Uni-t ut61e ohms/capacitance - Page 1
Forum section: electronics / repair

author: algorithm
author_rank: Regular Contributor
timestamp: July 29, 2022, 09:35:44 am
content: meter bit the dust. Everything works but resistance and capacitance.Been struggling to get anywhere fixing this. Ive tested lots and found nothing that made me sure.So on resistance I get resistance with the leads separate. I think around 15k but it varied. Its not self zeroing anymore to OL.On capacitance mode I get a capacitance reading with leads separate. Iirc 0.230 µF. Well my meter used to not have that reading. I think it would show OL until testing capacitance. But I read many people saying their meter had Nywhere between 0.50-0.300 µF but if anybody could clarify on that? Guess its irrelevant if testing is accurate but it appears like it wouldnt be due to the stray µF?So I have a spare meter of ut61e. Comparing between boards the following differences. But the boards themselves arent identical. Working ut61e ommits r36a-d and r39 at least. Also different placement of transistors footprint and some side waffling. Or pancaking rather cause theyre flipped.like r29a-r32.Bad --------------- goodD5 and D6 give short beep. But removing thrm they test good. Q5 and q6 also made me suspect them with beeps but they were good off board. On good they dont beep even on board lol.On ca+ it reads 47k for bad. On good 220 ohms. (I dont have a meter to test pF but I thinks thats supposed to be 1pf?.)I get 3.6 M ohm resistance between common and r6 and that yellow line wiper track on bad5.16M on good.On q1 emitter that has continuity to common, testing from collector and base to common post was 3.5M ohm on bad. But now after lots of testing that resistance is missing from q1 and q8 on both boards. Weird.Do any of those things give any clues? I again am limited by my meter only reading so much capacitance. (Fluke 12).I tried reading resistance on the small capacitors to do with ohms. Like c7, c13, c14, c15 and c16.But I saw such random results I couldnt trust it I felt. But testinv now my fluke does show a difference on c13-c16. On bad its 7.5 M, on "good" its 3.65M. Weirder I saw that but opposite earlier. The bad had 3.65M. And the "good" 7.65M. So I have no confidence or trust in that. But I figure I might have triggered something via transistors? To have seen it both ways both boards... I put good in quotations because Ive not confirmed the newer ut61 is calibrated perfectly. But its a unit out of the box.thanks for any advice or ideas.

author: Per Hansson
author_rank: Unknown
timestamp: July 29, 2022, 12:06:42 pm
content: Did you actually test it when you removed the protection devices Q1/Q8 and Q5/Q6?I suspect the fault will be there, if so removing them should make it behave again untill you can buy some new replacements, take a look at this thread:https://www.eevblog.com/forum/repair/uni-t-ut61e-diode-mode-repair/

author: algorithm
author_rank: Regular Contributor
timestamp: July 29, 2022, 12:55:56 pm
content: Quote from: Per Hansson on July 29, 2022, 12:06:42 pmWell before reading this I only took q5/6 out since they connected to the 2 diodes I got short beeps across. But yeah now have taken q1/8 off as well and they both have 2 diode junctions.Took d1 off, but it tests good too... crikeyYeah I had read your topic. Was a pleasant surprise to see a response from you. Reax every topic I think lol. But yeah one thing though I dont have a smd tester like yours so im probing by hand. Might be missing somethjng my way. Well guess if I take enough parts off eventually will fjnd it.

author: Per Hansson
author_rank: Unknown
timestamp: July 29, 2022, 01:06:42 pm
content: Quote from: algorithm on July 29, 2022, 12:55:56 pmIsn't it working ok now then after you removed these faulty transistors, surely something must have improved?

