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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 23rd Apr 2007, 5:36 pm   #1
liamoliver
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Default 486 based computer

Having grown up with a 486 powered machine and having fond memories of the old MS-DOS games (that just don't run properly on modern systems), I decided to build one from old parts. I completed it months ago; however the mouse port (standard RS-232 serial) does not work. It is definetly the port, and the cable that connects the 9-pin D-sub socket to the mother board is not fitted backwards. Also, the primary slave, while recognising the hard drive's presence, does not seem to work. Does anyone know what could be wrong, or is the motherboard just faulty?

Here is the machine's specifications:
It has four megabytes of ram (fitted in the correct sockets), two hard disks on the primary controller (though the slave doesn't work properly), a working Sony CD311 on the secondary controller, a sound blaster 16 and an unknown VGA card. The processor is the 33 Mhz one. The motherboard was manufactured by TMC research, but that is all I can remember.
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Old 23rd Apr 2007, 5:41 pm   #2
jim_beacon
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Default Re: 486 based computer

Liam,

the quick way round the problems (HDD and Serial), is to look for one of the old 16 bit multifunction cards. These have serial, parralell, HDD and floppy on a single ISA card, and bits can be diabled by jumpers. Disable the faulty motherboard ports in BIOS, and use the relevant bits on the expansion card.

Jim.
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Old 23rd Apr 2007, 5:43 pm   #3
liamoliver
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Default Re: 486 based computer

I plugged in one of those cards once, but I couldn't get it working. Do they require special settings?
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Old 23rd Apr 2007, 7:38 pm   #4
Kat Manton
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Default Re: 486 based computer

Hi,

There were two ways which the serial port header on the mainboard was wired, consequently there were also two different ways in which the ribbon cable was wired up to the 9-pin-D connector.

They're not compatible. So, provided the serial port works, it's likely that you've got the wrong type of cable.

Some types had a shroud which could be slid back to reveal the soldered connections. If you have a few of them, examine them all. The different wiring is obvious.

One wiring scheme has the wires from the ribbon soldered alternately to pins on the top and bottom rows of the D-connector. The other wiring scheme has the wires from the ribbon split, one half goes to the top row of the D-connector, the other half to the bottom row.

This page explains it well, along with photographs of both wiring schemes.

Cheers, Kat
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Old 23rd Apr 2007, 8:33 pm   #5
liamoliver
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Default Re: 486 based computer

Thank you very much. I don't know where I'll get the other sort of those cables, but I'm sure one'll turn up eventually. Were there also different wiring methods for parrallel and 25-pin serial?
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Old 23rd Apr 2007, 8:38 pm   #6
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Default Re: 486 based computer

Which one have you got and which one do you need? I think I have one or two either here or at work, but I'm not sure which version they are.

Or, of course, you could modify an existing one if the cover will come off as in those photos. It's a bit fiddly to solder, but not too bad. Some are moulded lumps that don't come apart though.
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Old 23rd Apr 2007, 8:50 pm   #7
liamoliver
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Default Re: 486 based computer

The one I have is straight-through, so I will presumably require the crossed wire one.
Thank you for your help. How much would you want for the cable?

P.S. I don't suppose that anyone has a turbo switch (one that fits into the case front)? The case used to have one until I plugged it into the wrong socket on the motherboard (not this one) and it melted.
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Old 23rd Apr 2007, 8:59 pm   #8
Paul Stenning
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Default Re: 486 based computer

If I have a cable, you're welcome to it FOC. I'll have a rummage tomorrow (most of this stuff is in boxes stored at work due to the house move), and send you a PM if I find one.

With the turbo switch, you could just fit a jumper link between the pins on the motherboard so it's always on turbo mode. There is no point in running at the slow speed. The switches vary with case designs.

In fact a lot of 486 motherboards remain on turbo speed all the time anyway, and the switch just turns the LED on and off. It was all a bit pointless (unless running old PC AT software that is CPU speed critical) and the idea was soon dropped.
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Old 23rd Apr 2007, 9:08 pm   #9
liamoliver
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Default Re: 486 based computer

Thank you ever so much. If you find two, they could both be useful as I've never found one serial port to be enough.

As for the turbo switch, I do have some old speed critical software (I didn't know it was from the AT era) that runs fast on the turbo speed. Is there anywhere I could find one?
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Old 23rd Apr 2007, 9:13 pm   #10
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Default Re: 486 based computer

It would be worth posting a photo of the faulty switch or the mountings where it used to be, so people can see if they have something like it in their junk boxes. It'll just be an ordinary latching push button switch - but you need one of the right physical shape and size to fit the case. If the button is missing you could have more trouble finding a replacement.
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Old 23rd Apr 2007, 9:16 pm   #11
liamoliver
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Default Re: 486 based computer

I'll see if I can find one of the non-latching ones; it'll do for a photograph.
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Old 23rd Apr 2007, 9:33 pm   #12
paul.brett
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Default Re: 486 based computer

Rather than messing with a Turbo switch, there are also software options for slowing down the 486.

Look for slow286.com or slowat.com on the DOS archives.
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Old 24th Apr 2007, 9:18 am   #13
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Default Re: 486 based computer

Quote:
Originally Posted by liamoliver View Post
Also, the primary slave, while recognising the hard drive's presence, does not seem to work.
Issues with IDE drives were common, with diifferent brands not 'playing nice'. I remember I had an old Alps 210MB in my 386DX/40 and it wouldn't work with other brands in some configrations - from memory it wouldn't slave but it's been over 13 years so I can't really remember clearly.

Also watch drive size - its unlikely a 486 will work with anything bigger than 527MB although you may be lucky if you have one of the last ones.
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Old 24th Apr 2007, 12:11 pm   #14
Dave Moll
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Default Re: 486 based computer

What Arjoll has said reminded me of an old HDD that I have which refuses to share its IDE channel. Is that what was meant by "it wouldn't slave"?
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Old 24th Apr 2007, 12:32 pm   #15
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Default Re: 486 based computer

Sorry, but I couldn't find any serial leads while rummaging through my stuff stored here at work this morning. They could be in one of the boxes right at the back which I didn't get to, but it'll probably be months before we get to them again.
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Old 24th Apr 2007, 7:12 pm   #16
liamoliver
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Default Re: 486 based computer

Quote:
Originally Posted by arjoll View Post
Also watch drive size - its unlikely a 486 will work with anything bigger than 527MB although you may be lucky if you have one of the last ones.
Do you mean a later motherboard or processor? I happen to know that the motherboard was manufactured very late in the day for a 486 class (1996), but I think the processor dates from '90 or '91.
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Old 24th Apr 2007, 7:20 pm   #17
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Default Re: 486 based computer

He means the motherboard.
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Old 25th Apr 2007, 9:14 pm   #18
jay_oldstuff
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Default Re: 486 based computer

your in look i've just had a rummage throught my junk box and have the serial lead you need send me a PM with your address and i'll pop it in the post to you.

Jay
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