Having scoured the forums for relevant information, and finding no info on some aspects, I decided to post my experience here.
I got a Performa 475 for 50 euros on eBay, without description, but with some documentation, cables, and CDs. Being interested in 475 range, I thought how bad can it be. Hard disk viewed on another Mac showed the computer was bought in 1995 and last used in 1996. So it spent 30 years in storage. Battery was removed, fortunately, so it did no damage. Caps showed residue around them, but not much. Astec power supply seemed to give very stable voltages.
Of course, I put in a new PRAM battery, as this model is not supposed to start without it. On startup, speaker emitted a happy chime and HDD spun up, but there was no further activity and no video signal (via Griffin MacPnP adapter and an LCD monitor). Removed extra RAM, swapped power supply with known good one, swapped VRAM, to no effect. ADB keyboard blinked and had power, but Cmd-Opt-P-R had no effect. Recapping (my first try) and vinegar bath (should have done it before installing new caps) did not change anything.
My one remaining suspect was the VGA adapter. Tried other LCDs, other settings. Could not find definitive information whether 475 can boot without monitor. More on that later. At rare occasions, the Performa emitted sad boot sequence (8 tones). It was not repeatable.
Finally, the vinegar bath seemed to have exposed a break in one trace, which was not immediately visible to me before (and I stared at this spot for hours already). It was directly on the other side of C128 power supply capacitor, next to on-board RAM. It was damaged apparently by electrolyte. Looking at schematics, it was a write-enable line between memory controller and all on-board RAM chips. And it had in fact no continuity. Even though the gap was just a fraction of millimeter, I could not bridge it with solder alone. Based on other post here, I took a strand of CAT5 wire and bridged it this way.
This finally made a difference. Computer booted from the original hard disk (MacOS 7.6.1), and later from a BlueSCSI (System 7.1p3) I put in. I put everything nicely in the case ... and it would not boot at all. Would not even chime. But that is a story for another time. There must be another transient fault. I found though that when the Performa is cold, I have about 15 minutes of play time before it warms up and locks. Then I have to go and do something more productive. Come to think of it, it's a useful feature!
Now coming back to the question of booting without monitor. I can see now what the Performa is doing even without display, connecting via BlueSCSI WiFi and Timbuktu server. In my limited testing, if there is nothing connected to the video port, the OS does not seem to come up. If I only have the Griffin adapter plugged in but no monitor, the OS boots and can be viewed remotely with resolution 640x480. Probably, the adapter provides the necessary sense lines (simply grounded pins) to indicate that there is a display. So this could be used as a headless server - another question I could not find a definite answer to.
Sorry for the long post. I hope the photos are half-way visible here - thumbnails look very washed out.
I got a Performa 475 for 50 euros on eBay, without description, but with some documentation, cables, and CDs. Being interested in 475 range, I thought how bad can it be. Hard disk viewed on another Mac showed the computer was bought in 1995 and last used in 1996. So it spent 30 years in storage. Battery was removed, fortunately, so it did no damage. Caps showed residue around them, but not much. Astec power supply seemed to give very stable voltages.
Of course, I put in a new PRAM battery, as this model is not supposed to start without it. On startup, speaker emitted a happy chime and HDD spun up, but there was no further activity and no video signal (via Griffin MacPnP adapter and an LCD monitor). Removed extra RAM, swapped power supply with known good one, swapped VRAM, to no effect. ADB keyboard blinked and had power, but Cmd-Opt-P-R had no effect. Recapping (my first try) and vinegar bath (should have done it before installing new caps) did not change anything.
My one remaining suspect was the VGA adapter. Tried other LCDs, other settings. Could not find definitive information whether 475 can boot without monitor. More on that later. At rare occasions, the Performa emitted sad boot sequence (8 tones). It was not repeatable.
Finally, the vinegar bath seemed to have exposed a break in one trace, which was not immediately visible to me before (and I stared at this spot for hours already). It was directly on the other side of C128 power supply capacitor, next to on-board RAM. It was damaged apparently by electrolyte. Looking at schematics, it was a write-enable line between memory controller and all on-board RAM chips. And it had in fact no continuity. Even though the gap was just a fraction of millimeter, I could not bridge it with solder alone. Based on other post here, I took a strand of CAT5 wire and bridged it this way.
This finally made a difference. Computer booted from the original hard disk (MacOS 7.6.1), and later from a BlueSCSI (System 7.1p3) I put in. I put everything nicely in the case ... and it would not boot at all. Would not even chime. But that is a story for another time. There must be another transient fault. I found though that when the Performa is cold, I have about 15 minutes of play time before it warms up and locks. Then I have to go and do something more productive. Come to think of it, it's a useful feature!
Now coming back to the question of booting without monitor. I can see now what the Performa is doing even without display, connecting via BlueSCSI WiFi and Timbuktu server. In my limited testing, if there is nothing connected to the video port, the OS does not seem to come up. If I only have the Griffin adapter plugged in but no monitor, the OS boots and can be viewed remotely with resolution 640x480. Probably, the adapter provides the necessary sense lines (simply grounded pins) to indicate that there is a display. So this could be used as a headless server - another question I could not find a definite answer to.
Sorry for the long post. I hope the photos are half-way visible here - thumbnails look very washed out.
