Lyokian159
Member
Hi All!
I am looking for a little feedback on next steps in repairing an attic found Mac Plus.
Background: Arrived deader than disco. Sad Mac + Analog Board issues - NE2 voltage clamp was firing. Re-capped the analog board and got all voltages in spec. Reflowed all connectors and any suspect pins on Analog Board.
Sad mac was traced back to a bad SIMM. Replaced all 4 with known good 256k SIMMs.
The machine Finally booted and ran for about 5 minutes before locking up. I tried to power cycle the machine but it would not bong, and no video (crt is glowing).
I left the chassis off for about a day, came back and it bonged, tried to boot, then crashed back to no video, and no bong on subsequent warm boots.
Checked voltage on the floppy drive ports after the machine locks and am getting steady +5, +12, and -12v where expected.
I gave the board a good vinegar scrub to remove some corrosion on the connectors, then an isopropyl 99% bath, and 2 days dry. Same behavior persists.
The machine will boot cold, stay on for about 30 seconds, then crash to black and wont boot until hours later when it will bong again.
Dead Mac Scrolls pointed to the PAL chips and I thought maybe a cold solder joint due to the intermittent behavior so I have tried reflowing the PAL (LAG, BMU2, and CAS) chips, and I get the same behavior; including if I use another working analog board.
I am curious if anyone has seen a similar behavior and can point me in the next step to test?
TLDR: Mac Plus starts to boot when cold and crashes to black screen after ~30 seconds. Wont bong or show video again unless left alone for a few hrs. Tested with known good Analog Boards.
Thank you all so much!
I am looking for a little feedback on next steps in repairing an attic found Mac Plus.
Background: Arrived deader than disco. Sad Mac + Analog Board issues - NE2 voltage clamp was firing. Re-capped the analog board and got all voltages in spec. Reflowed all connectors and any suspect pins on Analog Board.
Sad mac was traced back to a bad SIMM. Replaced all 4 with known good 256k SIMMs.
The machine Finally booted and ran for about 5 minutes before locking up. I tried to power cycle the machine but it would not bong, and no video (crt is glowing).
I left the chassis off for about a day, came back and it bonged, tried to boot, then crashed back to no video, and no bong on subsequent warm boots.
Checked voltage on the floppy drive ports after the machine locks and am getting steady +5, +12, and -12v where expected.
I gave the board a good vinegar scrub to remove some corrosion on the connectors, then an isopropyl 99% bath, and 2 days dry. Same behavior persists.
The machine will boot cold, stay on for about 30 seconds, then crash to black and wont boot until hours later when it will bong again.
Dead Mac Scrolls pointed to the PAL chips and I thought maybe a cold solder joint due to the intermittent behavior so I have tried reflowing the PAL (LAG, BMU2, and CAS) chips, and I get the same behavior; including if I use another working analog board.
I am curious if anyone has seen a similar behavior and can point me in the next step to test?
TLDR: Mac Plus starts to boot when cold and crashes to black screen after ~30 seconds. Wont bong or show video again unless left alone for a few hrs. Tested with known good Analog Boards.
Thank you all so much!
