How to Permanently Disable the Beeping Alarm on an APC Back-UPS ES 500 Battery Backup

An APC Back-UPS ES 500 that needs a little modification
An APC Back-UPS ES 500 that needs a little modification

I wanted to take a recently repaired APC Back-UPS ES 500 Battery backup (I replaced the battery) and have it provide backup power to my AT&T U-Verse modem and wireless access point.  The problem is, I have small children whose rooms are right above this room.  When the power goes out (or the batteries go bad), these APC’s let off an obnoxious piezo-electric beep-beep-beep, which is not cool to your wife when it wakes up the napping kids!!!  I’ve read that you can disable the alarm with the windows software but I’ve not had any luck linking it up with an APC and I’m a Mac user anyway so I just wanted to permanently disable the alarm.  Here’s how you do it:

How to Permanently Disable the Beeping Alarm on an APC Back-UPS ES 500 Battery Backup

Tools Needed:


Step 1: Unplug the APC.

You don’t want to get shocked.

Step 2: Flip the APC over and remove the battery.

I have detailed the steps to swap out the battery on the post below:

How to Replace the Battery in a APC Back-UPS ES 500 Battery Backup

Step 3: Remove the 5 phillips-head screws from the case.

They are located deep in the holes as follows:

Five Case Screw Locations

Step 4: Separate the halves of the case.

Be careful not to lose a screw as they will fall out and hide if you’re not careful.  You will need to feed the positive and negative cables through the slot they feed through the lower case.  The circuitboard may come out of its slot and there are a couple other cables that may become disconnected as you separate the halves, but don’t worry about that–I tell you how to re-assemble it later.

Separating the case halves

Step 5: Feed the battery cables completely through their slot and remove the lower case.

The picture below shows you what you’ll see if everything stays in place (which wasn’t the case for me).  I actually took the picture below when I was re-assembling it because I forgot to take a picture when I was disassembling it.

Lower case removed and all the internal components in their place

The transformer will be loose, the power plug grommet will come out of the case, the reset button will come out, and the circuitboard will come loose too, and this is what it probably will look when you get yours apart (note that the circuitboard came up and out of its slot and the transformer is sitting on the desk out of the case, and a couple wire connectors came off too):

Add caption

Step 6: Locate the alarm buzzer.

Mine was almost in the middle of the board and was labeled BZ1:

Buzzer Location overview
Zoomed-in buzzer location

I considered putting a piece of tape over the hole in the top of the buzzer but when I placed my finger over the hole I still could hear the buzzer quite a bit so I felt like I needed to do something more extreme.  I considered lowering the volume by putting a resister across the buzzer and tried 10K Ohm and 1K Ohm resisters, but that still didn’t lower the voltage any noticeable amount:

Resister in parallel with buzzer

The buzzer must have a much lower resistance than 1K so that is why it didn’t make any difference to have the resister installed.  My single digit-sized resisters are huge and high powered (and there’s not enough room on the back side of the board and I didn’t want to waste a $4 resister) so I opted to take it to the next level…

Step 7: Remove the Buzzer.

I took some solder braid and removed the solder from the back of the board.  I then grabbed the buzzer on one side and pulled gently on it while I heated each leg individually and popped out the buzzer.   With my light behind the board you can see the round silhouette of the buzzer through the board:

Solder point locations for buzzer–note you can see the silhouette of the round buzzer through the back-lit circuit board

Here’s what it looked like when I got it out:

The removed buzzer

No more buzzer:

The buzzer is long gone

Step 8: Reassemble your completely-quiet APC.

The first step for me was connecting the white and black wires under where the circuitboard sits.  Note that the color of the wire is imprinted on the plastic behind the connectors:

Black and white wire connector locations under the circuitboard

Step 9: Reinstall the power button (if necessary).

Mine came off so I snapped it back on the push switch:

The power button put back on its switch

Step 10: Guide the circuitboard back into place.

Watch to make sure the power button goes in its hole.  There is a slot on either side of the case, which holds the circuit board in place:

Circuit board slot on one side of the case

Step 11: Make sure the transformer is in its place.

There is a square spot in the case for it to set:

Transformer in its spot

Step 12: Re-seat the power cord grommet.

It is round on the side that goes in first:

Power Cord grommet in place

Step 13: Re-seat the reset button (if necessary).

It has a place moulded into the case to hold it in place.

Reset Button back in place

Step 14: Run the wires back down in their channel in the case.

There is a groove in the case designed to run them through:

Wires down in their channel

Step 15: Feed the battery cables through their slot in the lower case.

Feeding the battery cables back through their hole in the case

Step 16: Re-seat the lower case and reinstall the screws.

I actually installed the battery at this point, before reinstalling the screws just to make sure it was working correctly.  Be careful that the battery connections are tight.  When I replaced the battery in my other post I took a pliers and squeezed the connecter closed a bit so that it made a good connection.

Reinstalling the lower case screws

Step 17: Reinstall the battery.

