Stig Vidar Hovland

Repair instructions for APC Back-UPS RS 500

I have two of these units with the same fault and I have also read about this problem on usenet. The problem is that the Back-UPS RS 500 stop charging the battery. For me it was easy and not expensive to repair them. If you have some experience with soldering it should be easy for you too to do the repair work.
Before you start, remove mains power and the battery. This unit is generating high voltage from a 12 volts battery and a battery like this contain a lot of energy. Please take notice of any safety precautions.
Front panel
Here is the front panel with model name. I suppose yours are similar.
Back panel
Remove the two screws on the back panel
Opening, step 1
Lift the panel out at the bottom. It snaps in position at the top and you maybe have to use some force to take it off completely.
Removing side panel
Lift out the side panel and disconnect the red and black battery wire. Make sure you know where to reconnect those wires when assembling the unit.
Control panel
Take a sheet of paper and make a drawing of the circuit board and all the wires to the transformer and back panel. Disconnect all the wires and remove both the transformer and back panel.
Removing control panel
Remove the circuit board on the front panel.
Main board
Remove the main board. It is fastened with two clips on the back side.
Main board overview
Main board with the faulty capacitor.
Main board, charging unit
Charging unit and the faulty capacitor.
Capacitor polarity
Make sure you take notice of the polarity of this capacitor.
Capacitor specifications
Replace the capacitor with a new one with similar or better specification. I bought mine from here: Elfa 
Charging voltage
After the unit is assembled, connect it to the mains and measure the voltage at the battery terminals without a battery connected. It should be approx. 13.6 Volts.
Charging battery
Disconnect from the mains and mount and connect the battery. You probably have to buy a new battery if the old one has been completely discharged and been like that for several weeks. Batteries are easily damaged if discharged over a long time. Connect it to the mains and measure that it is charging the battery. The voltage should be rising slowly up to 13.6 Volts.

Comments (129) -

Thank you for this very detailed fixit. My RS500 failed a few days ago with this problem and replacing the capacitor (with a 33uF 35v component) does seem to have fixed it. I'm watching the battery charge back up again as I type this.   I wonder what causes this capacitor to fail? According to my meter it is open circuit and exhibits no capacitance at all and that is a very unusual failure mode!  Anyway, thank you again for a very timely posting - you've saved me from spending some money on a new unit. The power of the Internet!  John L (G3WGV), England.

Thanks, fabulous tip, I above thank for you and the people like You Ricardo

It worked like a charm i replaced it with a 22uF x 25V 85°C Capacitor it works!! Now i have to check if the battery is dead... Thank you a lot

thanks, my RS 500 again live. Mirob, Slovakia

Same problem here!!! Thanks for the tip, I'll fetch the soldering iron ASAP 8-)

APC said my battery had died, but I tried this and my UPS is as good as new! Unusual that this is happening on a large number of devices, and disappointing that APC gave me the wrong "solution" when I even linked them to this page to see if they would admit the capacitor was at fault. However, as an electrical engineering student, this was very fun too! Thanks so much for your advice.

muy buena solucion hace meses que buscaba la solucion. Gracias ( thanks you)

Replace with a 105c cap not a 85c that was in it. A 85c cap works good with 60hz, A switching power supply has a much higher freq and a 85c cap with over heat and develop high ESR, due to drying out. Clarence Southwest Monitors & Printers POS SWMP@VERIZON.NET



Cured mine fine, I think I may replace the other caps as several are reading a bit high with my ESR meter, the faulty one would not give any reading. now all I need is some non corrosive silicone to dampen the buzz from the inductors. Ben. NB I used a 105c 35V 22UF low esr capacitor. Thanks for saving me the time of finding the fault.

Desde Buenos Aires Argentina, agradezco sinceramente de corazon, la solucion brindada por este tutorial.- Ya daba por perdida mi confiable APC RS 500, cuando descubri esta solucion, por la decima parte de un dolar , volvio a tener vida la tan valiosa ups.- Recomendare este link en los foros de electronica sin duda.-Gracias a su autor.-  Thanks !!!!!!!!

