Power Macintosh 7500 issues

duk1975

Member
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!
 

duk1975

Member
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

Well-known member
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

Member
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.
 

Byrd

Well-known member
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

Member
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

Member
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

Member
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.
 
Top