Replaced the banged up keyboard socket and filled (after cleaning!) the battery solder tab points:

Also fitted sockets and new oscillators in place of the robbed-out originals and jumpered them to match the defaults:

Sadly.....

Card indicates reset constantly held, and no CLK signal, so there's either something I've bridged when fitting the new oscillator sockets, or another issue that I haven't spotted yet.

On a hunch that perhaps the processor was faulty, I swapped it out with another of my Harris-20 parts:

So that's an improvement - RESET is no longer held and there's a CLK signal to the diagnostic card. Still no error codes though.

Hmm, I'm thinking that some of the issues could be down to the warped board - I can make the CLK signal come and go by putting slight pressure on the board either side of the bend.

This is going to be a difficult one - there's no visible cracks or broken traces, and I'm fairly sure that this is just a two sided PCB; holding it up to the light there doesn't appear to be any middle layers.

Is this dirt or corrosion, or just an artefact?

Just for the record - what´s the missing fuse "F1" for?

There is corrosion/dirt there, you're right, but connectivity is still seems to be okay. It could do with a further clean though.

Fuse F1 appears to be optional - the manual states it is either fitted and jumper JP5 is open, or no fuse is fitted and JP5 is closed. JP5 is currently closed.

It's possible one was fitted previously, as it's just a push in fuse, not soldered.

Yep, connectivity is there, but those pads were just a little oxidised and dull:

There has got to be some marginal connection(s) somewhere for the very slight flexing of the board to change the ISA slot CLK signal to appear/disappear when you put a single finger of pressure on various parts of the board. I'll see if I can capture it.

Here's what actually happens:

https://youtu.be/bRRa8gKHs-8

the MB-1216V I posted about on the previous page was also badly warped. I had to reflow the VL82C201 and 203 chips to get it working reliably

maxtherabbit wrote on 2021-03-14, 19:50:

the MB-1216V I posted about on the previous page was also badly warped. I had to reflow the VL82C201 and 203 chips to get it working reliably

Really? Now that's interesting to know. I wonder if it was something common to Biostar boards of the period?

I'd be willing to try that, but I suspect it will be a pain, with the VL82C311L, unlike the 200-series, being a 160 pin QFP 🙁

Just use a lot of flux and keep your tip clean, QFP reflow isn't that bad

megatron-uk wrote on 2021-03-13, 14:20:

BIOS ROM image for the Biostar MB-1220VE: […]
Show full quote

BIOS ROM image for the Biostar MB-1220VE:

Biostar_MB-1220VE.zip

The BIOS ID string appears to be: 20-0001-D61223-00101111-050591-SCAMP286

A poke around the image with a hex viewer shows a lot of memory optimisation options, as you would expect to find in a decent 386 era BIOS. So it looks to be the same as the one linked to that forum, several pages back. I suspect it's a dual use BIOS used on the 386-only VL82C311 as well as the VL82C311L for the 286, since it also has references to cache memory settings.

Haven't yet finished repairing the board yet (battery tabs removed and the very tiny amount of corrosion cleaned up) and I've now identified a broken tantalum capacitor (fortunately I have a couple spares), it still needs a pair of DIL-14 sockets fitting for the missing oscillators. I'm guessing that one is for the main processor clock (this appears to be a 40MHz can in most images I've found; which corresponds to the 20MHz Harris processor), and the other possibly for the FPU (this is usually a 32MHz can on the boards it is fitted on - which is not all of them). There's also a hard set link next to the secondary oscillator, my guess is that this is, like the Eurosoft HT12A, to feed to the FPU with a more standard 14.318MHz clock, rather than from the optional oscillator.

Thank you very much for BIOS ! I will try it with my working 286 SCAMP.
BTW. Not to long ago, I also bought non working 386SX SCAMP motherboard (without cache) with battery damage.
I've fixed all broken tracks and vias, but unfortunately board is still dead - I can see only "----"on POST card analyzer .
Don't have osciloscope (yet), so I don't know if all the oscillators are OK. But I want to bring it to life, so I am watching your thread with interest and I wish you good luck !
😀
Those are interesting for me because with VL82C311+VL82C113 duo, you can easily implement PS2 mouse. As I did for my 286.

got a working 80MHz oscillator finally - this Biostar VLSI board screams at 20MHz 0-wait (writes too!)

benchmark posts to follow in coming days

Landmark CPU and CheckIT Dhrystones are near-as dammit the same as my VLSI 82c201 board at 20mhz 0ws. maybe 1-2% off, but near as makes no difference.

Tseng labs speed also looks to be on the money.

Only thing off is the FPU: the CheckIT comparitive rating is well below mine and the Whetstone about 90k less. What have you got fitted?

I haven't had the time to look at my Biostar board any more yet, so it's still in the "to finish" pile.

megatron-uk wrote on 2021-03-27, 23:23:

Landmark CPU and CheckIT Dhrystones are near-as dammit the same as my VLSI 82c201 board at 20mhz 0ws. maybe 1-2% off, but near a […]
Show full quote

Landmark CPU and CheckIT Dhrystones are near-as dammit the same as my VLSI 82c201 board at 20mhz 0ws. maybe 1-2% off, but near as makes no difference.

Tseng labs speed also looks to be on the money.

Only thing off is the FPU: the CheckIT comparitive rating is well below mine and the Whetstone about 90k less. What have you got fitted?

I haven't had the time to look at my Biostar board any more yet, so it's still in the "to finish" pile.

It's a 287xl, but the catch is this Biostar clocks it at a fixed 7MHz using the pin 53 output from the VL82C201. I've been meaning to get around to modding it to run synch with the CPU instead.

Pin 53 (MH27) outputs oscillator output divided by 2.
I need to get an oscilloscope and measure what exactly it outputs.
Is it he crystal oscillator (in your case 80MHz) divided by 2, or divides one more time the already divided by 4 frequency ?

Also, these 387 cores in 287 bodies are a bit ambiguous. 2/3 and 3/2 internal dividers, etc.

I have this on my to-do list. Will see when i can get to it.

pshipkov wrote on 2021-03-28, 02:49:

Pin 53 (MH27) outputs oscillator output divided by 2.

Yes, but it's the 14.318MHz oscillator divided by 2, not the fast clock

Ugh, right.

I looked briefly at the VLSI PCB and cannot trace where this goes.
The current mod i can think of is to get a frequency multiplier and insert it between the pin and pad.
Not sure how the Keyboard controller will react to the higher frequency, but from experience with overclocking other systems - they are fine all the way up to 60-70MHz (the actual freq applied to them, but not the clock generator).