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Thread: Intel Professional Workstation 486 - How to Deal with Propitiatory Power Supply?

  1. #1

    Default Intel Professional Workstation 486 - How to Deal with Propitiatory Power Supply?

    Hey all,
    So I recently got a Intel Professional Workstation 486, and I've been doing my best to try and get it going again. I actually did a video demoing this system (https://youtu.be/fK7QMAX0BmQ), and am hoping someone here might be able to help. It's an EISA based/SCSI monster with some pretty non-standard stuff.

    Right now, the system is suffering dead Dallas-itis, so I'm waiting for a replacement to arrive from DigiKey; I'll only dremel the DS1287 if I absolutely have to. That part isn't a major problem.

    The problem is the PSU in this system is a pile of dog doodoo. The video shows it pretty clearly, but I feel like this entire thing is just waiting to go *poof*, and more problematically, the PC speaker lives *in* the PSU. To be honest, I'm sorely tempted to bin the thing and see if I can rig an adapter to a micro-ATX or similar. The PSU label says it provides 12+/12-/5+/5- so I'll likely need an adapter board to get the -12V rail out of anything modern. The mainboard has a 20 pin pin connector that the PSU sorta slots into, so I'm guessing I need to rig some sorta breakout board. If I remember my electrical theory 101, I need to be in series to measure voltages which should make this a semi-interesting challenge. (I'm not an expert here).

    Alternatively, I could try and rehabilitate this PSU and re-cap it; the caps seem good, and it's def. working, but there I'm stemmed by a stripped screw in a very inaccessible locations. I've got a small set of pliers on the way that might be able to reach the stem and turn it, but I'm not super optimistic.

    Any advice would be welcome; also, is there anything specific I need to know about EISA systems specifically? I did find the EISA configuration utility and reference files for this system, but I'd prefer to know any potential landmines *before* I hit them. I've posted some stills here (https://imgur.com/a/jZJci2W), and can post more if they will help.

  2. #2

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    I'm not seeing anything that suggests that PS is as bad as you describe. Remove the PCB and replace the EMI X and Y caps at the front end and the DC smoothing caps at the output.

  3. #3

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    The PSU works as best I can tell, but I'm rather uncomfortable w/ it because it feels rather shoddily made. if the PC speaker slides, it could literally short against the inductor. At the moment, recapping is also stymed by the fact that it's held in by stripped screws.

  4. #4

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    Quote Originally Posted by NCommander View Post
    Any advice would be welcome; also, is there anything specific I need to know about EISA systems specifically? I did find the EISA configuration utility and reference files for this system, but I'd prefer to know any potential landmines *before* I hit them.
    Of a physical nature, in that EISA requires more NVRAM to hold the configuration than what the DS1287 provides - I'll need to look inside my unit.
    Disclaimer: The username IBMMuseum and domain IBMMuseum.com are not affiliated with IBM in any manner

  5. #5
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    On the RTC, you might wish to pay a visit to Glitchworks - They've got a 1287 repair kit that'll make tapping the internal battery a bit easier if you opt to go that route, or if you want a wholesale replacement the 12887 kit is backwards compatible in many cases iirc. (Come to think of it, the 12887's extra NVRAM might just be what you need for those EISA config storage limitations.)
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  6. #6
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    Hey, that looks like it's Intel Xpress related! They made a number of EISA systems of that era, targeted at workstation/industrial control/server use. I hadn't seen the little pizzabox you have, before! Haven't watched the video yet, so I can't currently offer further comment. I still support the close relatives of thing as part of my day-job business

    Quote Originally Posted by IBMMuseum View Post
    Of a physical nature, in that EISA requires more NVRAM to hold the configuration than what the DS1287 provides - I'll need to look inside my unit.
    These really do just use a DS1287, I don't know if there's additional stuff held in Flash or what, but that's all that exists in Intel Xpress and friends.

    Quote Originally Posted by MrArgent View Post
    On the RTC, you might wish to pay a visit to Glitchworks - They've got a 1287 repair kit that'll make tapping the internal battery a bit easier if you opt to go that route, or if you want a wholesale replacement the 12887 kit is backwards compatible in many cases iirc.
    Thanks for the mention! The GW-12887-1 (and DS12887, of course) works fine in Intel Xpress systems, I'm running GW-12887-1s in both the shop testbed systems and in some of the production systems I maintain.

    Quote Originally Posted by MrArgent View Post
    (Come to think of it, the 12887's extra NVRAM might just be what you need for those EISA config storage limitations.)
    The system did originally include DS1287s, as far as I know none of the Xpress line will use the extra RAM in the 12887s.

  7. #7

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    Quote Originally Posted by NCommander View Post
    The PSU works as best I can tell, but I'm rather uncomfortable w/ it because it feels rather shoddily made.
    As do many power supplies in other very expensive workstations. They are purchased by the systems integrator at the lowest cost the market can provide, and replaced in the field as a unit, not repaired. As restorers we have to get past that. The good thing is that a working supply can be given additional life with just a few replaced parts.
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