Behringer X1222USB - Broken SMPSU43 - Page 1
Forum section: electronics / repair

author: ic3solo
author_rank: Newbie
timestamp: August 01, 2025, 03:12:09 pm
content: Hello Repair Gurus,Disclaimer: I am a complete electronics novice and general all-round idiot. Let me know how I can not blow myself up when trying to fix this switching PSU. Thanks.I've had this mixer for several years, and it's basically never been turned off. We had an overload on the house circuit, and I reset the RCD.The mixer then decided not to work properly anymore. Every LED on the panel was flickering in unison (about 4-5 times a second), and pushing buttons and moving sliders only turned more LEDs on and off.I took apart the unit, and discovered that R20 - which was a ceramic-coated resistor - was flaking off, and had some burn damage on the board! Oh no! I did a horrible botch job of removing it.In order for me to fix this, I think I need to:1) Order and replace this broken R20 with the correct one. The problem is, I can't find any schematic of this particular switching PSU on the Internet. To my noobie eye, I don't think it matches..2) I used a ESR meter on the capacitors (whilst in circuit), and despite not bulging, they all look cactus to me. My theory is that the caps went, and then that blew up the resistor.Am I doing it right? Can anyone help with working out what R20 is? And how can I not blow myself up when I test this thing?Failing all that, a new SMPSU43 is about $200 AUD, but that's admitting defeat.Thanks!

author: Kean
author_rank: Unknown
timestamp: August 01, 2025, 05:28:53 pm
content: I know it seems to be labelled R20 (hard to read in the photos), but are you sure it was a resistor? Did you take a photo before removal?The reason I ask is that looking at that similar schematic, as well as the TOP245Y datasheet, it seems that the component there could also be D2 a P6KE200 diode.The P6KE200 is a high voltage TVS clamping diode. It is discontinued, but the P6KE200A is pretty similar and available (e.g. Digikey).If it was a resistor, then one example design in the TOP245Y datasheet has a 68k 2W resistor in that position for a 30W design using a TOP244Y.This is possibly a cost reduction for lower power designs, and the TVS diode is needed for higher power. The example 250W schematic has the TVS and two resistors in parallel with the capacitor.Getting this part wrong won't necessarily stop the PSU from working, but could affect electrical noise emitted by the PSU.Can you check the marking on the multi-pin switching IC mounted on that heatsink - I think it will be TOP244Y or TOP245Y.You may have seen this other post which mentions a repair on the same design, and in addition to the caps being bad a different diode was shorted (D6).https://vk4ghz.com/behringer-x1222usb-power-supply-failure-fix/So I'd suggest making sure none of the diodes in that area are shorted.

author: ic3solo
author_rank: Newbie
timestamp: August 02, 2025, 02:12:31 am
content: Thanks for your reply Kean.No photo prior to removalThe R20 component had the same cream coating as the other resistor, and it looked like the same size and shape.It was a dark greyish cylinder with (what looked like) a thin yellow/gold wire winding around it several loops.The IC is a TOP245YN."Getting this part wrong won't necessarily stop the PSU from working, but could affect electrical noise emitted by the PSU."So I guess I can use my oscilloscope to measure the output voltages to see ripple / noise on the lines? I'm not sure what would be acceptable tolerances for this mixer..I think testing diodes arn't shorted (leaky?) involves de-soldering, and testing both ways with the multi meter?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 02, 2025, 04:25:07 am
content: My 2ctPersonally, I wouldn’t run the PSU without R20. Together with C22 and D3, R20 forms a snubber network across the primary winding, protecting the MOSFET from negative spikes when switching off.SMPS units that stay permanently on mains and fail to start after a power outage often have one of these issues:Open (burnt) high-value resistor from U+ to the switcher IC – I call it the “housekeeping” resistor, needed for initial startup.→ in your case this is made up of three resistors in series: R16, R17, R19 (or maybe R18?). Check their resistance – I can’t read the value clearly (474??? = 470 kΩ). If one of them is blown, the PSU won’t start.Dried-out electrolytic capacitor coming from a secondary primary winding with a diode in series, keeping the switcher IC powered after startup.→ The usual suspects here are capacitors C1 or C3. Measure their capacitance (after proper discharging!) – often they’re down to 1/100 of their original value. Once desoldered, I’d recommend replacing them anyhow.Known for craziest effects (pumping with variations in frequency depending on load) is the main capacitor (400V, xxxµF) when at end of his life by dryout. Discharge it before measure! Otherwise it bites your testing instrument

