Don't Miss

APC UPS Model PR550i Repaired

By on October 16, 2008

The complaint for this APC UPS Model PR550i was it can’t charge and sometimes (intermittently) all the front panel LED’S lights up. A new battery was replaced with no improvement. Since the problem have some similarity with some other models then the problem could be a corrupted EEPROM DATA.  In order to confirm this problem, a similar working UPS EEProm IC was taken and placed it to the faulty UPS. The result was, it start to work normally! Since we have know that the data had been corrupted so the Pony prog eeprom Programmer was used.

First , save the good eeprom data file into the hard disk and then over write the corrupted IC with the good data. For your information, eeprom IC rarely have problem, most of them the problem was only the data corrupted. Once reprogrammed, it will work as good as a new IC!  By the way the EEPROM IC part number is 93C46 SMD type as seen from the photo below together with the Pony Prog eeprom programmer.

93c46 ic

pony prog programmer



  1. henry

    March 7, 2009 at 5:30 pm

    Hi jesting,

    I have APC 650 it stopped working the charge don't last,

  2. admin

    March 8, 2009 at 4:12 pm

    Hi Henry,

    Try directly replace the UPS BATTERIES.


  3. Waleed

    March 18, 2009 at 3:27 pm

    hi, i have one that stopped working all together. no charging and not even power light on the front. I suspect a bad power transformer. any ideas where to get one on the web or find a way to repair it? thanks

  4. admin

    March 22, 2009 at 2:29 pm

    Hi Waleed,

    Sorry no information on that.



    April 9, 2009 at 12:18 pm

    Hi Jestine Sir,
    That was a very good information.
    But can you tell more about the Pony Prog EEPROM Programmer.

  6. admin

    April 9, 2009 at 11:18 pm

    Hi Suresh,

    Please visit


  7. kingsley

    August 8, 2009 at 8:29 am

    i have a 650 mercury ups that doesnt backup at power failure. what do i to fix it?

  8. admin

    August 8, 2009 at 12:23 pm

    HI Kingsley,

    Check the battery first and if possible try directly replace and retest it again. Battery contributed about 80% of UPS fault.


  9. antonio samia

    August 8, 2009 at 8:36 pm

    Hi mr.yong ihave a problem on my ups if i plug it on ac outlet the fuse always blow.

  10. admin

    August 10, 2009 at 7:48 pm

    Hi Antonio,

    Check the corresponding components that lead to the Fuse. Pay more attention on the semiconductor especially the power FETs.


  11. Chris

    October 21, 2009 at 2:28 am

    Hi Jestine and congratulations for your site!

    My APC Back-up PRO ups suddenly stop working.
    I had the battery replaced with a new charged one but no luck!

    No light in the UPS panel, no output voltage when connected to AC and very low output voltage to charge the battery (4 ~ 8 volts)

    The fuses are ok…

    Do you know what is wrong?

    Thanks you!

  12. admin

    October 21, 2009 at 10:23 am

    Hi Chris,

    It could be the fault of an EEPROM too. But first the EEprom must get the 5 volt supply. You may need to test the supply before checking on other circuit/components.


  13. Ehimwenma izevbigie

    November 12, 2009 at 4:47 pm

    i want to know more about ups. what do i do?

  14. admin

    November 12, 2009 at 7:15 pm

    Hi Ehim,

    You may need to find more info from google seacrh as i do not have full explanation on UPS.


  15. Altaf

    March 16, 2010 at 6:41 am

    dear jestine
    i have UPS when i power on it show on but its not giving out put voltages.
    what is the problem. plz help
    ur student Altaf

  16. admin

    March 16, 2010 at 7:54 am

    HI Altaf,

    Have you check/replace the battery, fuse? Since UPS is so cheap nowadays, i don't really put lots of afford in this equipment repair. Generally i just replace the battery, check the fuse and reprogram the eeprom IC.


  17. Stanley

    August 12, 2010 at 4:51 am

    hi ineed to know more in repairing ups.because ilearn more Lcd & Power supply.can you please help me with ups again. thank you

  18. admin

    August 12, 2010 at 8:36 am

    HI Stanley,

    Most of the problems in UPS was bad batteries, bad fuse, shorted Mosfet and bad EEPROM IC (Depends on model). I don't really concentrate on UPS repair as compare to others because the price already very cheap and the spare parts are expensive.


