Dell proprietary PSU repair [SOLVED] - Page 1
Forum section: electronics / repair

author: spilihps
author_rank: Regular Contributor
timestamp: June 09, 2016, 09:52:21 pm
content: Hello!Well, i decided to try to better understand how a PC psu is built, and since i had an dell SFF with a bad psu sitting, i thought that would be a good project. Turns out it may not be.I opened it up, and found that there have been black dust expelled from the W7NK90Z MOSFET (its completely shorted when measured out of circuit), and also that the top of a mysterious IC on a "daughterboard" had blown of. (see picture)For starters, i cannot find any info about the CL2181 IC, what it does or how it works, neither any replacement, well i found replacements in china though..I did some poking on the little daugtherboard and found that the large mosfet is connected to the IC:ICpin1 = sourceICpin3 = gateAlso found that a resistor called R301 (cant see the value, either there were no printed from the start, or it have gone missing in this) is open circuit. The rest seem OK though.The question is. Can this be repaired? What else to look for? What value of resistance to replace the R301 with? Can the CL2181 be replaced with something else, more widely available?It would be a fun and a good learning exercise to do this repair, but maybe im in over my head. Also it would save a nice computer, that has less value than a replacement PSU on ebayAny help and input in this would be greatly appreciated.Thank you

author: wraper
author_rank: Unknown
timestamp: June 10, 2016, 01:28:59 am
content: Just get one on ebay or Aliexpress.

author: spilihps
author_rank: Regular Contributor
timestamp: June 10, 2016, 07:34:35 am
content: Yes i think i will do that then.But i really need some way of figuring out the value on the resistor though..

author: wraper
author_rank: Unknown
timestamp: June 10, 2016, 09:09:47 am
content: You haven't said to what that resistor is connected. How someone can tell the resistance if there is no schematic and unknown where it is used.

author: wraper
author_rank: Unknown
timestamp: June 10, 2016, 09:21:44 am
content: All I can find. But in this schematic it is connected to the mosfet through the transformer.

author: spilihps
author_rank: Regular Contributor
timestamp: June 10, 2016, 11:05:24 am
content: Hello.Thanks for your help.The R301 is connected this way:CL2181 pin1 -> R301 -> pin3(Source)MOSFET

author: raz221
author_rank: Contributor
timestamp: June 10, 2016, 12:06:05 pm
content: Maybe I'm missing something, but where exactly is this resistor you're talking about (in the picture you've posted)?All I see is a transistor, a chip and 3 electrolyte capacitors. Also, it might help if you'd provide the full model number of this PSU.Quote from: wraper on June 10, 2016, 09:09:47 amBy the color coding and a simple online resistor calc:Code:http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-4-bandEach resistor has color coding (4, 5 or 6 bands) which specifies it's unique resistance value.I always use this calculator before measuring resistors (unless I have the schematic), and sometimes get em out of the circuit for verification if I get the wrong value or no reading (if they're connected in parallel with other ones, the reading can be inaccurate). But the above only applies to regular (metal or carbon film) resistors of course. For SMD resistors, some of em have the resistance value written on em (which often requires a magnifier to see), and for others, you really can't tell without having the schematic. But even if you got the correct value (and the resistor turns out to be faulty) sometimes manufacturers use custom-made resistors (with non-standard values) which can make repairing difficult.

author: wraper
author_rank: Unknown
timestamp: June 10, 2016, 12:49:39 pm
content: I guess that likely is SMD resistor. You can check if the circuity around pin1 and pin 15 is similar and check the values. If R221 on you picture is close in value with your circuit, then there is a good bet you can use 2.7k instead. Also check if the resistors connected to the source are fine, they tend to blow up together with mosfet.

author: spilihps
author_rank: Regular Contributor
timestamp: June 10, 2016, 04:19:04 pm
content: wraper, thank you again very much for your help.Yes its a SMD resistor.Ive done some quick checking on the circuit diagram that you provided, the R221 is the same exact value as on my board. Also, the circuit around those pins seem to be the same. I also checked some of the others, and they seem to be the same also..Thanks for the tip about the resistor, and this is the resistor for the source, so you are right there also i guess?