author: algorithm
author_rank: Regular Contributor
timestamp: July 29, 2022, 01:52:36 pm
content: Quote from: Per Hansson on July 29, 2022, 01:06:42 pmSo are you saying that there shouldnt be 2 diodes?Like in your linked topic tests. A junction from b to e and b to c? It should be like your original q8 test?My tests match your final photos where base has a diode both ways. If those were the failures pictured thenhopefully thats solved. I dont have smd 8050 but I think I have some through hole. Probably should use the right thing though. Might need to make another part order.

author: Per Hansson
author_rank: Unknown
timestamp: July 29, 2022, 02:21:56 pm
content: Quote from: algorithm on July 29, 2022, 01:52:36 pmYes to the bolded part!Q1 in myreply #1with the extra diode from E to C is failed, this is why the meter always reports a diode in testing, wasn't this clear in my text?You can test your meter without these components, just don't hook it up to any high voltage things because there will not be any input protection any more!And in all honesty the meter is pure crap so even when you have replaced those components don't hook it up to any high energy circuits as you can see in my last reply to the thread you will just end up repairing the meter more than the equipment you are actually working on!

author: algorithm
author_rank: Regular Contributor
timestamp: July 29, 2022, 06:29:16 pm
content: Well bad news tested a new throughhole 8050 and those tested the same as what came off the board, both q1 and q8. So still no idea.

author: algorithm
author_rank: Regular Contributor
timestamp: July 30, 2022, 10:32:03 am
content: Anybody know or able to find the value of ra+?Both versions of pcb I have have it but that schematic seems to be missing it. Also r39 isnt there but its on the older of 2 pcbs...So far thats the biggest difference I could find. Is ra+. Was hoping to get lucky with transistors or diodes, but those all seem good. Also now on d5/6 on both boards, I get a short beep both ways despite the diode being good. Can anybody confirm or deny if those diodes traces have 9 ohms across both pads?Because Im pretty sure I tested the newer and older, initially newer didnt have a short beep. But at this point ive tested every resistor and everything else I knew how to a few times across both. Also both boards are slightly different in layout so might have been my confusion in the chaos of desperately trying to fix this.anyway thanks

author: algorithm
author_rank: Regular Contributor
timestamp: July 30, 2022, 11:24:18 am
content: My dumbass finally got the bright idea a few minutes after posting to read the resistor via magnifier.Those values were correct for the part. Both ra* were different. Older pcb ver with r39 has 47k 473. Newer has 220 ohm.Hmm so I started trying to test around the relevant fc track wiper vias. That led me to c35 and c36. Well the 1a fuse first. On said fuse I had from 1 whole ohm up to 10 dancing all around. C35 tested solidly, c36 though was also dancing a lot. From the expected range of 17 microfarads up to 60. The tc1 tester says its a diode. So hopefully this will fix it.On c35 I get 34µF. On c36 get 16µF. But on bad board c36 sometimes shows open or random values.Could w1 be causing this? Sometimes the capacitor value is correct and I have to wonder if it will be correct off circuit.

author: algorithm
author_rank: Regular Contributor
timestamp: July 30, 2022, 12:39:00 pm
content: Took those caps off. Still no good... still a shit load of resistance on the 1A fuse. I think I saw even more ohms after cleaning those caps up.But did notice c35 had resistance that steadily decreased, when it reached a certain amount of ohms it went back up to like 47k and started counting down again.I wish I had the ut61e to test the ut61es caps. But 1 is missing a lcd so...

author: Per Hansson
author_rank: Unknown
timestamp: July 30, 2022, 01:02:48 pm
content: Quote from: algorithm on July 30, 2022, 11:24:18 amJust make an adapter for your TC1 to be able to test SMD components?A PCB prototyping board + 3 pin headers would not take 5 minutes to solder up, or just solder some legs on the SMD transistors?

