VOGONS

5.25” FD1157C Floppy Drive Analog chip burnt

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First post, by khaled

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Hi There,
When I tried to rebuild my retro PC I managed to get everything repaired a lot of recapping for power supply, motherboard, and graphics card and tons of cleaning.
The only thing that I couldn’t get it to work is the 5.25” floppy drive, it was working 35 years ago 😀, after a lot of troubleshooting I found that the analog chip responsible for picking up the signal from the heads and amplifying it, it is Motorola MC2875-002, it gets very hot and could read any signal just noise.
Unfortunately I can’t find this chip on any reputable source, just some suspicious websites that have no prices they provide RFQ, I requested price from some of them but I doubt they will reply.
Anyone have idea how to order such chip or any replacement?

Thanks

Reply 1 of 2, by Deunan

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khaled wrote on 2025-08-03, 10:15:

The only thing that I couldn’t get it to work is the 5.25” floppy drive, it was working 35 years ago 😀, after a lot of troubleshooting I found that the analog chip responsible for picking up the signal from the heads and amplifying it, it is Motorola MC2875-002, it gets very hot and could read any signal just noise.

I see a scope (and VGA Copy running, though I prefer IMD for these jobs) so I assume you've checked the head amp test points? You sure you got that right? A weak floppy and bad head misalignment can also look like no signal, just noise, especially on the inner tracks. And some of these chips do run hot, but usually it's the older drives that do that. I think I have NEC FD1157C but I's in a box, so I'd need to dig it up. I can check how hot my chip run and what test points to check for head signals.

Reply 2 of 2, by DaveDDS

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Yes, some of theme do run hot...

Also be aware that if you're truly seeing a LOT of noise, this too can contribute to running hot (figure out where it's coming from)

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal

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