386 Restoration

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Andy1979
Posts: 61
Joined: Mon Mar 27, 2017 9:04 pm

386 Restoration

Postby Andy1979 » Mon Jul 24, 2017 3:00 pm

Having gotten my Acorn kit up and running I decided to rescue another load of retro computer gear from my parents' loft.

In addition to a Pentium 133 system in component form (which is now up and running, and awaiting IDE to CF and SD adapters) I found this 386, which I first cobbled together 15 years ago out of:
- Tower from a Pentium system where the motherboard had died
- AMD 386SX40 motherboard, 4x1mb SIMMS and an ISA graphics card that I'd found in a 'junk box' at a computer fair about 20yrs ago
- Basic ISA I/O card that had seen previous use in my pentium

In addition at some point I was given an old 5 1/4 inch floppy and a Tandon 21mb MFM hard drive and Western Digital controller card which I thought I'd try and get working in this.
IMG_3731.JPG


First job was to tackle the dreaded battery leakage. As you can see one of the tracks (in this case to the keyboard connector) had actually lifted.
IMG_3715.JPG


After a soak in white vinegar, a rinse with distilled water and finally IPA, this was the result:
IMG_3735.JPG

One of the pins on the keyboard bios socket was damaged, which I was able to fix with a small piece of metal.

Managed to do a 'stealth repair' on the broken track on the bottom of the board. Could have done with some thinner wire really, but it works:
IMG_3737.JPG


After all that, the board boots into the bios, and I managed to get DOS loaded on 3.5 inch floppy. There is some odd behaviour still to be addressed though:
- I can't get either my IDE or MFM hard drive controllers to work. BIOS displays 'HDD Controller Failure'. Apparently this is common, and I might just need to try random expansion slot combinations until it works. Worst case there is battery damage within the board that I can't see.
- Instead of 4096k RAM the BIOS displays 3840k, which is 256k short. The board won't accept more than 4mb RAM, which is probably a design limitation given small size of the board.
- If I get all that working it needs a new battery. Don't think I can use a single AA like with the Acorn, so am thinking a 3.6V cordless phone battery is a good option.

Considering that this board was built in 1992, it has served to demonstrate just how much better and user friendly my A3010 was at the time. It's easy for someone my age (mid-30s) to forget that given the ubiquity of PCs these days. The only real thing in its favour is the ability to (hopefully) repair it using more modern parts, but even they (ISA cards, AT PSUs, IDE drives, 30 pin SIMMs, etc) are very hard to get hold of these days.

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1024MAK
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Re: 386 Restoration

Postby 1024MAK » Mon Jul 24, 2017 3:53 pm

Andy1979 wrote:- Instead of 4096k RAM the BIOS displays 3840k, which is 256k short. The board won't accept more than 4mb RAM, which is probably a design limitation given small size of the board.
That’s more than likely the "memory hole" for the BIOS ROM and the I/O card boot ROM space. Or for Video RAM.

Andy1979 wrote:- If I get all that working it needs a new battery. Don't think I can use a single AA like with the Acorn, so am thinking a 3.6V cordless phone battery is a good option.
A 3V lithium coil cell with a diode (to prevent charging) and a 4.7k resistor (to limit fault current to the cell if the diode should ever fail short circuit) will do. Or use a Varta 3.6V 150mAh NiMh memory back up battery like this one from CPC: Image
They are also available from many other electronic suppliers and from eBay.

Mark
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Prime
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Re: 386 Restoration

Postby Prime » Wed Jul 26, 2017 8:21 am

I find it odd that itt will only accept 4Mb of RAM IIRC the 386sx could address up to 16mb, and the motherboard has 8 sockets, so I would have thought that it should be able to access more. Though your simms do need to be fitted in pairs.

The hard disk error may be that you need to access the cmos settings and enter the correct geometry for the hard disk. In the case of the mfm you may also need to low level format it, some bioses of that vintage had an option for that.

Cheers.

Phill.

Andy1979
Posts: 61
Joined: Mon Mar 27, 2017 9:04 pm

Re: 386 Restoration

Postby Andy1979 » Wed Jul 26, 2017 9:03 am

Thanks both. Some success:
IMG_3748.JPG

Turns out I was an idiot and despite checking multiple times failed to spot a missing jumper on the I/O card. Amazingly the 81mb Connor IDE drive I am using seems to be in fine health. Will still replace with a CF card though for ease of getting files onto it.

