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badCaps

Help resurrecting a 7500/100

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Hello all, I have a decent looking Power Mac 7500/100 that I picked up recently.  I did a little cleaning on the exterior, blew out the dust bunnies and powered it on only to find that it won't boot.  The power supply clicks on, power LED on the front works, keyboard LEDs blink, HDD spins up, CD drive ejects but no startup chime (or any sound) and no video. 

 

I have tried the following:

 

Swapping/removing the 4 memory modules.

Removing the PRAM 3.6v battery on the board (tests 0v, dead).

Pressing the button on the board under the CPU card.

 

At this point I will be doing a little more research.  I did find an Apple service guide covering the 7300+ series that I started looking through. 

 

A few questions for the community here:

I did notice that the ROM SIMM is not present, is this required to boot?  My searches give mixed results (maybe only required on 9500?)

Also not sure if the PRAM battery has to be present to boot? (Have a few on order in the meantime)

 

At my disposal I have a working 8500/120 and working desktop beige G3.  My next step is to try and use the 601 CPU card in the 8500 (if this is supported?), and maybe the working G3 power supply in the 7500.  I'm hesitant to try any working parts in the 7500 in case the power supply is damaged and kills my working card. 

 

I wont be able to tackle this until the weekend but wanted to get some preliminary direction until then.

 

I would appreciate any suggestions, comments or help you may offer.

 

 

 

 

 

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ROM is usually soldered on those. Look for four near-identical mid-size DIP chips. They should have an Apple copyright date on them. 

 

You will require VRAM to be installed if you want video output. These are the four mini-DIMM slots toward the back. If they're all empty you'll have problems. 

 

Also try booting with the L2 cache removed, if present. 

 

If you get no chime, video, or attempted disk access, to me this suggests a bad CPU, bad PS, or bad logic board. You can use the 8500 to test the 601 card. If that doesn't work, suspect the PS or logic board. The 8500's PS would work in the 7500 but the G3's, while in a physically similar case if a DT model, has different connectors and won't work. 

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On the 7500 the ROM is four PSOP (surface mount) 44 pin packages.   They're about 1.1" long X .5" wide.   IIRC, the ROM chips on the 7500 are located on the back of the circuit board.   Should be labeled something like 341S0168 through 341S0171.  

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First off, thanks for all the suggestions and good information.

 

Second, it's working!

 

I tried the 601 card in the 8500, worked just fine.  Put it back in the 7500 and it chimed and booted to floppy icon due to a bad hard drive (click of death).  Looks like I just had to re-seat the processor card since I didn't change anything else.

 

Now I just have to find a spare SCSI hard drive or one of those SCSI to SD boards I've seen around here.

 

Appreciate all the help and happy to have another Mac up and running.

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1 hour ago, badCaps said:

Now I just have to find a spare SCSI hard drive or one of those SCSI to SD boards I've seen around here.

If you're not planning to fill out your PCI slots with other things, you can get one of those ATA or possibly SATA cards to go in there. The cards are usually cheap (~$20-30) and if you've already got a spare ATA drive sitting around, it'll cost less than one of the SCSI2SD boards.

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2 minutes ago, Franklinstein said:

If you're not planning to fill out your PCI slots with other things, you can get one of those ATA or possibly SATA cards to go in there. The cards are usually cheap (~$20-30) and if you've already got a spare ATA drive sitting around, it'll cost less than one of the SCSI2SD boards. 

Great suggestion, didn't know that was an option.  I'll have to do a little digging and find one in that price range.  Might just try one of my old PC cards and see if it works.

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On 4/14/2019 at 1:05 AM, Franklinstein said:

If you're not planning to fill out your PCI slots with other things, you can get one of those ATA or possibly SATA cards to go in there. The cards are usually cheap (~$20-30) and if you've already got a spare ATA drive sitting around, it'll cost less than one of the SCSI2SD boards.

So does any PCI-SATA, or PCI-ATA card work or does it need to be a Mac specific one?  I'm looking at doing the same with a 7600 and 7300. 

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I had the same question!  After searching the forum and reading various threads, the consensus seems to be that you need a card that is a Mac version so that you can boot from it.  There were a handful of different manufacturers for these but they should all specify Macintosh compatibility.  Some PC cards can also be flashed with a Mac bios to work. 

 

 I ended up finding one on ebay for $35 but it wasn't listed as a Mac card, but did have the correct part number in the description and a label on the board.  Most of the Mac versions were going for the usual ebay buy it now ridiculous price.

 

I'm going to install it this weekend and report back!

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InstQuick update on the progress:

 

Installed the PCI ATA card in the 7500 and attached a working 4GB drive from a beige G3 desktop but it did not boot.  Booted using a 9.1 CD, ran drive setup but the drive did not show up there either.  Put the ATA card in the G3, same issue, no boot, does not show in drive setup.  Loooong story short, ended up swapping drives, cables, PCI slots, drive jumpers etc. etc. etc. only to find out that the drive actually shows up in drive setup but as a SCSI non-initialized drive.  Awesome!  Yeah if i would have just skimmed the included instruction manual in the beginning that would have saved me a ton of time since it called out that fact.

 

The manual also mentioned that it would only work system 8.6+.  However, I got it to boot on system 7.5.3 successfully! 

  • I pulled a spare 40GB WD drive from a PC and connected it to the 7500.  Booted the 7.5.3 CD but drive setup would not detect the drive.
  • Booting from the 9.1 CD, drive setup sees the it as SCSI non-initialized.
  • Using drive setup I initialized it using HFS Standard and a 1GB partition to start. 
  • Booted 7.5.3 CD and after initialization, the partition shows up!
  • I was then able to fully install and boot 7.5.3 (my OS of choice for this Mac)

 

Last issue I'm working with is packaging.  The standard length IDE cable has no easy path from the PCI card to the drive I've installed in the front bay.  I believe it will be as simple as finding a long enough cable to go from the PCI slots to the other side of the case where the SCSI cable enters the drive cage area, then to the drive.  I'm estimating it needs to be 24"+ to make this happen.   If I were to install the cable over the drive cage the case would put pressure on the cable and if I had a CRT sitting on top, it would likely damage the cable.

 

After that's all buttoned up, I'm planning on running some benchmarks to see how much the Ultra ATA card and drive improves performance over a SCSI drive.  I have one from an 8500 that I can just swap in for testing.

 

That's it!  Just wanted to share the success and add the tidbit of ATA info I found along the way.

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