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Macintosh SE failing to POST - grey screen


Active member
Hi all,

The same Macintosh SE I have been discussing here is showing a weird and intermittent fault.

About 50% of times it's powered up, it BONGs, the screen turns on with the grey pattern and about 17 seconds later the pattern gets brighter, I hear a click from the speaker, the mouse pointer shows up and then the system tries to boot up - or the Floppy-Question mark appears if no drives are connected.

The remaining 50% of times the Mac Bongs but the display remains grey forever (I think it's fine diagonal lines rather than the solid grey I see later at boot) no more progress. This happens with no drives connected as well so this is not a drive struggling to come up online.

- If I press the debug button when it stalls, I have 0000000F 0000000D which I understand it's the code for "nothing to report".
- If I reset by pressing the reset switch, the system then boots up fine 90% of times. Sometimes it needs another go
- This happens when cold or hot
- I checked the power rails with scope and meter. They seem ok. Reset line starts LOW and 250ms after the voltages are up, it goes HIGH, as it should.
- Once the computer has booted up, it seems fine (but my mouse does not work for now so I cannot test much, see other thread)
- The computer had memory issues at the beginning (corrosion) so I tried downgrading from 4MB to 2MB (changing the jumper as well of course) and swapping SIMMs to make sure it was not a bad memory module.

The intermittent nature of the fault makes it a bit difficult to diagnose. Has anybody seen this happening before? I have researched a bit but I do not see anything about that. The amazing HW manual describes the booting process in details but I do not see any mention of how the process works in between the POST and the BOOT.

Any ideas are welcome! :)


Active member
I thought a video might help.

Today it took MANY resets and reboots to come up alive - never done that before. The Mac was cold - literally. I will try identifying the issue with cold spray/hot air station but I feel it's the VIA. I do see activity on the data lines of the processor but I don't see activity on the ADB - which also happens not to work so maybe this is just a by-product of the same fault. As soon as I see activity on the ADB - 2 seconds after a reset - then it WILL boot.

Mac in the video had no drives connected.

I have replacements ICs, just waiting for sockets. I hope once the ADB is back, the Mac will stop this.

If someone has any ideas, I am all ears!


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Well-known member
Especially given what you said about seeing ADB activity, the VIA seems like a reasonable guess to me. The SCSI IC and SWIM (and probably other bits) can also stall the machine at that stage, which isn't helpful...


Active member
Thanks, I'll definitely go with the VIA first as I can decode the correct keyboard keystrokes on the ADB side so that seems ok (it doesn't mean that the VIA side works though).

If that doesn't fix the booting issue, is there a way to find out what it could be? Anything that could be removed from the board without preventing it from booting

Thanks for now!


Active member
Today I socketed both the VIA and the ADB. It turns out that a replacement PIC ADB fixed BOTH the mouse and the booting failure!

I guess when I saw the ADB bus not doing anything at boot - which was when the Mac was failing to boot - it was indeed the ADB failing to work and stopping the boot process!!