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Thread: Power supply for original Wang Professional Computer (PC-XC3-2 or PC-002?)

  1. #1

    Default Power supply for original Wang Professional Computer (PC-XC3-2 or PC-002?)

    I need a power supply for an original Wang Professional computer, PC-XC3-2, of failing that a schematic of the power supply. I believe the power supply was made by Harris.

    My Wang PC has the wider body, allowing a couple extra cards, and the power supply is turned on & off by a switch on front of the computer -- not the back.

    Any leads, advice, or whatever would be appreciated.

  2. #2
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    Have you tried repairing the PSU? Often times (>80% of the time), the problem is bad capacitors.

  3. #3

    Default Repairing the PSU?

    While I'm an Electrical Engineer (Retired) I have never been that into power supplies and what I did learn, is now obsolete with all these switching power supplies.

    Inside the power supply box (a bit larger than a regular PC PSU) there are two cards mounted at right angles to each other and one is plugged in to the other. This makes it really difficult to do any live troubleshooting. One board seems to be dedicated to power line to DC conversion and I think the other board does the switching action.

    It is too difficult for me to troubleshoot without a schematic and some voltage values.

    The large capacitors look ok and are not warm to the touch.

    No voltages are being output -- +12, -12, +5, and maybe another. All are zero.

    One question: is it safe to troubleshoot these power supplies with no load on the output voltages?

    Thanks for your help and I look forward to more suggestions.

  4. #4
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    Most switching PSUs have undercurrent/overvoltage shutdown, so they need some sort of load. A good dummy load is a spare hard disk drive (an old IDE drive is fine).

    The problem with the larger electrolytic capacitors is that they tend to dry out. The ESR of most electrolytics is pretty far from infinite when used at the 25-40 KHz switching frequency used in these things. They get warm and they dry out after a decade or two. With linear supplies, you don't see this problem as frequently because you're only dealing with ripple frequencies of 50/60 or 100/120 Hz.

    I'm assuming that you've checked in the line input filter (if any) and the associated fuse (sometimes a pigtail type located on the main PCB).

    A note on the capacitors--often, you'll see a nonpolarized one in the primary circuit--don't try to use a regular polarized one in that position.

  5. #5

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    Yeah, the fuse is fine. It is an 8 amp fuse, in series with the AC power. Inside the box, which is very difficult to get to (I wonder how many thousands of dollars Wang technicians made replacing that little fuse!).

    I have concluded that I have to have a schematic of some sort to isolate where the problem is. I'm searching the web trying to find a diagram somewhat close to what I have. I don't see any chips, just discrete components, power transistors, and lots of diodes. That should make tracing out the circuit a little easier and possibly replacing bad components.

  6. #6

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    I can't help you, but I just picked up one of these myself this evening.

    Mine works, but the Winchester drive is bad. Need to look at it.. Maybe it get spinning one more time.

    https://www.facebook.com/media/set/?...1&l=13b0dc4161

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