(Maybe solved?) Why is my monitor power supply broken (WITH SCHEMATIC!) - Page 1
Forum section: electronics / beginners

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 06:44:39 pm
content: See attachment for schematic, as well as images of the PCB (front and back, both aligned to proper component location). Power supply from Samsung 245B monitor.Problem: Standby power (5V) is present. When shorting SB power to PS_ON, 24v & 5.3V rails do not come alive.Tested so far: All fuses (3x) are all present. The yellow gunk was originally present on this PCB but has been removed. The output capacitors for the 24v & 5.3v show no bulges (but they were NOT pulled from circuit to test). The main AC filtering + bridge rectifier appear to be fine (120V AC reaches the bridge rectifier, 160V DC on the output). This dead power supply was swapped with a working one and the monitor worked, showing that the backlight, main control, and all other parts of the monitor are working without issue.The problem is isolated to this power supply.Potential issue?: The PFC IC (TDA4863G) IS NOT getting 15.46v at VCC (it's getting approximately 0.3V). In the schematic, I circled where the 15.46V is supposed to be derived (QB802). I however lack understanding of what exactly the circuit near QB802 does and how that circuit is getting power.Notes: There are 3x transformers on the PCB; the one in the center (surrounded by a square of metal;LP801), one surrounded by some component heatsinking (with fins;TM801S), and one tiny transformer (TB801S).Final thoughts: This schematic goes above my knowledge level so I'm not entirely sure what I should be probing and in what order components should be powered. I would have THOUGHT that the PFC IC should be always on, but that does not appear to be the case?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 07:09:07 pm
content: Other schematics:ICE3B0365J(SMPS Current Mode Controller with integrated FET) =https://www.infineon.com/dgdl/Infineon-ICE3BXX65J-DS-v02_09-en.pdf?fileId=db3a3043394427e4013953109b207cb2TDA4863(PFC IC) =https://www.infineon.com/dgdl/Infineon-TDA4863-DS-v02_00-en.pdf?fileId=db3a304412b407950112b427d2d23ce8F9222L(mosfet? Resonance Controller?) =https://www.datasheetcafe.com/f9222l-datasheet-pdf/

author: wasedadoc
author_rank: Super Contributor
timestamp: August 17, 2023, 07:09:51 pm
content: Both the 5 V standby PSU and the 5v/24V PSU are fed from the 292 Volts. If the standby is OK then the 292V is OK and unless BP802 inductor is open circuit the problem is in the PSU at the bottom of the schematic.What is BB803 coming in at the very bottom?

author: BillyO
author_rank: Super Contributor
timestamp: August 17, 2023, 07:16:21 pm
content: C8808 looks like it's bulging.Pull it and test it. If you can't test it just replace it and see if that helps.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 07:21:01 pm
content: Quote from: wasedadoc on August 17, 2023, 07:09:51 pmCP803 (largest electrolytic; image S3) is only measuring 160V DC with my multimeter, which leads me to believe that 292V is not actually working?BB803 is circled in image S4.Quote from: BillyO on August 17, 2023, 07:16:21 pmPlease disregard any yellow goo or buldging caps in S1/S2. I just pulled those high res images from Google.

author: wasedadoc
author_rank: Super Contributor
timestamp: August 17, 2023, 07:22:41 pm
content: Quote from: BillyO on August 17, 2023, 07:16:21 pmIt is CB808. That is in the 5 V standby supply. Even if bulging it isn't going to stop the other SMPS working.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 07:29:59 pm
content: Quote from: wasedadoc on August 17, 2023, 07:09:51 pmOn my multimeter it's showing ~ -18v (yes, negative voltage, in respect to the transformers secondary side ground). In AC mode, ~7v.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 17, 2023, 07:37:39 pm
content: You should see the power after the diode DB871, if not the zener DZB871 might be shorted, but this shoud be OK as 5V_stby is working.Measure the voltage after the diode DB803.Measure or replace CB872 (22u 50V), it might be dry and causing the stby circuit to self-reset, same for CB806(68u 63V).Measure RB803, QB801, RB805, RB806, RB807, and the all the circuitry around CB802 / QB803.Test for short between their emitters and gnd, other circuit might be shorting out the power.Overall, measure everything between RB803 and QB802/803.PSON turns PC802S optocoupler, which enables QB801, who send power coming from RB803/DB803 through RB805-807 resistors.QB802 and 803 will regulate the output voltage: The emitter voltage is limited by the zener diode at the base, thus they're simple linear regulators.QB802 is the only responsible for powering the TDA4863.QB803 powers the main switching ic, F9222L.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 07:53:28 pm
content: Thermal camera testing:When SB power is floating, the only IC to get warm (~30C) is the ICE3B0365J.When shorting SB power to PS_ON, ICE3B0365J remains approximately the same temperature. Resistors RB807, RB806, RB805 get warm (~30C). These 3x resistors have already been replaced with brand new resistors of identical values and power ratings, with the yellow gunk removed. This was from a previous failed solo attempt at repairing this board,image s5.Interestingly (to me), RP820 gets to ~50C and CP810 (image S6) gets to around 60C. The nearby TO220's are not getting hot. These two components previously had the yellow gunk on them but neither have been replaced. I can't find them on the schematic??? I'm inclined to believe one or both of these parts to be faulty?

