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Old 02-19-2020, 09:24 AM   #1
jinu_j
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Line Voltage: 230VAC 50HZ
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Default APC BACKUPS-RS550 not charging battery

Hi Folks

I have a APC BACKUPS-RS550. This was lying idle for over a year. Now when i checked it was not working (no power). Checked the battery and found it to be dead( zero Volts). So i replaced it with a new battery.

Now it powers on and functions properly, but the battery does not charge so the UPS works till the battery voltage falls and then dies. I need to figure out why it is not charging. I checked the onboard fuses and it seems fine. The caps also dont seem to have any issues (atleast visually). can anyone help identify why it is failing to charge.

The pic of the PCB is attached. Any adivce on how to troubleshoot the issue ?
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File Type: jpg PCB.jpg (548.3 KB, 45 views)
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Old 02-19-2020, 04:31 PM   #2
sam_sam_sam
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Default Re: APC BACKUPS-RS550 not charging battery

CAUTION you have line voltage at this section of this power supply so please be careful when taking voltage measurement ( 120 volts DC or higher )



With out the battery installed

First check the fuse just before the capacitors and ( IC7 )
Also check to see if you have any voltage on those two capacitor if you have voltage on the capacitors
( then go to —> )

Second

Do you have voltage on ( C43 )

If you do not have any voltage on ( C43 )
Then replace the IC chip with the part number TYN274PN ( IC7 )

Then go from there

I do not see the start capacitor for this switching power regulator or then again some of them do not have one it does have one it is ( C45 )
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9 PC LCD Monitor
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30 Desk Top Switching Power Supply
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6 18v Lithium Battery Power Boards for Tool Battery Packs
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15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
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Last edited by sam_sam_sam; 02-19-2020 at 04:55 PM..
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Old 02-20-2020, 09:07 AM   #3
jinu_j
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Default Re: APC BACKUPS-RS550 not charging battery

HI Sam

Thanks for the guidance.

All tests were conducted with the battery disconnected

I checked the fuse F3 and that is fine, its not open
There is voltage at the two capacitors (c50 and C51) about 165V each

At C43 the behavior is very weird. when i disconnect the battery and check i see about 11.45V (which is same as the current battery voltage). So i short the terminals of the capcitor so that the capacitor discharges. Now when i check the voltage is near zero but very very gradually increasing at the rate of 5mV per second. Switching on or off the 230V mains has no impact on this behaviour. I cant understand how the voltage is increasing if the mains are off. After crossing 0.5V the rate at which voltage across the capacitor increases slows down further.

So does this mean the IC is IC chip with the part number TYN274PN is bad ?? Any way to cross verify this ?


Thanks once again
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Old 02-20-2020, 05:11 PM   #4
sam_sam_sam
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Default Re: APC BACKUPS-RS550 not charging battery

Probably I would just go ahead replace it

It switching power regulator does not seem to be switching at all

Here is the data sheet for this ic chip

https://www.power.com/sites/default/...tny274-280.pdf

Last edited by sam_sam_sam; 02-20-2020 at 05:17 PM..
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Old 02-20-2020, 10:26 PM   #5
jinu_j
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Default Re: APC BACKUPS-RS550 not charging battery

Ok will replace this and get back. What should the ideal voltage be at C43?

BUt i still dont get it, the UPS works fine, and will move to battery power when the mains go off and go back to main power when the mains come back. The only problem is once the mains come back the battery does not charge. Is the above component part of the charging circuit ?

Last edited by jinu_j; 02-20-2020 at 10:40 PM..
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Old 02-20-2020, 10:46 PM   #6
sam_sam_sam
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Default Re: APC BACKUPS-RS550 not charging battery

Yes this is the charging circuit
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Old 03-07-2020, 01:53 AM   #7
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Default Re: APC BACKUPS-RS550 not charging battery

Finally the replacement TYN274PN came in today and i changed in and it started working fine. Thanks a lot for your help.
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Old 03-07-2020, 05:59 AM   #8
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Default Re: APC BACKUPS-RS550 not charging battery

One more item that did not make it to the land fill

Good work on this repair
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