English Amiga Board - View Single Post - 2000 - black screen... Chips good... PSU good...

chiark · 04 September 2008, 22:37

well, here's one to keep me challenged!

I got a known faulty 2000. It's in good condition cosmetically, but fails to do a thing.

The psu gives the right power
I've swapped every socketed chip with a known good machine. the known good machine works with the duff machines chips. The duff machine doesn't work with the good machine's chips.

Keyboard, when plugged in, doesn't give any errors: caps lock lights then goes out. Caps lock then turns on and off, which I think means that the processor is working (68000 as opposed to keyboard)?

The CPU is getting 5v between pins 14 and 16.

Jumpers are all identical, and right.

Only strange thing is that U541 and 540 are soldered into some sort of upside down daughtercard... I think these are just octal latches so shouldn't cause problems like this. Maybe. but I really don't know.

Strangely, F1 has been replaced with a socketed fuse which suggests something somewhere may have drawn too much current, but there's still 5v going to that. Hm....

Any ideas where to start on this one?

04 September 2008, 22:37	#1
chiark Needs a life Join Date: Jan 2008 Location: England Posts: 1,707	2000 - black screen... Chips good... PSU good... well, here's one to keep me challenged! I got a known faulty 2000. It's in good condition cosmetically, but fails to do a thing. The psu gives the right power I've swapped every socketed chip with a known good machine. the known good machine works with the duff machines chips. The duff machine doesn't work with the good machine's chips. Keyboard, when plugged in, doesn't give any errors: caps lock lights then goes out. Caps lock then turns on and off, which I think means that the processor is working (68000 as opposed to keyboard)? The CPU is getting 5v between pins 14 and 16. Jumpers are all identical, and right. Only strange thing is that U541 and 540 are soldered into some sort of upside down daughtercard... I think these are just octal latches so shouldn't cause problems like this. Maybe. but I really don't know. Strangely, F1 has been replaced with a socketed fuse which suggests something somewhere may have drawn too much current, but there's still 5v going to that. Hm.... Any ideas where to start on this one?