Mega STE problem - black screen in low/med res but high ok

[MRAtari]

i have a Mega STE which has a prob, basically it works fine in high res mode with an SM 124

BUT not in colour low or medium resolution or with a TV either, it's just a dark screen with some randon vertical lines BUT i can hear sound in these modes (key click)

someone told me the U501 chip which is surface mounted and custom to the mega STE

can anyone advise what else i can look at?

thanks

[Zogging Hell]

This is a common problem, recently had just the same thing wrong with mine. The chip you need to change is probably U504. As Simbo suggested to me, you need to test this it the fault by cutting pin 7 (see the second thread below) on the chip. This will disable mono mode and hopefully it should now work in colour. That way you know the chip is at fault. The chip is annoyingly hidden under the expansion shielding so you will have to take that out to get at it.

See this thread - http://www.atari-forum.com/viewtopic.php?f=15&t=20533
and this thread - http://www.atari-forum.com/viewtopic.ph ... en#p143282

With the other machine, perhaps try reseating the RAM and other socketed chips. If that doesn't work, try changing out the simms one at a time. Simms need to be in banks 1 & 3 or 2 & 4 or both of these. Presuming of course it is a STe?

[MRAtari]

ok thanks for your help and yes i have now changed that U504 chip and it works........ almost!

all 3 resolutions work but low/med in colour on TV and monitor is dark, also look at the below picture and you will see where the desktop is supposed to be green it's kinda yellow

it just boots to this, nothing to do with me changing colours

any advice as to what i can look at next?



Uploaded with ImageShack.us

[Zogging Hell]

Have a look under the desktop background colour options, the Mega STe boots with a kind of dithered green pattern which is lighter than the normal garish one you get from earlier GEM versions. If you change the consistency of the desktop to solid (which is represented by black) it should go back to the normal green colour. If not then I'm not sure and there are better people on here to answer your question. It might be the video cable your using, your tv/ monitor, your shifter chip, or even the power supply.

[MRAtari]

hi

yeah i know what you mean by the lighter green screen on the Mega, it's actually the TOS 2.06 default

the video cable and PSU are all fine as it all works on another Mega i have

it's a mobo issue for sure.....

[MRAtari]

repaired! 2 broken tracks between Q501 / Q502 / Q503

looks like they got so hot they melted?! anyway repaired and so far ok.....

[Zogging Hell]

Cool!