  19. shahid shah

    September 9, 2010 at 1:55 pm

    very useful information

  20. peter

    May 7, 2011 at 12:48 pm

    Hi Jestine,

    I wish to commend you for this forum.

    I JUST started to repair UPS. I am very interested in components replacement in 10kva APC Board. i want to know which components in UPS apc 10kva board likely goes bad.

    there is one i am working at now. there is no output when switch on. the network management card read ac power input, inverter fault, no power output. i have change the battery the problem still remains. what components should i change in the inveter board

    once more your forum has been a great help to me


  21. admin

    May 8, 2011 at 9:58 am

    HI Peter,

    I rarely repair UPS because of the price is getting cheaper and cheaper. Usually problem with UPS is either the bad Mosfet, bad batteries and eeprom data corrupted.


  22. peter

    May 10, 2011 at 9:36 am

    hi Jestine,

    I want to know how to program ups EProm IC with pony prog.i Just started to use is the connection done? which hardware to buy and which port serial or parallel to use. thanks


  23. admin

    May 11, 2011 at 9:36 am

    HI Peter,

    You need to solder the eeprom out from the board and place it onto the board provided by ponyprog. Before this you must have the good hex file of this eeprom data in order to overwrite the bad eeprom data.


  24. chhoton m

    June 3, 2011 at 3:08 am

    In One SUKAM Falcon i Home UPS, the problem is that when I select the UPS mode, the inverter runs ok but when the mains AC supply comes back, the inverter does not run on MAINS, and it continues to run in inverters. plz help me out.
    thanks in advance

  25. admin

    June 4, 2011 at 9:26 pm

    HI Chhoton,

    I'm sure about this model because for other model a bad eeprom data could cuase such problem. Before that you must also make sure your batteries is in tip top condition.


  26. MuneebAhmed

    July 31, 2011 at 2:53 am

    My problems that the UPS are not charge batterre
    please tell me. What do i can . please tell the problems of my
    UPS OK

  27. admin

    August 2, 2011 at 8:03 am

    HI Muneed,

    Have you replace or check the batteries?


  28. Clifford

    July 21, 2012 at 9:11 am

    I have a blue gate UPS, I think the battery is working alright but when plugged, no sign of power is shown, but when I place my tester on the circuit board it shows there is current flowing. Also, it uses the battery power even when plugged to an outlet.

    • Jestine Yong

      July 21, 2012 at 11:57 pm

      Hi Clifford,

      How long the UPS has been in service? If it is more than 2 years then the batteries could at fault. Some batteries will test good with meter but will fail when under load. Not only that a weak battery could cause lots of weird problem and you may think it is the mainboard faulty. You may also need to take noted that a fault EEPROM IC data also could cause many different type of problem.


  29. Rohmell Brills

    September 18, 2012 at 6:51 pm

    Hello Mr. Yong,
    Perhaps you should install special clamshell socket to save wear and tear on your PCB from constant soldering/desoldering.
    Socket such as this:

    • Jestine Yong

      September 19, 2012 at 12:44 am

      Hi Rohmell,

      I've just got one but have yet to use it. Thanks for the tip.


  30. A.T.Sellar

    October 1, 2012 at 12:17 pm

    can a eeprom ic in a circit ,can we read it

    • Jestine Yong

      October 1, 2012 at 8:52 pm

      Hi At sellar,

      You need an eeprom programmer to read those data inside an eeprom ic. Try


  31. Reza

    December 12, 2012 at 1:16 am

    Hi jestine,
    This is Reza, may I ask you to send me any schematics for MGE pulsar max 5000 UPS (if its possible) please!
    Best regards,

    • Jestine Yong

      December 12, 2012 at 7:10 am

      HI Reza,

      Sorry I do not keep schematic-try


  32. Saif Silmi

    September 9, 2020 at 12:41 pm

    Hi Jestin ,
    Is it possible to reprogram the 93C46 epprom for APC 1000Av for upgrade it to 1400AV , i have many APC 1000AV and i want to upgrade it to 1400AV .. if it possible can you tell how ?


Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.