Macintosh Plus repair...smiley postage stamp

[T-Man]

Sorry if this is obvious or posted somewhere else, but I have a Macintosh plus that chimes and then HAD a small postage stamp with smiley face and no error code. After a few off and on's, it now has a thin line the width of a postage stamp in the center of the screen. It still chimes and I assume it is booting off of a floppy as after I give it time, the disk will eject with clover leaf and E. The screen never changes, small line maybe 2 pixels high and 8 pixels in length at the center of a black screen. I've washed the main board reseated RAM and socketed chips, reflowed Flyback., analog connectors.

 

[Nixontheknight]

Can you take a photo of what comes up on screen?

 

[T-Man]

 

[Nixontheknight]

View attachment 25762

That's vertical collapse, and I think there's something in the dead mac scrolls about this

 

[T-Man]

Yes...after removing the double sided tape on the analog board, there were a couple of broken solder joints at J1; so after reflowing, I am back to the smiley postage stamp pictured, it seems to boot based on disk drive activity but the screen remains as pictured . The screen looks about right otherwise so will switch some RAM around.

 

[T-Man]

Parts machine; have a Cutting Edge external drive and plugged the internal cable in off 1 pin; now no screen, no beep.

 

[Nixontheknight]

The Dead Mac Scrolls may be able to help you here:
https://archive.org/details/mac_The_Dead_Mac_Scrolls_1992/

 

[T-Man]

Still pulling this one out every so often. So no charge or any activity on the screen, however, the analog/screen combination work fine when I put in a known working logic board.
On start up about half of a second noise from the internal floppy, a minimal static from the speaker; nothing at screen no static electricity no brightness/light with brightness control turned up; no bong ..MAYBE the start of a bong vs static on flipping it on. The 2 ROMs work in the other board as does memory, get a clock signal, 68000 reset low then high. I get -12,12 and 5 volts on external floppy connector. Dead Mac Scrolls recommends replacing 3 PAL chips, which I haven't be able to locate other than another board......not really worth the expense there.

Given events the damage I think was high voltage feedback through the external floppy port with the external floppy drive cable misaligned...given the way it dimmed then failed when I plugged it in...although I did get rid of the external floppy drive pretty quickly without trying it on another machine, didn't want to risk coming across it later and repeating.

 

[wskjinfen]

PAL chips can now be completely replaced. When I repaired difficult problems before, I replaced them in this order: ROM, CPU, VIA, SCC, PAL, and 74TTL. Except for IWM, which cannot be repaired, replacement parts are available for others.