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Those are resettable SMD125 fuses similar to this one. The theory on their operation is well explained in this Wikipedia article. The fuse ABOVE the 342S0440-B ASIC is probably not the right one. It should be a fuse sitting between the ADB connector and the ASIC. Moreover, you should see a...

I would highly recommend the Badcaps Powersupply Troubleshooting Forum. There are some high qualified techs around there helping to identify old and obscure components and giving precious advises on replacement parts. They have helped me to revive my Astec PSU (from PowerMac 6100), see this thread.

No, it's a kind of misleading information spread across the Internet. PowerMac 6100 can address max. 264 MB, i.e. 8 MB soldered onboard memory + 2 SIMMs x 128 MB. See this post and this post.

Yep, already done + understanding and commenting it  :) That's a good idea indeed. The biggest problem could be CUDA's clocking. Although it's clocked by an external 32768 Hz crystal, it has a built-in phase-locked loop synthesizer (PLL) that is capable of rising the MCU internal clock up to...

68HC05E1

Yes. IIRC, three different CUDA firmware dumps are currently accessible: 341S0060, 341S0417 (CUDA v2.35 from Color Classic) and 341S0788 (CUDA v2.37 used in Quadras AV and PowerMacs). EgretManager has a call called read 6805 address allowing the programmer to read values from an arbitrary MCU...

Because Q700 doesn't have CUDA, it uses the "Bit-bang" ASIC instead, Apple part number either 342S0440 or 342-0440-A or 342S0440-B, see Mac Technical Notes.

Please post a bigger picture of your Q700 board here and we'll try to find the CUDA chip on it. If your board does have CUDA, it should have the PRAM battery as well. It's a small, 1/2 AA size lithium 3,6V battery. CUDA MCU is usually located near that battery... Everything correct. CUDA is a...

If there even was a hardware possibility to address 256 SIMMs in PM 6100, you'll still need to overcome the software limit of 128MB! I can say it with a high degree of certainty because I performed an excessive analysis of the firmware in the past as part of the MAME emulation project. When the...

To be honest, I doubt these boards will work longer than 10 years. Looking at the quickly progressing corrosion of my two PM 6100 logic boards, I'm sure they will start to fail here and there and I won't be able to prevent that. Let's think about a memory slot for a minute - if such a slot...

Can those modern SMD caps be used as replacement for the old ones? Why do other people prefer tantalum caps instead?

Probably yes. You need to break large files into smaller pieces and use several 1.44 MB disks to transfer them to your Mac or find another solution (Floppy Emu, network transfer)...

IIRC, tantalum caps need to be properly derated, i.e. a 47µf, 16V need to be replaced with a 47µf, 35V tantalum cap. For further details, see this thread.

I know this might be a stupid question but I assume you're connecting your drive to the both machines using the same ribbon cable. It works on one but not the other, right?

Oops! It looks like I've posted a link to the wrong page. Sorry! This link shows a pin diagram for the IDC 20 male connector.

That's quite possible - the board still contains eleven ancient SMD caps, three of them are located near the FDD connector. I'll try to replace these three caps first. What's the best replacement for them? All electrolytic caps are 47µF, 16V. Various Internet sources advocate the use of...

My floppy drive is actually fine! I just tested it with another PowerMac 6100 board. ;D The funniest part about it is that the drive works after it has been completely disassembled and then reassembled. No alignment or tuning was ever necessary! Well, I put some markings on the stepper motor...

Hi folks, and now comes the funny part [ :) ] Today I received another PowerMac 6100 logic board to play with. I attached my supposedly faulty floppy drive to it and ...... trara! The drive works! That's good news! > :( The funniest part about it is that the drive works after it has been...

I'd also check the voltages on the drive board for sure, both +5V and +12V rails. It should be definitely done under load, i.e. the drive need to be connected to the logic board. For pin position and numbering, you can refer to this page. +5V rail -- pin 11 +12V rail -- pins 13,15,17 and 19...

I agree with you that this kind of measure is very coarse. Anyway, it's one of those quick troubleshooting techniques helping to rule out reasonably simple issues like missing contacts or shorted traces. Any other issues would require attaching an oscilloscope to the board and do a complex logic...