sit overnight.  Put a note on the oven so that the wife/kids dont turn the oven on by mistake.

You probably have some corrosion or cap fluid down in some of the vias or under some of the chips like turbokon said.  Washing it will take care of any extra cap fluid that's still present.  Worse case we may have trace down which vias are causing an issue.

[DeshDildo]

Thanks guys, I removed a few things and cleaned a few more areas that looked like I missed before.  I still have the same issue so I'll toss it in the dishwasher and see what happens.  Thanks again!

[DeshDildo]

I might have some progress.  I just fired it up after drying all day.  The good news is no more static.  The bad news is extremely faint sound.  Whatever connection was flaky is now no longer so it should be easier to diagnose now.  Stay tuned.

[turbokon]

This will sound crazy...

You probably need to wash the board.  As in dishwasher.   Remove the super cap, throw that sucker in the dishwasher with just a bit of detergent.  Set it on the light cycle and turn OFF heated dry.   When its done, turn your oven on to the lowest temperature (180 or 200 or whatever)  once heated, turn the oven off and put your board in there.  Let it sit overnight.  Put a note on the oven so that the wife/kids dont turn the oven on by mistake.

You probably have some corrosion or cap fluid down in some of the vias or under some of the chips like turbokon said.  Washing it will take care of any extra cap fluid that's still present.  Worse case we may have trace down which vias are causing an issue.

This is crazy, I will try this someday:)

[BlueBMW]

I learned the technique from thesteve...  I thought he was crazy at first too but then he reminded me that all circuit boards go through a similar industrial wash when they are manufactured.  The key is drying in the oven.  It gets all the water out from under chips etc.  I've had a few things that I've recapped that still had issue and then were perfect after a good wash.   Its not to say there isnt a risk to doing it but so far I havent had anything damaged in the process.  I've even washed X68000 compact mainboards.  That might be a good one for you to try it out on turbokon.  I usually wash before I install the new caps though.

[pulstar]

I've done this dishwasher/oven technique before with arcade PCBs that were dirty. Works a treat and they come out looking almost new. Although I never put any detergent in when I chuck mine in, don't suppose it will do any damage if you use a little though.

[NightWolve]

I learned the technique from thesteve...  I thought he was crazy at first too but then he reminded me that all circuit boards go through a similar industrial wash when they are manufactured.

Oh, I thought this was your idea, didn't know it came from steve as I've never seen him personally suggest it.

[DeshDildo]

UPDATE... At this point I still haven't found anything.  I have checked all traces off the Mitsu multi-plexer and op amps and back from all typical caps that would cause a low sound issue.  I haven't found anything open in the circuit at this point.  I will dig some more tonight but I am starting to wonder if I just plain have a bad op amp.  The aggravation continues.  I keep telling myself it will all be worth it in the end.

[Fidde_se]

The dishwasher always sound like the craziest things ever but it's not.

It's used all the time for removing flux from circuitbords in high end production or before boards are being cast in epoxi.

Use a Miele at work for this and they are dishwashers plain and simple, they just use vigon instead of the standard tablet.
http://miele-pro.com/us/prof/products/14071_19560.htm

They heat the blended water/vigon mix to 75 degree celsius so I wouldn't worry leaving the heat on the dishwasher.
Some component usually states 85 degree but thats operational temperature and when they were soldered they were nearly 250 degrees.

[BlueBMW]

Here's a few partial schematics I found from some old posts...

Abbreviated schematic of DUO audio circuitry, part 1:


Abbreviated schematic of DUO audio circuitry, part 2:

Heres what you can do....  build one of these out of some wires or whatever.  Connect it to a TV or some amplified speakers or whatever and use the "probe" end of the wire to test each point along the audio circuit.  You should be able to hear the system sound using the probe and figure out where it is stopping.  If it stops at a pin on an amp and doesnt come out of it then you know the problem is there with the amp, either its bad or the power / ground isnt there or whatever.

i905.photobucket.com/albums/ac253/bmcdanold/Repair/audioprobe.jpg

[DeshDildo]

You're my boy blue!  I can't even begin to thank you for the info.  P.S. check my raffle post in the non-obey console area.

