Ray, As I don't have any 128DCR (only a 128D and a flat 128), I cannot answer these questions. I'll pass them on to the cbm-hackers mailing list. Marko On Sat, 17 Nov 2001, Raymond R. Carlsen wrote: > Marko, > I have two repair jobs on the bench... both 128DCR motherboards (PCB > 250477) with the same problem: no boot in any mode and the drive LED stays > on. Tracing the fault was easy. Both boards had the reset line held low > because of a logic low out of U108 pin 32, (the drive R/W amplifer chip) > connected to the reset one-shot U27 pin 8 (input trigger). Disconnecting > that line allows both computers to boot in all modes. The internal drive > reads (no write) with one motherboard and will not even read with the > other. Of course external drives work fine with the internal disabled. > My question is: what is that line between the chips for? It is not > even shown in my Sams Photofact schematic, but it is on the schematic on > Funet.fi. My guess is it's there to prevent the chip from going into write > mode during boot time. I opened that line in my own working 128DCR and > it made no difference... read, autoboot, format all work fine. In the bad > boards, the DC resistance of U108 pin 32 measures about 100K to ground, so > the chip must be generating the logic low all the time... but why? Can I > have two bad SMD chips here (what are the odds?) or is something else > causing it? Take your best shot... I'm all ears. Thanks in advance! > If I do have two bad chips, is there any hope of finding a MC2871A > anywhere? > > Ray > > PS Both boards belong to some guy in England, and he shipped them all the > way to me in the USA for repair. > > Message was sent through the cbm-hackers mailing list
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