On the memory front I only have 4x1mb SIMMs and 2x256k SIMMs, so perhaps it's that combination of 4.5Mb it doesn't like? One "pair" of 1mb SIMMs is slightly mismatched in terms of manufacturer, but they appear to have the exact same chips and board layout. As it's a 386SX the SIMMs only need to be installed in pairs is my understanding. Perhaps it would work with 8x1mb SIMMs, but to be honest 4mb is sufficient for this machine and there's 64mb in my P133 system.

Next problem is trying to find a driver that will let my PS/2 wheel mouse work with a serial port adaptor in Windows 3.11. Have just found an open source universal DOS driver called 'Cutemouse' that should at least let me test if it's working.

At the weekend I'll have another crack at the MFM drive and try to get the 5.25inch floppy working. The card has lots of jumpers and its own BIOS (which can by bypassed) so is hopefully a matter of finding the right settings. Whether the drive itself works is another question.

SarahWalker
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Re: 386 Restoration

Postby SarahWalker » Wed Jul 26, 2017 4:15 pm

Prime wrote:I find it odd that itt will only accept 4Mb of RAM IIRC the 386sx could address up to 16mb, and the motherboard has 8 sockets, so I would have thought that it should be able to access more. Though your simms do need to be fitted in pairs.

It may be a genuine limitation, 386SX boards (particularly the late-model cheap and nasty variety) were a bit like that.

Alternatively, some of the SIMM sockets may be faulty...

Andy1979
Posts: 61
Joined: Mon Mar 27, 2017 9:04 pm

Re: 386 Restoration

Postby Andy1979 » Wed Jul 26, 2017 4:44 pm

SarahWalker wrote:
Prime wrote:I find it odd that itt will only accept 4Mb of RAM IIRC the 386sx could address up to 16mb, and the motherboard has 8 sockets, so I would have thought that it should be able to access more. Though your simms do need to be fitted in pairs.

It may be a genuine limitation, 386SX boards (particularly the late-model cheap and nasty variety) were a bit like that.

Alternatively, some of the SIMM sockets may be faulty...


It's definitely cheap and nasty - think most people had moved onto 486s by 1992, and the only identifying mark on the board is 'made in China'. Can't actually find any boards with this layout the various internet databases that catalogue this stuff. Found a similar one with an SX-33, but that had a few other differences, and manufacturer was also unclear.

What puzzles me is that if you're going to limit to 4mb, why bother putting 8 SIMM sockets? Most cheap boards only had 4. I suspect the 'real' limit is 8mb if I had some better SIMMs, but I don't intend to buy any and find out.

Andy1979
Posts: 61
Joined: Mon Mar 27, 2017 9:04 pm

Re: 386 Restoration

Postby Andy1979 » Sat Jul 29, 2017 10:17 am

Some further success. Found the jumper settings for the MFM controller, and after a lot of trial and 'ROM BASIC' errors it finally booted into DOS with a working copy of QBasic (yay - Gorillas!) It's very slow, but I love the physicality of the drive as you can see the servo turning back and forth. Looks like the machine it came from was last used in 1994.
IMG_3766.JPG


I also got the 5.25inch floppy going. Turns out the Epson 621-L is only a 360K drive, but that's OK as I only have DSDD floppies from a Beeb anyway.

Next job is to fit the new CMOS battery and get the CF card set up. Must remember to park the heads on the drive first though!

Andy1979
Posts: 61
Joined: Mon Mar 27, 2017 9:04 pm

Re: 386 Restoration

Postby Andy1979 » Mon Jul 31, 2017 9:44 am

Project is now complete. Soldered pins in place of the CMOS battery and mounted a 3.6V NiMH pack from a cordless phone safely away from the motherboard using sticky velcro. Struck me that this would have been a good solution for my A3010. Seems to be keeping time and remembering the BIOS settings after leaving it on for a day to charge up.
IMG_3774.JPG
IMG_3777.JPG

CF card is also mounted and working. Left the older MFM and IDE drives in situ in case I ever want to use them. Also installed an ethernet card.
IMG_3781.JPG
IMG_3789.JPG

Just need to dig out a more period correct keyboard now.


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