Desde Buenos Aires Argentina, agradezco sinceramente de corazon, la solucion brindada por este tutorial.- Ya daba por perdida mi confiable APC RS 500, cuando descubri esta solucion, por la decima parte de un dolar , volvio a tener vida la tan valiosa ups.- Recomendare este link en los foros de electronica sin duda.-Gracias a su autor.-  Thanks !!!!!!!!

The C7 had used a 50V 22uF 105c with unknown manufacturer. Other caps are gold color Jamicon.

Este tutorial es excelente, le cambié a 4 UPSs el condensador y están cargando perfectamente.  Gracias de nuevo.

Hello My name is Willan  Can you help me? I have have a UPS APC BR1500, and in this moment it is on OVERLOAD state, I repleced the batt and it dont operate, so I see all the electronical elements and I did not found nothing  Please, if you have any idea you can help me?  PD I am sorry my english is very very bad  I from Ecuador

Hi folks, it worked for my APC. It was 1 year broken and now it is charging a new battery. Thanks U and the web.  Sleyo

Excellent fix!! I was just about to buy a replacement UPS. Many thanks.  Neville      UK

Do you have anything on fixing power relay?  My unit charges the battery but when unpluged from external power it fails to transfer load to battery supply.    Harry

Using another apc product. Everything is fine except circuit not charging the battery.  How to identify the batery charging capacitor? How do you check faulty capacitors?

Indeed works.  Thanks  

Congratulations on the capacitor replacement instructions -- but I have a different problem with my RS500 (BR500I, 240 V version).  It's a new unit, and as soon as I plugged it in it started to give off a scorching smell that has not gone away after 24 hours. The hot spot seems to be near the top vent, on the left-hand side as you look at the front of the unit.  This is a replacement for an RS500 that failed with overheating around R28 on the main board -- I suspected the K2608 MOSFET nearby but am not enough of an electronics person to be confident of diagnosing a fault.  Does anyone else have experience of overheating with these units?

Thanks from Finland friends.

I have one exactly the same problem and the capacitor replacement indeed fix the problem.  regards, john_t Subic Bay, Philippines.

BCB was burned around R28 of my APC, even plastic case was bit melted

My UPS disarching battery, what problem?

hi in my unit the large resisters have been damaged (burnt out) can you please post or email me there codes or values thanks  par_0020 hotmail.com

Where can I find repair solutions like this for my APC BackUPS 500?  It is operational with power coming from the battery but when AC power returns, nothing happens. It operates as if there is no AC power at the input.  This is a very good repair guide here.

Hello, I have same issue with overheating, I have two RS500 with smoked top and PCB, one of them was deformed by high temp just above R28 and R29. I also hear some stertorous noise when main power cord is plugged into UPS. How to fix that?  Thanks.

I forgot to mention, there are different dates on PCBs, older one is APC C2001 08/03/2002 640-0259_REV05 and second one is APC C2004 640-0259A_REV06, both have same issue and newer one overheated more.

Sorry, but I can't help you here. I have a few RS500, but all of them are working and in continous use. It isn't easy for anyone to tell what is wrong with your units, but if someone has experience with this spesific problem, please send me some text and photos and I could add them to the blog.

I bought one of these last week and i already want to throw it away. The buzz is killing me any sugestions? Would realy apreciate it. Thanks

i have the same problem, but i have bought a new one, prolink ups. when i read your post, i tried to fix the problem. first thing that i do is plug the power cable and turn on the power. but no sign of power on (no lights on). do you think that if i replace the capacitor, ill fix all the problem?? please reply, i really need your help. thanks

up side very hot one of place]  how i repaire

i've repaired 2 unit (same symtom) and it work like a new one, by replaced all cap (85->105c) i hope it won't need any cap replacement again for 2-3 years Laughing

I wish I had the same fault..... Got a new CS 650  that is driving me crazy with the charger control circuit with audible noise. You wouldn't believe it but the noise is comming from  a RESISTOR # R3 on this rev6 board. (March 2008) I've never heard of a resistor making this much noise. Has any tech experienced this - however works yet it produces high frequency noise. Weird.  Capacitors  - chokes are fine.