author: wraper
author_rank: Unknown
timestamp: June 11, 2016, 01:40:11 pm
content: By resistor to the source I mean some higher power resistor(s) which passes all of the current from the source to GND (most likely). Not this resistor which is solely for feedback.

author: spilihps
author_rank: Regular Contributor
timestamp: June 12, 2016, 03:07:10 pm
content: Hello yes, sorry i misunderstood you the first time.And yes, i have a resistor that is connected to the source that is also OCit is red, violet,silver gold, so i guess its 0,27ohm?Will be very interesting to see if this is infact repairable, seem to me to be a rather large "crash?"The components found bad this far:IC301 CL2181R301 (2,7kOhm according to the above circuit)Q102 MOSFET W7NK90ZC125 102K capR105 Red, violet,silver,gold resistor.Again, thanks for your help and input.

author: wraper
author_rank: Unknown
timestamp: June 12, 2016, 03:10:23 pm
content: Yes, it's 0.27R. Be sure to use replacement of not lower power than original is, can be estimated by it's size. Fault happened in the way it usually does. BTW MOSFET model is STW7NK90Z. 102K is 1 nF 10%

author: spilihps
author_rank: Regular Contributor
timestamp: June 13, 2016, 04:57:11 pm
content: Now i made some research about what resistors to choose. ( I have sourced the CL chip from china, so it will be a loooong wait)The larger 0.27R have a diameter (on the thickness part) of 3.45, and length of 9.46 and the one that comes closest is a 1/2 watt. Do you think this would be safe?The SMD resistor, i looked just on the gap between the pads that seem to be correct with 0603, that says 0.9 and i got 1.0 when measuring the board..I used the charts at resistorguide.com

author: wraper
author_rank: Unknown
timestamp: June 13, 2016, 05:28:07 pm
content: Quote from: spilihps on June 13, 2016, 04:57:11 pm1/2 W or 0.6W resistors usually are much smaller. Use 1W or small 2W metal film resistor. Likely you looked on dimensions of some crappy carbon film resistors.

author: wraper
author_rank: Unknown
timestamp: June 13, 2016, 05:31:52 pm
content: As you can see from the following table, in such size it can be even 2W resistor.

author: spilihps
author_rank: Regular Contributor
timestamp: June 13, 2016, 05:38:01 pm
content: Oh i see. And yes the chart said "carbon and metal film". So i guess that chart is nothing to trust.Good catch..I use a 1W then. Better look for another SMD-chart also to be sure

author: damn_dirty_ape
author_rank: Contributor
timestamp: June 14, 2016, 02:39:15 am
content: This is probably repairable with the right equipment, which might be worthwhile if you're just trying to learn, but from a practical standpoint you should probably just get a new supply. Repairing surface mount stuff takes a lot of practice, and I've totally destroyed a couple boards by not using the correct equipment

author: spilihps
author_rank: Regular Contributor
timestamp: June 14, 2016, 07:33:58 am
content: In this case, the power supply is not worth getting for the money they are asking. Seems like these supplies fail often. And the time invested is the price for learningYes SMD parts can be a hassle, but i have experience with it and the only SMD part in this case is a resistor, and its already out so no drama there.Thanks for your input also.

author: spilihps
author_rank: Regular Contributor
timestamp: June 16, 2016, 09:09:05 pm
content: Hello again.Tried to send you a PM (wraper) But i dont think it worked.However, tonight im trying to source the parts, and i was just wondering if you have any idea of what wattage and voltage the 0603 SMD resistor should be in this case?

author: spilihps
author_rank: Regular Contributor
timestamp: August 09, 2016, 09:44:07 pm
content: Late update on this.So ive manage to source the parts, and meanwhile i did find several more that needed to be replaced, so ive done that now.Still no go though.The PSU does now source +5v standby, but nothing happens when grounding the green wire.. Also It seems though that the +5v standby is completely separated from the rest of the psu.When grounding the green the only thing that happens is that i can hear a very very very faint high pitch sound and that output goes from 0,000v to 0,001v.There seem to be no voltage over the optos LED pins during this time either..Any input on what to test and/or measure from now is greatly appreciated.Parts found bad so far:IC301 (CL2181)R301 2,7kOhm smd resistorR104 0,27RC125 102KQ102 W7NK90ZR51 1R (To the 5v supply)FuseQ104 KSP2222A (transistor for one of the optos) it had E-B fail

author: stj
author_rank: Super Contributor
timestamp: August 10, 2016, 05:58:48 pm
content: post a foto of the main area where the fet is.i bet it has a snubber ceramic and a fuseable resistor to one side.this issue sounds like a similar problem on a newer psu.