[DeshDildo]

Fuck fuck fuckity fuck!  I thought for sure my last op amp was bad (IC506) I have good sound coming in on leg 2 and 6.  I have correct voltage at legs 3, 5 and 8.  I did NOT have any audio coming out on legs 1 and 7. 

I don't have any of these buggers on hand so I robbed the amp for the headphone circuit.  I'm feeling pretty good about myself and fire it up... and... same damn shit.  F!  I even rechecked my connections and verified good audio in, correct voltages and good ground. 

Back to Stumpedville USA.

[BlueBMW]

Did you check your ground line to pin 4?  I've seen grounds get screwed up from a corroded via and make the op amp not power up.

[DeshDildo]

Did you check your ground line to pin 4?  I've seen grounds get screwed up from a corroded via and make the op amp not power up.

Yes.  I don't know why I forgot to mention that.  I have continuity to any ground on the board to pin 4.  I guess it's possible but far fetched that both amps were bad.  I'm looking into the rest of the circuit working backwards.  I just don't see why there would be a problem closer to the source if I have sound where I should at the last amp in line.

[BlueBMW]

In fact, I think both of the op amps share a ground that goes through a via that has a bad tendency to get corroded.  Let me try and find the thread....

[BlueBMW]

Hmmm.. guess it was something different...

https://www.pcengine-fx.com/forums/index.php?topic=3249.msg232905#msg232905

Might have some useful info buried in there anyways.

[DeshDildo]

In fact, I think both of the op amps share a ground that goes through a via that has a bad tendency to get corroded.  Let me try and find the thread....

Shit you are on to something here.  When I had the amp off I checked continuity and visually inspected the vias hidden underneath.  I also had continuity to ground from pin 4.  For shits and giggles I soldered a wire directly to ground and attached to pin 4 of op amp 506.  It's not a complete success but the sound output is quite a bit louder than it was before (still only about 1/2 of what it should be).  I will continue the quest as time permits tomorrow. 

Thanks again for all of the help.

[BlueBMW]

Sweet!  Hopefully you'll track down the issue really soon!

Also, not sure if it is your problem but there is a via right next to R322 on the top of the board... it goes through near IC503 pin 5.  It always seems to be a problem VIA.  Might be worth checking continuity through.

[DeshDildo]

Sweet!  Hopefully you'll track down the issue really soon!

Also, not sure if it is your problem but there is a via right next to R322 on the top of the board... it goes through near IC503 pin 5.  It always seems to be a problem VIA.  Might be worth checking continuity through.

Before I removed the top op amp again to check the ground again (I did have continuity and low resistance, only about .14 ohlm) I looked at the via you mentioned here.  It did look a bit discolored so I tested it and it seemed to be fine then I re-tested it and the circuit to ground was open.  I repaired that via and fired it up.  Now I'm back to no sound.

I checked voltage again at the top amp and only have 1.2VDC on pins 1 and 3 and 2.4 VDC on pin 8.  I also then followed the circuit back to the first bank of amps and have the same readings.  So now after repairing a questionable ground I now have a power issue somewhere.

[thesteve]

small SMD transistor in the cap jungle by the heatsinks is your 8V source

[DeshDildo]

small SMD transistor in the cap jungle by the heatsinks is your 8V source

Thank you thesteve!  Only 4.2 VDC from the emitter.  I pulled the transistor and tested it.  It tests bad.  Any specific specs I can use to replace it?  I have a bunch of spare PNP's laying around.

[thesteve]

It's a 100mA NPN

[DeshDildo]

It's a 100mA NPN

Thank you!  I saw the arrow on the circuit board pointing in to the emitter and assumed it was PNP.  I'm a noob with this stuff and learning as I go.

[DeshDildo]

MISSION ACCOMPLISHED!  I replaced the transistor, fired up the DUO and BAM!  Full on static free sound.  I really can't thank everyone enough for all of the help.  THANK YOU!