Question about APC Silcon UPS System

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I have several APC Silcon 20KW 208 Vac. some of them were working fine, but the control panel didn't respond. Some day i had to turn off the UPS and when i tried to restart i couldn't because de control panel still without respond. After that, and apc technicians change one board (21446-3)and the problems was fixed. I have 3 board with the same symthom so i'm traying to repair them. (APC new board are around $3000 us). Do you have some experience reparing this boards? what are the major components with fails? Thanks in advance

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  • epelaezi Jul 21, 2009

    Thanks. I have a questíon. i don't know what is the name of the board 21446-3. Is Com controller or is the DM controller?

    I'm electronics profesional and i have test equipement but this board doesn't have visual evidence of fail.


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since it is a UPS it has these stages:

A) a power supply / charger which automatically charges the two batteries and a change-over circuit for output selection

B) Batteries to supply the inverter stage of the UPS

C) Inverter circuits which produces the necessary output if there is AC power interruptions

Troubleshooting the circuit board maybe done by isolating the two circuits
1) the automatic charger
2) the inverter

The automatic charger, Preliminary Testing
these will be done outside the panel
1) locate the main AC input
2) check for output voltages
if there is output , check it with a series ammeter to be precise

3) if OK , then we go the Inverter Circuits

The inverter Circuits compose of a sine-wave circuit oscillator, an astable multivibrator IC.

driver output transistors, output stage transistors or scr and the output transformer.

This inverter circuit only powers-up when there are no ac input signal detected.

The actual trouble shooting of the board requires test equipment for the stages i have mentioned.

the actual fault can be trace and detected by isolating stages.

If there are Schematic Diagrams that you can possibly show me, there will be a high chance of possibility of being repaired.

Another option is the actual picture of the circuit board, at the least we can isolate where or what stage are malfunctioning

if I can see the actual component ,in good pictures ,a possibility of identifying the electronic components and knowing its function for.

a possibility of advising what replacement might be needed for a certain electronic part. or parts

the defective circuit board can be repaired outside the main unit, with a help.

Hope i have helped you, thanks for using Fixya!

Posted on Jul 22, 2009

  • Rommel Cana
    Rommel Cana Jul 25, 2009


    the best thing would be divide and conquer

    isolate the stages

    test it manually, with external supply and load

    even go to the extent of testing the electronic parts one by one


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There are capacitors on these boards that fail. Look for any swelled up capacitors, any burn marks. A capacitor can be tested with capacitor tester or multi-tester. The capactitors control the amount of current flow to each circuit.

Posted on Jul 21, 2009

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