Step 18: Reinstall the battery cover and battery cover screw.

Step 19: Plug in and press the power button (it may be on already though).

The LED is green when it is on and working correctly.  Now you have a completely silent APC.  You will need to monitor the led light because it now will be your only physical indicator that the APC is running correctly (aside from any software monitoring you may have installed):

Power LED light is green–you are back in business (and completely quiet)

All my APC Battery Backup Posts:

Other relevant links:

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  • I simply removed the cap from the buzzer. No soldering required, just grab a pair of pliers and yank it off. You can reduce the volume of the buzzer by loosely putting the cap back on. The looser it is, the quieter it becomes.

    • Good idea Aaron–that will give the future readers an option to desoldering. I happened to be soldering iron happy that day so I attacked the problem with the tool at hand. Thanks for sharing.

  • Glad to share this info with you and other web-cruisers seeking info about this model of UPS.

    The contacts are formed out of continuous strips of metal and placed within slots in the case. The “grip” is a function of the springiness of the strips, but APC apparently missed a metallurgy class or something to impart the necessary magic because the contacts just lose the will to spring.* As mentioned, APC had this problem in other products so this seems a fundamental design issue rather than a bit of poor QC.

    I suppose with much futzing you could bend them back and make them work. For a while, until they give up again.

    But I wouldn’t bother since A) you’ll never truly overcome the design flaw and thus will still have a cheap fire hazard under your desk, and B) you you can pick up a very nice high power metal cased APC Smart-UPS without batteries, add a 9617 network card or similar, all for $50-100 on eBay etc. Then pick up new batts at a local battery supply house. You can have a very nice very expensive UPS for a fraction of what it cost new. No company wants to sink money into APC replacement battery packs since they tend to be crazy expensive, so they just buy new, especially when the IT mentality is all about the 2-3 year life cycle. I also notice IT depts are just clueless about actually fixing anything, and the idea of buying aftermarket batteries and taping them together is just overwhelming! Too bad for them, good for us, because APC batteries are commonplace AGP batteries with a sticker on them. They’ll cost you a bit for a good brand (don’t buy the cheapest possible) but again at the end of the day you’ll have a wicked nice UPS that you would never buy new.

    One more comment about the Smart-UPS line in particular: They do have a couple of quirks that you need to learn about, like the “battery constant” issue which is a variable stored in the brain of the UPS to calculate run time. The constant is adjusted by the UPS as the batteries age, and it needs to be reset when installing new batteries. Otherwise, the UPS will do weird things like run for a minute on brand new batts then shut off, which leads the IT guys to conclude it is impossibly broken forever and it gets surplused. You can explore this issue on links such as this:

    Also note on that site a reference to a utility called “apcfix.exe” that makes resetting the constant to the factory values. It works well, once you get past the Russian language issue.

    The other noteworthy quirk is that some of the very old Smart-UPS models maintain the batteries with too high a float charging voltage which shortens battery life quite a bit, cooking them and sometimes bulging them in the process. Sometimes to the point you have to take the UPS apart to get them out.
    See here:

    Saving the planet, one piece of gear at a time.

    *I’m sure this is how engineers would describe this.

  • Not surprising. I’ve been using the 500 as a heavy weight press since learning about APC’s crappy company and their equally anal customer DIS-service.

  • John,
    A WARNING about the Back-UPS series by APC: I discovered a serious issue with an ancient Back-UPS 725, the same design as your 500, where the receptacle contacts lose tension over time. It was the contacts for the hot & neutral connections failing, but not the grounding one. The good tension of the ground masked the fact that the other two were a high-resistance potential fire waiting to happen. I happened to discover this accidentally when I picked up the UPS and the ungrounded 2-prong items plugged in simply fell out!

    Moral: Might want to check yours for this condition, and remove it from service if it has this problem. Cut the cord off so when you get rid of it nobody tries to put it back in service.

    Ironically, APC had a line of plug strips the same vintage as this UPS series that were subject to a recall generated by the CPSC due to fire hazards associated with weak contacts. Probably the only reason this UPS series didn’t get similar attention is because nobody plugged in high current loads to a unit this small, minimizing the meltdown potential.

    • Haef, thank you for taking the time to comment! I will need to check the receptacles on my UPS. I have mine in storage at the moment so I’ll need to wait till it comes back out. Did you see a way that they might be repaired? When I had mine open I wasn’t looking at the receptacles. Thanks again!

  • What’s causing it in the first place, if:

    1) The load does NOT exceed 500 VA and

    2) The battery checks out at 13.4 volts, even after the buzzer goes off

  • Hi,

    I want disable no load feature of this APC UPS. As it takes only high load i want to make to operate only for router, charger without PC connected. it will turn off automatically if low load connected. how to disable this no load feature?

    • Thanks for the question Shiv. I haven’t had to deal with this issue but I did some searching and found a solution here. Please check back in and let me know if you try it and if it works for you.

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