JP 12V 10A switching PSU only producing about 5 volts - Page 1
Forum section: electronics / repair

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 02:02:07 pm
content: HiThe issue is as above.I don't see anything obviously wrong with the PCB.I am aware that working with a SMPS is risky but if there is anything that I could quickly check, I'd give it a go.I cannot find a schematic.Thanks

author: glarsson
author_rank: Frequent Contributor
timestamp: April 17, 2018, 02:07:54 pm
content: A 10A supply with a 7.5A fuse?

author: bd139
author_rank: Super Contributor
timestamp: April 17, 2018, 02:23:36 pm
content: That looks hooky as hell. I'd throw it away.What was it out of?

author: oldway
author_rank: Super Contributor
timestamp: April 17, 2018, 02:36:47 pm
content: Are you a candidate for Darwin awards?Trying to repair a cheap, poor quality, crap power supply without a schematic by making a dangerous repair attempt, you are a good candidate ....Do you own at least a good isolation transformer?

author: CJay
author_rank: Super Contributor
timestamp: April 17, 2018, 02:41:39 pm
content: Quote from: oldway on April 17, 2018, 02:36:47 pmWhy does not having a schematic make anyone a candidate for the Darwin awards?I'd suggest that needing one would make it more likely that you can't think for yourself.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 02:45:36 pm
content: Quote from: oldway on April 17, 2018, 02:36:47 pmNo need for the insult thanks. I have already acknowledged the risks associated with looking at it.It wasn't a cheap eBay or the like purchase and the case is labelled with a well known (in the hobby) brand.The fuse is the one that came with it but I've only typically drawn about 4 amps from it.I don't particularly need it as I have been using my DP832 instead.However, as I said, (if someone recognises the board) if there was anything obvious that it could be, I could consider swapping out the part, just for the pleasure of not throwing it in the bin.

author: CJay
author_rank: Super Contributor
timestamp: April 17, 2018, 02:49:39 pm
content: Post some pics of the underside of the board.Make sure the 47uF capacitor is discharged then check underneath it.Are you measuring the output with load or not?

author: Nusa
author_rank: Super Contributor
timestamp: April 17, 2018, 03:04:18 pm
content: "well known brand" isn't a very useful search term, if you were actually hoping someone would find the schematic for you.

author: grifftech
author_rank: Frequent Contributor
timestamp: April 17, 2018, 03:07:05 pm
content: What is the voltage supposed to be?

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 03:10:03 pm
content: Quote from: CJay on April 17, 2018, 02:49:39 pmThanks for the constructive commentsI have been watching out for the 400V cap, and everything else.There is some browning at the bottom of the PCB but there isn't anything top-side that I can see has over-heated, including under that large cap.The measurement was with a DMM with no load.Thanks again.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 03:10:54 pm
content: Quote from: grifftech on April 17, 2018, 03:07:05 pmI have edited the title to include a 'V'. Twelve volts thanks.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 03:11:55 pm
content: Quote from: Nusa on April 17, 2018, 03:04:18 pmIt is a JP Ultrapower 12V 10A Power Supply 240V.

author: bd139
author_rank: Super Contributor
timestamp: April 17, 2018, 03:16:13 pm
content: Looks like the capacitors overheated. Probably dried out, went short or high ESR and then the feedback goes wonky. The crispy goop on top and the burn marks on the board are the indicator.A big worry is the lack of slots and isolation on that. Not a very pretty design.Even a 7.5A fuse is pushing it by the looks.

author: CJay
author_rank: Super Contributor
timestamp: April 17, 2018, 03:56:47 pm
content: It's been getting hot (that crusty brown glue is a giveaway for that) so, as m'learned friend BD139 suggests, the caps are probably in pretty poor shape but I would also recommend you scrape off that glue as well.In addition to that I would definitely be checking resistor values.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 04:04:58 pm
content: Quote from: CJay on April 17, 2018, 03:56:47 pmSo really, I may as well dump it then. It isn't worth the hassle.Thanks for the input guys

author: CJay
author_rank: Super Contributor
timestamp: April 17, 2018, 04:14:24 pm
content: Up to you, only you can decide how much it's worth, if it's a cheap thing to replace then you're probably right to dump it, if you wanted to learn then it's worth a bit of time and money to repair.TBH, I manage to lay my hands on a *lot* of 12V 3-5 amp PSUs so I don't bother repairing, nor do I bother collecting them all but the skill and knowledge to do so is always handy if I'm stuck with a faulty supply that's an odd value.