author: spilihps
author_rank: Regular Contributor
timestamp: August 10, 2016, 08:42:48 pm
content: Hello!Thanks for your helpIve attached a picture of it here.Ive got a tip from another user to measure the voltage over the optocoupler during the moment it tries to turn on, and for a brief second it actually rises.Dont know if this rules anything out completely?

author: wblock
author_rank: Regular Contributor
timestamp: August 10, 2016, 10:49:08 pm
content: A failed Dell power supply, with L-tec capacitors (not the worst of the worst, but not the best of the worst, either)...Even if those L-tecs checked out okay on an ESR meter (they might; it's happened), I'd replace them all. That involves measuring all their dimensions (height, diameter, lead spacing) and trying to find the spec sheet to get something close to their claimed ESR. If it was worth it, which it probably isn't, but it sounds like this is a learning experience or quest.

author: stj
author_rank: Super Contributor
timestamp: August 11, 2016, 01:17:31 am
content: if that snubber cap is 1Kv rated, and discoloured then uprate it to 2Kvthere is a newer supply that fails a lot (as in - all of them!!!) because the snubber cap is under-rated and cooks until it fails killing the fet and blowing the control circuits.

author: spilihps
author_rank: Regular Contributor
timestamp: August 11, 2016, 04:19:09 pm
content: Quote from: wblock on August 10, 2016, 10:49:08 pmHello and thank you for your reply. The small blue one is to the left of the FET is one that i replaced because the other one was blown, it was a brown one, marked with 102k, and replaced by this that is also a 102k. the exact type i can look up on my order sheet if necesarry. And you are completely right, this is a learning experienceQuote from: stj on August 11, 2016, 01:17:31 amHello and thanks for your helpThe small blue one is a new one that ive replaced, because the other one was blown, it was a 102k.However the large blue one, checks OK with capacitance measurments, so i left it.Could that one be causing it not to start up?

author: stj
author_rank: Super Contributor
timestamp: August 11, 2016, 07:26:19 pm
content: if the fet blows,you have to check *everything* related to the controller.meter every resistor, and diode.and look for burns on the controller i.c.

author: spilihps
author_rank: Regular Contributor
timestamp: August 11, 2016, 07:44:56 pm
content: Quote from: stj on August 11, 2016, 07:26:19 pmThe controller is replaced, and some components surrounding it that also did not check out OK.The thing is that measuring the voltage over the opto, directly when plugging it in, it jumps up a bit, and then shuts of. Probably some safety thing.Now, does that rule out the primary side, or can it still be both sides?

author: stj
author_rank: Super Contributor
timestamp: August 11, 2016, 08:42:58 pm
content: it could be the opto - i have had one that was bad

author: spilihps
author_rank: Regular Contributor
timestamp: August 13, 2016, 04:01:25 pm
content: Sorry, i forgot to mention in my earlier post, that i replaced all three optos, just to be sure. Eventhough they did check out in a test circuit

author: wblock
author_rank: Regular Contributor
timestamp: August 13, 2016, 04:37:09 pm
content: Quote from: spilihps on August 11, 2016, 04:19:09 pmElectrolytics can fail and still show reasonable capacitance. An ESR check is the only way to really know.

author: spilihps
author_rank: Regular Contributor
timestamp: August 13, 2016, 04:48:58 pm
content: Quote from: wblock on August 13, 2016, 04:37:09 pmThanks for your input!Alright. I do not have access to a ESR-meter, but i may just have to get hold of one thenHowever, just to be sure we are not chasing the wrong part.The thing that it for a breif second gives output to the Opto and then shuts of. Can this be because of this electrolytic? Feels like the safety circuit kicks in or something like that?

author: stj
author_rank: Super Contributor
timestamp: August 13, 2016, 07:21:57 pm
content: from experience, you will *eventually* find some smd resistor that does not meter the same as it's markings or a bad smd diode.when i was fixing the newer ones, it was a real pain in the ass.http://www.badcaps.net/forum/showthread.php?t=50864

author: spilihps
author_rank: Regular Contributor
timestamp: August 13, 2016, 09:56:00 pm
content: Sorry, iam not following you?

