Mac IIsi - SoG?

Sean Caron scaron at
Tue Oct 27 20:03:27 CDT 2015

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 ...



On Tue, Oct 27, 2015 at 7:42 PM, Jules Richardson <
jules.richardson99 at> 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
> 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

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