In Japan they had similar upgrades for 386DX systems, a plug in 486 board with its own memory that required a special driver to utilise. I am not aware of any such upgrades for 386SX systems though.

Your idea could certainly work, but the snap on socket you are talking about would make your project awfully expensive to produce. Plus, I would think that all the weight of the memory and the 168pga CPU might make the upgrade prone to coming loose.

What I'd really like to see is a snap on 386SX module with a test socket that lets you drop in NOS PQFP100 386SX type chips with an optional VRM. For example, I have unsoldered TI486SXLC2-66 chips that I would like to use to upgrade my 386SX boards, but I can't simply do a cut and swap because they're 3.3V parts.

Seems like a strange idea.

If you want a 486, you buy a 486 and appropriate motherboard.

What you are proposing is more or less building a 486 motherboard on a daughter board to plug over an existing 386 CPU.

Another problem I see is that clipping over the top of a BQFP is an electrically poor connection, subject to intermittent faults over time. Had no end of troubles with a clip on PS2 modchip back in the day.

Thanks for the input - in this case I'm looking to upgrade an Amiga bridgeboard. I might make my own instead, but I figured I'd try this out. So the mounting/etc will be specific for this scenario, and I can't simply swap to a 486 motherboard. Thanks guys!

Anonymous Coward wrote:

What I'd really like to see is a snap on 386SX module with a test socket that lets you drop in NOS PQFP100 386SX type chips with an optional VRM. For example, I have unsoldered TI486SXLC2-66 chips that I would like to use to upgrade my 386SX boards, but I can't simply do a cut and swap because they're 3.3V parts.

I'd been thinking about this for the 3.6v IBM SLC2 chips. The 386sx package is annoying, because it has the wings (BQFP, b as in bumpered), and the pin pitch is difficult - 0.635mm - to work out to .25mils when doing PCB layout - this was JEDEC standardized but the pin pitch for QFPs didn't go much further than the 386EX.

There is a very hard to get part (I had to have a courier in Japan find it) that I have on the way, a Yamaichi IC 149-100-028-B5. It's cool because the footprint matches the device you are replacing. It looks like this:

Sometimes on 386sx motherboards, you'll see what was meant for 3 rows of pins on the outside of the processor. That is for a somewhat larger socket:
3M 2100-7243-00-1807 - if you search on ebay you can find it.

I'm still looking for the snap on part - it's a difficult find. I'm hoping TopLine (who has previously manufactured the socket) still has it, as they still manufacture the dummy 386 chips (for practice soldering).

The way these things seem to work is that the hold the FLOAT# pin on the real CPU, and then take over.

Anyway, happy to hear more input.

I have test sockets very similar to the one on the lower part of your post (alps?). It's not very useful though unless you want to fab your own PCB.
What I'd really like is the one you found in Japan. Please fill me in on the details of how to get some, and what you paid for it.

I have a Make It 486 adapter coming which has a TISXLC2-50 an a VRM. I'd really like to get one of these yamaichi test sockets to replace the CPU on the upgrade board...but so far haven't been able to find any.

I finally got ahold of these sockets from Japan - they had about a 2 month lead time but may have spares now. You may need to use a courier to get this to the US: https://direct.daitron.co.jp/shop/g/gEC10390089/