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 17, 2023, 07:54:33 pm
content: Also check CP811 for high ESR. It's kind of a bootstrap circuit that feeds the Vcc pin of ICP801 (TDA4863) so if this capacitor is bad, the chip won't start.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 08:09:17 pm
content: Quote from: DavidAlfa on August 17, 2023, 07:37:39 pmDB871 = 3.5-3.9V AC, 13-14V DC across the diode. Is not a short, tests as a diode in-circuit.DZB871 = Same as DB871DB803 = ~30V across the resistor, ~ -9V (correct, negative 9v) between secondary-side ground and the diode.Will continue to test additional recommendations, leaving this here for now.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 08:27:09 pm
content: CB809 = 5.1v DCCB872 = 13-14V DC (varying voltage)CB806 = 28v DCCB802 = Jumps to 36v, slowly drops to around 13v, and then jumps back up to 36v.BB802 = Across this component = 0V? I'm not sure how to measure this component.Quote from: LooseJunkHater on August 17, 2023, 07:21:01 pmAddendum to this: When shorting SB power to PS_ON, this capacitor goes to 400V.Quote from: LooseJunkHater on August 17, 2023, 07:53:28 pmRP820 tests as the correct value (~48 ohms), CP810 tests as 0.078nF. The capacitor has the writing "B 101K 1V" written on it, so I assume that's close enough? It's really odd to me that it's running at 60C.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 17, 2023, 08:37:40 pm
content: Quote from: LooseJunkHater on August 17, 2023, 08:09:17 pmDB871: Measure the voltage between primary ground and the diode cathode! (The side with a line mark)Quote from: LooseJunkHater on August 17, 2023, 08:09:17 pmThis is the primary, the secondary is isolated! Measure against the primary ground.The primary ground is the gnd of CB806, CB810, CB872...If you have 30V there, then the problem is in the QB802 area... or in the TDA4863.Measure resistance between primary ground and TDA4863 VCC pin. If very low, remove CP811 and CP805 capacitors near it.If still the same remove the TDA4863. If the short is gone, here's your offender.If resistance test is ok:Measure voltages at both sides of RB808.In diode mode, measure QB802 B-E and B-C.QB802/ QB803: C1008 =2SC1008.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 09:57:30 pm
content: Minor update:I've tested all the components inimage s7in-circuit. Yellow = component tested correctly (capacitor showed right capacitance, resistor correct resistance, diode showed as a diode one-way). Purple = unsure result (since the 3x ceramic capacitors don't have a listed value on the datasheet. None are a short).DM811 was tested out-of-circuit as it wasn't being measured properly.QB803 + QB801 + QB802 do not have any shorts between any of their pins (they could still be faulty or open-circuit I guess? I'll test them later as they're annoying to desolder).Optocouplers not yet tested.Question: For my own understanding, if 5vSB is being created, why am I being told to test components around ICE3B0365J as it seems to primarily create the 5vSB power?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 10:39:25 pm
content: Quote from: DavidAlfa on August 17, 2023, 08:37:40 pmNo short to ground with the TDA4863 (resistance is greater than 1M).QB802 & QB803 show a resistance of 2k between B-E (both directions; there's a 2k resistor present). Diode mode shows 0.6v one way (B-->E), 1.8v the other way (E-->B). No direct shorts for QB802 & QB803. Collector shows 1M+ resistance.QB801 shows no shorts and measures 1M+ between all 3 pins.I was probing PC801S (optocoupler) and noticed a diode-drop both ways when measuring; would this be the fault or is it something in-circuit? Should I remove the part to test it?Where's RB808 on the schematic? I don't see it on the PCB nor schematic?(Disregard this; RB808 + RB809 are 2.2k)