author: stj
author_rank: Super Contributor
timestamp: August 13, 2016, 09:58:39 pm
content: the link was an expample of how much damage can happen.

author: spilihps
author_rank: Regular Contributor
timestamp: August 13, 2016, 10:14:51 pm
content: Yeah that is almost exactly the same amount of damage that mine have,except only the main fet was shot..So i wonder were to go from here

author: stj
author_rank: Super Contributor
timestamp: August 13, 2016, 10:18:57 pm
content: if the fet shorted either high voltage pin to the gate pin then your testing all the resistors.

author: spilihps
author_rank: Regular Contributor
timestamp: August 13, 2016, 10:22:04 pm
content: The fet was shorted to all three(!) legsIve checked all the non-smd transistors. And i Went over the smds also, but only for opens since those were still in circuit.

author: spilihps
author_rank: Regular Contributor
timestamp: August 22, 2016, 04:33:57 pm
content: Hello again everyone!Well, i invested in an ESR-meter. (EVB)And it arrived today.But, it seems like the suspected caps, that are 102k, and 103M and such, are not fit for testing like this. Ive tested them out, and it just "-" so i thought, great, their bad.However, i had 8 brand new 102k laying around so i tested them also. Same thing with them. And i did double-check with my DMM, and sure enough they measure OL.. Even though they test fine in capacitance measurement..So it was kind of a bad investment at least for this project.Dont know how to go further with this now..

author: wraper
author_rank: Unknown
timestamp: August 22, 2016, 04:55:37 pm
content: ESR meters are for testing electrolytic capacitors. Ceramic and film capacitors don't need for ESR to be checked. Also, below about 0.5-1 uF you won't be able to check ESR anyway. For checking such capacitors, measuring capacitance and checking if they are not leaky (checking DC resistance, should measure like open) is completely enough.

author: spilihps
author_rank: Regular Contributor
timestamp: August 22, 2016, 05:05:25 pm
content: Thanks wraper.In the previous posts, it seemed like i needed to check these caps also. But no problem. I will probably have use for this handy ESR-meter later on anyway.However, i really dont know were to go from here now..

author: stj
author_rank: Super Contributor
timestamp: August 22, 2016, 06:08:05 pm
content: check all the smd resistors with a meter set to ohms setting.

author: wblock
author_rank: Regular Contributor
timestamp: August 23, 2016, 01:29:24 am
content: Quote from: spilihps on August 22, 2016, 05:05:25 pmCheck all the electrolytics on that board.

author: spilihps
author_rank: Regular Contributor
timestamp: August 23, 2016, 11:46:29 am
content: Hello,So im back from checking the electrolytics, (with my new handy ESR-meter) and they all seem to be within spec, on both primary and secondary.So i checked all the smds and also the "regular" resistors, they are all good. And for a while ago, when i replaced the PFC-chip, i had that "daughterboard" out and then i know i checked all of them on that one too.Now, it have a second "daughterboard" that have a power-management chip on it. I Have had that one out also, but i may need to yank that out again, since im not 100% sure ive checked all on that one, as i am with the pfc-board. I think i did.That one is on the secondary though.

author: spilihps
author_rank: Regular Contributor
timestamp: August 23, 2016, 02:48:51 pm
content: So ive yanked out the board with the WT7507 on it.All the resistor tests OK, also the transistors pass diode-test, likewise the regular diodes.However, with the ESR, ive found that three of the very small electrolytics (16v 22uF) gets around 8-10ohms resistance. This is way up it seems. The charts say it 0.8 on those.I have no idea if those even could make this fault?

author: stj
author_rank: Super Contributor
timestamp: August 23, 2016, 04:42:29 pm
content: they are bad, and they are obviously needed.

author: spilihps
author_rank: Regular Contributor
timestamp: August 25, 2016, 04:50:47 pm
content: Yep, replaced those.Still the same fault.So, both "daughterboards" caps, and resistors are checked. All the mainboards resistors and caps are checked.Now i really have no clue what to do next..

