My IIsi is not booting

[corbinq27]

Hello all,

I’ve been quite enjoying the many wonderful threads on this forum especially in regards to troubleshooting old Macs (and especially the IIsi). I have a IIsi that is not booting.

The specific issue: at power up, the only sound the machine makes is a sort of clicking static noise (it does not make a boot chime and it does not make the sad chord). the display shows a red background with white horizontal and white vertical lines making lots of red squares (see attached photo).

Steps I’ve taken so far:
- recapped power supply (the machine didn’t power on until I did this)
- recapped logic board (the machine exhibited the red checkerboard pattern before I did this)
- I’ve checked the power rails. I’m fairly sure it’s putting out 5V and 12V on the rails as expected.

Not quite sure where to go from here.

I suppose I should also mention that I think the 57.2832 oscillator isn’t working.

 

[Phipli]

Hello all,

I’ve been quite enjoying the many wonderful threads on this forum especially in regards to troubleshooting old Macs (and especially the IIsi). I have a IIsi that is not booting.

The specific issue: at power up, the only sound the machine makes is a sort of clicking static noise (it does not make a boot chime and it does not make the sad chord). the display shows a red background with white horizontal and white vertical lines making lots of red squares (see attached photo).

Steps I’ve taken so far:
- recapped power supply (the machine didn’t power on until I did this)
- recapped logic board (the machine exhibited the red checkerboard pattern before I did this)
- I’ve checked the power rails. I’m fairly sure it’s putting out 5V and 12V on the rails as expected.

Not quite sure where to go from here.

Have you cleaned the board after recapping, and have you inspected under a microscope / magnifying glass for trace damage around caps?

 

[corbinq27]

Have you cleaned the board after recapping, and have you inspected under a microscope / magnifying glass for trace damage around caps?

I did do an hour isopropyl bath. Microscope not yet. Not a bad idea though.

 

[joshc]

Can you take a large/high res photo of the logic board please?

 

[corbinq27]

Here's a shot of the top of the board from my iPhone. let me know if this is high-res enough.

 

[robin-fo]

Check the behaviour of the /PFW and Reset signals with a scope. My IIsi initially showed similar symptoms when powered by an ATX PSU.

 

[joshc]

Check continuity around the caps - I would apply some flux to the solder pads for each cap you replaced and touch those up, some look a bit dry, or have too much solder.

 

[JC8080]

I have tried to repair two IIsi boards - one I have relegated to parts, the other one I successfully repaired. Check out this thread: https://68kmla.org/bb/index.php?threads/new-iisi-project-any-tips.42463/

Based on my experience as well as all the reading I have done about these boards there are very likely one or more broken traces, most likely near the old leaky capacitors. If you don't have a hot air rework station it would be a good idea to get one, there are a couple chips you will probably want to remove to get a good look underneath and at the pads. I bought a cheap one off Amazon that works great: link

Edit: you will also want to use a dental pick to gently poke at the legs of the chips around the leaky caps, you might find legs that look good at first glance but have actually came loose. On one of my boards I had multiple pins on the CPU that had come loose, the cap electrolyte had corroded the solder under the legs.

I purchased an inexpensive microscope off Amazon, it isn't great but works well enough for my projects. Here is the link, I see this particular model is no longer for sale, however I think it is a generic Chinese model sold under many different names so I'm sure you can find something similar. If I had it to do over I would probably buy a version with a larger 7" screen, but this smaller screen works fine. I also purchased this gooseneck stand since it gives a bit more room under the microscope, quite helpful for working on these PCBs.

 

[corbinq27]

A quick update:

I found a fair price on a new logic board and recapped it. The IIsi is now working. I’ll be shelving the broken logic board indefinitely.

Thanks to everyone for the good advise!

 

[Phipli]

A quick update:

I found a fair price on a new logic board and recapped it. The IIsi is now working. I’ll be shelving the broken logic board indefinitely.

Thanks to everyone for the good advise!

View attachment 64022

Very realistic hard disk icon

 

[corbinq27]

now trying to get that old logic board working again. Thought I'd share that I took UJ5 (ROM chip closest to the power socket) off with a hot air station, cleaned up the pads and desoldered it. The screen now displays a solid blue (still with no boot chime). I'm probably going to tackle the closest ALS245 chip next in a similar manner.

I've gone around the board with a multimeter looking for continuity flaws. I can't say I've checked every trace of course but the most suspect ones seemed ok except for some potential chip contact intermittentness. Hence why I'm going chip by chip.

I've been contemplating investing in an oscilloscope and do this more the Adrian's basement way though.

Getting UJ5 off and back on took the better part of 90 minutes for me (it was my first time).

 

[Cory5412]

I apologize so much for the delay cleaning up the spam that was previously here, huge thanks to everybody who sent in reports!

 

[dv-]

You might want to check all the traces going in and out of the onboard RAM; those are used for VRAM. (U[F|G|H|I][6|7]) A lot of people seem to end up having to replace the chips.

C9/C10/C11 are required for sound to work; if you're getting anything weird sound-wise, you might have to resolder those. Similarly, the contacts underneath the motherboard that go to the speaker sometimes get dirty and cause connectivity issues to the speaker.