Weird Duo problem (supply related?)

[Sensato Kuro]

Hi guys,

I’ve got a Duo with a weird problem here. What happens is that it’s an intermittent thing. Sometimes the unit powers on, but the audio is slowed down and the picture is black & white and all snowy/distorted. The laser seems to work fine in that case too (it checks to see if a CD is in when I push Start at the Duo boot screen).

Other times, when I turn the switch on, no picture or sound show up at all, and the laser doesn’t work either.

I’ve tried the Duo with two different working AC adapter. I also did on full cap kit on the unit and it didn’t fix anything. I am starting to think a trace might have been cut by a leaking cap somewhere but I have no idea where too look for it. I suspected it might be a VCC issue but both 7805 seem to output correct voltage. I’ve also checked most of the testpoints recommended here: http://www.pcenginefx.com/forums/index.php?topic=7376.msg123430#msg123430. Everything seems ok.

I’m starting to run out of ideas but I am thinking about scoping the video IC of a working system and comparing it with the faulty system’s one. Any other ideas? Thanks!

[thesteve]

your issue is related to system clock/crystal.
could be corrosion

[Sensato Kuro]

Ok, I'll check that out.

If a trace is corroded/cut somewhere, I'll have a hard time finding it. I'm seing two crystals on top of the Duo PCB, I'll check their output and maybe try to replace them. I'll also check pin 10 of HU6280 and pin 2 of HU6260. which are supposed to be the clock for those ICs according to the PCE netlists found here: http://gamesx.com/wiki/doku.php?id=pcenetlist

What's the distinction between clock and crystal and how does this translate to the Duo?



This is what my Duo boot screen looks like:

[thesteve]

the crystal generates a set frequency, thats all.
clock refers to a frequency used to step logic chips.
the video encoding frequency needs to match the TV displaying it, and is set by a clock.