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Thread: IBM 5160 repair

  1. #1

    Default IBM 5160 repair

    So, my 5160 is dead... following this guide so far it seems pretty comprehensive. http://www.minuszerodegrees.net/5150...iag_config.htm

    Got as far as testing the 12V+/- and found a short (my PSU fan runs btw). I snipped off the 12V caps with my hackkos but no dice. So dug a bit deeper...

    For an XT it has a very nice quiet 180w PSU... so I want to get that working it appears to be just a beefed up half bridge PSU but like I said it has a big quiet fan so doesn't add much noise to the system. I'll post photos here later. I think it's aftermarket?

    I cracked open the PSU and found that the 4A fuse in there was blown... I picked up a few fuses at walmart will test later. Hopefully I get some beep statuses out of if once I get the PSU fixed.

    If anyone has any tips/insights let me know! Bear in mind I'm a computer engineer that designs microcontroller boards and HMIs by day... and haven't touched a PC or XT in about 20 years (5150/5153 was my first PC) I useually fiddle around with Sun machines as a hobby.. but those are a bit complex to actually repair anything at all in them other that perhaps NVRAM batteries and caps.

    Also KiCAD has recently added some spice support.... I might try modeling a SMPS with discretes using it at some point.
    Last edited by cb88; July 9th, 2018 at 07:54 PM.

  2. #2
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    Being an engineer, how are you at SMPSU design? You know, discretes?

    That being said, a PC PSU will usually just let the overcurrent sense kick in and simply refuse to supply any voltage. Blowing a line fuse indicates something on the primary side. Have you checked the diodes on the primary side? How about the line RFI filter caps (often those are the old Rifa film caps and have even been known to explode) Of course, caps and transistors on the primary side.

    Here's an example

    Good luck!

  3. #3

    Default

    Nothing else in there looked toasted but since you say that I'll post some photos tomorrow of the innards.

    I have a vague idea of how it could be done with discretes... but having read a bit on that just now I'm fairly certain i'd let some blue smoke out for awhile before I got one working that way. As far as I'm aware a sort of halfway solution would be to use 555 timers... to generate a voltage controlled variable duty cycle pulse train... even that would require some care in design though compared to how straight forward modern integrated controllers are.

    I've designed an DC swich mode PSU before with an integrated controller... basically just following the datasheet recommendations seemed to work well in what little testing I've done on it. Mine is based on the LMR16006 http://www.ti.com/lit/ds/symlink/lmr16006.pdf which can take up to 60v and drop it down to whatever you set it for.

    Also thanks for the schematics those should help... and you are right of course it's unlikely that fuse blew without something being wrong with the PSU itself.
    Last edited by cb88; July 9th, 2018 at 07:47 PM.

  4. #4
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    Actually, there's no need to design your own. Many just gut an ATX PSU and stick the innards in the 5160 PSU case. You don't get the -5V from most ATX PSUs, but then, the 5160 doesn't really use it for anything. On the 5150, Rev 1, it was used for substrate bias on the 4116 (3 rail) DRAMs. There may be a board out there that uses it, but you're unlikely to encounter one.

    But it's always nice to have original equipment, so dig around a bit. I always marveled at Bob Boschert's operation--back in the day, designing SMPSUs was a black art. A lot of his early stuff looked like it had come off of someone's workbench.

    If you do think you've got the 5160 PSU working, bear in mind that it won't operate without a load--the overvoltage crowbar will kick in and you'll see nothing. A hard drive should be an adequate load.

  5. #5

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    My board does have this mod which is apparently from factory to support 32/8KB roms or some such? http://minuszerodegrees.net/5160/mot...socket_mod.png

    It uses an integrated bridge recetifier KBL06 https://media.digikey.com/pdf/Data Sheets/Fairchild PDFs/KBL005.pdf

    Seems to be fine there I measured 0.54vish across two terminals and 1.1v across the full bridge which I think is correct.

    I put a small Fuse in just as a test to being with and powered it up, blew the fuse... so removed the 5 large caps on the board all seem to be bad (at least my multimeter doesn't read them in it's capacitance mode and they show 0ohms) Powering up the PSU without the caps installed does not blow the fuse.
    Last edited by cb88; July 10th, 2018 at 02:51 PM.

  6. #6

    Default

    Replaced the 2 large electrolytics on the incoming power and 3 of the output filters... powered it up and smoked the fuse so somthing is still amiss.

    Those 5 caps I pulled were definitely dead so perhaps one of the smaller electrolytics has failed short also...

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