A4000D - Yellow screen

[RetroPassion]

If you get a yellow screen, your chip ram is fine, green screen means bad or missing chip ram. The issue maybe a simple thing of broken tracks around that area, as there is some green, clean it all up and start testing the area for continunity between compoents and VIAS. it will take time but worth it :-)

[RetroPassion]

Happy New Year!.

Ive been checking over the board with my multi meter (Santa got me a new one). Continuity looks to be ok so far (i need to remove the coin cell battery holder to get to Pins 1 -5 of U177. Ive used Amiga PCB explorer as my reference guide together with Anthony Hoffman's guide to repairing the RTC.

What I have noted is the voltage on R994 is c2.52v the voltage on all the other resistors in that bank are close to 5v; 4.93 - 4.94v. PCB Explorer shows it should by 5v. Output from the PSU is ok close to +12v +5v all check out ok.

I have a set of diag ROMs arriving this week - plan is to install them and see what happens. I also have a new 2MB SIMM coming for the Chip Mem. The double sided SIMM I have I cant remember if its the original or not and I dont think Ive got an old motherboard I can use to check if its ok.

If U177 is knackered (Ive read that it is often a culprit) where can I get a replacement part and how tricky a job is it to de-solder the existing one and solder on the new one?

Weed

Hot air and flux is the best way without risk of damage, if you need the chip we can send you one free of charge if needed.

[RetroPassion]

I would remove those chips, test for continuity and replace with new, this saves a lot of time :-)