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 17, 2023, 11:26:29 pm
content: Quote from: LooseJunkHater on August 17, 2023, 10:39:25 pmCP811 can still be high ESR. I'd check that if you haven't already.Quote from: LooseJunkHater on August 17, 2023, 09:57:30 pmBecause that circuit supplies power to the PFC circuit via QB801,RB805, RB806, RB807, & QB802, which connects to pin 8 of the TDA4863G.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 17, 2023, 11:45:32 pm
content: Quote from: Kim Christensen on August 17, 2023, 11:26:29 pmBoth caps measure less than 1 ohms and their correct capacitance out-of-circuit using an LCR meter.I now noticed that there is now 13v getting to VCC of the TDA4863 chip. Not sure why I wasn't getting any voltage before but the IC is now getting power. Still no 24v & 5.3v rails.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 18, 2023, 12:03:48 am
content: Now that you have the 13V, it might be worth measuring the voltages in the table:(All relative to pin 6 of the TDA4863)

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 18, 2023, 01:28:47 am
content: QB802 & QB803 are both showing ~13v on collectors + emitters when shorting SB power to PS_ON. QB801 is also working and shows ~20v.ICE3B0365J is receiving 12v between VCC and ground. Drain is showing ~390V DC. There is a 70khz switching frequency between drain and ground, which lines up with the datasheet ("The switching frequency is fswitch = 67kHz"). I now understand why the 5vSB is present.F9222L is also receiving its12v (the schematic says it should get 19v, which I find a big discrepancy. The datasheet doesn't list a voltage range. Could this be a problem?). Using my scope, it appears that the drain2 (pin23) is not switching. After I short SB power to PS_ON, the voltage to the pin climbs to around 30V and then flatlines; no switching at all (is this how it's supposed to work?, per the datasheet? Maybe?). However drain1 (pin19) is indeed switching at 79khz with a very low duty cycle (likely related to minimal load).Quote from: Kim Christensen on August 18, 2023, 12:03:48 amI did measure the voltages and they were pretty close, except pin 3 (which I feel like is related to the measured resistor-chain on the PCB being 1.07M vs the schematics 1,380‬M).1 = 2.5v2 = 2.18v3 = 0.9v4 = 5mv5 = 4v (on oscilloscope, frequency of 640khz, low duty cycle; my multimeter could not measure it)7 = 10v (again, on oscilloscope, frequency of 640khz, low duty cycle; my multimeter could not measure it)

