PC Engine Duo - No Power After Cap Replacement

[plokplok]

Alright, I'm hitting a wall on my own so I think it's time to ask.

I was doing a cap replacement on my PCE Duo, following Red Ghost's chart.  The system originally functioned, but had no audio at all.  Upon opening it, I found that a complete cap replacement was far overdue -- most of the original capacitors had some degree of leakage on them.

I replaced all the caps and did an excessive amount of cleaning.  There were a few places where the corrosion had eaten into the board, but even post-cleaning I did not see any broken traces.  I double checked my capacitor ratings, polarity, ensured I had no bridging, and checked traces throughout before attempting to power it on.

When I power it on with a HuCard in, I get nothing at all.  No light, nothing.  The fuse is still intact.  If I power it without the HuCard, I get a similar response, but if I press RUN on the controller, the light will start flashing and the CD drive will spin.  I still get no video or audio.

This isn't anywhere near my first full-cap job but this is the only time I've ever had an issue.  This, however, is my first PCEDuo.

Any suggestions of where to check?  I've been testing all my vias to make sure none of them were damaged by corrosion but beyond that I'm at a loss.  I work with a grounding strap and an antistatic mat, so I don't think something could have fizzled in that way.

[Duo_R]

make sure the caps are all orientated correctly, you might have some backwards

[BlueBMW]

Also make sure you dont just have a bad or failing A/V cable.  You might just be making poor connection.

[thesteve]

power works
the system is booting
you may have a broken trace near the power switch affecting video.
your sound still doesnt work

[plokplok]

Thanks for the replies, I'm going to dig in this afternoon and see if I can figure anything out.  I've pulled out the magnifying glass and I'm still not seeing broken traces, but I'm going to check the vias again to make sure I didn't miss a broken one somewhere.  Also, I'm thinking of bridging the few spots where the top coating on the board was eaten away.  Even though the trace seems intact, maybe it isn't.

All the capacitors are in the right direction, and I double and triple checked that the ratings are all correct.  I tried a different A/V cable with no luck, so I don't think that's the issue.

[thesteve]

look closely at the 470uf cap by the power switch, as its you video coupling cap.
there  is a small trace from it on the top of the board that breaks easy when changing the cap

[plokplok]

look closely at the 470uf cap by the power switch, as its you video coupling cap.
there  is a small trace from it on the top of the board that breaks easy when changing the cap

Thank you! That helped amazingly, it was seriously a break of probably ~0.4mm or less so I missed it.  I'll need to fix it better but for now I have a wire from the positive leg of the cap to the lower-right via it lead to.  Now I just need to track down the audio problem.  Sound is present, but I need to max out my receiver to hear it.  I probably have a few open connections somewhere nearby the A/V port.

[thesteve]

look for open via's/traces near the heatsink

[plokplok]

look for open via's/traces near the heatsink

Still no luck finding where the breakage is.

Are there any common test points for the audio?  I'm not receiving any (or very little amplification) on either of the outputs, I need to put my receiver to MAX just to know that all sounds are present.

[thesteve]

start with power on the amps.
it should be about 8V
the amp power is supplied by a SMD transistor in the capacitor Forrest behind the heatsinks.
once the 8V is confirmed check voltage at C322 (should be about 2.5V)

[plokplok]

start with power on the amps.
it should be about 8V
the amp power is supplied by a SMD transistor in the capacitor Forrest behind the heatsinks.
once the 8V is confirmed check voltage at C322 (should be about 2.5V)

OK, I'm definitely getting the 8V, but I have just under 5V at C322, so something seems to be off in the area.  This image has my voltage readings, I think something's wrong with R322?  https://imgur.com/bSwLd

EDIT:  I think the trace is gone between R322 and the trace just to the right of it -- it IS supposed to connect, correct?

[thesteve]

flipthe board and check the via's
start with the one you marked 0V
0V is correct there

[plokplok]

flipthe board and check the via's
start with the one you marked 0V
0V is correct there

flipthe board and check the via's
start with the one you marked 0V
0V is correct there

Right, just to confirm my 5V at C322 (positive side) IS an anomaly, correct?  I think that via where I marked 0 is broken on the bottom side, which would be causing issues for the 4558 directly underneath that (I missed that one ).

By the by, thanks thesteve for your help so far, you're a lifesaver.  I don't know my way around these boards for anything, Sega Genesis variants are much more my usual speed.

[thesteve]

yes the 5V is an anomaly
that via is almost always broken

[plokplok]

And again, you're right!

My test CD game is Dracula X, and it's revealed that I have one last hurdle to jump!  Regular audio is coming out from both channels.  However, CD audio is only coming out of the right channel at any volume, and the left channel CD audio is extremely quiet.  Still, a huge improvement!  The sound is clear and clean, and ANY audio is something I've never heard out of this system before.

[thesteve]

this thread https://www.pcengine-fx.com/forums/index.php?topic=960.0
should help you get the rest of the way there.
and this https://www.pcengine-fx.com/forums/index.php?topic=7328.msg153079#msg153079

[plokplok]

Thanks, already finished it.  Thanks for the guiding hand along the way.  Right near the OTHER bottom op-amp there was another broken via.  Repairing it solved the CD audio balance!

Now this thing works and sounds great!

[Bernie]

Another saved Duo.  Awesome.