Hi,
First a little introduction, I have recently acquired and been repairing a Mac LC III. The machine came without a PSU, so obtained a PSU and recapped it. Machine is running 7.5.5, from BlueSCSI device, it does have a memory and VRAM SIMM. Have OpenTransport 1.1.1 on it, with OpenTransport PPP 1.0.1.
The issue is the Modem and Printer ports. On a US Robotics device, I just see the SD light on when plugged in. The Modem does not dial, or seem to respond. I see CTS and DTR lights flicker. If I put an RS232 breakout box in the cable I see data on the RD line as the Mac tries to command the device. Checked the -5v line and can see voltage, also checked Pin 10 on U3 and U0, and they appear to be also have -5v on them. Pin 10 does not look like its lifted off the board at all. Verified work against Bombard circuit diagram.
Weirdly enough I have had it dial a few times when the top was off, and the PSU put to one side, but on reassembly it does not work again. But I do know the Modem cable is fine (it has worked, and verified wiring with multimeter).
Could it possibly be C22? I see there is a couple of threads on thats orientation. Original CAPs on this board have been replaced, and it looks the cap was installed with the band to the + on the silkscreen. If C22 is removed or failed, will the modem/printer function at all, or intermittently? Re-orienting C22, per the threads, does not seem to help; both pads have continuity to ground and -5v supply lines.
Hope someone seen something like this before.
David
First a little introduction, I have recently acquired and been repairing a Mac LC III. The machine came without a PSU, so obtained a PSU and recapped it. Machine is running 7.5.5, from BlueSCSI device, it does have a memory and VRAM SIMM. Have OpenTransport 1.1.1 on it, with OpenTransport PPP 1.0.1.
The issue is the Modem and Printer ports. On a US Robotics device, I just see the SD light on when plugged in. The Modem does not dial, or seem to respond. I see CTS and DTR lights flicker. If I put an RS232 breakout box in the cable I see data on the RD line as the Mac tries to command the device. Checked the -5v line and can see voltage, also checked Pin 10 on U3 and U0, and they appear to be also have -5v on them. Pin 10 does not look like its lifted off the board at all. Verified work against Bombard circuit diagram.
Weirdly enough I have had it dial a few times when the top was off, and the PSU put to one side, but on reassembly it does not work again. But I do know the Modem cable is fine (it has worked, and verified wiring with multimeter).
Could it possibly be C22? I see there is a couple of threads on thats orientation. Original CAPs on this board have been replaced, and it looks the cap was installed with the band to the + on the silkscreen. If C22 is removed or failed, will the modem/printer function at all, or intermittently? Re-orienting C22, per the threads, does not seem to help; both pads have continuity to ground and -5v supply lines.
Hope someone seen something like this before.
David