Well, designers of this circuits were… (censored)  I have had the same problem, analyzed the switching power supply and found the same problem. Consulting the data sheet of UC3842B, the 22µF capacitor seems to be underestimated.  At least in RS500 230V version REV05 one of resistor around eats permanently about 2 Watts and generates a lot of heat.  That is why I decided to do a more radical change:  Replace the capacitor with much larger one: 220µF.  Remove the parallel 3.3kΩ resistor R139 without any replacement.  Replace large hot 50kΩ resistor R28 by 220kΩ of the same size (probably even more is possible).  It decreases power current by 2 Watts and temperature there by 40°C at cost of 1 second delay after connecting the power plug.  Purpose of such modification:  Original design used a very hard divisor that divides the plug voltage to supply ~10mA. It is nearly enough for running the oscillator, so 22µF was (nearly) enough.  But the divisor should be used just to start oscillation. Once the oscillator runs, it is powered from the transformer and the divisor is not needed. You can verify this fact by disconnecting the large divisor resistor, touch, and remove. Oscillator runs.  The datasheet says, that when there is no power to run oscillator, the IC eats less than 0.5mA.  It means, that the divisor could be designed to provide only 0.5mA, not 10mA.  In this case, capacitor must be larger (e. g. 220µF), because the complete start of the oscillator is powered nearly exclusively from it. It must have enough juice to keep voltage above the minimal voltage until the transformer start to give power.  Happy hacking  Stanislav, http://www.penguin.cz/~utx/

Following an overnight power surge I noticed in the morning the three lower leds flashing continuously and no backup power. So I soldered off of an old  pentiumII motherboard a 16V 22μF 105C capacitor and replaced the one shown in this tutorial. I plugged in and for a few seconds the three lower leds flashed till the power on (green) led lit (I guess meaning that the battery was completely uncharged and now it is charging).  Many thanks again

Hallo.  I just documented my more radical modification described above:  http://www.penguin.cz/~utx/apc-ups/  Apropos, if anybody is able to read values on R138 and R150, please let me know. My UPS had them damaged so it was imposible to measure them or read the value. They are replaced by 10R on my images, but I am not sure, whether it is correct.  Thanks, Stanislav

Hallo,  Thanks a lot for this repair instruction - the best I've ever seen! My RS 500 is now working again, I used a capacitor with 47uF/16V because it was sunday and there was no original capacitor in my box. RS500 runs very well with 47uF!  best regards,  Bill from Germany

We have the same problem ,it was not charging the battery so i have seen your procedure for repairing and now it is up to the mark   Another thing plz tell us the specification of Resistor R28 in  circuit boared of UPS .    Junaid

I had two apc 500 units with this problem, both of them are fine thanks to you! So thank you twice!  Alkis from Athens, Greece

Newer version of RS 500 unit with 50V 22uF capacitor fixed with replacement from an old Base10-T network card.

100uF/35V 105C Works Smile  Matony

Thanks a lot. My APC BR500i work again.

Last month, during a power failure I plugged my APC BE500U-CN into a120V generator that has the ground potential of 40V and now it started beeping, and does not offer any battery backup power. The battery measures 13Volts AND THE units battery charging leads show 13.5V with battery removed. any ideas how to fix?

Could somebody tell how to disable the alarm in this model... apc  rs 500... take in account that I not an engineer....thanks  dapal55@yahoo.es

Following an overnight power surge I noticed in the morning the three lower leds flashing continuously and no backup power. So I soldered off of an old  pentiumII motherboard a 16V 22μF 105C capacitor and replaced the one shown in this tutorial ( I plugged in and for a few seconds the three lower leds flashed till the power on (green) led lit (I guess meaning that the battery was completely uncharged and now it is charging).

