Flickering Screen On A1200...

[Franko]

Never came across this problem before...

On an old A1200 I bought from eBay (MB Rev 1D.4) any access made by the floppy or HD causes an annoying flicker all over the screen...

I've tested it in turn with  the HD, Floppy and extra ram board disconnected and 5 different power supplies but the result is the same each time, this annoying background flicker on the screen (whether in composite or RGB)...

Anyone came across this problem before or have any ideas about the cause of it...

Cheers

Franko

[Franko]

I've got 4 other REV 1d.4 boards never seen this problem on them though, oh well another Amiga goes to heaven...

Hmmm... Kesa's typing something now... wonder what pearl of wisdom he'll offer...

(@ Kesa, kinda suspected something like that... )

[Franko]

Maybe... I'll runs some tests on it tomorrow and check it against some of my other ones, no big loss really...

[Franko]

Hopefully I've found the answer in a post on EAB, gonna give it a try tomorrow...

Flickering Screen On A1200

[Franko]

It might be the power connector socket on the A1200 is loose. It's not grounding properly.

Gave all the connections and solder joints a thorough check with a large magnifying glass, everything looks ok. The boards actually in near mint condition the previous owner said it had been lying in his loft for the past 12 years, so hopefully it's just some caps that have dried out...thanks anyway...

[Franko]

Did you ever give it a try tone... did it work...

[Franko]

My brother's old A1200 had this problem -- it was a bug in that particular board revision I think, mine didn't have the issue.  The fix?  Eliminate any colours in the screen's palette set to 255,255,255 (full white)!!  Bizarre, I know, but it did the trick for his machine -- he even wrote a little daemon to monitor the palette of the top screen and adjust to 254,254,254 any such offending colours!

Unfortunately that's not the problem with this one, even on boot up when the screen is still all black the problem can be seen...

Going to try the capacitor hack just shortly hopefully it will work as it seems to have worked for those who tried it on EAB...

[Franko]

:banana:Woo Hoo,:banana:  it worked like a charm simple 10 minute solder job and bob's your uncle no more flicker, took some pics myself, need to thank the guy on EAB for this brilliant little tip...

Before...


After...


(Sorry... forgot to say thanks to Tone007 as well...