author: Kean
author_rank: Unknown
timestamp: August 02, 2025, 11:08:59 am
content: Quote from: ic3solo on August 02, 2025, 02:12:31 amBe careful as you cannot measure the mains side safely without a suitable differential probe. There are high voltages present on this side of the circuit referenced to mains earth. You could hurt yourself, or just damage your oscilloscope.But certainly you can measure the output voltages, ideally under load. Dave has a good video on measuring noise of power supplies that might provide some tips.And yes, it is going to be best to remove components from circuit for measurement if you don't know the exact schematic and how to analyse its effects on measurements. Even worse when there could be unknown components that have failed in various ways.Quote from: Uunoctium on August 02, 2025, 04:25:07 amOh the snubber is definitely required to reduce EMI and unintended destruction of the SMPS driver MOSFET, but I was implying that the exact value of the original resistor is probably not too critical.What you call the "housekeeping" resistor is what I believe is typically call the bootstrap resistor, often distributed across multiple SMD parts for increased power/voltage ratings.I agree with your comments on the capacitors. I've just recently been diagnosing/reviewing a batch of failed LED drivers for a client with dried out capacitors.

author: MedievalSpawn
author_rank: Newbie
timestamp: September 29, 2025, 05:58:19 am
content: Hey! did you figure out this component? I have the same exact issue.My mixer was plugged and turned on pretty much 24/7 for 2 years, after a few power outages the thing started flickering all leds same as you.I have blown off c23 and c27 and R20 is flaking off. I can't make up the colors.For what I can see there are 4 bands, Brown, White, White, Gold but that would turn up as 19G resistor! so I don't think that's true.

author: MedievalSpawn
author_rank: Newbie
timestamp: September 29, 2025, 07:34:44 am
content: I took off the resistor and it measured 15.4K (an odd reading for 4 bands, but given gold tolerance, who knows).Since the PSU was working I put the same resistor and replaced the blown caps. It works. No flickering!The 48v rail was only 46 though... but I guess its fine for what it is? (phantom power).

author: MathWizard
author_rank: Super Contributor
timestamp: September 30, 2025, 09:33:49 pm
content: So it's an audio mixer board ? So why do you leave them on 24/7 for years ?? If I recorded music, I wouldn't work 24/7 and I'd turn it off when I leave it. Sometimes I leave my stereo on when I leave home tho.

author: themadhippy
author_rank: Super Contributor
timestamp: September 30, 2025, 09:57:46 pm
content: QuoteBecause the most common time for failure is at turn on,also it avoids the risk of someone powering up/down the sound system in the wrong order which can damage speakers.

author: MedievalSpawn
author_rank: Newbie
timestamp: October 04, 2025, 01:56:48 pm
content: This el cheapo consoles and are perfect for home studios (Like mine) in which I plug in instruments, route my interfaces, and also have multiple sources feeding constantly.My console receives inputs from my TV, Bluetooth receiver, my bass/guitars, and it goes to my Interface that has my near field monitors connected. Those are turned on 24/7 and have been like that for 5 years without any problems.I also route my computer audio and pretty much anything, this is not very uncommon for consoles to stay turned on under desks, the real issue here is the crappy chinese components Behringer used on those SPSUs. This problem is fairly common and they break after warranty so...I spent 2 bucks in caps and repaired it myself, at least I didn't even had to disassemble the front panel that has a shit ton of knobs, faders, nuts.The console is X1222 USB.

author: MedievalSpawn
author_rank: Newbie
timestamp: October 04, 2025, 02:08:13 pm
content: I strongly belive there is no reason for a PSU to go out after 2 years of use! I thought capacitor quality had improved after seeing this problem in the motherboard caps crisys 15 years ago... it's just stupid a somewhat reputable brand falls for this kind of crap. And obviously, that resistor is poor design, it emits way too much heat to the point of messing up with the board. It should be a split resistor or better valued to account for dissipation. They must know this was an issue from design stage.