Try pulling the accelerator board out of the PDS slot ... I've seen a lot of accelerator boards go bad over time but when removed, the underlying Mac is actually okay ... You should just be able to yank the board; it's all plug-n-play for the most part.
There should be Macintosh ROMs on the motherboard; look for a few 20-some-odd-pin DIL packages with (C) APPLE on them ... I believe the ROM SIMM slot is just there for upgrade potential (never utilized). No service processors or anything here; the CPU on the logic board (or on the accelerator board) does it all. If you're getting a startup chime, that implies the battery is providing sufficient "juice" (or the logic board doesn't care that much) to power on; the PSU is providing nominally sane voltages to the logic and it's managing to execute at least a little bit of the ROM ... Best, Sean On Tue, Oct 27, 2015 at 7:42 PM, Jules Richardson < jules.richardso...@gmail.com> wrote: > On 10/27/2015 12:54 AM, Sean Caron wrote: > >> AFAIK there's nothing special about the video on the IIsi ... pretty sure >> that if the adapter and monitor will work with i.e. a standard Mac II >> 640x480x8 NuBus board (or equivalent) it should work with the IIsi. >> > > Hmm, looks like this one has issues, then. I don't have an operational > 'scope here, but I did set my meter to the frequency range and put it on > both the hsync and the green video line, but it didn't read anything - I'd > expect to see something in the tens of KHz range on one or the other. > > I pulled the NVRAM battery (it was completely dead) and for now have > replaced with a 3V pack consisting of two AA cells - I would expect that to > be enough (compared to the correct 3.6V battery), but I suppose it's > possible that it's not. Anyway, I did the command-option-P-R sequence to > reset the NVRAM at startup (and got the second chime to suggest that it had > done the reset), but unfortunately no dice. > > The board caps are visually good - i.e. no obvious leaking/corrosion. > > All the board fuses check out OK (quite probably not related to the video > circuits anyway) > > +5V and +12V are OK; I've not located a good/simple spot to check for -12V > yet. > > I noticed that there's no W1 jumper fitted. According to section 2.5.7 at > http://macfaq.org/hardware/logicboard.shtml there should be if the board > is running from the on-board ROMs rather than a ROM SIMM - but if I fit > that jumper then I no longer get the startup chime; can anyone confirm that > macfaq is correct and I'm supposed to have the jumper fitted if the machine > *doesn't* have the SIMM? > > One final note: the system has a Carrera '040 board fitted in the > accelerator slot. The working state of that board is unknown (just like the > rest of the machine) - if I remove it for now, do I need to change any > jumpers or anything on the main system board so that the on-board '030 will > act as primary CPU, or should that happen automatically? > > I wish I knew at what point the chimes are generated - I don't know if > it's just some lowly service processor which produces those, or if it > implies that basic ROM, RAM, CPU etc. are all OK for it to ever get that > far (talking of which, I haven't tried swapping RAM; I suppose it might be > faulty in such a way that it's knocking the video out entirely). > > cheers > > Jules > >
