cj7hawk
Veteran Member
Hi All,
Yesterday, I got my first Mac. In fact, my first "Apple" product ever. Unfortunately, the 128K Euro model had been internally modified, partially by what looks like it might have been a factory upgrade to 512K and part of which was performed by the rain, as the whole unit looks like someone found it on a junkpile after the rain had gone.
Presently, it switches on but the display is just a series of white lines ( left to right ) which are relatively thick - I think around 70 or so of them. They appear to have some pixels missing in places and are stable, so I suspect the monitor itself is fine and it's the logic board. I read that the boards are pretty bulletproof somewhere and only the memory fails, so I removed one of the 256K banks and upon post-removal checking of the RAM chips found that they all worked perfectly, so I assume it's something else.
Present plans are to remove and test the second bank also, then clean the board up with some alcohol and solder in sockets for the RAM, and I found some schematics for the 128K, which also appear to show the additional 253 chip (MUX) for the memory upgrade that someone soldered on top of one of the existing 253 chips, but this is my first MAC repair, and if anyone has any suggestions for resources, I'd be highly appreciative.
Also, if anyone has a suggestion for any common faults that would reduce the central Mac screen to a series of horizontal lines, I'd also be highly appreciative ( My current guess is that it might be Mux related, but that's just a guess at this point ). I have the usual hobbiest repair equipment - Oscilloscopes, Logic Analyzers, Desoldering tools, Prior experience in repair work etc. But at the moment I have less than an hour experience on the Mac at all, so thought I'd ask quickly for suggestions to help bootstrap me into the world of repairing the 128k/512k I ended up with.
Thanks for all and any suggestions and comments -
David
Yesterday, I got my first Mac. In fact, my first "Apple" product ever. Unfortunately, the 128K Euro model had been internally modified, partially by what looks like it might have been a factory upgrade to 512K and part of which was performed by the rain, as the whole unit looks like someone found it on a junkpile after the rain had gone.
Presently, it switches on but the display is just a series of white lines ( left to right ) which are relatively thick - I think around 70 or so of them. They appear to have some pixels missing in places and are stable, so I suspect the monitor itself is fine and it's the logic board. I read that the boards are pretty bulletproof somewhere and only the memory fails, so I removed one of the 256K banks and upon post-removal checking of the RAM chips found that they all worked perfectly, so I assume it's something else.
Present plans are to remove and test the second bank also, then clean the board up with some alcohol and solder in sockets for the RAM, and I found some schematics for the 128K, which also appear to show the additional 253 chip (MUX) for the memory upgrade that someone soldered on top of one of the existing 253 chips, but this is my first MAC repair, and if anyone has any suggestions for resources, I'd be highly appreciative.
Also, if anyone has a suggestion for any common faults that would reduce the central Mac screen to a series of horizontal lines, I'd also be highly appreciative ( My current guess is that it might be Mux related, but that's just a guess at this point ). I have the usual hobbiest repair equipment - Oscilloscopes, Logic Analyzers, Desoldering tools, Prior experience in repair work etc. But at the moment I have less than an hour experience on the Mac at all, so thought I'd ask quickly for suggestions to help bootstrap me into the world of repairing the 128k/512k I ended up with.
Thanks for all and any suggestions and comments -
David