Kindly tell the value of resistance R28.


resistance value R29 email at peweelocsin@yahoo.com

It is a very nice tutorial. I found it when i did a research about repairing my CS 500.  When the unit is connected on power source there is a yellow light "On battery", even when there is no battery inside. The unit won't turn off. Do u have any idea what i should do?  Thanks in advance.

Thanks for the nice tutorial and great solution to my problematic rs 500.  I would like to help some other users and publish values of resistors that may be erased because of overheating.  R28 = 50K 2W 5%, R29=3,3K 2W, R75=2,2R 2W, R157=20R 1/4W.

I just replasced the capasitor and the r28 resistor and it works!

Excelente tutorial, recupere 2 UPS.

Hi, I have have a UPS APC CS500, and in this moment it is on OVERLOAD state.

I have just repaired my ups using your instructions.  

Hi, I have have a UPS APC RS1500, and in this moment it is on OVERLOAD state. how i repaire

Almost one year following heimes' instructions, [comment 8.11.2009: A zillion thanks!! Following an overnight power surge I noticed......uncharged and now it is charging). Many thanks again], my rs500 died again!!! I followed the more radical modification www.penguin.cz/~utx/hardware/APC_UPS_RS-500/  and guess what:  It's ALIVE again (cost <1euro)  Many thanks to all the electronics gurus

This text help me solve similar problem. On CS500 from AC input it goes to fuse(SMD) then to gretz(4 diode) and to charger. After gretz it has similar capacitor(10uF 450V 85C) which was blown and made short circuit dameging PCB(+&- undernith capacitor are VERY close), blowing fuse and stop charging battery(and not doing self-test). After replaceing capatitor, fuse and repairing PCB everything OK! Thanks

can anyone confirm the "radical modification" (www.penguin.cz/~utx/hardware/APC_UPS_RS-500/) works also on cs 500 rev06? thanks marco

Muy bueno el articulo si no es mucha moelstia podrian ayudarme a buscar el diagrama del APC UPS RS-800 el problema es que se apaga  por ratos Gracias

i am manjula i want 600VA ups circuit diagram my mail id-sntmanjula@yahoo.com

Thank you very much for that great tutorial! Greetings from Patagonia Seb

Worked perfect for me although I did not see any damage on capacitor on my RS 500. Greetings from Switzerland

Looking at the pcb, I founded these two resistors, C65 and C66, are snubbers that protect the contacts for two of the tree existing  relays; there are places not populated for the third relay (C67 and R152). I think that two relays are used for the regulation of the AC incoming from the wall, and the third is for transfer the supply from AC to inverter during the outages. Perhaps the best decision is to replace the resistors for other  of 10 ohm, but made from metalfilm and with 1 watt or more.  I replaced C7 and the unit satrted to work fine again, but it is very noisy now, at least it seems to me with the whole circuit of the original case; is the any clue for the reason of this?.  Excuse me by my basic english, is not my native language; tahnks!.  Hernán

It's working!!! I'll write a dissertation about this)))!!)!)!)!

thanks, my RS 500 again live. mclareniak, Slovakia

Work!!! thank for the tip! cómo descubrio la solucion?

Sorry.... Brain bug: P  how  discovered the solution?

i thing this is the diagram of the circuit  www.eserviceinfo.com/.../APC_UPS%20500.html  thanks for the post VNC

where can i buy the r28 resistor or what ever its called from ? mine has burnt out and make the case turn yellow  i found the capacitor  in the 1st post on ebay but dont know any thing about r28 so any info would be good.  thanx

I have replaced C7 Capacitor and my UPS started to charge the battery again. Thanks for the article.

Thank you very much! It was the same problem for me, but how you've understand that problem is in this capacitor? In my case bad capacitor was 12uF --- it's not very bad. Original value was 22uF, 50V. More over, may be you know, Is is a capacitor problem or bad circuit design?

My UPS RS 1000 is not holding on battery supply for more thant 30 second.. Pls advice me.

