new DUO sound issue!

[Tatsujin]

i've got a new DUO these days and there is a sound issue, similar to the one we're aware of and could be fixed with replacing the caps aroun the amp.

but this time it's a little bit different and strange a well.

all Hucards running fine, so absolutely no sound issue there as for the cinch-connector also for the head phone output, crystal clear tones. 1AAAA+!!

but, when playing a CD, all the red-book audio seems to be very very muted. you can hear it, if you turn on the speakers to the max. this applies also for the head phone output.

so i don't think it's the usual problem with the caps of the final stage amp, since all the PSG/ADPCM sounds are OK, but just the red book cd tracks are muted.

an other strange thing i discovered is, sometime when a track changes, you can hear it in perfect volume for about 0.5~1s, then it mutes again.

is this defective characteristic familiar to anyone, and probably know how to fix it? is there a pre-amp after the CD Device, before it get mixed together with the PSG/ADPMC tunes, which could be defective?

thanx a lot

[SignOfZeta]

I'm pretty sure this has been mentioned here before.

[Tatsujin]

as up to now, i know about following sound issues:

1. no or very muted/distorted sound via the cinch-connectors, but no problem via the headphones -> amp caps dry out!
2. no or very muted/distorted sound via the cinch-connectors also via the headphones -> amp caps dry out (also for the headphone amplifier section (but a rare case)).

if someone is familiar with my case, i would like to know whether this can be fixed or not and what's the cause of the problem

[Michael Helgeson]

Replace ALL the caps. Let us know if the problem still persist afterwards.

[Tatsujin]

there are about 365 caps on board (smd incl.). any advises?

[SNKNostalgia]

Find caps that are near the audio traces and next to audio related chips. Pretty much any of the smaller caps on the top region of the board.

[turbokon]

difinitely caps issue. Mine had static n distortion sound when using both via earphone n audio/video cable. I replaced the 22uf on the preamp side n that fix it.

[omnedon]

I've seen a couple of DUO's now that seem resistant to the 'traditional' audio fix. With virtually all surface mount caps replaced, the problem persists. Very very (for all intents and purposes inaudible) quiet redbook audio.

All that is left to try is the large caps around the heatsinks, the 220, 330, 470, and 1000 caps. I will report if that solves the problem. I don't stock caps of that rating, so will have to order some.

[Michael Helgeson]

Actually I think people had been replacing those caps too since the heat helped speed up the drying out of the caps. Those have been known to go bad too in that area. Best bet is to really set time aside and replace as many as possible,even ones that would normally not be replaced. I wouldn't trust any caps on the pcb.Spend a week doing it. Considering it a refurbishing of sorts.

[Platinumfungi]

Quite awhile back I made a Duo cap replacement chart here in the tech/modding forum. It's listed as "Updated 7/23/07 - US and PC Engine Duo total capacitor replacement chart +". I'd replace all 55 of those caps and then see if you still have issues. I have everything listed and easy to follow. The 3.3uF needs to be a 50V but other then that all caps can be replaced with 16V.

D-Lite and I were talking many moons ago about some different things to mess with if you still have issues after all 55 of those caps. I brought up the multiple silver pots on the board that I had no clue what they did. D-Lite thought perhaps something to do with the cd-rom. I have no clue.  Just thought I'd bring that up in case someone knows...?

[nat]

They adjust the laser. Gain, sensitivity, focus, voltage, etc.

[Platinumfungi]

Thanks Nat Can an oscilloscope measure those stats or do you have to have some other pro gear?

[nat]

Not sure. I actually tune it "by ear" as proper settings vary from console to console. Also, the proper "calibration point" drifts over time.

So even with pro gear that could read the stats-- the values wouldn't be the same from console to console.

[Michael Helgeson]

Tats,did you ever get this fixed?

[geise]

If you replace all the 10uf 16v caps and the 22uf 16v caps the sound should work perfectly fine.  First I just replaced all the 10uf caps and still had the issue.  I didn't know which other ones to replace till Duo_R mentioned replaceing the 22uf caps in D-Lites audio thread.  If you replace those it should work.