LC 550 Logic board debug

[Fizzbinn]

I have a LC 550 logic board that I'm trying to get working and would appreciate any thoughts and/or advice.

It came to me looking pretty good, maybe some signs of leaking capacitors but no obvious signs of trace damage. I did test it prior to re-capping in a known working LC575 chassis: On keyboard soft-power up the front power light turned on, the fan started, the display showed a gray screen with square corners, but no start-up chime or Happy Mac icon...

I recapped the the board with no issues and cleaned it in my ultrasonic cleaner. Rinsed it with IPA, dried it in the oven at 150F for 30 minutes, then with a fan blowing on it overnight. Still no joy, and actually now I'm not even getting the gray screen, just the power light and fan turning on with soft-power on. I had the ROM chips removed while it was in the cleaner, so those have been reseated.

I tried leaving it plugged in, rear switch turned on overnight, with no change in behavior.

I've read the sound chip can be problematic on these board as its surrounded by 4 capacitors that can leak their contents under it so removing it and cleaning under it may be the next thing I try. Also could try the same with the EGRET chip...

 

[jajan547]

L1 and L2 can cause sound errors if they short out, try seeing I’d that at least fixes sound?

 

[Fizzbinn]

L1 and L2 can cause sound errors if they short out, try seeing I’d that at least fixes sound?

Remove L1 and L2, clean under them, and resolder?

 

[jajan547]

Remove L1 and L2, clean under them, and resolder?

Maybe but I know L2 was bad on mine and it restored sound. As far as the other symptoms I’d imagine a line to the SCSI chip may be bad.

 

[Fizzbinn]

Can you point me to what I'd order for replacements?

If it was the SCSI chip I would think I'd get video, just not be able to boot a SCSI device? Still I'm looking over the board again under the microscope...

 

[jajan547]

Can you point me to what I'd order for replacements?

If it was the SCSI chip I would think I'd get video, just not be able to boot a SCSI device? Still I'm looking over the board again under the microscope...

The reason I say might be something to the SCSI is that the machine initialized the scsi first so if it can’t initialize it sits. For example if it was initialiaing correctly you’d see a ? For no HDD detected assuming one failed or isn’t connected or a happy mac booting into Mac OS. Do you have any photos before recap?

 

[Fizzbinn]

The reason I say might be something to the SCSI is that the machine initialized the scsi first so if it can’t initialize it sits. For example if it was initialiaing correctly you’d see a ? For no HDD detected assuming one failed or isn’t connected or a happy mac booting into Mac OS. Do you have any photos before recap?

Just these:

 

[jajan547]

Here’s what I’m gonna say try first #1 reflow the EGRET and #2 do a PRAM reset (cod+shift+p+r) this may take 2-3 tries.

 

[Fizzbinn]

The chips look pretty darn clean. Cleaning just the same. I actually hadn’t thought to try PRAM reset as i didn’t think I was getting far enough with boot for that to apply.

 

[jajan547]

Chips look great give PRAM. A try.

 

[Fizzbinn]

...yeah, but first I need to figure out to get that 4 sided chip back. Unlike the egret where I've done drag soldering across the legs this guy's legs go under the chip, not sure drag soldering will work the same. Also thinking about tinning the pads, putting the chip in place and using the hot air wand thingy (which I used to remove these guys).

 

[jajan547]

Flux and hot air

 

[Fizzbinn]

That was easier than I thought. ...but all back together and no change. Holding Command-Option- P-R right after soft-power on for a good minute doesn't seem to have any affect. sigh.

 

[jajan547]

I assume this is powering on via ADB keyboard with soft power, most likely confirming working EGRET, any chance you can take a video so I can see what the screen corners do? Does it boot from floppy?

 

[Fizzbinn]

The screen does nothing, the fan and front power light come on with ADB keyboard soft-power key press. Prior to my recapping and cleaning I was also getting a gray screen with square corners, no mouse icon or any icon. I'd be overjoyed if I could get to a blinking question mark. Will try sticking a boot floppy in tomorrow but don't think it's getting that far.

 

[jajan547]

The screen does nothing, the fan and front power light come on with ADB keyboard soft-power key press. Prior to my recapping and cleaning I was also getting a gray screen with square corners, no mouse icon or any icon. I'd be overjoyed if I could get to a blinking question mark. Will try sticking a boot floppy in tomorrow but don't think it's getting that far.

I'll tinker around here with mine and see what more I can dig up.

 

[Fizzbinn]

I'll tinker around here with mine and see what more I can dig up.

Thanks, I appreciate the help!

 

[jajan547]

Hey looking at the images I found a trace break.

 

[Fizzbinn]

Hey looking at the images I found a trace break.

OMG! I feel like I've been all over the board and somehow missed this! There are a bunch of other glancing nicks I've checked out exposed copper and not found continuity breaks but this is most definitely a break! THANK YOU!

 

[jajan547]

OMG! I feel like I've been all over the board and somehow missed this! There are a bunch of other glancing nicks I've checked out exposed copper and not found continuity breaks but this is most definitely a break! THANK YOU!

Please do let me know if she fires up again.