Now it works ,Faults was in power storage!It fail to store power for along time.  

Hi,  i am planning to use RS800 as inverter , off-grid power  do you know who to bypass / reset the relay to switch to battery mode without prior ac input

My Back-UPS RS 500 rev 06 is back in duty with new 22uF/50V/105c for nearly no cost ;) Thanks!

Hi,  I have have a APC BACKUP-UPS 800, and in this moment it is on OVERLOAD state. When I checked the out put connections with line tester it shows both wire live ( Phase & neutral ). Please let me know the problem. Thanks in advance.  bk35@hotmail.com

anybody here knows how the RS 1000 works or have circuit diagram here

Thank you man. Very useful guide. Thank you again Smile

what should i change or modify if APC Back-UPS RS 500 use with large battery..

Helo, Thanks for your advise regarding RS-500 Repairing , it really works,.  I am planning to have manufacturing UPS, Assembling UPS, so can you provide me detailed information to how to assembling/manufactre UPS.   Email : gisplindia@gmail.com Contact : +91-9428222374  Thanks dear ,  From : Dhaval Chauhan, India.  

Thanks very much. Changed the cap and all is well.

thank master..solved my problem

My UPS mother board is completely different, and i could not figured out which capacitor was faulty. mine is Indian version, can somebody help me??  baba dot maal gmail.com  Thanks

Thank you!  A-P,Finland

Thank you so much for posting this.  At C7 I used a 47uF 35v 105C cap I had hanging around ands it seems to be fine.  Nice one.  Thank you.  Jon (Australia)

I just made Stanislav's modification on a REV06, it works nice now. So after some years you still deserve a thank you everybody Laughing !

can my br500 replace the battre with 12v 50ah?

how about the socomec sicon ups net0600-pe how to repair .. the ups is not charging, what should i do to  repair ..., anybody there can help.. thks   cris (philippines)

thank lot for share i can fix the problem on my UPS RS500 just change another one cap 22 mF with a new one  thnks so much

I have a Ups APC CS 500 I changed all transistors and few capacitors. Ups shows me is overload and off. What are the possible faults on Ups, some of your suggestion ? Help me, thank you,  Best regards, Nikica Subat (from Croatia).  

Thank you very much for the information. I searched in google for the same fault that I have with model RS 800 and suddenly I found information for model RS 500. 1 year it was unused into my storehouse with the same fault. I changed the capacitor, which seemed to be okay with a new and repaired the damage. Thanks again for your help for a component with the least of cost repair my ups. If anyone know what is the corresponding capacitor for model RS 800 with the same fault please report it here.

Hi all!  I've an apc rs800 Ups shows me is overload. I'm changed the battery's. The 12V and the IC11( KA7812 ) good!  Another apc rs800 Ups is switching between inverter and AC mode.  What are the possible faults on Ups, some of your suggestion ? Help me, thank you, Best regards, Frank webmaster100@freemail.hu

Hi to every body, i have the same problem, but i've got another motherboard, exactly 640-0287c_rev08  , and I can't find the capacity mentioned before. Is there anybody with same problem and same mb, that have solved ?

thank you   flavio (Italy)

i have apc sc 620 if power on ups continious ly buzzer and red light on and no 220 volts out put

My UPS indicates the beep tone as A\C not connected, but power cable had been connected to the main line (fuse and power wire also good). whats wrong with it? (inverter works well)

Hi,  I need PCB scanned TOP Layer and Bottom Layer of APC UPS 700, APC UPS 1000 and APC 250I UPS.  Thanks  umerbajwa94@hotmail.com

BackUPS RS 500 - rev 06. It have alredy 105C version, but have same problem.  I replaced it with 22uF for now with 85C, only one I had at home now.  Old one showed me about 1.5uF only - so really bad one. Now I can see that UPS is charging.  Really thank you !!!!

how can i fix it....some one help.thanks

your advice really helps me, my RS500 has wait getting dust in my storage room since 2005, I has resisted to put in trash. Now it looks like new one. Thanks  Saúl (South America, Peru)

