I own a power mac 7500/100 that seems to have a bad processor card. If I am to replace this card, I'd like to upgrade at the same time. On ebay, I have found an Apple Macintosh Mac 820-0780-A G3/G4 Computer Processor Card. Is this card compatible with my power mac?
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resurrecting/upgrading power mac 7500/100
- Thread starter fjm_48
- Start date
Zippy Zapp
Experienced Member
The 820-0780-A is not a G3/G4 card. Apple didn't make a G3 processor card for the older PCI macs. At least not that I recall. I know 3rd party cards are available as I have a G3 made by another company.
The 820-0780-A is a 150 Mhz 604 CPU. I think originally paired with an 8500 or 9500. It will work and it will be an improvement over the 100 Mhz 601 stock CPU card.
The 820-0780-A is a 150 Mhz 604 CPU. I think originally paired with an 8500 or 9500. It will work and it will be an improvement over the 100 Mhz 601 stock CPU card.
Thank you for that answer and information. Right now, I'm replacing all aluminum electrolytic caps on the logic and processor boards. If that doesn't fix my power mac, I will try that replacement processor card (820-0780-A).
Zippy Zapp
Experienced Member
Yeah if the problem is the CPU card then it wouldn't hurt to upgrade it. None of the PowerMacs I have seem to have any cap issues. The only PowerMac I have needed to recap was a 6100 as the caps were leaking and literally falling off the board. I don't know if they used better caps on the PCI Macs but last time I checked they were still shiny and no signs of leaking. Of course if they are leaking then best to replace them. That said even with the caps off the board on the 6100 it still worked mostly.
Good Luck with the repair and I hope you get it working.
Good Luck with the repair and I hope you get it working.
While I'm waiting for a replacement/upgrade processor card, I want to continue with troubleshooting. I am not getting a chime on power up. Obviously to get the chime, I need a speaker, the logic board, and a power supply. I'm guessing also a processor card is required. Do I need RAM and/or video RAM Installed? If I have a minimum configuration needed for a chime and do not get a chime, then one of the installed components must be at fault. That might exonerate HDDs, CDROMs, FDDs, and memory devices.
ClassicHasClass
Veteran Member
To boot up with a display on the monitor you'll need a processor card, RAM (remember to install in pairs in this unit), and either VRAM or a compatible PCI video card (which may be easier to come by than the VRAM sticks). It's possible to make it start to a serial port but this is a little involved to do. I'm also skeptical the caps are the problem; they're not currently a common failure with the Outrigger PCI Macs, and certainly not to the extent you'll find with '030s.
GiGaBiTe
Veteran Member
Those SMD lytics can hide the fact they're leaking for a really long time. The space between the can and the plastic base, and again from the plastic base to the board will wick electrolyte via capillary action. So they can have a slow leak that will keep the electrolyte under the cap. The cap falling off the board is because the electrolyte is conductive and whenever the board is powered up, it allows electrlysis to occur and eat the pads and the legs of the capacitor.
I've had plenty of those caps that look fine, but removing them showed a considerable amount of damage under them. It's best to just replace them all at this point.
Zippy Zapp
Experienced Member
It certainly can't hurt unless you do damage while recapping. I have a 7200/75 logic board I don't use and took a few caps off just to see and none of them had any signs of leaking. But yeah they are almost 30 years old at this point so they should all be considered time bombs...
That 6100 board that I recapped was a computer that was in storage for probably 15 or 20 years. The case was so brittle that it cracked just looking at it wrong. When I discovered the caps it had not been powered on at that point. But it was saved with very little damage to the pads.
That 6100 board that I recapped was a computer that was in storage for probably 15 or 20 years. The case was so brittle that it cracked just looking at it wrong. When I discovered the caps it had not been powered on at that point. But it was saved with very little damage to the pads.
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Thanks for the answer. Though I have a replacement processor card coming, I was hoping to do additional troubleshooting without it. I'm not getting a chime on power up. I was trying to determine what is needed to get the chime only.
If replacing the processor card does not fix the problem, I will re-cap the logic board. Every other possible failure source will have been eliminated - processor card, power supply, DRAM. Then if re-capping doesn't work, there is always the trash can
Zippy Zapp
Experienced Member
I hope that fixes it. I seem to recall there is a CUDA chip reset button on the logic board. I seem to remember having to use that button in order to get one of my PCI Power Macs to boot after swapping CPU or something. When you get your new CPU card and it still doesnt boot, try holding that button for 3 to 10 seconds or something... It's worth a shot I suppose.
ClassicHasClass
Veteran Member
You'll still need a CPU card for that, and probably some RAM.
Thanks for the reply. That's what I thought but wanted to verify.
I have an Apple 820-0928-01 Power Mac 604 200MHz Processor Card available that I replaced with a Sonnet G4 800 mHz card some years ago. Was working fine at the time, but I sold my 7600 with the upgrade and just re-found the original card.
If you are interested, make me a reasonable offer... DM with your address for best shipping rates. I'm out of Mississauga, Ontario. I also have other Apple items and compatible parts and devices.
Thank you for the offer. I already have a processor card coming from an ebay purchase that I made. I briefly worked in Mississauga (at Honeywell).
Update: no joy! I have now tried all logical combinations of two logic boards, two cpu cards, two power supplies (one of them is an ATX PSU with adapters) and three pairs of RAM modules. Either I am still missing something, or I was sold bad components that were represented as being functional. I have an SCSI pci adapter coming; so, I can retrieve my files from the HDDs. My next step is the trash can unless someone would like to come to Tucson, AZ to claim this mess.
GiGaBiTe
Veteran Member
Did you recap the logic board? And be careful with those ATX adapters, many of them aren't built correctly and send the wrong power to the wrong place.
Also, what is the machine doing when you try to power it on?
I re-capped to top of the logic board; I forgot to count the caps on the bottom. I can order the remaining needed caps, but I'd like to verify their performance in circuit first. I believe that the failure mode of aluminum electrolytic caps is shorting (or high current leakage). That would result in lower than specified voltage at the positive terminal of the capacitors. Do you have other thoughts?
I built the PSU adapter and verified proper voltages and signals at all of the connections.
When I power on the system, the power LED illuminates immediately, there is a 1 second delay before I get about 3 seconds of white noise from the speaker, then nothing.
I will continue trying as long as you and others offer sensible advice.
GiGaBiTe
Veteran Member
Failed electrolytic capacitors can have numerous different failures, here are a few:
- Short Circuit
- Open Circuit
- Out of spec capacitance (too low or too high)
- High ESR
- Turning into a resistor
- Electrically leaky, passing DC instead of blocking it
You need to replace all of the capacitors, not just some. Replace the rest of the capacitors and try to boot the board again. You also should clean the board well with something like CRC Lectra Clean. IPA is junk and usually just smears things around and leaves white streaks.
I'm not familiar with the 7500, but it may need a ROM SIMM to boot. It also may need a good PRAM battery, there are several mac models that won't boot or have erratic behavior with no PRAM battery installed.
ClassicHasClass
Veteran Member
The 7500 should not need a PRAM battery. Only early 7500s would need a ROM SIMM; most of them don't.
skate323k137
Experienced Member
It's been a moment since I restored mine but I seem to remember holding a reset button for about a second every time I make any changes to the machine, before powering it on. Much more about it here though https://68kmla.org/bb/index.php?threads/powermac-7500-100-dead.19371/