author: algorithm
author_rank: Regular Contributor
timestamp: July 30, 2022, 04:32:28 pm
content: On resistance I get 65M but it starts at like 120M and counts down.Strangely after I replaced the 1A fuse it TRIES to OL but after displaying OL it shows resistance even without probes and counts down to 65M.Milivolt range does the same but it claims the numbers are mv. Also saw it show ridiculous opposites like -60 from 100. Jumping around but initially counting down.Capacitance mode shows 0.50 so I guess thats alright since others said thats normal and nobody corrected it.Still dont know what to blame... any of what I described point to anything in the eyes of someone who knows? This is really bothering me and Im past my wits end.

author: algorithm
author_rank: Regular Contributor
timestamp: July 30, 2022, 05:09:39 pm
content: Got the idea to test the thing powered by clipping a battery on.Got 0.190v across com plug hole and volt ohms hz plug hole.Also was seeing about that much on 3 r36s. 1 only on 1 side, the other 2 on both sides.I had already halfway desoldered that 200k resistor to test. It tested good. Should I fully take it off? Or is it going to be explainable by the circuit why it had that on both sides of resistor?R36c had 0.180 on half. R36d had it both sides. And r36A had it both sides but sometimes didnt.Actually r36a was getting 0.230v.And I saw that 0.230 going into q6 3rd pin if the single pin side is 1R36a tested 202k, would that be enough to cause problems?Quote from: Per Hansson on July 30, 2022, 01:02:48 pmWhat voltage should I see on q1 and q8?Or q5 q6?I did try that but failed at the 3rd wire. Than trying to geg 3rd wire reattached 2nd came off. But it still tested the same on dmm. Of course oblivious of vbe or hfe. But yeah.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 30, 2022, 05:54:24 pm
content: From what I have seen, UNI-T in particular are more sensitive to ESD. Normally with the 61E, it damages the controller IC. I did a whole series of videos on the 61E explaining the problems with it. Hopefully your IC was not damaged.***Also, I have a few friends who purchased 10 or so UNI-T meters around the same time. I think we have seen four switch failures so far.

author: algorithm
author_rank: Regular Contributor
timestamp: July 30, 2022, 08:49:49 pm
content: So c21 measures OL. I thoughf haha finally. But took it out and replaced it with a new good esr cap. Also OL. Damnit!!Does that mean the ad737 is to blame? U2. Bono got me again. Itz funny, cause I still havent found what im lookjng for.

author: Per Hansson
author_rank: Unknown
timestamp: July 31, 2022, 07:04:00 am
content: Quote from: algorithm on July 30, 2022, 05:09:39 pmPlease watch EEVblog #1157 that I linked from my UT61E diode mode repair thread.The circuit formed by Q1/Q8 and Q5/Q6 is only there to provide a dead short to allow the PTC's to increase in resistance and actually protect the meter.As you can see from the schematic they are connected ONLY to the emitter: so no voltage should ever be present on the other side of the junction.That is unless you do something "horrible" and hook the meter in Ohms, Capacitance, Frequency/Duty cycle or Millivolt mode up to a voltage source higher than the VEBO rating of the transistors.In that situation their purpose is to draw some current so that the PTC's in the schematic heat up and actually limit the current by increasing their resistance.I hope it is clear now that there should be no voltage on their collector side in normal situations, but also that if they fail the meter will always see a diode for example in these test modes, referring to my reply quoted here:Quote from: Per Hansson on July 29, 2022, 02:21:56 pm

author: algorithm
author_rank: Regular Contributor
timestamp: July 31, 2022, 10:28:19 am
content: I see like -0.080v on q8 and q1 b/c.-0.060v on q5 and q6 b/c pins.Also saw the same amount I saw on r36s going into emitters of q5 & q6. Also q8 and q1 iirc.Weird thing is my diode mode doesnt read a diode. It zhows OLSo I still have to wonder if the faults the same.That 1a fuse I replaced was dancing all over upwards of 50 ohms even out of circuit. So something fried that. Bad thjng is I dont know because I let someone borrow it for work.Well thanks for your help and image per hansson. Hopefully you are right and those transistors will fix it.Gonna hVe to order some though. so more time wasted.I have to say I hooked my meter up in diode or resistance to ac and dc/charged caps like 7 times before it fjnally died over the years of having it. That was 120v mains stuff but still a testimony of how strong these meters can be. Also I cant afford a better meter than the ut61 so I wouldnt say its crap. But if it doesnt work its crap. LolThanks again. And hopefully when I report back the meter is just dandy.