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 18, 2023, 02:37:15 am
content: Quote from: LooseJunkHater on August 18, 2023, 01:28:47 amLooks like the PFC circuit is working then.QuoteDrain2 (pin23) is not supposed to be switching since it's connected to the 392VDC supply rail. Q1 & Q2 form a push-pull output pair with pin23 as the supply rail, pin19 as the output, and pin4 as the ground return via a current sense resistor (RM803).I have this feeling that you are sometimes using the wrong ground reference for your measurements.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 18, 2023, 03:23:58 am
content: The F9222L datasheet says it turns on at 16.5Vcc.30V seems a lot, perhabs there's a problem in the zener controlling QB803.To my understanding both QB802 and QB803 shouldn't be supplying any voltage when PSON is off.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 18, 2023, 06:41:19 pm
content: Quote from: Kim Christensen on August 18, 2023, 02:37:15 amEarlier in my post I was 100% using the wrong ground references since this was way above my knowledge, but I'm getting a better grasp of the circuit. I think I'm measuring things correctly now.Quote from: DavidAlfa on August 18, 2023, 03:23:58 amThey are not supplying any voltage when PSON is off.___I did some repeat probing in circuit. Refer to image S8.At the pink circle (QB801 emitter) the voltage starts at 26.5v (oscilloscope) and then quickly drops to a steady 20.5v (multimeter). At the green circle (CB808) the voltage starts at 19.2v (oscilloscope; image O10.It has a strange waveform?) and then quickly drops to a steady 14.5v (oscilloscope and multimeter; less than 200mv noise, switching frequency ~666khz). At the blue circle (CP811) the voltage is between 13.5-14v multimeter (less than 400mv noise, switching frequency of 70khz and higher frequencies seen as well). Idid notcheck to see if there was a voltage drop at the blue circle.QB803 (red circle) showed a steady emitter voltage of 13v, while QB802 showed a steady emitter voltage of 12.9v (blue circle). I'm wondering if these are both simply not being supplied with a high enough input voltage?I removed CB806 and it's capacitance measured 60uF and less than 1ohm ESR. I'm still wondering if that's the problem (or something nearby?) because of the voltage dropping so quick, as well as that when I used my oscillscope to measure across the capacitor, I did see some 2V 180hz noise (image O9).My idea of the problem?: I'm inclined to believe the problem is somewhat near CB806 because of that quick voltage drop, leading to F9222L not being powered properly. I'm wondering if I decrease the resistance of RB805, RB806, and RB807 (between the pink and green circles) slightly, that it'll increase the voltage high enough for QB802 and QB803 to create their proper voltages. Or is it possible that something related to the optocoupler PC803s is causing the circuit to be dragged down too much?Edit: I also just noticed that the voltage seen at VCC of TDA4863 appears to vary quite a bit between my measurements, from 12.9 to up to 14v, even within this single one comment.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 18, 2023, 07:09:52 pm
content: Just telling, are you aware of the dangers of connecting the oscilloscope to the primary ground?If your scope is earthed, it might cause a huge short between live and earth.No need to say that if you isolate the scope, anything metallic will be HOT!Repeat the procedure, measuring boltage between these points.I've replaced tons of optocouplers which no longer conducted properly (Probably the emitting led was degraded).You shouldn't see more than 100-700mV across theoptocouplerorQB801.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 18, 2023, 07:18:16 pm
content: Also measure the main DC feed coming in with the scope and meter:EDIT: Don't connect scope if the DUT isn't powered via an isolation transformer as per DavidAlfa's warnings below. I assumed this is what you were already doing.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 18, 2023, 07:22:34 pm
content: Quote from: Kim Christensen on August 18, 2023, 07:18:16 pmDude, with the scope?? Good wayto blow it up. Did he say anywhere he was using an isolation transformer?Also, remove the transistors and measure the zeners. That's the voltage you should normally get at the outputs.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 18, 2023, 07:28:31 pm
content: Quote from: DavidAlfa on August 18, 2023, 07:22:34 pmHe's already doing it. Didn't you see his post right above mine?

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 18, 2023, 07:35:32 pm
content: I'm not so sure! He just posted some pictures... But he didn't said he was using isolation?And he's mixing up primary and secondary grounds... It really feels dangerous!

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 18, 2023, 07:56:05 pm
content: You were right to have warned him. He didn't mention isolation, but I was pretty sure that he was already connecting his scope to the "black arrow" in the diagram that he posted with the scope screenshots.Not sure if he's floating his scope, using a differential probe, or using an isolation transformer. LooseJunkHater, which method are you using?Quote from: LooseJunkHater on August 18, 2023, 06:41:19 pm

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 18, 2023, 11:34:00 pm
content: I'll be able to do the additional measurements tomorrow.In regards to probing, I have my oscilloscope ungrounded to NOT destroy my scope. I'm in the process of making an isolation transformer that I'll use on the DUT. Just using a regular 1x10x scope probe.

author: magic
author_rank: Super Contributor
timestamp: August 19, 2023, 12:29:06 pm
content: I suppose it's not exactly ungrounded but "grounded" to the negative of the primary, which is of course at mains potential for 50% of time.For the record, this means the whole scope is live too and any exposed metal part or any external scope insulation failure can give you a kick.Not sure if you really need all that hassle? It looks like so far you are debugging a stupid linear power supply on the primary. It should be enough to probe voltages (with a fully isolated DMM) until you find something that doesn't make sense...

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 19, 2023, 08:12:06 pm
content: Measuring between C-E of:QB801 = 738mvQB802 = 900mvQB803 765mv(I didn't yet measure between base and ground of QB802 + QB803 when removed (to see the zener diode voltages), as I really am trying to avoid desoldering those two transistors in fear of breaking the traces/delamination of this single-sided PCB).The voltage drop between RB807-RB805:3.5v (varying between 3-4v pk/pk, via oscilloscope) initially, then jumps to 6v (5-7v pk/pk, via oscilloscope) and stays there. Further measured the resistance to be 222ohms (vs 204ohms per datasheet).Seeimage O11for the rolling voltage of CB806. CB806 floats at ~28v while PSON is OFF. Upon shorting SB power to PS_ON, the voltage drops to ~24.5v, and then drops further to 21.5v over time, staying pretty consistent at 21.5v.Measuring between both legs of thetransistorsof the optocoupler:PC801S: 2.9vPC802S: 51mvPC803S: 7vMeasuring between both legs of theLED'sof the optocoupler:PC801S: 1vPC802S: 1.15vPC803S: 2.2vBetween Gnd of ICB801S and B292V = 393v DC with scope and multimeter._____I did measure to see whether the drop in voltage of CB806 correlated with the increased V-Drop across RB807-RB805 by using 2 channels of my scope, and they do indeed correlate (Image O12).