author: bd139
author_rank: Super Contributor
timestamp: April 17, 2018, 04:31:30 pm
content: Conversely the last one I repaired caught fire instantly so YMMV

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2018, 04:40:13 pm
content: Quote from: netdudeuk on April 17, 2018, 03:10:03 pmUse a scope and a bulb for a load.Probably output cap stuffed.The brown gunk is that horrible sealant that hardens and gets brittle but worst of all is hydroscopic. Scrape the muck off and use neutral cure RTV.

author: picburner
author_rank: Frequent Contributor
timestamp: April 17, 2018, 05:00:05 pm
content: Looking at the second underside pic it would seem that the transistor (TR1?) welds are all cold.

author: oldway
author_rank: Super Contributor
timestamp: April 17, 2018, 07:07:43 pm
content: Quote from: netdudeuk on April 17, 2018, 02:45:36 pmIf you consider a simple joke as an insult, it's not my fault ....But there are truths behind this joke:1) To troubleshoot a SMPS, it is often necessary to turn it on and make measurements.The voltage on the primary side is 320 Vdc with an unlimited current far exceeding 30 mA.This can be lethal.In the event of an error or wrong operation, you risk not only damaging your oscilloscope, but also electrocuting yourself.2) It seems that you do not have much experience with SMPS, the proof is that almost all the participants of this topic have noticed that it was a product of low quality and technology and you do not .As Dave would probably say if he were to review such a power supply: bullshit.3) to work efficiently and safely, it is better to know exactly where one connects his oscilloscope .... It is, in my opinion, essential to have a diagram.The first thing someone who would have experience would have done is to do some reverse engineering and draw a "DaveCad" schematic at the very least of the primary circuit.You did not do it, which shows no professionalism on your part.So, yes, if you happen to have a serious accident repairing a dangerous smps, poorly made while it is not worth it, you deserve a Darwin Award .... maybe not in the top 15,

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 07:25:59 pm
content: Quote from: picburner on April 17, 2018, 05:00:05 pmYou have good eyes. Yes, it is TR1 and a slight push on it showed all three pins moving freely backwards and forwards.A quick reflow and here is what I see without a load.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 07:32:29 pm
content: Quote from: oldway on April 17, 2018, 07:07:43 pmWell, I know that there are no modern SMPS ICs on there and I can see that it is a SRBP board, not FR4. I can see that there are no slots between the high and low voltages. I've seen Big Clive, etc, go over this time and time again.I had no intention of connecting a scope to it. I have seen Dave's how not to blow up your scope video more than once.The reflow process seems to have fixed the issue. So, apparently, no schematic or a single measurement required.As far as professionalism is concerned, this is a hobby, not a job.

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2018, 07:54:54 pm
content: Quote from: netdudeuk on April 17, 2018, 07:25:59 pmIt's surprising now many PCB faults you can find withjustcareful inspection.Even more when using a jewelers magnifying headset.

author: picburner
author_rank: Frequent Contributor
timestamp: April 17, 2018, 08:17:18 pm
content: Fortunately you did that pic with a particular inclination, impossible to see the defect from the other pics.The instructions in fact say that the no-load voltage is 15V while with the full load it falls to 14V.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 17, 2018, 08:36:40 pm
content: as noted you have cold joint solder on the two to220 transistors / rectifiers and som in the middle of the board, you see small rounds in the solders .... redo the board at first before anything else ... and im sure it is not an 10 amps psu or its the wrong fuse at 7.5 amps on the pcb ??

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 17, 2018, 11:59:33 pm
content: Quote from: coromonadalix on April 17, 2018, 08:36:40 pmI'll do that thanks.Interesting that the 12 volts 10 amps PSU puts out 14 volts under load at no more than 7.5 amps. The PCB legend, the fuse and the manual (http://airtekhobbies.com/downloads/jpultrapower.pdf) all say 7.5 amps.

author: Rasz
author_rank: Super Contributor
timestamp: April 18, 2018, 11:50:09 am
content: Quote from: netdudeuk on April 17, 2018, 11:59:33 pmits normal, those are Chinese ampspeople already told you its a noname garbage, and no, 'jp ultrapower' is not a brand

