Sorry I saw that you have an external one

Yes I've tried with and without the battery and it doesn't seem to make any difference. Actually I've never encountered a mainboard which would refuse to post when no battery is present, but who knows, there might be some!

It depends, sometimes it can happen that a PC does not start if there is a low battery. I have the same POST-CARD, if I can tomorrow I try it on a 386 DX40 that works, I want to see which LEDs are on, I don't know if it can help you.
At the moment I'm trying to restart a Siemens D1120 (i810), in the Post-Card I have the Reset LED always On, while normally it should be off.

I'd like to say that my board has become unstable out of blue, freezing randomly. I have tried different cache, RAM, PSU, clock speeds and it still does it. I'm pretty much out of ideas, maybe these boards have some sort of manufacturing flaw that makes them unstable over time...

Tiido wrote:

I'd like to say that my board has become unstable out of blue, freezing randomly. I have tried different cache, RAM, PSU, clock speeds and it still does it. I'm pretty much out of ideas, maybe these boards have some sort of manufacturing flaw that makes them unstable over time...

Many boards come with electrolytic capacitors that simply dry out over time. Tantalum capacitors don't.

Capacitors aren't an issue, i have placed higher value polymers in strategic locations and all of them are fine.

What I did find out is that when I desoldered the onboard CPU and used a PGA one the board functions right for the most part. But when I add a sound card things get iffy, games tend to freeze when they play sound for a little or such (and in some music continues to play). This makes me think of DMA and/or interrupt controllers and those live in the 8xC206 chip. I already ordered a replacement and will report back once I have swapped out that chip.

ph4nt0m wrote:

Many boards come with electrolytic capacitors that simply dry out over time. Tantalum capacitors don't.

They tend to short out as they age. I've had one board recently with one tantalum exploding on power on, and I had another board that didn't get out of reset because tantalum cap in the reset circuitry was shorted to ground, effectively holding the reset button pushed all the time 😀

To OP - when you press RESET, does the diagnostic card show any activity on the RESET LED?

Kubik wrote:

ph4nt0m wrote:

To OP - when you press RESET, does the diagnostic card show any activity on the RESET LED?

Yes, it did show on the diag card when I tested it.

Kubik wrote:

ph4nt0m wrote:

Many boards come with electrolytic capacitors that simply dry out over time. Tantalum capacitors don't.

They tend to short out as they age. I've had one board recently with one tantalum exploding on power on, and I had another board that didn't get out of reset because tantalum cap in the reset circuitry was shorted to ground, effectively holding the reset button pushed all the time 😀

If a board is stored properly, i.e. not exposed to excessive humidity, it will be fine. Moisture kills tantalum caps.

This sadly didn't help, it still freezes every once in a while... I'll swap some of the logic chips here and there later.

You could install a socket for that 82C206 as well as other DIP chips you are going to desolder.

There's no point in a socket, it is only gonna increase amount of work and it is far more effort to get a socket off board intact than a chip if it comes to a point I declare the board unfixable and want to cannibalize it of all the parts. All the other parts will be known good parts or brand new ones so I will not need to swap out them anyway.

Allright, so I'm the new owner of that board, so I'll continue that thread if I've got anything new ^^

Also I have an old analogue oscilloscope that can go up to 20MHz, but it's still new to me. I think I've seen someone saying to check if there were signals somewhere, right ?
Can you tell me what I should probe ? ^^

Also I've checked few things I thought could be an issue : the clock pin on the CPU socket which corresponds to the quartz, the reset pin, and also a VCC pin that do output +5V, so * apparently * there's nothing wrong with the CPU socket if you were wondering. (or at least, nothing that simple)

I got a Forex board with FRX36C300 and FRX46C402 and did a chip transplant of the 402, and the board I have now finally functions with cache again while the other board with my old 402 chip stopped working altogether. So it does seem chipset failure is not out of question with these boards...
The 300+402 board showed better memory performance but can only do 128KB of cache at most while this board can do 256KB. It would be nice if I could get the other board to function properly too but first glances showed that FRX46C402 chip is not something you can go and buy anywhere.

20MHz scope is not gonna be overly useful for digital signals, all the high freq squarewaves turn into a mush on it but it can help with diagnosing still. Clock, reset, memory access strobes etc. can all be looked at aswell as various bus management signals and any ready type signals.

Well considering all the previous test having been made with that board, I think the problem is deeper than it looks, so the chipset might be dead as you imply. I'll test to swap it if I can find a NOS one 😀

ph4nt0m wrote:

Many boards come with electrolytic capacitors that simply dry out over time. Tantalum capacitors don't.

That's generally true, but not 100% true.

Tantalum capacitors ARE "electrolytic capacitors", just with different chemistry & tech.
(So are several kinds of Polymer caps. >> Electrolytic.)

There are several types of Tantalum capacitors and some are Wet-Lytics just like the Aluminum Wet-Lytics you are thinking of.

The Wet Tantalum type were the earliest version.
They quit making them because when they leak (which wasn't that uncommon) the acid inside is very strong.
It will eat your PCB much faster than leakage from any CMOS battery.