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 19, 2023, 10:13:14 pm
content: I wonder if you place a bit of a load on the S_B 5v (Standby 5V supply output) whether that will raise the other voltages enough to satisfy the F9222L's VCC?(placing a load will cause the feedback loop to compensate so that ICB801S increases it's duty cycle)ie: Measure the DC voltage across CB806 and see how much it increases when you put a small load on the 5V standby supply rail. Not sure what it's rated for, so maybe start with 47(100mA) or so. If you know what it's rated for, then try a 50% load.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 19, 2023, 10:18:46 pm
content: 6V through 222ohms is 27mA.Not a lot, but that's where the voltage is dropping to 14V.When you remove these transistors ans check the zener voltage, we'll see what the voltage should be.Probably something is consumign too much current.Lift the diode DM811 or the choke DBM801 (Pin 7 of F9222L),This will isolate the power from it, now check again the voltages across the 3x 68R resistors and the output of QB802 / 803.My guessing is the F9222L is bad or something near it.Check CB, CS, CON, VREF pins.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 19, 2023, 10:40:49 pm
content: Alright so I did decide to remove QB802 and QB803.Image S13shows the respective voltages. For easier Ctrl-Fing, the voltages are 26v, 24.65v, 21v, 15v.Quote from: DavidAlfa on August 19, 2023, 10:18:46 pmI'll put the transistors back in and try this. I did also try shorting across one of the 68ohm resistors and the power supply still did not work, but the voltage at F9222L did raise to 16v.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 19, 2023, 11:38:30 pm
content: Removed DM801. The voltage now at QB803's emitter starts off at 22.5v and then quickly decreased to 17.5v (oscilloscope) and then fluctuates between 17.5-18.5v (multimeter). The voltage at C811 (image S14) is now 14.9v, which is much closer to the schematics listed 15.46v.Further I noticed that the schematic is actually a bit off from what is being done on the PCB.Image S13shows both the original schematic and how it's actually laid out on the PCB. I had actually noticed a minor mistake for a different part of the schematic, but it was simply a mislabel. I'm not entirely sure if this makes any difference.I honestly have no idea what else I should do/test.Edit:Removed image S14, changed withimage S15, made a minor change to RM820, as that was also drawn wrong in the original schematic.

author: BillyO
author_rank: Super Contributor
timestamp: August 19, 2023, 11:47:13 pm
content: Quote from: LooseJunkHater on August 19, 2023, 11:38:30 pmHave you tried replacing CB808 yet?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 19, 2023, 11:59:23 pm
content: Quote from: BillyO on August 19, 2023, 11:47:13 pmNope, but I don't really see why I should. I pulled it out of circuit earlier and I remember it testing fine. Do you really think I should? I guess my scope did show quite a weird waveform when measuring it (refer back toimage O10), but it wasn't nearly as bad as CB806's waveform (image O9, which also tested good)?

author: BillyO
author_rank: Super Contributor
timestamp: August 20, 2023, 12:07:08 am
content: Quote from: LooseJunkHater on August 19, 2023, 11:59:23 pmWell, if it measures the way you said, then replacing it should not make any difference, but since you are out of options and it's an easy thing to do, give it a try. It would not be the first time that normal measurement does not show up a fault. It's certainly in a position to cause grief.