author: wraper
author_rank: Unknown
timestamp: August 25, 2016, 05:43:33 pm
content: Quote from: spilihps on August 23, 2016, 02:48:51 pmIf those are of extra small size, then such ESR is likely OK for them. 0.8 is a bit too low for 22uF 16V, expect up to a few ohms for such.

author: stj
author_rank: Super Contributor
timestamp: August 25, 2016, 06:34:13 pm
content: they are low esr caps.

author: spilihps
author_rank: Regular Contributor
timestamp: August 25, 2016, 06:53:52 pm
content: Well, no problem.. Those were a longshot anyway.Any tips or ideas on moving forward on this is appreciated..It would be great to atleast confirm what specific part of the PSU the problem lies?

author: wraper
author_rank: Unknown
timestamp: August 26, 2016, 05:13:30 pm
content: Quote from: stj on August 25, 2016, 06:34:13 pmFor what reason they should be? They are not filtering any of output power rails, nor experience any high ripple current.

author: wraper
author_rank: Unknown
timestamp: August 27, 2016, 09:16:11 pm
content: Check if there is power on pin 4 of CL2181, referenced to GND, (pin 10)

author: spilihps
author_rank: Regular Contributor
timestamp: August 27, 2016, 10:30:27 pm
content: I dont Think i can get a probe to that pin when it is mounted on the mainboard.However, i may be able to see in my notes if that pin is connected directly(via some resistor or something) to a pin on the mainboard.I know that after having the cl2181 board out several times, there is no open Connections on it. i will see what i can come up with

author: wraper
author_rank: Unknown
timestamp: August 27, 2016, 11:02:33 pm
content: solder a wire to it.

author: spilihps
author_rank: Regular Contributor
timestamp: August 28, 2016, 10:53:56 am
content: Hello.Wraper, thank you very much for your help.I get ~1.6v on it. And it jumps to ~3.8 just when first turned on.. (it could be more if the DMM is not fast enough)Edit: ~ is approximately, not AC

author: wraper
author_rank: Unknown
timestamp: August 28, 2016, 11:04:14 am
content: too low, start searching from there.

author: spilihps
author_rank: Regular Contributor
timestamp: August 28, 2016, 11:39:30 am
content: Alright,So it is connected directly from the board, to the Q104 transistor (That i replaced, the OPTOcoupler one)The collector of that one is connected via a resistor and a zener to a larger "island" that is interconnected via jumpers, to another large "island" that have one leg of the main cap.This is also connected (to the left of the board instead) to the source of the large FET.Does this make any sense?

author: spilihps
author_rank: Regular Contributor
timestamp: August 29, 2016, 03:53:06 pm
content: Alright. So, tracing some further. that is directly connected to one of the legs on the little board with the thermistor and the relay i was talking about.Does it give us any hints?Edit: will desolder the zener and test it OCEdit2: The zener might have fooled me in circuitIt measures ~0.150v both ways and likewise ~150ohm both ways?How can one identify it. The only readable text on it is "16" the rest have been under the manufacturing glue(i think)

author: wraper
author_rank: Unknown
timestamp: August 29, 2016, 09:14:38 pm
content: likely it is 16V rated. post a photo

author: spilihps
author_rank: Regular Contributor
timestamp: August 29, 2016, 09:22:44 pm
content: Here is a Picture.It measures 3,45mm in lenght

author: wraper
author_rank: Unknown
timestamp: August 29, 2016, 09:26:44 pm
content: to which parts it is connected?

author: spilihps
author_rank: Regular Contributor
timestamp: August 29, 2016, 09:46:25 pm
content: Lets see if i can take this by text!CL2181 pin 10 - Emitter on Q104 (npn transistor)Collector on Q103 - > resistor -> one side of zener parallell with one of the optosThe other side of the zener is connected back to the cl2181 board(not sure of what cl2181 pin) and parallell with source of large mosFETMake any sense?

author: wraper
author_rank: Unknown
timestamp: August 29, 2016, 10:21:36 pm
content: Should be zener, 16V also seem to be about right. Find some 16V replacement. You also can use a 2 lower voltage zeners in series to achieve needed voltage.

author: spilihps
author_rank: Regular Contributor
timestamp: August 29, 2016, 10:44:42 pm
content: Great I will see if I can find one. Don't have any on hand thoughIt seems to be SOD-80, and 16v what about zener-resistance?

