blaine@worsel.UUCP (Blaine Gardner) (07/02/89)
A friend's A500 died a couple of days ago, so he brought it over to have me fix it (seems I'm the only guy around with a Torx screwdriver :-). The 500 was not making through the boot cycle, but looping part way through the self test (it was on a monochrome screen, so I don't know what color it was failing at). I suspected the old loose Fat Agnus problem, but the chip was seated just fine (and had a clip over it too). Closer inspection showed a transistor to the rear of the 68000 with a disconnected leg. I'm fuzzy on the details because I didn't make any notes, but I think it was a 2N3906. Two legs were soldered to (in true ECO style) nearby holes in the PCB, and the third was hanging in the air, near a small piece of wire-wrap wire that was soldered to another hole in the PCB. The wire had just been tack soldered to the leg of the transistor, not wrapped around it for strength, and the solder joint had broken. It was simple to fix the right way, and there was enough slack in wire to wrap it around the transistor leg. A happy ending and all that, but now I'm curious. What does this ECO do that is so vital to the boot process? It looked like (again, this is from my fuzzy memory) the base was tied to ground, the collector ran under the ROM, and the emitter (the leg with the wire) ran under the 68000. Nothing like this shows on the A500 schematics in the A500/A2000 tech manual. Anyone care to satisfy my idle curiosity (George, Dave)? -- -- Blaine Gardner @ worsel UUCP: uunet!iconsys!caeco!i-core!worsel!blaine "Nobody will ever need more than 64K." utah-cs!caeco!i-core!worsel!blaine "Nobody needs multitasking on a PC." UUCP at work: utah-cs!esunix!blgardne