Yesh if the 387DX is running at 40Mhz is way overclocked !
The 387DX can run Synchronous or Async modes. To run in Async it must have it's own Xtal or a clock divider to downgrade the CPU clock to something less (or more) applied to NUMCLK2 pin and there must be a jumper to put the FPU into the Async mode. In Async mode the 25Mhz 387DX will work with a 40Mhz 386DX (25/40= .625 which is the lowest supported (minimum ratio of 10/16).
I cannot read the two IC's U16 and U17 near JP11. That jumper with 1x/2x may hold the key (or not) to running Sync/async. All the other jumpers seem explained quite well in the silkscreening.
So far nothing shows up on a quick search for manual or jumpers...

Horun wrote on 2022-06-06, 02:06:

Yesh if the 387DX is running at 40Mhz is way overclocked ! The 387DX can run Synchronous or Async modes. To run in Async it must […]
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Yesh if the 387DX is running at 40Mhz is way overclocked !
The 387DX can run Synchronous or Async modes. To run in Async it must have it's own Xtal or a clock divider to downgrade the CPU clock to something less (or more) applied to NUMCLK2 pin and there must be a jumper to put the FPU into the Async mode. In Async mode the 25Mhz 387DX will work with a 40Mhz 386DX (25/40= .625 which is the lowest supported (minimum ratio of 10/16).
I cannot read the two IC's U16 and U17 near JP11. That jumper with 1x/2x may hold the key (or not) to running Sync/async. All the other jumpers seem explained quite well in the silkscreening.
So far nothing shows up on a quick search for manual or jumpers...

I didn't see a change with that jumper before, but I just tried it again. Still won't pass POST with the 387 installed, but benchmarks with the 386 are still giving me the same numbers/it's still 40MHz. I have no idea what that 386 2x/1x jumper does.

Attached photos are all the jumpers over there. There is just one additional cache size jumper on the left side of the board.

Thanks ! ok can read the chips, the U17 is a standard flip-flop which could be used as a divider with JP11 but you saw nothing changed.
If it were my board would put a 33Mhz Xtal in it and try a 486DX-33 to see if it works, after changing the jumpers, also odd the crystal clock has no markings like they were scrubbed clean...
Can you post another picture of the boot screen w/o the 387 ? showing the AMI bios string at the bottom like in this picture: download/file.php?id=80433&mode=view

Horun wrote on 2022-06-06, 03:27:

Thanks ! ok can read the chips, the U17 is a standard flip-flop which could be used as a divider with JP11 but you saw nothing changed.
If it were my board would put a 33Mhz Xtal in it and try a 486DX-33 to see if it works, after changing the jumpers, also odd the crystal clock has no markings like they were scrubbed clean...
Can you post another picture of the boot screen w/o the 387 ? showing the AMI bios string at the bottom like in this picture: download/file.php?id=80433&mode=view

BIOS string attached.

I did order a 4C87DLC-40 this morning, but will need to wait some time for it to arrive. I don't have another coprocessor to install.

I guess Jumper 11 determines if the (386) CPU is fed with 1 x oscillator-frequency or 2 x oscillator frequency.
If you use a 40MHz CPU and a 20 MHz 387 and set JP 11 for "2x" it should work. You would have to select the x-tal so it fits the NPU.
Just a guess...

majestyk wrote on 2022-06-06, 05:49:

I guess Jumper 11 determines if the (386) CPU is fed with 1 x oscillator-frequency or 2 x oscillator frequency.
If you use a 40MHz CPU and a 20 MHz 387 and set JP 11 for "2x" it should work. You would have to select the x-tal so it fits the NPU.
Just a guess...

It came set to 2x. In the last photos I had it set to 1x, with no change in behavior. I figured it was worth a test.

Weird labeling, but neither helped this coprocessor work. I imagine that it worked at some point, due to the fact that this thing had five different, intact, "warranty void if removed" stickers throughout. It has to have all been original.