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 18, 2018, 12:03:17 pm
content: Quote from: Rasz on April 18, 2018, 11:50:09 amNo, but J Perkins ishttp://jperkins.com/

author: LateLesley
author_rank: Frequent Contributor
timestamp: April 18, 2018, 12:38:17 pm
content: NetdudeUK,I'm not saying this to be nasty or anything, or to discourage you from repairing things, but there is a reason many in this thread have been telling you to just bin this PSU. IT is NOT a quality made PSU, no matter the branding on it. You only need to look at the supply to see that. Things you would look for in a quality supply is input filtering with inductors, X rated and Y rated capacitors, and some protection circuitry, of which this has none, bar a fuse - which also happens to be in the neutral line. If that fuse blows, the unit could still be live, and KILL YOU. It is a danger, and a fire hazard.I do commend you trying to fix things, but please also learn when it is worth fixing something, and when to just burn it with fire. Do yourself a favour, and strip it apart, salvage the good components for you to play around with in low voltage projects, and buy yourself a quality PSU which won't kill you if something goes wrong.I only say this in the interest of your own safety.Theres many videos about on PSUs and ones which are dangerous. Here's one example.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: April 18, 2018, 01:12:27 pm
content: Thanks for the reply. I've seen a few Big Clive videos, as per my previous comment.I have another PSU

author: LateLesley
author_rank: Frequent Contributor
timestamp: April 18, 2018, 01:36:06 pm
content: oooooo! Fancy! I'm well jealous! lol! That PSU looks awesome.I've got one of those cheap chinese PSU's, a QW-MS3010D - it's not very accurate and a bit clunky, but it does for what i'm doing, just messing about with stuff, or powering up rails in equipment to find faults. I just make sure to set it with a meter beforehand.https://www.image-tmart.com/prodimgs_v2/8/8802/1713/88021713/QWMS3010D-30V-10A-Adjustable-DC-Stabilizer-Power-Supply-EU-Standard-White_800x800.jpg?1469780213I also recently got my hands on a wee DPS3003, and it's a cracking wee power supply for the money. I use it in conjunction with my MS3010D when I need a bit finer control of voltage and current. And it's great. I highly recommend it. It does need an external PSU to go with it right enough, but for poor folk like me, it's brill.

author: bd139
author_rank: Super Contributor
timestamp: April 18, 2018, 01:55:12 pm
content: If you want some cheap but decent quality bench supplies Look out for Thurlby PL series supplies on ebay. Can score proper bench supplies for £30/40 a pop. I've got a PL154 (15V 4A) and PL310 (30V 1A).https://www.ebay.co.uk/sch/i.html?_sacat=0&_sop=15&_nkw=thurlby%20power%20supply&LH_Complete=1&LH_Sold=1&rt=nc&_trksid=p2045573.m1684Avoid the black and white ones though. The grey ones are top notch however. Better quality than anything HP knocked out for a number of years. Virtually impossible to blow up - they will handle a dead short or running at full load 100% duty cycle all day every day for a decade and just carry on.

author: LateLesley
author_rank: Frequent Contributor
timestamp: April 18, 2018, 02:10:57 pm
content: Thanks BD139. I may just do that at some point, once I get my workbench built. I've been procrastinating for a long time (I suffer from depression) but I'm hoping to get a work area built in the back of my kitchen (I live in an old Glasgow tenement, it's the old bed recess from the old room n kitchen setup). I'm currently faffing about building a couple of kitchen units, and got a bit of worktop to cut which will sit across them, and be my work area. Then on the list is to get a cheap oscilloscope, and start getting through a lot of unfinished projects I have laying around. I'm just trying to get my passion for electronics back, and build up my confidence again. I've had it knocked a lot in recent years.Thanks for the advice though, its good to know from folk with experience. (I just need to figure out now what you mean about the Black/white/grey ones, I cannae tell the difference, except the front panels look slightly different, either two-tone, or pretty solid color apart from the displays.) Thanks again.

author: bd139
author_rank: Super Contributor
timestamp: April 18, 2018, 03:02:03 pm
content: Been there so completely understand the confidence thing. I had a long hiatus from electronics from about 2001-2010 I think it was.Have a look at the following thread:https://www.eevblog.com/forum/testgear/tti-thurbly-thandar-and-age-of-older-models/... horrid ones are the one with the black band and brown cases. There's grey knobs and a push button switch for the current damping on the good ones.

author: Rasz
author_rank: Super Contributor
timestamp: April 18, 2018, 08:42:25 pm
content: Quote from: netdudeuk on April 18, 2018, 12:03:17 pmYes, J Perkins is distributor, not a manufacturing company, they just slapped their own label on ..chinese garbageand lied about true parameters in the process, seems very reputable.