Ferrix97
Well-known member
Hello!
I recently scored three ED Macs, two Macintosh Plus EDs and a Macintosh ED (which is a 512ke).
The Mac ED only needed a quick reflow of the J1 connector.
The first Plus ED produced a very quick ticking noise no matter if the logic board was connected or not. I quickly noticed that the flyback diode was shorted. I replaced the flyback, the diode and the transistor and now it is working perfectly as well!
The second Plus is driving me crazy: it has a slower ticking noise, I don't think it is coming from the speaker.
The flyback seems in good shape, I swapped it with a NOS one and it still has the same issue. Did some other measurements on various diodes (according to Pina's books) and they all look fine. I also replaced two capacitors and the optocoupler.
If I disconnect the logic board the ticking gets a bit faster. After heating up the board, I was able to briefly stop the ticking, but still no chine and no video. I measured the +12V line and it was about 15V, the trimmer on the analog board does absolutely nothing. +5V is also way too high, about 6.5V. After taking the measurements I removed the logic board and tested it in the other Plus and it survived he high voltages. I also noticed that somebody clipped the third lead (output) of the 79045 regulator. maybe the power supply killed it (but it is used only for the serial ports, which I don't need).
There is very little dust inside, the HV area looks very clean, so it's possible that it broke when it was still in use (I got it from an Apple Dealer)
The analog board is the 220V INTERNATIONAL model with the W12 jumper removed.
I think there is an open/shorted component in the power supply area, but I cannot find it!
I recently scored three ED Macs, two Macintosh Plus EDs and a Macintosh ED (which is a 512ke).
The Mac ED only needed a quick reflow of the J1 connector.
The first Plus ED produced a very quick ticking noise no matter if the logic board was connected or not. I quickly noticed that the flyback diode was shorted. I replaced the flyback, the diode and the transistor and now it is working perfectly as well!
The second Plus is driving me crazy: it has a slower ticking noise, I don't think it is coming from the speaker.
The flyback seems in good shape, I swapped it with a NOS one and it still has the same issue. Did some other measurements on various diodes (according to Pina's books) and they all look fine. I also replaced two capacitors and the optocoupler.
If I disconnect the logic board the ticking gets a bit faster. After heating up the board, I was able to briefly stop the ticking, but still no chine and no video. I measured the +12V line and it was about 15V, the trimmer on the analog board does absolutely nothing. +5V is also way too high, about 6.5V. After taking the measurements I removed the logic board and tested it in the other Plus and it survived he high voltages. I also noticed that somebody clipped the third lead (output) of the 79045 regulator. maybe the power supply killed it (but it is used only for the serial ports, which I don't need).
There is very little dust inside, the HV area looks very clean, so it's possible that it broke when it was still in use (I got it from an Apple Dealer)
The analog board is the 220V INTERNATIONAL model with the W12 jumper removed.
I think there is an open/shorted component in the power supply area, but I cannot find it!