The Dry types fell out of favor on mobos because while some are low ESR, they don't handle large amounts of ripple very well.
As signal voltages became ever smaller with newer techs, having close to no ripple at all became more important.
(Examples: AGP went from 3.3v to 1.5v to 0.8v. PCI went from 5v to 3.3v. CPUs did similar. Those are SIGNALING, not power voltages.]
- Enter Al-Electrolytics, removing vast amounts of ripple is what they are good at.
- Poly are better but became popular later due to early-on they had limited sizes and much higher costs.

Dry Tantalum are small (seen on laptop mobos long long after desktop boards moved to Al-Electrolytics) and they rarely fail.
However, when they do let go, they sometimes explode or catch fire.
And yes, the Dry Tantalum can have strong acids too. It's just more like a paste than a liquid.
(Not saying all of them do, but they can.)

========
And now that I'm past my obligatory capacitor rant. (I think it's genetic... Maybe OCD?)
... I'll move on to why I really logged in today.

I have a (just acquired) FOREX 386 Cache motherboard too, but it's not the same board as the OP has.
Details and questions to follow. (I write slow.)
.

The OP's board. (I think - corrected.)
https://www.stason.org/TULARC/pc/motherboards … -486-MB-4F.html

My board
https://stason.org/TULARC/pc/motherboards/M/M … -386-CACHE.html

[My Board]
This is what I know so far.

Model: FOREX 386 CACHE
OEM Distributor: Micro Express, INC.
Manufacturer: Taiwan Turbo Technology Co., LTD

BIOS String: 40-0500-001719-00101111-121291-FORX-8
Mfr 1719 = Taiwan Turbo Technology Co., LTD
Chipset = Forex 46C411/402 WriteThru (Matches the numbers on the chips)
BIOS Date = Dec 12 1991

[The story]
This showed up in an AT case I bought from rip-off-bay.
The ad said "unknown motherboard/condition" and such.
I just wanted the dirty old AT case for a 440BX based project so I didn't care.
.
It has:
The above mobo with a fixed AMD 386DX-40 installed
Jumpers indicate 64k Cache installed. All the chips are there.
8MB RAM x8 sticks in 2x sets of 4 matching. (Ouch, I just bought some of that.)
Video, 256k SVGA 16-bit = MCT-VGA-16 (TDVGA 3588 BIOS v1.04A)
... Like this one: https://ibm.retropc.se/rom/photo/MCT-VGA-16.jpg
Weird HD= Kalok KL3100 Spins-up, sounds okay, but not otherwise tested yet.
Slightly rusty Newtronics FD. (Not tested yet, main chip looks a bit melted in spots.)
[ HD & FD controllers MIA. I have some, I haven't dug one out yet.]
Some IBM modem card. (Not explored yet.)
Battery is not leaking. (Thanks for that!)
And a PSU.
Some stickers (on case) indicate it belonged to some Tech Research firm.
I REALLY wanna see what's on the HD! Just haven't gotten that far yet.

I didn't really want a 386 but it's here...
... so I figured, what the heck, let's see if it fires as is.

-> Booted right up and I can access the BIOS.
(with audio effects provided by a very loud squealing PSU fan.)

I didn't even want it, but it works and now I'm jazzed!

But I have some questions...
Though I have some fully built 286/386/486 around for testing RAM and such, I haven't newly set anything that old up in maybe 15-20 years.
I don't remember (or haven't seen) some of settings and such in Stason's Settings-Configuration page.

1: There is a jumper setting, JP101, "DRAM parity check" Enable/Disable.
What does that actually do?
Does that mean I can switch between using Partity and Non-Parity RAM?
Or does that just stop/start some boot-up check?

2: I know what a 80387DX NPU is, but what does it mean when it's written as "80387DX/3167"?
Is that (3167) a specific version of 80387DX or an alternative to it?
(If I decide to keep it then I want to add the NPU chip.)

Thanks all!
.

Hi PCBONEZ, haven't seen you here in a while, welcome back.
I think the parity jumper just must be set in accordance with the RAM you have installed on board. If set to "Parity" and your SIMMs are missing the parity chips, probably an error message will pop up.
The 3167 is a Weitek co-processor, quite different from the i387. Your socket supports both types.

The 3167 is one of these Weitek Abacus FPU, which works differently than a regular 80387 FPU. I don't remember the details but the Weitek FPUs had a much, much different design than your garden variety 387. Notably, the Weitek FPUs were memory-mapped. (I'm not going to go into the specifics, as I don't know much about these.)

On some 386 motherboards, you'll see that the 387 socket usually has more rows of pins to accommodate either a Weitek FPU or a regular 387.

Edit: beaten by Quicknick.

Edit 2: here is more information about the Weitek FPUs: http://www.geekdot.com/weitek-abacus-fpu/

Edit 3: removed redudent statement.

Vynix wrote:

Edit: beaten by Quicknick.

Yeah, but I was in a hurry, mistakes were made, I had to edit 😁