Electronics > Repair

APC BR1500GI F02 Output Short

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paul_g_787:
I have an APC BackUPS Pro BR1500GI which I bought new in 2013. It has been sitting in the cupboard faulty until now.

The problem arose after a power spike The AC voltage went to 315V for a couple seconds I have no idea why to this date). The UPS went to battery then when it went to switch back to AC I had the error code F02 displayed with a constant screech for help that cannot be muted. There was no funny smells or magic smoke at the time of the fault.

From the sound the UPS is making it appears to be in terrible pain!!

This screeching error code happens constantly. With batteries and without. With or without devices connected to the outputs. The unit cannot be powered off or silenced apart from unplugging the AC.

I of course, tried new batteries, which did not help so I bough a second-hand unit (which I have been using since) and put the batteries in that one which is fine now 2 years later.

All the manual says regarding F02 is:

--- Quote ---F02 On-Battery Output Short
Turn the Back-UPS off. Disconnect non-essential
equipment from the Battery Backup outlets and the turn
Back-UPS on.
--- End quote ---

This advice does not help at all.

I got onto APC three times in 2019 and they basically said "naf off" to me when I asked for customer support. I even said I was prepared to send it to them for service and they said I would have to post it to the USA and the cost is $950 plus shipping and they won't guarantee the repair. I definitely will not be buying new products from APC ever again!

Searching the F02 fault online shows up dozens of other people with the same F02 fault code, some with other models, some saying their UPS were brand new!!! So it is a common issue! Especially with the BR1500 models which are mentioned a few times

So now I have a little more electronics knowledge I have been brave enough to take it apart. I found two faults.

The first was C83 100µF 25V. It was bulging and had an ESR of 124Ω and capacitance of 1.6µF. I have replaced this with a new capacitor.
The second fault was another capacitor that had one leg never soldered to the pad from new! It was just flapping in the wind! I tested it's value and ESR and it is good so I soldered it in place correctly. (see photos).

I tested the ESR of every other Electrolytic cap on the board and they are good.

I have tested the MOSFET transistors on the big heat-sinks for shorts. They appear to be fine!

So I am hoping someone here may be more knowledgeable than I am regarding this issue and might be able to help me find the fault.

fzabkar:
Something must be sensing the current draw. Look for low value, high power resistances. Alternatively, the unit may be sensing the current via a winding in a transformer.

I would think that the battery charging circuit must have some current sensing circuitry.

johnkenyon:

--- Quote from: fzabkar on October 16, 2021, 11:53:04 pm ---Something must be sensing the current draw. Look for low value, high power resistances. Alternatively, the unit may be sensing the current via a winding in a transformer.

I would think that the battery charging circuit must have some current sensing circuitry.

--- End quote ---

To the best of my knowledge APC use current transformers to measure AC current, in this case on the output, and in some cases on the AC input feed as well,
It is possible that the circuit that conditions the current transformer output has been damaged - either the load current is being reported as too high, or maybe reported as being zero when the the UPS knows full well that it isn't.

My advice would be to try and find a schematic*, and try to trace how power gets from the line to the sockets, keeping your eye open for a transformer marked "CT" (=current transformer) rather than "T" (=input power transformer or inverter output transformer)

If the BR1500 is anything like my SU1400, then look for any transformer marked "CT" rather than "T". For example on the SU1400 there are CT1, CT2.
Then look at what each current transformer feeds - look for clamping diodes, burden resistors across the output, then look at where the signal goes afterwards.
On the SU1400 CT2 senses the output current (it's the last component before the "HOT-OUT" connector, and the transformer output goes through two op-amps before arriving at an ADC.

If you have a schematic, you have a fighting chance of at least locating the fault. Without one (IMHO), you might as well give up...

/JK

* Use the elektrotanya.com search, search for APC then manually look through the results.
 

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