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Need help input with an APC BP 420 (UPS)

Posted on 1998-05-11
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Last Modified: 2012-06-27
Hello;

I am looking for any help and tips:


It's about the APC BP 420 (Back UPS pro system)) it stopped working 10 days ago, in
fact I heard some beeps at the reboot, first I thought it was my computer but after
looking a little closer I saw the input circuit breaker tripped, I tried to reset it but
it won't it stays in upper position loose.

the self test works and no lights other than the green one is on.

what should I do to be able to use my BP 420 again?

what happened?

now I have my pc plugged into a regular APC surge protector and everything works fine.

the APC was not even overloaded:

on it there are:

Pentium 75 upgraded with a pentium 200
Monitor 14" color
USR external modem

that's it, was working fine before the incident.

Thanks for any input and ways to repair it!

Fabrice Robbe
frenchship@poboxes.com
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Question by:Fabrice
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jhance earned 70 total points
ID: 1135240
These things do fail and it sounds like yours did just that.  Usually one of two things go wrong with an UPS.  The battery dies and develops a short internally or the output circuit develops a short.  Either way, the usual response is that the circuit breaker trips and then trips again every time you reset it.  If you are "electronic repair" experienced, a UPS is usually quite simple to repair.  They are little more than heavy duty battery chargers.  I'd start with the battery first.  They are almost all 12V sealed lead-acid gel batteries.  You should be able to measure about 12-14V on it's terminals.  Put a load on it to draw about 10 AMPS and see if it holds the voltage.  If not, it's dead and should be replaced.  APC will sell you one but they are pretty generic.  A mail order house like Mouser Electronics can probably get you one cheaper.  
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Author Comment

by:Fabrice
ID: 1135241
Thanks for the info;
about the battery I hope it's not dead because it's a replacement unit APC sent me last Nov 97 and they say they changed the battery.

also the self test works, and so red light is on afterwards indicating the battery is dead or so.

Do you think it could have taken a heat of some sort?
what other causes besides the dead battery could indicate the symptoms I 've got?

Do I will nead to replace the input breaker stuff on the rear?

do you think any repair on that is worth?

Thanks again!


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Expert Comment

by:jhance
ID: 1135242
You do raise a couple of new points.

If the battery was new (or supposedly new) in 11/97, then it should still be OK.  I'd recommend checking it anyway.  It's possible that the input circuit breaker is failed but that would be very unusual unless it has been tripped a lot.  If it's loose, however, and can't be reset when the unit is OFF and the battery is disconnected, then it might be bad and can be replaced.  Besides the battery, the next most common failure are the switching transistors used to drive the output transformer in the 12V DC to 120V AC converter of the UPS.  These are usually MOSFETS and can usually be replaced with generic replacements from TV repair parts sources.  You may have to do some hunting if the part numbers on them are "house brand" instead of commercial part numbers.  I assume that it's not under warranty anymore, if not, then I think APC has a standard repair price for these things.  I suspect that they just send you a rebuilt unit and send yours off to a repair depot.

As far as being worth repairing, that's your call.  A 420 VA UPS is not that expensive.  It will probably cost you at least $20 just to ship it somewhere due to it's weight.  Let's say they will fix it for $100.  Now you're out $120.  A new 400VA UPS is around $200-$250 so you might be better off chucking that one and just buying a new one with a warranty and new battery.
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Author Comment

by:Fabrice
ID: 1135243
Thanks I think when I have more time I will look into the repair cost and probably try to resell it for parts or to somebody who can fix it, I am very disapointed with APC 2 problems in less than 6 months with 2 different units not reliable to me.

also I got a message about the MOV, do you know what's it?

message is:

It sounds like the MOV circuit went.  The MOV's are the surge protection
circuit. The MOV's are designed to blow in the case of a surge.  When they
blow they trip the rear breaker. The rear breaker won't reset because the
MOV that blew is causing a short between hot and ground.  

what's MOV stand for?

is that easy to repair?

Thanks!

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Expert Comment

by:jhance
ID: 1135244
MOV is a Metal Oxide Varistor and it is possible that this device failed.  The most common failure for a MOV is to open circuit and therefore no longer offer the protection.  Usually these are red in color and are disk shaped about the size of a dime.  You can test remove them from the circuit by cutting their leads and see if that fixes the problem.  You can also find these at Radio Shack and other electronic outlets if you want to try and replace them.
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Author Comment

by:Fabrice
ID: 1135245
Thanks a lot for your valuable comments
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