author: Per Hansson
author_rank: Unknown
timestamp: July 31, 2022, 02:48:51 pm
content: Quote from: algorithm on July 31, 2022, 10:28:19 amWhat the meter shows will depend on the type of failure of the transistor, see my last replyin the other thread.Notice how the transistor tester reports a capacitor inside the transistor? (referring to file: Q1-2021.jpg)Quote from: algorithm on July 31, 2022, 10:28:19 amI've said this before: you don't need to have Q1/Q8 and Q5/Q6 in circuit for the meter to work, just remove them.If it works after that you found the fault, and know what parts you need to order to restore the protection.If not you just need to keep looking.Quote from: algorithm on July 31, 2022, 10:28:19 amIn my opinion the meter should survive this easy to make mistake, I never saw a Fluke fail due to such mishaps!The Brymen BM235 is a pretty cheap and decent meter if you want an actual recommendation for something that doesn't break the bank.

author: algorithm
author_rank: Regular Contributor
timestamp: August 01, 2022, 09:58:07 am
content: Another weird thing I noticed while testing virtually every part imaginable.I get no resistance / continuity on r28.On the pcbs pads specifically. If I move dmm probes up on the wire theres resistance, but more than 0.01.Could q1-q8 cause that?Could r28 being open across the pads cause the resistance issue?Or possibly 1 of the 2 adjacent diodes?Ive ordered the transistors.Even if those arent the problem good to have sot23 variety in the parts stock.I havent had a chance to remove transistors but I left the meter on accidentally after my last test. Like 30 min.I tested the voltage on q8 collector which ties to q1 collector but q8 had -0.107vLooked at the screen and 107Meg ohm was there.Not sure if that definitively says anythjng but I figured it was promising. Not a coincidence at least. I hope. LolI watchdd thd eevblog 1157 on clamps with bjt. Interesting. Some of it went over my head or left me a tad puzzled, but the whiteboard shows 0.60v so I was wkndering since I saw -0.060 on q5/q6 would that entail they are good. Or am I just sadly mistaken there by assumption.Sorry for my ignorance

author: Per Hansson
author_rank: Unknown
timestamp: August 01, 2022, 08:00:23 pm
content: Quote from: algorithm on August 01, 2022, 09:58:07 amNo, the Amps and Milliamps input has nothing to do with the Ohms/Voltage/Capacitance modes.Please watch this EEVBlog video: EEVblog #373 - Multimeter Input Protection Tutorial:Quote from: algorithm on August 01, 2022, 09:58:07 amAs I said in my previous post:"As you can see from the schematic they are connected ONLY to the emitter: so no voltage should ever be present on the other side of the junction."Quote from: algorithm on August 01, 2022, 09:58:07 amThe only time there will be voltage on the other side of the transistors is if you have an active overload condition, or if the transistor is leaky (broken).Your time would be better spent making a testing PCB for SMD components for your TC1 transistor tester, here is one good example:DGW Homemade SMD to DIP adapter:

author: algorithm
author_rank: Regular Contributor
timestamp: August 04, 2022, 02:00:41 pm
content: Took off q1, q2, q5, q6, d1 (because if was connected to blown 1a fuse with high resistance undulating)But still shows a value of megaohms in resistance. It flashes like 190 or something then goes like 60M generally.I get like 7M ohm across com and v posts.God damn it.Well haVe to keep looking.

