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LC III FPU?

Posted by: derFunkenstein on 2025-06-28 10:23:04

I just picked up an LC III with maxed RAM and I’ve got a ZuluSCSI on the way to put in a hard drive. Very excited about it, honestly.

My question is about the FPU. It has an empty socket on the motherboard. Can I just get any old 68882 off of eBay and slap it in there? I also see PDS cards that have one. Can someone tell me the best way to do it? If I can keep the slot open for Ethernet that would be awesome but I don’t know that I really need Ethernet with a ZuluSCSI. 😆

Tried searching but couldn’t find any discussion. Surely someone has done this before though.

Posted by: Melkhior on 2025-06-28 10:30:28

The best way is to use the onboard socket, but beware that a lot of '882 for sales are remarked and not necessarily what they pretend to be :-( For a stock 25 MHz LCIII, most PLCC '882 should be fine, but there's always a risk if the source is not reputable (either lower frequency '882 remarked as higher, or defective, or something else entirely passed of as an '882).
If your LCIII is a III+ at 33 MHz, or if it is somehow overclocked, then it makes the risk higher than a fake '882 won't be able to keep up.

Posted by: derFunkenstein on 2025-06-28 10:36:45

Hey thanks for the reply! I had no idea there were fakes out there, so I guess I need to be careful.

Mine is a stock LC III, so 25 MHz, and I have no ambitions to overclock it. So hopefully I'll be able to make one work.

When I googled for "legit 68882" the first Google result that came up was of course from here. Looks like there's some good info for me to glean before I go dropping an Andrew Jackson on a used chip from the 90s. https://68kmla.org/bb/index.php?threads/sourcing-legit-mc68882-fpus-data.46717/

Posted by: Franklinstein on 2025-06-28 13:37:15

Yeah counterfeits are a thing. It's less so much of a problem with midrange chips than those at the high end (i.e., you're more likely to get a counterfeit 50MHz 68030 than a counterfeit 25MHz 68030). Generally be wary of "NOS" chips because these are easier to re-mark than a used chip (you expect a new chip to be shiny, but not a used one). If you get a chip that's suspect, try to use something like rubbing alcohol on the lettering. If it comes off, it's probably fake. The surface of the chip should be lightly textured, so if it's smooth, it's suspect. Also, PLCC and other plastic-encased chips of this vintage were always silk-screened, so if you get an etched one, it's also fake.

There were plenty of legit examples of BGA chips that were re-binned at the factory (often with the part number printed on a black background vs. directly into the substrate/on the die), so don't immediately discount those as fake. Do be wary of re-marked high-end parts (such as >400MHz 604evs, >500MHz 7410s, >1.2GHz 7447/7448s, >800MHz 750fx, any 750gx chips) that are suspiciously clean and cheap, though.

Posted by: zigzagjoe on 2025-06-28 13:59:56

See here for some info on sourcing FPUs. https://68kmla.org/bb/index.php?threads/sourcing-legit-mc68882-fpus-data.46717/

If I wasn't about to leave on vacation, I have a supply of legit FPUs. If you still need one in a weeks' time I should be able to help you out.

Also, PLCC and other plastic-encased chips of this vintage were always silk-screened, so if you get an etched one, it's also fake.

This is incorrect. I have legit FPUs that are etched, though I think they were mostly 1J23S mask.

Posted by: Franklinstein on 2025-06-28 14:26:39

Were they old-school Motorola chips or newer Freescale-branded ones? I may have seen some etched Freescale PLCC chips but they're a lot newer than the Moto ones. Maybe it'd be more accurate to say "etching PLCCs wasn't common until the late '90s/early '00s"? I don't remember etching/engraving being a common practice in general until the FCBGA era (1996ish).

Posted by: zigzagjoe on 2025-06-28 14:33:00

Were they old-school Motorola chips or newer Freescale-branded ones? I may have seen some etched Freescale PLCC chips but they're a lot newer than the Moto ones. Maybe it'd be more accurate to say "etching PLCCs wasn't common until the late '90s/early '00s"? I don't remember etching/engraving being a common practice in general until the FCBGA era (1996ish).

I think they are the Freescale ones, yes, but I would need to pull my tubes out to verify.

Posted by: derFunkenstein on 2025-06-28 15:14:30

See here for some info on sourcing FPUs. https://68kmla.org/bb/index.php?threads/sourcing-legit-mc68882-fpus-data.46717/

If I wasn't about to leave on vacation, I have a supply of legit FPUs. If you still need one in a weeks' time I should be able to help you out.

This is incorrect. I have legit FPUs that are etched, though I think they were mostly 1J23S mask.

I'm not in a big hurry. I'd be happy to wait until you're back since I know I'd be getting what I'm hoping for and not taking a shot on eBay.

Posted by: zigzagjoe on 2025-06-28 18:05:46

I'm not in a big hurry. I'd be happy to wait until you're back since I know I'd be getting what I'm hoping for and not taking a shot on eBay.

Sounds good. Send me a PM so I don't forget!

Posted by: Melkhior on 2025-06-28 21:47:23

I know I'd be getting what I'm hoping for and not taking a shot on eBay.

An information that isn't very useful because of the cost, but that delights me that it simply exists, you can still get them from the continuation manufacturer: MC68882EI25AR (they even have 50 MHz parts in PGA if you're willing to spend >$120 on each...).

Posted by: ESM-NL on 2025-06-29 06:44:50

I bought this one on eBay last january:

Genuine MC68882FN16A or 20A or 25A HCMOS Floating-Point Corprocessor x 1pc | eBay

Genuine MC68882FN16A or 20A or 25A HCMOS Floating-Point Corprocessor x 1pc | Business & Industrial, Electrical Equipment & Supplies, Other Electrical Equipment & Supplies | eBay!

ebay.us

I bought the 25Mhz version for my Colour Classic. It also works in a Colour Classic II, so I assume they work on an LC III as well.

Posted by: jmacz on 2025-06-29 17:41:44

Eric Woo’s listings on eBay are legit. I have bought other chips from him and other members here have purchased from him as well.

But be careful and check the eBay ID as I have seen other sellers reusing Eric’s pictures.

Posted by: shirsch on 2025-06-29 19:19:57

+1 on Eric Woo. I've bought a handful of CPUs from him and every one was gen-u-ine.

Posted by: derFunkenstein on 2025-06-30 05:31:04

That's super helpful, thanks! I just sent him a message about a 25 MHz one, since his listing says to message before ordering.

Posted by: Performa450 on 2025-07-03 00:36:16

That's super helpful, thanks! I just sent him a message about a 25 MHz one, since his listing says to message before ordering.

Yep, genuine chip was sent well packed to me too, I’d definitely recommend

Posted by: cheesestraws on 2025-07-03 00:45:16

Eric Woo has an excellent reputation and the stuff I've previously got from him has been sound.

He's not immune to his suppliers sending him crap - but then who is? - but he seems to deal with that situation well when it occurs. And that's about al one can ask.

Posted by: derFunkenstein on 2025-07-03 05:25:33

The email alert was a good reminder to follow up - I've got one from Eric on the way. Thanks everyone!

Posted by: zigzagjoe on 2025-07-03 10:11:06

I have spent thousands of dollars with Eric and he's on the level. Second what cheesestraws said.

Posted by: derFunkenstein on 2025-08-06 09:16:54

The 68882 from Eric, along with a full-fat 68040 33 MHz to stuff into my Quadra 605, arrived while I was out of town. Finally got them installed (removing the LC 040 from the 605 was nerve wracking!) and both seem to be working flawlessly. I'll be getting my chips from Eric from here on out.