PC Engine Duo White Screen problem :(

scrappysphinx · 07/14/2017, 07:30 AM

Hi all, i have a PC Engine Duo i got off ebay cheap as it wasn't working. It arrived and would boot my everdrive fine however cd's wouldn't spin at all. After replacing caps i got the cd drive working and the machine was fine and dandy. However while playing some bomberman from my everdrive i noticed the power light was off and i lost video but audio continued. I turned the machine off and back on but now i only get a white screen, this is the same with the everdrive connected or disconnected. The cdrom doesn't move if i press down the lid switch. I had a quick hunt around and it was suggested in other threads that one of the HU chips may have failed. I have replaced the HUc6260, HUc6270 & HUc6280 with known working chips from a pc engine but still i get nothing but a white screen. The fuse is fine. I removed the power led and put in a new one thinking it had blown however the new failed to function too. I checked with a multimeter and i am getting 5v on both the anode and kathode.

Any tips or help would be appreciated

Thanks

NichlasEk · 07/14/2017, 12:22 PM

If the powerlight went out while playing.. it might be a short?
Hopfully the 6280 wasnt damaged. Maybe check the bigger solo cap on the bottom left corner, under the cart connector. Think that one will cause video to die if shorted or missing. Also if RGB modded, small shorts on the 6260 legs will cause white screen ( i used conductive flux this was enough to cause intermittent shorts before wasing it wit isoprop)

scrappysphinx · 07/14/2017, 12:34 PM

Hi, thanks for the reply. No RGB mods on this machine, just standard composite signal. I have replaced all capacitors on the board and all 3 hu (6260/6270/6280) chips from a known working pc engine but still getting a white screen. The odd part is that both the led anode and cathode on the pcb are at 5v when checked with a multimeter so the ground side is receiving a positive charge from somewhere.

NichlasEk · 07/14/2017, 02:01 PM

Well thats strange. You mean both legs are at 5v+!?
I guess it could be lots of things, like a shorted IC. But a shorted bypasscap is more likley i would think. I usuely put the meter on ohms and set about finding the lowest resistans between the + and - rail and then start ripping components untill the short/semishort is gone.

I guess a transistor would be likley also, if its just around the led you get strange readings.

Thats all I have

thesteve · 07/14/2017, 06:53 PM

it doesnt have a power light
it does have power chokes, that could be damaged by a short

scrappysphinx · 07/15/2017, 03:25 AM

you're right, its not a power led, its a busy, cd rom activity, led. Maybe that was always off , i just noticed it was off when the video died. Still both legs of that LED are at 5v when power is on which is not normal is it? Any idea's on what to check first?

Thanks

thesteve · 08/20/2017, 12:46 AM

actually that is normal
white screen normally is in the core system, not the cd circuit so start there

MobiusStripTech · 08/21/2017, 10:46 AM

Quote from: scrappysphinx on 07/15/2017, 03:25 AMyou're right, its not a power led, its a busy, cd rom activity, led. Maybe that was always off , i just noticed it was off when the video died. Still both legs of that LED are at 5v when power is on which is not normal is it? Any idea's on what to check first?

Thanks

As thesteve said, 5v on both legs is totally normal. You've got an issue somewhere in the main part of the system. Might as well focus on testing the hucard side.

thesteve · 08/21/2017, 11:46 PM

a short in IC520 will also do it as thats the interface chip between the systems