I Have a APC bakup UPS PRo 800 with the Overload and replace batteries leds blinking....After changing the batteries the ups doent stay on Online mode but only stays in On Battery...What can i do to fix this? It is not a battery problem!  jstrotos@gmail.com

UPS was not charging the battery i have find that the IC7 was busted i cant able to finde the IC number if any one have the same model ups please send me the IC number my email id is kanda_rcs@yahoo.com

I have a problem with my APC 650 that when i connect the battery to ups and connect it to line it is not charging and overload light turns on and a beep continuous beep tone starts, when i turn on ups on battery same thing happens, please help me for some repair , fahad.farooq7013@gmail.com

Can anyone tell me the model of mosfet's monted on radiator on model CS or RS 500 ? marian_d_89@yahoo.com

Hi...  I have an APC RS-900 model, new batteries but no changing.....any Ideas?

Hey....please help me to inform the type of push button switch used in PCB for power ON OFF.... robinaghera007@gmail.com

Hi, I have both these models with me but the specified R28, R139 and C7 doesn't match. Here C7 is a SMD Capacitor, couldn't trace R139. C50 & C51 are 22µF 400V - replaced with 47µF 450V but no luck. C2 & C5 are 22µF 25V - replaced with 220µF 35V, still no luck with stopping battery getting discharged easily. R28 is a SMD resistor of 50KΩ and habe a large 150KΩ resistor R77. I couldn't find either 2SK2608 or UC3842B in the boards. Please hrlp to solve this problem. sameasin@gmail.com

Guys, You're all the hidden gems of this lovely world of ours. I've been reading your posts from Nigeria, 'cos of my 'Smart Power' UPS which lasts <1 min with my router (and your wildest, craziest imaginations can't come close to the horrid power situation here).  Anyway, my unit's problem seems much different. Any1 know how to test the batt or unit for the drain? Bought the batt in dec 2012. Much appreciated. Again, pls keep up the good work. Joseph. debaj10@gmail.com

First: Thank You Very Much!  This Article showed me the way to repair my UPS. It seems like it is a common faulty design around the UC3842/3/4/5B along many UPS's manufacturers.  In my case it was an UC3845B with a defect C25 (47µF/50V/105°C). According to the dust-marks on the inside of the top it was obvious that there is a very hot spot around C25 during opperation. The 105°C specification alone is not a warrant for continious opperation. Obviously the capacitor has lost its electrolyte without leaving a trace (no marks around it and no deformation of the cap - like I've seen many on broken PC-Mainboards).  Now I have replaced C25 with a general-purpose-capacitor with the same values and the UPS is opperating like a charm (again) - Horray! - I will replace it with a high temterature low-ESR-type very soon and hope for the best that it will work seamless over the next years.  --------------- Zuerst einmal: Vielen herzlichen Dank!  Dieser Artikel hat mich in die richtige Richtung zur Reparatur meiner USV gelenkt. Es sieht so aus, als ob es ein generelles Problem bei der Beschaltung rund um den Baustein UC3842/3/4/5B gibt, der von vielen Herstellern von USVs eingesetzt wird.  In meinem Fall war es ein UC3845B mit einem defekten Kondensator C25 (47µF/50V/105°C). Aufgrund der wärmebedingten Staubablagerungen an der Innenseite des Metalldeckels war ersichtlich, dass es in der Gegend um den Kondensator im laufenden Betrieb recht warm wird. Also alleine der Einsatz eines Kondensators mit einer Spezifikation von 105°C ist kein Garant für einen langen Betrieb. Offenbar ist das Elektrolyt doch im Laufe der Zeit verdampft ohne sichtbare Spuren in der Umgebung zu hinterlassen (auf der Platine ist nichts auffälliges unter dem Kondensator zu sehen und er ist auch nicht aufgebläht, wie ich es von defekten Hauptplatinen in PCs kenne).  Ich habe jetzt erst einmal einen Wald-und-Wiesen-Kondensator mit den entsprechenden Werten eingesetzt und die USV arbeitet wieder ordentlich; den werde ich aber zügig durch einen Low-ESR-Typen mit hoher Temperaturfestigkeit ersetzen. Ich hoffe danach für die nächsten Jahre an dieser Stelle keine Probleme mehr zu haben.

