IIci logic board issue

[Byte Knight]

Hey guys,

I recently acquired a IIci that just gives me a gray screen upon boot. I've got 12V and 5V at the HD power connector, so I'm assuming the PS is good. The board has some corrosion in the expected places near the surface caps, and C10, C13, and the IC at UD13 basically fell off with a little probing. I gave the board an isopropyl bath, recapped it, and put the IC at UD13 back in its spot. I checked all the traces (I think) in the affected areas and get good continuity. Unfortunately I continue to just get the gray screen upon boot. I can turn the computer on with the keyboard and button on the back but can't turn it off without unplugging it.



I'm also getting continuity with all the 5V rails to all the GND rails, even at the PS receptor (pins 2,3,4 with 5,6,7). I'm guessing that's not a good thing for normal computer function. Any idea what would cause this?

Thanks!

 

[retr01]

Hi @Byte Knight. I noticed a possible scratch on the PCB. See the area circled in red below. You may want to check to see if you have continuity in the two affected traces.

 

[Byte Knight]

Hi @Byte Knight. I noticed a possible scratch on the PCB. See the area circled in red below. You may want to check to see if you have continuity in the two affected traces.

Good eye, but it looks like it's just a superficial scratch - the traces check out fine.

 

[rikerjoe]

Check your CPU. Can’t tell if it is the pic or not, but around pins 11 and 12 there looks like a solder ball. I got a gray screen with my IIci due to some bent pins touching on my CPU. I also wrote about my experiences working on the soft power circuit area here: https://tinkerdifferent.com/threads/mac-iici-success-story.1656/post-15850

 

[retr01]

Good eye, but it looks like it's just a superficial scratch - the traces check out fine.

So glad! Whew! Trace repair can get messy.

 

[retr01]

Good eye, @rikerjoe. It looks like tiny solder balls that may be bridging CPU pin pads. I labeled those possibilities with the arrows:

 

[Byte Knight]

Check your CPU. Can’t tell if it is the pic or not, but around pins 11 and 12 there looks like a solder ball. I got a gray screen with my IIci due to some bent pins touching on my CPU. I also wrote about my experiences working on the soft power circuit area here: https://tinkerdifferent.com/threads/mac-iici-success-story.1656/post-15850

Good eye, @rikerjoe. It looks like tiny solder balls that may be bridging CPU pin pads. I labeled those possibilities with the arrows:

Thanks for taking a look, but no solder balls - it must be some sort of artifact in the picture.

It sounds like the soft power circuit has nothing to do with getting the gray screen, so I'm off to look closer at the audio circuit where the reset signal is sent.