Compaq Presario 425: The 486 all-in-one

Discussion in 'Retro & Arcade Worklogs' started by Pierre32, Nov 3, 2019.

  1. Pierre32

    Pierre32 New Member

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    This is my pickup from the Yarra Valley auction last month. A Presario 425 in stock spec, with 486SX25 CPU and 4MB soldered RAM. It has integrated Cirrus Logic 512k video, and no sound card. CPU and RAM are upgradeable. More info in this old review:

    https://www.atarimagazines.com/compute/issue167/99_Compaq_Presario_425.php

    I bought it from interstate based on a single photo on the auction site, with no idea if it worked or even had internals. A bit of a risky bid! A couple of nervous weeks would pass before I could find out how big the mistake was.

    (Note: I'm a newbie, so I can't use the OCAU image uploader yet. Using ImgBB for now because it lets me use thumbnails, and I will rehost them when I'm a grownup. The machine is a bit of an oddity, so I'll post plenty of pics across multiple posts.)

    The original, and only listing photo. Covered in stickers, muck and mystery.

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    The first unboxing. I really wish I'd taken more pics of the top and rear of the case, which was pretty ugly. But look to the right here and you'll see some kind of drippy treacle mess...

    [​IMG]

    Of course I had to brazenly jump into powering it up without investigating the insides first. And power up it did, loading straight into Windows 3.1. Clearly an old office PC, it was loaded with all sorts of boring things including the Novell Perfect Office suite. And running like a dog thanks to all the bloat.

    [​IMG] [​IMG] [​IMG]

    But it did all look stunning on the little CRT. It would have been such a cool unit back in the day, even if underpowered for the time. It gave me a similar feeling to the Macs and Amigas that I lusted after at the time, when I was stuck in an old XT-powered DOS prompt. But funnily enough, that's where we're taking this thing next.

    With nothing to hold my interest in the Windows install, it was time for a fresh DOS 6.22 installation, and a quick game test before I cracked it open.

    [​IMG]
     
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  2. OP
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    Pierre32

    Pierre32 New Member

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    After removing two screws at the rear, the whole mobo assembly slides out on a tray. Apparently a design borrowed from Apple, and it's great. Here it is before & after sound card installation.

    [​IMG] [​IMG]

    Pretty clean really. Eagle eyes might notice some corrosion on the little transformer near the top right. This component is elevated from the mobo, and doesn't look to be an imminent threat. I have opted not to touch it and unleash a bunch of iron flakes onto the surrounding PCB. Something to monitor and perhaps replace in the future. I do need to do a closer inspection of caps and CMOS battery, but at a glance everything looks healthy.

    Here's the front and rear of the mobo tray, and also the edge connector that it slots into. This connector delivers power into the mobo, and video back out.

    [​IMG] [​IMG] [​IMG]

    All the labels:

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  3. OP
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    Pierre32

    Pierre32 New Member

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    Opening up the top portion of the case, I was able to see the impact of the treacle-mess. The first pic is upside down; you see where something has dripped in from the top. And man, did this little PC get lucky. The mess seems to have made its way down to one bottom edge of the case - dodging all the upper circuitry (CRT etc) and not making its way into the mobo tray.

    What mess it did make was thick, sticky and scabby.

    [​IMG] [​IMG] [​IMG]

    Thankfully the cleanup was fairly easy, and there was no deep damage to the chassis or the case. My only regret is the crap masking job I did before I hit it with the Galmet - haha. But that's hidden away inside now.

    Gave it some new feet too, as the old rubber ones were rotted.

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     
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    Pierre32

    Pierre32 New Member

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    And here is the re-assembly. I absolutely love this little thing!

    [​IMG] [​IMG] [​IMG] [​IMG]

    That's almost all I need to do for now. I'm targeting late 80s / early 90s gaming on this machine, so I have no need to upgrade the CPU or RAM. I do need another sound card though, as the plan is to drive a Roland MT-32, and the current card (some shady no-name built around the ES688F) is not supported by SoftMPU.

    The 425 has a pretty nerfed BIOS, with limited ability to control hardware addressing. I'll need to take this into account when selecting a card. I tried installing a Labway A151-830, but could not resolve an IO conflict (and the card has no jumpers).

    [​IMG]
     
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    Pierre32

    Pierre32 New Member

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    The new sound card landed this week. The requirements were: Real OPL3 chip, non-PnP, IDE header, SoftMPU support, and not a clone. The SB16 CT1740 fit the bill.

    [​IMG] [​IMG]

    The DSP revision is 4.11 which means it is susceptible to the hanging note bug. But I'm not running any of the worst affected games on this machine, so we'll see how it goes.

    Setup was painless. Quick jumper adjustment, ran the SB setup program, and it was blasting out FM as well as MIDI to the MT-32 in no time at all. No small thanks to Phil's CT1740 guide:



    Only one task remained to call this job done: Install the CF reader. Based on the last install I did, this would take all of five minutes! Then I had two realisations:
    • That's not an IDE header on the sound card. It's a Panasonic CD interface. Oops!
    • I have no facility to power it.
    So not only would I have to slave it to the HDD, I'd also need to route some power. There are no spare molex plugs hanging around in this case; the HDD and FDD are powered from a single header on the mobo. The IDE headers are tucked into the same area. All these cables are only a few inches long. Not an inch of copper wasted here, and not a design that encourages expansion.

    [​IMG]

    I'm also running pretty short on molex cables, and don't have a floppy power connector at all for the CF drive. What I do have for some reason is a big bag of CD audio cables... and the flat black headers on those happen to fit on the floppy power connectors if you're polite about it.

    I had a very short male-female molex cable which turned out to be perfect. I could chuck it inline with the HDD power, and tap into it with a CD cable.

    First pic shows where I will tee off for the card reader. Second pic shows the new plug going into the drive. Third pic shows the soldered & taped up junction stuffed underneath, and you can see the round grey CD cable heading away.

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    In my mountain of IDE cables I found one that I can only describe as miraculous. You can also see the grey CD/power cable connected up.

    [​IMG] [​IMG]

    Looked lovely. But wasn't working yet.

    Unlike my other machine which simply said "oh hello flash drive" and had it running after a quick Fdisk and format, the Compaq threw its toys out of the pram. The simplified BIOS in this thing has very limited auto-detect ability, so the mystery hardware borked the whole system. But it does allow manual drive config, if you can tell it how many sectors etc your no-name CF card has.

    This was new territory for me. I found a utility called WhatIDE (which I downloaded from this forum post) that polls your IDE channels and spits the numbers out.

    [​IMG]

    I entered the figures from Fixed Disk 1 into BIOS and finally, everything came good.

    The final learning was that the Compaq apparently apparently can't see drives bigger than 500MB. I had to format my 1GB card as such, so I've lost half its capacity. I'm not too sad about that, as 500MB is still pretty impressive removable storage for this vintage (especially when the HDD is only 200MB).
     
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  6. Vanne

    Vanne Member

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    Wow, nice little compaq, my ex-GF in Dundass had a simlar one, cant remeber the exact specs, but remvber that it was a cool little go-er. hers sadly had no sound and had to make do with PC speaker...
     
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