But it came without NPU?
It all depends on the current x-tal. If it´s a 40 MHz type everything was fine with Jp11 -> 1-2 and a 40 MHz 386. If you add a 25 MHz 387 it runs at 40 MHz also and gets overclocked.
Try it with a 20 MHz x-tal and Jp 11 -> 2-3.

Or - if it came with a 25 MHz NPU it was way overclocked and the 387 died at some point.
Or - the x-tal is 20 MHz, the x2 setting for the CPU is correct, but you just have a broken NPU.

The zip tie around the x-tal looks quite new. Normally those have turned a bit brownish on old 386 mainboards. Maybe - although all chips are original - someone tinkered with the x-tal?
Have you tried without L2 cache?

majestyk wrote on 2022-06-06, 06:08:

But it came without NPU? It all depends on the current x-tal. If it´s a 40 MHz type everything was fine with Jp11 -> 1-2 and a 4 […]
Show full quote

But it came without NPU?
It all depends on the current x-tal. If it´s a 40 MHz type everything was fine with Jp11 -> 1-2 and a 40 MHz 386. If you add a 25 MHz 387 it runs at 40 MHz also and gets overclocked.
Try it with a 20 MHz x-tal and Jp 11 -> 2-3.

Or - if it came with a 25 MHz NPU it was way overclocked and the 387 died at some point.
Or - the x-tal is 20 MHz, the x2 setting for the CPU is correct, but you just have a broken NPU.

The zip tie around the x-tal looks quite new. Normally those have turned a bit brownish on old 386 mainboards. Maybe - although all chips are original - someone tinkered with the x-tal?
Have you tried without L2 cache?

I haven't added anything - I received it with the coprocessor installed and this jumper was set to 2x. It's possible someone messed with that part of the board, since none of the system components/warranty stickers would have had to be removed (even the motherboard tray was stickered to the case - I was tempted to leave it all as it was just for the audacity of all those illegal stickers, but would rather have had everything get cleaned). With the Money Manager sticky note on the front, I could see where the coprocessor would have helped decades ago, lack of soundcard or anything else, and that all the expansion covers are matching and of similar finish/age, I don't think anyone was in here turning it into a retro box.

Still getting some of this verbiage down - so the x-tal you reference is the oscillator without markings. I'd have to buy another oscillator to try the parts swap, and I wouldn't know where to begin to source the part. It may be easier to just wait for the 40MHz chip to come in and install that as a test.

All the zip ties around the case looked good - I clipped a few after breaking all the stickers to take everything apart for cleaning. The system didn't look 35 years old, that's for sure - that's why I was happy to buy it for the price without seeing it run. I mostly wanted the case, so the hardware inside was a nice surprise.

I haven't removed the L2 cache, but I've tried disabling both cache levels in the BIOS to no effect on the FPU at POST time, but a big hit in non-FPU use.

Masejoer wrote on 2022-06-06, 06:38:

I haven't added anything - I received it with the coprocessor installed and this jumper was set to 2x. It's possible someone mes […]
Show full quote

majestyk wrote on 2022-06-06, 06:08:

But it came without NPU? It all depends on the current x-tal. If it´s a 40 MHz type everything was fine with Jp11 -> 1-2 and a 4 […]
Show full quote

But it came without NPU?
It all depends on the current x-tal. If it´s a 40 MHz type everything was fine with Jp11 -> 1-2 and a 40 MHz 386. If you add a 25 MHz 387 it runs at 40 MHz also and gets overclocked.
Try it with a 20 MHz x-tal and Jp 11 -> 2-3.

Or - if it came with a 25 MHz NPU it was way overclocked and the 387 died at some point.
Or - the x-tal is 20 MHz, the x2 setting for the CPU is correct, but you just have a broken NPU.

The zip tie around the x-tal looks quite new. Normally those have turned a bit brownish on old 386 mainboards. Maybe - although all chips are original - someone tinkered with the x-tal?
Have you tried without L2 cache?