author: xavier60
author_rank: Super Contributor
timestamp: August 20, 2023, 12:44:50 am
content: SMPS control ICs need to see some minimum amount of VCC voltage to become active, usually 16V. When active, the VREF pin will go high, to some specified voltage.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 20, 2023, 12:47:41 am
content: QuoteYes. The other thing on the schematic that looks weird/wrong to me is how the transistor of PC801s is wired. WTF is going on there? They are feeding straight off the transformer and into the emitter of a NPN transistor and then into the feedback pin of the switcher IC! No rectification or anything. That part really makes no sense to me so it's probably another error. Maybe the emitter of PC801s is supposed to be connected to 0v (Pin 8 of ICB801S)?And then they have CYB805S feeding the high frequency switching AC into the isolated ground side.QuoteYou could try loading the standby supplyas I mentioned earlier.I mention this again because they do some odd stuff with the standby voltage feedback path when you enable PSON. (See QB851, RB852, RB853, etc) Seems like they are lowering the standby voltage level when you enable the main switcher supply. Unless this is another schematic error.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 20, 2023, 12:47:54 am
content: Quote from: BillyO on August 20, 2023, 12:07:08 amI replaced both CB806 and CB808 just for good measure, and nope, unsuccessful.Quote from: xavier60 on August 20, 2023, 12:44:50 amI also just tried to externally power F9222L with 19.5V DC (while DM801 was removed) but still, 24V & 5.3v were not created at the output.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 20, 2023, 12:50:38 am
content: Quote from: BillyO on August 20, 2023, 12:07:08 amShould I load it while 5V_SB is connected to PS_ON, while it's floating, or both?

author: BillyO
author_rank: Super Contributor
timestamp: August 20, 2023, 12:53:53 am
content: Hmm, last quote was not mine.However, this is odd. Did your monitor experience a thunder storm or a multiple power failure, or did it just die one day?

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 20, 2023, 12:59:44 am
content: I'd say to get a new F9222L. Maybe you can find new PSU boards for little?

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 20, 2023, 01:06:56 am
content: Quote from: LooseJunkHater on August 20, 2023, 12:50:38 amBoth. Try it first with PS_ON floating. (Supply in standby) Then connect PS_ON to 5V_SB while the load is still present.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 20, 2023, 01:10:15 am
content: Quote from: BillyO on August 20, 2023, 12:53:53 amNo idea, I found it on the street many years ago, not working. I wanted to get it working as a learning experience but at this point I'm beginning to lose faith, especially after voltage injection failed? I'll try to inject voltage in a few more places and see if it works (as well as loading 5V_SB) but I'm losing hope.Quote from: DavidAlfa on August 20, 2023, 12:59:44 amNot worth it. The monitor sells for around $30 used, while the PSU sells for $100+ used. It just makes more sense to buy a different (or same) working used monitor. Realistically if I can't fix this, I'll be e-wasting it.It is really confusing and odd to me that the voltage rails appear to be fine initially, but then quickly drop to much lower voltages. It makes me wonder if there's anything wrong with one of the IC's feedback networks, but all the components within them tested fine.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 20, 2023, 01:17:15 am
content: Quote from: DavidAlfa on August 20, 2023, 12:59:44 amNow that I think about this more, I still do have my other identical (and working) Samsung monitor. I'll consider probing it for voltages and potentially swapping the F9222L between them. This may cause me to have two dead power supplies but considering the monitor isn't worth a lot, it may be worth it.

