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Thread: Data IO 29b and magic smoke...

  1. #1

    Default Data IO 29b and magic smoke...

    Hi guys,
    Just wondering if there are any Data IO 29b Aficionados in the house?

    Today I was moving my 29b to another area of the house. I'm in NZ which is 240vac, but up until now I was running the 29b off a step-down transformer at 100vac. I decided to change the voltage to 240vac which I did by setting the dial thingy on the back of the unit. Pretty sure this is the first time it's ever been set for a voltage other than 100v.
    I turned it on for about 30 seconds, and all seemed fine. I turned it off at the back of the unit, and went about routing the cables under the table. About 2 or 3 minutes later. I heard a sizzling and crackling noise and I emerged from under the desk to find smoke (a lot of smoke) billowing out of the 29b. I quickly unplugged it at the wall, picked up the unit and rushed it outside (so that I didn't have to suffer the wrath of the wife...too late, the house stank!!!! That horrid sickly burnt capacitor smell).

    I expected to easily find a destroyed capacitor considering how much smoke and noise was produced, but upon opening the unit I have't yet been able to find a single component that looks burnt or damaged!!!!

    I guess my questions are.
    1) Why would it do this when the unit was turned off?
    2) Is it possible that it's not a capacitor thats burnt out (although the smell is very capacitor like). Could it be the internal transformer?
    3) I'm almost tempted to turn it back on so I can find the smoking part, but I'm sure you guys will say thats a bad idea...any other thoughts?

    Thanks for listening and any advice would be most welcome.

    Phil
    retro computing at: www.neoncluster.com ....is dead

  2. #2

    Default

    Replying to my own thread.

    Found the burnt out part. It's the Schaffner FN 370-4 filtered power entry module:

    http://www.mouser.com/ds/2/355/DS_FN...ilter-6234.pdf

    Thats why it could still smoke when the power was turned off to the unit.
    Does anyone know where I can get one, where shipping to NZ is $50!!!!

    Thanks

    Philip
    retro computing at: www.neoncluster.com ....is dead

  3. #3
    Join Date
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    Default

    RS New Zealand have similar items....
    ... but not cheap.

    e.g.

    https://nz.rs-online.com/web/p/iec-filters/7828662/

    more here

    https://nz.rs-online.com/web/c/conne...lters/?rpp=100

    but not cheap. I assume the one you have is well sealed. The cap that's gone will probably be a x-rated rifa. The case cracks, moisture gets in, they go bang, usually open circuit.

    e.g.

    https://electronics.stackexchange.co...-short-circuit


    If you could get in it may be replaceable. Actually notwithstanding the above article they usually fail open circuit so the beast may actually work.
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  4. #4

    Default

    You can probably run it just fine without the capacitor. It is there to help remove high frequency spikes, like from turning highly inductive loads on and off. Of course one of those loads is the transformer you have in the 29B. If your filter capacitors are weak, turning it off may short a power supply diode.
    In any case, it doesn't have to be an exact replacement. Most electronic equipment has a similar filter cap on its input. I suspect you can find another laying around you can scrap.
    Dwight

  5. #5

    Default

    Hi Dave, thanks for the reply.

    I didn't know about RS. so thanks for the heads up.
    I did find this one on their site, which is very close, only it's 6amps vs 4amps (for the original):

    https://nz.rs-online.com/web/p/iec-filters/4659072/

    Would it make any significant difference if I got this with it's higher 6amp rating?

    Cheers

    Phil
    retro computing at: www.neoncluster.com ....is dead

  6. #6

    Default

    Quote Originally Posted by Nama View Post
    Hi Dave, thanks for the reply.

    I didn't know about RS. so thanks for the heads up.
    I did find this one on their site, which is very close, only it's 6amps vs 4amps (for the original):

    https://nz.rs-online.com/web/p/iec-filters/4659072/

    Would it make any significant difference if I got this with it's higher 6amp rating?

    Cheers

    Phil
    That should have no effect, as long as the fuse in the unit is the same. It is more like using a 10 gauge extension cord, for a 100 Watt light. The light doesn't care.
    Dwight

  7. #7
    Join Date
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    Default

    Quote Originally Posted by Nama View Post
    Hi Dave, thanks for the reply.

    I didn't know about RS. so thanks for the heads up.
    I did find this one on their site, which is very close, only it's 6amps vs 4amps (for the original):

    https://nz.rs-online.com/web/p/iec-filters/4659072/

    Would it make any significant difference if I got this with it's higher 6amp rating?

    Cheers

    Phil
    I wouldn't worry too much about the extra current carrying capacitor. It may make the filter less effective as they are designed to operate into a specific impedance but it will still work.
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  8. #8
    Join Date
    Jan 2018
    Location
    Portland, OR
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    Default

    29B is a great machine, I have one with a UniPak 2B, and also recently got a UniSite with Site48 and SetSite modules. Between the two of them, it covers just about anything from the 1970s up to the 1990s.

    Unfortunately, the 29B schematic has nothing for the AC side of things, but based on the entry module datasheet, it looks like all the voltage selector does is route the filtered line power to a specific set of lugs. I'd expect to see those routed to the lugs of a transformer with sufficient windings to cope with all those inputs.

    If I had to guess, I'd say that the on/off switch only interrupts the AC hot line, and either that was on a different pin than expected, leading to mains voltage ending up in an unexpected place. I'm surprised your breaker didn't pop.

    I would start by metering the primary windings on your transformer to make sure they weren't damaged.

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