Power Macintosh 7500 issues

[duk1975]

Hello, everybody!

I need some help!

Two months ago I bought old Power Macintosh 7500 in rather good condition: no cracks, looks rather good. The seller assured me that it works fine. Instead of SCSI drive he installed Sonnet ATA 66 controller card with SSD ATA drive and ATAPI DVD-RW drive. 200 Mhz CPU card and 176 mb memory. With MacOS 9.1 it worked flawlessly and fast, at least on video.

When I received the mac, at the beginning everything was ok. But after 4-5 days of rare boots disk partition on SSD drive once crashed. I booted mac with MacOS 9.1 installation disk and had to initialize the SSD. After that, unexpectedly, I couldn’t install system on the drive: installation started, but after 2 minutes it stopped with no changes to the disk. The same repeated with MacOS 8.5, 8.1 and so on.
I bought used ATA drive to install OS on it, with no success.
I tried to pull out memory modules (there are 176 mb, all slots are taken), one by one, but with no success.
I got bluescsi v.2 and there was no success in installation too: system boots, but never installs, even from one disk image to another.
However I managed to boot my mac with bluescsi with the image of MacOS8.1 installed by Sheepshaver. With that way it boots and works but I still can’t install anything or even unpacking *.sit archives is not always successful. Though copying from one drive to another works perfectly. I.g. I couldn’t install MS office 98, but if I install it under Sheepshaver and then boot with that image my mac, MS Office works perfectly.

Where should I dig up? What it can be? CPU card? Mobo? Any suggestion are welcome!

 

[nathall]

Capacitors and PS would be what I’d look at first.

 

[duk1975]

Capacitors and PS would be what I’d look at first.

Thank you for answer! Excuse me my ignorance, how should I check up capacitors? Really don't know much about it. Didn't see any bulging capacitors though, that might be discovered obviously. And what PS stands for?

 

[nathall]

PS is power supply. You might be facing voltage drop.

For capacitors, the only way to reliably test them is to remove them and check with a multimeter. But if you’ve got them out, you should just go ahead and replace them.

 

[duk1975]

Thank you again, though it’s really the worst diagnosis I expected…

There is one more issue to take into account: the mac never starts/boots immediately when I power it on: chime sounds, but nothing happens. I have to reboot it manually (by pressing power button on the case and then again on the case or keyboard, or by pressing “magic keys” (ctrl+cmd+del+power). After that it chimes again, picture appears on the monitor, the computer boots.

 

[Unknown_K]

Does it work without the ATA card using a SCSI HD?

 

[Byrd]

Thank you again, though it’s really the worst diagnosis I expected…

There is one more issue to take into account: the mac never starts/boots immediately when I power it on: chime sounds, but nothing happens. I have to reboot it manually (by pressing power button on the case and then again on the case or keyboard, or by pressing “magic keys” (ctrl+cmd+del+power). After that it chimes again, picture appears on the monitor, the computer boots.

Had a similar PowerMac 7300 (actually two just recently!) do this, was related to it needed a working PRAM battery. I'd strip it down to the absolute basics, no cards, stock HD, dual known good RAM, clean the board, connectors, try to coax it back. The 7300 x 2 I found once I got booting to a basic desktop was able to add a component at a time.

 

[duk1975]

Does it work without the ATA card using a SCSI HD?

Hello! I have no original SCSI HD drive, only bluescsi v2. It does boot with it and without ATA card. But I can't install OS neither from one image on SD card to another, nor from real bootable CD to image, nor from image to SSD.

 

[duk1975]

Had a similar PowerMac 7300 (actually two just recently!) do this, was related to it needed a working PRAM battery. I'd strip it down to the absolute basics, no cards, stock HD, dual known good RAM, clean the board, connectors, try to coax it back. The 7300 x 2 I found once I got booting to a basic desktop was able to add a component at a time.

The seller changed the PRAM battery. So it is brand new, fresh, 2024-made. But I catch the idea and will try it today, thank you!

 

[duk1975]

Had a similar PowerMac 7300 (actually two just recently!) do this, was related to it needed a working PRAM battery. I'd strip it down to the absolute basics, no cards, stock HD, dual known good RAM, clean the board, connectors, try to coax it back. The 7300 x 2 I found once I got booting to a basic desktop was able to add a component at a time.

Hello! Unfortunately it didn't work. Nothing changed even when I left only one pair of memory modules and the drive.