author: wraper
author_rank: Unknown
timestamp: August 29, 2016, 10:57:00 pm
content: Quote from: spilihps on August 29, 2016, 10:44:42 pmIt this case any 500mW zener should work fine. Most likely it is used only for overvoltage protection of the IC. Normally it shouldn't clamp anything IMO.

author: spilihps
author_rank: Regular Contributor
timestamp: August 29, 2016, 11:03:19 pm
content: Alright!Will get one in a couple of days, you think that it could be causing this problem as it is right now?

author: wraper
author_rank: Unknown
timestamp: August 29, 2016, 11:08:47 pm
content: yes, it seem to short the power of CL2181.

author: spilihps
author_rank: Regular Contributor
timestamp: August 29, 2016, 11:48:03 pm
content: Great!Hard to wait for the diode thuough, haha!I do have another PSU-board that have zeners on it in the correct package. However, they are colorcoded like brown,blue,blue, no clue about the voltage or anything

author: Voodoo 6
author_rank: Regular Contributor
timestamp: August 30, 2016, 01:12:53 am
content: My Gateway 960 had an odd ball power supply, mainly for SCSI termination (3.3 vdc) to the SCSI back-planes. Here is what I did, I obtained a nice power supply and cut the connectors off the old power supply and wired them in. If the dell has a special plug going to the motherboard just snip it off and connect the wires accordingly. The other plugs are usually the same 12 / 5 volts dc going to the drives. Its fun to explore but digging out all that old potting is never fun. The original Compaq's use to have the low profile power supplies and getting the originals were fairly expensive, but we did manage to find a 3rd party vendor.

author: spilihps
author_rank: Regular Contributor
timestamp: August 30, 2016, 11:32:16 am
content: Quote from: wraper on August 29, 2016, 11:08:47 pmwraper, SUCCESS!!!!i found two 8v zeners laying around, hooked them up! It started right up! I almost dont believe it!Also now the relay clicked. It didnt do that before.Just one last question, i measured the 12v rail, and actually it seems a bit low. It comes in at 11.5v. Now this is completely unloaded with just the DMM hooked up. Maybe it have something to do with that?Edit: Hooked up a HDD as load and it went up to 11.8 so i guess we are alright?

author: wraper
author_rank: Unknown
timestamp: August 30, 2016, 12:11:01 pm
content: Congratulations!Output voltage is independent from that. It is compared against reference on the secondary side. Primary side only "knows" if it needs to increase or decrease PWM duty cycle depending on the signal from optocoupler. Also as there are multiple voltage rails with shared regulation, it is not perfect and voltage can change depending on how much each rail is loaded.

author: spilihps
author_rank: Regular Contributor
timestamp: August 30, 2016, 01:13:41 pm
content: Again, thank you for all your help!Then everything seem to be ok! I will order the right SMD zener and put it in!What do you think may have caused a failure like this? Seem to be kind of common.Is it the FET that die of age, or is there something else causing it?

author: wraper
author_rank: Unknown
timestamp: August 30, 2016, 01:38:58 pm
content: The first part to fail, most likely, was either mosfet or CL2181, all other things were consequences of everything going haywire. Reasons can be different, like hidden manufacturing fault or some transient in the mains, overheating under heavy load.

author: spilihps
author_rank: Regular Contributor
timestamp: August 30, 2016, 01:53:40 pm
content: Alright! Good to know. Well see how long it will run then.The CL2181 is a suspect since that one is found online in different circuits but it failed in the same way.Ive checked the main filter cap ESR, and it seem to be fine atleast..

author: wraper
author_rank: Unknown
timestamp: August 31, 2016, 10:17:58 am
content: Quote from: spilihps on August 30, 2016, 01:53:40 pmMain suspect is mosfet as power parts fail the most often. When it fails, PWM controller IC goes bust in most cases too, regardless of it's model.

author: spilihps
author_rank: Regular Contributor
timestamp: August 31, 2016, 12:31:18 pm
content: Alright. Yeah, it have both a thermalpad, and it had dried up thermalpaste, so ive removed the old and replaced it with new. It may very well have overheated the FET actually when thinking of it..