My CS650 cut the power to the load. I do not know why but I changed the condenser 22uF and I found that it have only 10uF. I see a warm cap with 470uF and I chage it, I measure it and it have less than 300uF. Now the UPS is working well.

Found burned capacitor c10 with 10 microfarad high ripple capacitor.  Still no dc output to battery.  I don't have any diagrams and neglected to map the wire plug on connections when making the repairs.  At present, I have no 110 vac input to the transformer at the point where the primary is connected to the board.  Any pictures of a connected board out there so I may check my reconnection of the xformer to the unit.

Has anyone gotten an answer or fix to the overload situation on the RS 500...   If so, please email me at jims-msn@hotmail.com.   Thanks,  Jim

Hi, I have apc ups. I heard a small blast and found that a coil inside ups had caught fire. Can anyone plz advice what this coil is. Will replacing only this help?

My APC Back-UPS RS550 not charging.  Fuse, IC TNY274 , 400V caps replaced. Still not charging. Pls help me.

Hi, My apc rs800 not charging plz tell me capacitor number i dont find this capacitor. plz tell me . smart_tech74@yahoo.com  Thanks

shekar avadhani
shekar avadhani

first of all thanks very much for a detailed explanation and repair suggestions.
I have the same UPS but a new one but same specifications.
My batteries kept running down in short intervals and finally I replaced
the battery with a 17Ah battery lead acid battery.(old one was 7Ah) .Initially
worked fine for six months or so but after that It stopped working beeping
intermittently indicating  low battery voltage, but when I checked battery
voltage it was 12.45 Volts and slightly high when in charging conditions.
Now it is not at all shifting to Invertor state(when AC  supply fails ).
I did check electrolyte levels looks alright.Can you suggest what to do ?
warm regards in advance

Scott James
Scott James

this also helped me repair a Fenton Power Pal 660 UPS.  It had a loud buzzing from the primary relay on the AC input (Charging circuit?).  I found a small 47uf 25v electrolytic capacitor that looked like a similar charging circuit you describe.  After replacing that capacitor, it is not buzzing any more and working great. thanks!

nice work

click meter
click meter


I have a APC rs 800, and in this moment it is on OVERLOAD state. I just inserted the new battery and tried to reset. I have noticed that there are three electrolytic capacitors in the inverter circuit. If you can send me info on clickmeter@hotmail.com Thanks in advance


Mohamed karamany
Mohamed karamany

Thank you so much, your instructions helped me to fix my unit...

I have APC RS800. I need schematic diagram.Send me email please...


I have an APC RS800.  At sensitivity 1(High) and 2(Medium) it clicks all time. At 3 (Low) = no clicks. On mainboard is 1x3300uf/35V, 2x10uf/450V and 1x390uF/50V. Could be a bad capacitor ?
Thanks !

shekar avadhani
shekar avadhani

It would be better to run it in Low sensitivity if your mains power supply
is reasonably with in limits.The problem you are facing might be some other
devise connected in your house which is drawing more current and varying the
input voltage to your APC. Try measuring voltage of mains input to the APC if
you find it changes and at speedy intervals of time, then check any other devises
connected and their intermittent on/off s.
A rare condition might be if anybody in your near neighborhood are using Arc welding
unit which usually draws lot of current like 40-60 Amps which is also culprit of varying
input AC voltage to you APC and the Clicks.keep me posted the results.

Hi !
I think it is a capacitor because APC was left with no power for 24h. At power on with Low sensitivity I heard few clicks from relay after that no clicks. Could be from a capacitor because ... when APC is heats up it is works well at low sensitivity.