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Can this 575 logic board be saved?

Jagmn

Well-known member
Long story short: I acquired a 575 logic board 'untested'. On testing it gave the boot chime followed very shortly by the death chimes. The board itself looked clean enough but I went ahead with a re-cap but this resulted in no improvement. After a wipe around with IPA, I can now see some clearly corroded and broken traces around the silkscreen for J10/C12:
IMG_6167.jpeg

Probing for continuity (mostly guessing here as I don't have a schematic) showed that only 3 of the traces are unbroken. I think they are beyond my ability to repair but I'm open to challenges and suggestions!

Thanks

PS: Apologies for the sloppy solder work around the new caps.
 

joshc

Well-known member
Looks like those traces were damaged by cap goo from C12 and C13.

This video might help you learn how to repair them.

 

Jagmn

Well-known member
Thanks for the pointers. The traces seem very small and close together for bridging with enamel wire or old capacitor legs but nothing ventured nothing gained! I'll grab some of the 40AWG stuff and see how I get on.
 

Jagmn

Well-known member
Brief update: I have run 4 bodge wires from vias next to the broken traces to the pins on the CPU socket that they seemed to need continuity with.
Tada: No more sad mac chimes! Thanks for the pointers and encouragement.

The system sounds like it is booting (hard drive activity and an error tone probably from when it warns about invalid date/time) but, unfortunately, the screen comes on and remains a solid purple. I've verified the screen/analog board with another logic board, so the problem is still on this board somewhere.

Also: it looks like I killed my original 68LC040 :( I thought I was being careful about ESD considerations, etc, but it's dead as a doornail. Thankfully I had a Performa 630 I was able to borrow from. Is the best place to find a proper replacement on eBay?
 

jajan547

Well-known member
Brief update: I have run 4 bodge wires from vias next to the broken traces to the pins on the CPU socket that they seemed to need continuity with.
Tada: No more sad mac chimes! Thanks for the pointers and encouragement.

The system sounds like it is booting (hard drive activity and an error tone probably from when it warns about invalid date/time) but, unfortunately, the screen comes on and remains a solid purple. I've verified the screen/analog board with another logic board, so the problem is still on this board somewhere.

Also: it looks like I killed my original 68LC040 :( I thought I was being careful about ESD considerations, etc, but it's dead as a doornail. Thankfully I had a Performa 630 I was able to borrow from. Is the best place to find a proper replacement on eBay?
Did you do PRAM reset and is there a new battery?
 

beachycove

Well-known member
It might be worth observing that if it happens to be installed in a Color Classic, like many 575 boards tend to be, it won’t boot to a screen without further work.
 

Byrd

Well-known member
Oh yeah don’t you need to move a resistor for that?

Resistor + ResEdit work for 512 x 384 resolution, bodge wiring and cutting a trace for 640 x 480, see here:


Nice work @Jagmn ; I've a sick LC575 board with VRAM/trace issues and the 72-pin RAM slot also needs replacing (death chime with anything in there, onboard 4MB works fine). Glad your purple hue is gone, sounds like a VRAM/trace issue was present too from cap corrosion/damage.
 

jajan547

Well-known member
Resistor + ResEdit work for 512 x 384 resolution, bodge wiring and cutting a trace for 640 x 480, see here:


Nice work @Jagmn ; I've a sick LC575 board with VRAM/trace issues and the 72-pin RAM slot also needs replacing (death chime with anything in there, onboard 4MB works fine). Glad your purple hue is gone, sounds like a VRAM/trace issue was present too from cap corrosion/damage.
Have photos?
 

Jagmn

Well-known member
Here you are. It’s $20 shipped.
Thanks for the link! Though I think I need to find 33Mhz parts? My assumption was that XC68LC040RC258 was speed binned for 25Mhz?

It might be worth observing that if it happens to be installed in a Color Classic, like many 575 boards tend to be, it won’t boot to a screen without further work.
Guilty; yes, it is in a CC (analog board recapped - suspect caps only - and PPT7 calibrated for functional voltages). I've already moved R116 to R109 and checked R110 is empty. I could solder a through-hole 4.7k resistor in R109 if it'll make a difference but the purple makes me think something could be whiffy around the graphics signal traces on the logic board (the original CC logic board boots fine).

Thanks for all the input folks!
 

jajan547

Well-known member
Thanks for the link! Though I think I need to find 33Mhz parts? My assumption was that XC68LC040RC258 was speed binned for 25Mhz?


Guilty; yes, it is in a CC (analog board recapped - suspect caps only - and PPT7 calibrated for functional voltages). I've already moved R116 to R109 and checked R110 is empty. I could solder a through-hole 4.7k resistor in R109 if it'll make a difference but the purple makes me think something could be whiffy around the graphics signal traces on the logic board (the original CC logic board boots fine).

Thanks for all the input folks!
Let us know, hope to hear more news soon.
 

Jagmn

Well-known member
Okay, after putting a through-hole 4.7k resistor to R109 I now get a grey screen - mostly fairly consistently.

I've verified the connections of the video signals (by examining the CC logic board + schematics) to U26 which, I am assuming, is the CLUT/DAC as per the 575 developer notes. I've also thoroughly eyeballed the surrounding traces, testing for continuity those I've been able to spot end-to-end. So far, nothing seems to be broken. There's still a few traces around the on-board RAM that look a bit corroded but still check out fine with the multimeter. If they didn't I'm sure that I'd still get the chimes of death.

Booting the board without the VRAM results in the display never coming on - I assume this is the expected result.

I'm open to suggestions for other avenues of investigation. Summarily:
  • There is no PRAM battery but booting with the PR reset keys results in a second chime but the same display behaviour.
  • The board consistently boots, judging from disk activity and error beeps. I can hit the power key followed by return to shut it down again.
  • The board is booting from an external BlueSCSI with a System 7.5 that I've tried with and without the software mod for a CC Mystic (no difference in boot behaviour either way).
  • The original CC board boots without issue.
  • Testing the voltage on the ADB port gives me 5.2V which seems pretty healthy.
Thanks!
 

Byrd

Well-known member
the purple makes me think something could be whiffy around the graphics signal traces on the logic board (the original CC logic board boots fine).

Move the VRAM while the computer is on to see if you get any colour improvements on the CRT - clean VRAM connector with electronic solvent spray, and edge connector of the LC575 board and mating connector inside the CC.
 

Jagmn

Well-known member
Thanks for the suggestion. I've done another thorough clean of the contacts (DeoxIT D5) for the VRAM and the board edge connector. Wiggling doesn't change anything on the screen for me. Though it does appear that the purple screen occasionally returns (instead of the more common grey screen) but only after a full power down cycle (not after a soft power down and up again). Continuity between the logic board and VRAM contacts checks out okay (that was a fun while spent with the probes…).

Unfortunately I don't have any other VRAM simms to try, so I might look some up on eBay.
 

jajan547

Well-known member
Thanks for the suggestion. I've done another thorough clean of the contacts (DeoxIT D5) for the VRAM and the board edge connector. Wiggling doesn't change anything on the screen for me. Though it does appear that the purple screen occasionally returns (instead of the more common grey screen) but only after a full power down cycle (not after a soft power down and up again). Continuity between the logic board and VRAM contacts checks out okay (that was a fun while spent with the probes…).

Unfortunately I don't have any other VRAM simms to try, so I might look some up on eBay.
So weird I’ve been having a similar issue with a LC475, can you upload a photo or video?
 
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