Mac IIsi - SoG?

Jules Richardson jules.richardson99 at
Tue Oct 27 18:42:10 CDT 2015

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).



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