Need some help with a battery damaged IIci (was almost working)

[CRG (Glen)]

Hello all, firstly let me introduce myself, I'm Glen from Belfast Northern Ireland. I'm a collector of various vintage computers and while I have a few apples in the collection I wouldn't be the most clued up on them.

I was recently sent a MAC IIci for the price of postage only, it was very heavily battery damaged and while the previous owner had a go he couldn't get any life out of it so I thought I'd have a go. I have previously repaired other battery damaged systems but this one is proving a challenge.

I removed the 4 roms chips that were heavily corroded, repaired maybe 20 traces and when powered up it chimed but produced a black screen. It then once and only once booted showing a grey screen with cursor and a floppy ? symbol. I was unable to repeat this but as there were vertical lines on the screen it was suggested maybe the ram or the 245s. The 4 simms tested ok and while the 245s looked ok on my logic probe I swapped them anyway with no change.

Its at this stage that things go backwards as now the board no longer chimes. It boots to either a white screen or a garbage green screen. I've double checked my repair work and its all fine, I can't find anything else broken.

One thing that I've so far been unable to test though are the ROMs. Given how heavily corroded they were I suppose its possible the problem lies within one or all of them. I have a TL866 so I was hoping to read out the roms on there and compare to known good images. Would anyone be able to tell me what type of rom chips these are? If I needed to source alternatives does anyone know what type of chip I need?

Beyond that I would be forever grateful for any further advice for where to look for further damage. I'm considering removing the MDU chip to inspect under it, its not beyond me but the extend of pins on it is just a pain to work with.

 

[Phipli]

Have you had the battery holder out? One of the ROM address lines or data lines goes right under the battery and gets eaten by a leaky battery.

 

[CRG (Glen)]

Yes the battery holder is out and the 2 traces directly under it and 1 close to it have been repaired. To give you some idea of the level of damage these traces were simply gone.

 

[CRG (Glen)]

One thing I should add is that the 2 diodes just above the battery area were heavily damaged. I've replaced these with through hole parts mounted surface while waiting for new parts to arrive.

In fact the board also has suffered severe leakage from capacitors which has all been cleaned up and its fully recapped but transistor Q4 was lost in the process. Thats been replaced again with a through hole 3906 mounted surface while I wait for parts.

All that said though the board did show life with a chime but black screen with these temporary parts fitted.

 

[CRG (Glen)]

OK we are back to a black screen and chime, found a bad solder joint on the MDU, the rom select pin. Going to reflow the rest of that chip on the off chance.

 

[imactheknife]

OK we are back to a black screen and chime, found a bad solder joint on the MDU, the rom select pin. Going to reflow the rest of that chip on the off chance.

I have had to replace roms on a few boards, well a friend does it for me. Also check all the traces in sound circuit. The sound chips sometimes, well most times need to come off due to corrosion etc.

 

[CRG (Glen)]

I was thinking last night am I maybe chasing a fault in the wrong place. Granted it might still be the roms themselves but I wonder if there is damage at the other end of the board where the leaking capacitors were. Is there anything up there that would stop the board from fully booting?
Taking a look with the logic probe last night, when it first powers up everything looks normal but after the chime and maybe 1-2 seconds later there is another pop from the speakers and its at that point the system partly dies. Part of the databus gets stuck i.e. stuck high or low, the output enable pins of the F245s are all high and the system is just dead.

To rule out the roms would anyone know how I could read them out on my TL866?

 

[Phipli]

I have had to replace roms on a few boards, well a friend does it for me. Also check all the traces in sound circuit. The sound chips sometimes, well most times need to come off due to corrosion etc.

Not entirely impossible, but that is mainly LCs that always have issues with the sound chip. The sound circuit is a bit less integrated on the IIci.