author: magic
author_rank: Super Contributor
timestamp: August 20, 2023, 04:40:39 pm
content: Quote from: LooseJunkHater on August 19, 2023, 08:12:06 pmPC803S: are you sure it's 2.2V on the LED? That's absolutely pathological. It may be this coupler dragging down power supplies on the primary, as it loads Q801 emitter with all the current it is able to sink.This circuit is weird, some sort of emergency shutdown or whatever?Check again if the coupler is really driven with 2.2V, then find out why.editOr not, because there is 7k5 in series with the transistor side of PC803S.I have no idea what this part is even supposed to be doing here. Schematic error?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 22, 2023, 09:34:49 pm
content: More testing, this time comparing the voltages between the good and bad PCB's. I'm less inclined to believe this to be a 5vSB problem and more of a F9222L problem, or something in that location. I did not attempt to load the 5vSB rail because the voltage of that rail was near-identical on both the faulty and working PSU, in the PSU power-off and power-on states, leading me to believe it to not be a problem in this area (and considering that the voltage of the LED's of the optocouplers being near-identical on the faulty and working PSU).Voltages on the good power supply (shown as: "power supply off*,* power supply on"):PC801s - trans (3.0-3.6, 3.0 steady)PC801s - LED (0.69, 1v)PC802s - LED (1.36, 1.15)PC803s - trans (0.33, 8.5v)PC803s - LED (1.0-1.3, 1.1)PC804s - LED (0, 1.1v)PC804s - trans (0, 1.1)CP811 - (11V on)CB808 - (11.9v on)CB806 - (27.7, 19.7)CB872 - (12.9-14, 10.9)CM802 - (0, 50-58v)RM807-RM805 - (7v on)F2229L VCC - (10.5v on steady)ICE VCC - (13-14v off, 10.9 on)F2229L pin 20 - (380VDC on)(shown as: "power supply off*,* power supply on")PC801s - trans (same, 2.85v) -PC801s - LED (same)PC802s - LED (same)*** PC803s - trans (same, 6.8v)PC803s - LED (1.0, same)PC804s - LED (same, 0v)PC804s - trans (same, 4.4v)CP811 - (14.5V on) ---CB808 - (15.4v on) ---CB806 - (28, 21.6)CB872 - (12.9-13.8, 11.7)*** CM802 - (same, ??-380V (primarily around 300v))RM807-RM805 - (5.5v on)F2229L VCC - (14v-15v on)ICE VCC - (same, 11.7 on)F2229L pin 20 - (?? - 380V (the voltage shoots up very high initially. My scope showed more than 500V, my meter simply shuts down, and then the voltage drops to a steady 380V))___I find it quite interesting how CM802 is a significantly lower voltage on the good vs bad power supplies, as well as that pin 20 of F2229L shoots up really high before dropping. The voltages on VCC of the good board are generally lower compared to the bad board; is this because something is wrong with the feedback voltages or that a device is not drawing the correct power (because of a faulty IC?)?I think I'm going to continue probing components near F2229L and see whether there is any obvious faults.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 22, 2023, 09:36:25 pm
content: Quote from: magic on August 20, 2023, 04:40:39 pmI think I measured it wrong, must have been 1.2v.

author: xavier60
author_rank: Super Contributor
timestamp: August 23, 2023, 12:06:39 am
content: Did you also measure the voltage on the F2229L's VREF pin 10?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 23, 2023, 12:53:54 am
content: At this point, I think I have given up on this. I've probed nearly all resistors near the 3 IC's, no shorts, capacitors test normal, no obvious faults, voltages are present, and all the transistors appear to be working (no shorts, test fine in diode mode).___And just when I was about to give up, I decided, for the hell of it, to remove CM801 and CM802, and you know what the problem was? CM801. Nobody had that on their bingo card.Pulled CM801 out of circuit, it wasn't detected by my LCR meter. What oddly lead me to finally pull these two caps was that when measuring around F9222L, sometimes my multimeter would shut off from that brief 500v + spike, as well as that CM802 was at 50v on the good board but like 380v on the faulty PSU.However the mystery isn't over yet. While I now have 5.4v on the output, my 24v rail is going from 16-9v, likely because I had broke a sot-23 QM801 while trying to test it.Now I need to find a replacement for CM801 (model "Pilkor WK0727") and QM801 (model sot-23 "ZH2H").After many days, I may actually fix this board.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 23, 2023, 02:13:37 am
content: Alright so I can't find any datsheet on the Pilkor part, nor the sot-23. Thankfully with the schematic, I was able to use a C1815 to-92 as a replacement for the sot-23 (which seems to be working fine?). I tried to use a 1uf 630v capacitor as the replacement of CM801 but all I get on the 24v output is ~3v, so I obviously need to go much lower. The schematic says the original capacitor was 630v 100n but I'm not sure exactly what type of capacitor it is (film?)? Maybe someone can help me find a datasheet of the Pilkor capacitor (images attached).

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 23, 2023, 02:55:32 am
content: Looks like it may be a Metallized Polypropylene (MKP) according tothis datasheet.The markings make it look like a 18nF 630V. Hmmm...

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 23, 2023, 03:44:14 am
content: Quote from: Kim Christensen on August 23, 2023, 02:55:32 amWhen I tested the capacitor from the working PSU, it was around 18nf, so possibly another datasheet error.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 24, 2023, 03:54:00 am
content: This will likely be my final post reply here.In conclusion, it was CM801. In the process of finding CM801 I actually damaged multiple SMD components and since I don't have the BOM and can't be bothered to purchase replacement components, this power supply will be left dead. It was a success story in finding the problem and learning a lot along the way, so thanks to all the contributors. However for the next device that I find that is faulty, I'll be able to repair it successfully. Just a few years ago, there was not a chance I would have been able to find this fault, even with significantly more assistance, so thank you.