I haven't added anything - I received it with the coprocessor installed and this jumper was set to 2x. It's possible someone messed with that part of the board, since none of the system components/warranty stickers would have had to be removed (even the motherboard tray was stickered to the case - I was tempted to leave it all as it was just for the audacity of all those illegal stickers, but would rather have had everything get cleaned). With the Money Manager sticky note on the front, I could see where the coprocessor would have helped decades ago, lack of soundcard or anything else, and that all the expansion covers are matching and of similar finish/age, I don't think anyone was in here turning it into a retro box.

Still getting some of this verbiage down - so the x-tal you reference is the oscillator without markings. I'd have to buy another oscillator to try the parts swap, and I wouldn't know where to begin to source the part. It may be easier to just wait for the 40MHz chip to come in and install that as a test.

All the zip ties around the case looked good - I clipped a few after breaking all the stickers to take everything apart for cleaning. The system didn't look 35 years old, that's for sure - that's why I was happy to buy it for the price without seeing it run. I mostly wanted the case, so the hardware inside was a nice surprise.

I haven't removed the L2 cache, but I've tried disabling both cache levels in the BIOS to no effect on the FPU at POST time, but a big hit in non-FPU use.

Any clues in this manual (EFAR-3486) - https://www.elhvb.com/mobokive/archive/unknow … -3486/e3486.pdf

PC Hoarder Patrol wrote on 2022-06-06, 07:10:

Masejoer wrote on 2022-06-06, 06:38:

I haven't added anything - I received it with the coprocessor installed and this jumper was set to 2x. It's possible someone mes […]
Show full quote

majestyk wrote on 2022-06-06, 06:08:

But it came without NPU? It all depends on the current x-tal. If it´s a 40 MHz type everything was fine with Jp11 -> 1-2 and a 4 […]
Show full quote

But it came without NPU?
It all depends on the current x-tal. If it´s a 40 MHz type everything was fine with Jp11 -> 1-2 and a 40 MHz 386. If you add a 25 MHz 387 it runs at 40 MHz also and gets overclocked.
Try it with a 20 MHz x-tal and Jp 11 -> 2-3.

Or - if it came with a 25 MHz NPU it was way overclocked and the 387 died at some point.
Or - the x-tal is 20 MHz, the x2 setting for the CPU is correct, but you just have a broken NPU.

The zip tie around the x-tal looks quite new. Normally those have turned a bit brownish on old 386 mainboards. Maybe - although all chips are original - someone tinkered with the x-tal?
Have you tried without L2 cache?

I haven't added anything - I received it with the coprocessor installed and this jumper was set to 2x. It's possible someone messed with that part of the board, since none of the system components/warranty stickers would have had to be removed (even the motherboard tray was stickered to the case - I was tempted to leave it all as it was just for the audacity of all those illegal stickers, but would rather have had everything get cleaned). With the Money Manager sticky note on the front, I could see where the coprocessor would have helped decades ago, lack of soundcard or anything else, and that all the expansion covers are matching and of similar finish/age, I don't think anyone was in here turning it into a retro box.

Still getting some of this verbiage down - so the x-tal you reference is the oscillator without markings. I'd have to buy another oscillator to try the parts swap, and I wouldn't know where to begin to source the part. It may be easier to just wait for the 40MHz chip to come in and install that as a test.

All the zip ties around the case looked good - I clipped a few after breaking all the stickers to take everything apart for cleaning. The system didn't look 35 years old, that's for sure - that's why I was happy to buy it for the price without seeing it run. I mostly wanted the case, so the hardware inside was a nice surprise.

I haven't removed the L2 cache, but I've tried disabling both cache levels in the BIOS to no effect on the FPU at POST time, but a big hit in non-FPU use.

Any clues in this manual (EFAR-3486) - https://www.elhvb.com/mobokive/archive/unknow … -3486/e3486.pdf

e3486.pdf

How did you find that? I spent probably an hour looking for a manual to no avail, and that pdf seems to match. Just curious about how you searched, so I can use similar tactics for future motherboards.

