PC Engine Duo white screen

[Ergot_Cholera]

Hello, new here. Wondering if anyone can help with this problem. I have acquired a Duo but it displays just a white screen when switched on. I have since replaced all the capacitors but the problem remains. The video display is just white, no audio and everything else is unresponsive. I don't think it is anything to do with the Hucard slot as it is in good condition and there doesn't appear to be any corrosion or signs of damage anywhere. I have tried video directly from the Huc6260 and get the same white screen.
Any help is much appreciated.

[Necromancer]

Welcome aboard!  Other than to check the a/v socket to make sure it's well connected to the pcb, I've got nothing, but I'm sure one of the techy guys will come along and offer some suggestions soon.

[Ghudda]

Not really directly helpful, but Retrogametech had a video once where he picked up a TG16 that was displaying only a solid white screen so his repair may be relevant to what you're experiencing.

Link to video: https://youtu.be/-GwMxTPyleg?t=7m42s
His problem was that a few of the legs on one of the chips were lifted or needed to be re-flowed. So maybe it could be an issue with the same chip he had problems with?

[thesteve]

solder work is a rare issue on the duo
bad traces are however common
white screen just means the video output chip hasnt been initialized
anything that keeps the system from starting will cause this

[Keith Courage]

Most likely bad traces or a bad chip as the steve suggested. Out of curiosity does it happen with and without a chip game? 

[Ergot_Cholera]

The white screen is present with or without a Hucard inserted. Are there any common bad traces as I have looked over the board and can't see anything obvious? TheSteve, I read a previous post of yours which suggested a wire to pin 40(luma) of the c6260.  I have connected a wire to this (obviously grounded too) and get the same white screen.
Are there problems with vias not being connected as you mentioned bad traces?
As far as I can tell (before I recapped it) nothing had been tampered with (no lifted legs etc).

[Ergot_Cholera]

Sorry for double post. I just want to say thanks for responding and especially for two of the most knowledgeable people on here to respond so fast.

[bozo55]

Were any of the caps you replaced leaking?  I would use a fiberglass pen to remove any discolored solder mask to make sure the copper below is still fine.

[Ergot_Cholera]

It is possible some of the old caps were leaking. The solder contacts on the volume wheel were dull, and when I reflowed them a bad smell resulted (burning electrolytic fluid?). There is a small chip near the back of the AV socket and the legs on that are also dull. I suppose I should check all the traces thoroughly around where the capacitors are.

[thesteve]

Yes the vias open, I was considering them as part of the traces

[Ergot_Cholera]

I have cleaned up the board where the bad caps were and removed  black gunk from some of the vias. I tested these vias for continuity and they seem fine. I held up the board to a window to see the traces better, and I can't see any breaks anywhere. Does this suggest something more serious?

[thesteve]

nope
the vias fail without cap fluid as well

[Ergot_Cholera]

Okay, I have tested continuity on a lot of the traces and vias. I won't pretend I have done them all as it gets tedious and is like trying to find a needle in a haystack. If traces and/or vias is not the issue then what is likely to be the problem? As I have stated before, the board is in really good condition with no obvious damage ( I wish it were obvious to be honest).

[bozo55]

Looks like you're going to get yourself a logic probe to try to see if any of the chips are not functioning correctly.  You will then need a parts system for a donor chip.  I got stuck at this part trying to fix a dead Genesis.  Replacing QFP's requires skill and equipment most do not have.   

[Ergot_Cholera]

This is the point where it gets way beyond my knowledge or capability.