Fairly basic really 😀 - given the EFAR chipset & the P/N beginning 'EF', I just searched for 'efar motherboard' and spotted the '(E 3486) USER'S MANUAL - elhvb' link at the bottom of the first page...I specialise in blind luck! Hope it helps.

PC Hoarder Patrol wrote on 2022-06-06, 07:21:

Fairly basic really 😀 - given the EFAR chipset & the P/N beginning 'EF', I just searched for 'efar motherboard' and spotted the '(E 3486) USER'S MANUAL - elhvb' link at the bottom of the first page...I specialise in blind luck! Hope it helps.

I was searching opti (per the earlier link of a similar board) and samsung part numbers, and pages that contained both 386 and 486, including a variety of notable jumper names/numbers that would be in reference documentation. Makes sense that the other chip could be useful in a search.

I also didn't think "efar" was the chip manufactuer. That "I" or something before it in the logo looked like it was the beginning of the word. Guess I was overthinking some of this.

I find it interesting that the manual tells the user to change the oscillator themselves - I didn't know that was a necessary thing back then (I thought maybe the 286 and 8088). I didn't really get into building (choosing parts) my own PCs until after the 486. Learned something new today.

So where should one source various oscillators for inventory? Seems like something that I should grab a few of, especially for my plans to more heavily get into the retro stuff in a few more years. Parts/components are what I'm obviously needing now.

Thank you everyone - I'm trying to learn more as I go! I started upgrading every year after 1995 or so, but just threw parts together back then. I've been learning a lot about underlying functionality from these forums, and it gives me ever-increasing respect for how systems worked prior to the 90's.

I want to add that I have most everything back in the case now, but the system booted up to DOS, with the FPU enabled, once and the cold boot, but started to stall at POST again after that. The Intel chip does get plenty warm, so it's powered. I'm thinking that the poor chip has been running at 40MHz for way too long, and this stability issue could have been a reason why the system was decommissioned. I know I read on here that people have had no problems running these at 40MHz, and without over-Volting, that shouldn't cause any notable/lasting damage, but with most semiconductors being younger than 35 years, and us not having great sample sizes of old components, I wouldn't be surprised if age could play a role in something not running as well as it may have in its younger years.

Looks like an oscillator swap (need a good source, including another 40Mhz unit), and 40MHz FPU swap will be in my future to narrow down the cause. Seems both should mitigate the issue.

I'm sure the EFAR logo / name had meaning to someone once (using the summation + integral maths symbols???) but who knows what - they were fairly short-lived as a company and were eventually swallowed up by SMC mid 90s.

Depending on your location, the various oscillators should be available from the big component suppliers like Mouser, Digi-Key, Farnell or RS Online, and failing that Ebay.

It's good that we've tied another board & manual together, and I'm sure the team at Ultimate Retro - https://www.ultimateretro.net/en/ - would appreciate a BIOS dump from your board for an enrty in their database.

PC Hoarder Patrol wrote on 2022-06-06, 09:32:

I'm sure the EFAR logo / name had meaning to someone once (using the summation + integral maths symbols???) but who knows what - […]
Show full quote

I'm sure the EFAR logo / name had meaning to someone once (using the summation + integral maths symbols???) but who knows what - they were fairly short-lived as a company and were eventually swallowed up by SMC mid 90s.

EFAR Microsystems logo.png

Depending on your location, the various oscillators should be available from the big component suppliers like Mouser, Digi-Key, Farnell or RS Online, and failing that Ebay.

It's good that we've tied another board & manual together, and I'm sure the team at Ultimate Retro - https://www.ultimateretro.net/en/ - would appreciate a BIOS dump from your board for an enrty in their database.

Yeah, I've ordered a TL866 II programmer to make eeprom work easier. I'm done with manually connecting to individual pins - I don't want to fuss with that much anymore, versus just plugging something in and reading/writing. Seems I'll be doing it more often than in the past, so makes sense to make things easier for a nominal cost.