author: Per Hansson
author_rank: Unknown
timestamp: August 04, 2022, 03:21:12 pm
content: Yea that sounds wrong, I posted this in another thread.You can follow the link in the quote if you want more details.You can compare the values to yours, just make sure you are in DCV mode for the tests like mentioned:Quote from: Per Hansson on July 18, 2022, 05:36:56 pm

author: algorithm
author_rank: Regular Contributor
timestamp: August 07, 2022, 12:36:04 pm
content: Took all r36s off. R36a was 202.x and 1 seemed to be open on the lower half of pad.But replacing all 4 with new 1% 1206s fixed nothing.With r36s removed the resistance was constantly jumping in ohms. It just flashed values up or down.If I probed parts of the trace for voltage with fluke and looked at uni-t display certain parts brought the resistance to 7M. Like r33 iirc. But r33 is what its supposed to be, at least in circuit (iirc 100k but its been a few days)Also a few timewhen I seemed to probe 1 of the main electrolytics it showed 0L. But returned shortly.I replaced those caps so dont think it was the capz. Thatz just what I tested voltage on to look at uni-t

author: algorithm
author_rank: Regular Contributor
timestamp: August 07, 2022, 07:58:16 pm
content: Think I found it. Luckily thought to check the cyrustek datasheet for es51922(i think?)Ohmc1-4 pins has filter caps respectivy. C15 was weird where in one polarity it just flashed 0.00µf.Reversing polarity zhowed.. yaagh I dont remember... like .168.C7 also seemed possibly suspect. Although tested identical to other pcb.Which for that matter in circuit tests all seemed kosher between the 2. C15 even.After removing c15 and c7. (Which c7 tested .5nf . But should be .3 apparently. Is that acceptable or could that be problematic?)C15 seems to test .100 nf over or so. But it has resistance across it. About 70M. Same as I last zaw on meter readout on ohms.I dont have any smd caps at 330nf. I do have ceramic and mylar throughhole. Could I use that? Or should I not?Thanks in advance for advice on those queries and much thanks to hansson. I appreciate your help.

author: Per Hansson
author_rank: Unknown
timestamp: August 07, 2022, 10:18:41 pm
content: It would not hurt to bodge in a through hole ceramic capacitor for testing, it might not be as accurate but fine to rule things out...I'm guessing that the OHMC capacitors should be of type C0G also known as NP0 for good temperature stability.Capacitor C7 sits directly on the input, protected by the transistors we tested earlier, it could be that the value in the schematic is wrong too.I would replace C15 and put back the original C7 and see how the meter behaves.

author: algorithm
author_rank: Regular Contributor
timestamp: August 08, 2022, 04:41:28 pm
content: Replaced c15, still a problem but auto zeroing worked longer initially.Opened it up for the damn umpteenth time and tested resistance on c7. In circuit I saw 3 or 4M ohm.But before I put it back on I tested for resistance with contact for a solid amount of time and it tested good. OL.After removing it twice, tested it off circuit and couldnt see any ohms.Could my reflowing twice have overcome something internally?Because across the 2 pads I dont get ohms either. But I did before...Im lost lol...To further my confusion and desperation c*1 is not in any schematic, newer or older.Wtf is it? I get continuity across it. Its directly on r4. But apparently a cap? It looks white.Even worse my spare ut61e pcb is the newer rev lacking r36/r39, and also lacking c*1. Or is it in the diagram and I just missed it?Anyway... not sure what to do.I could put a new c7 in. But if that doesnt fix it itll be a demoralizing defeat.Knowing what c*1 is supposed to be would help.Also confused because on d8/d7 I get .5xx/.4xx both polarities.On the newer working ut61e on d7/8 get .4xx both polarities.But thats just a 1n4007.D5 and d6 / d7 and d8 seem suspicious because they tie directly to that blown fuse. And ive seen some wonky fluctuations testing the relevant resistors r29a/b.I sure could use the ut61e to try to fix the ut61e. Not having a capable meter makes this a ordeal too.I cant swap the lcds much more lol. But I had to to test those caps. But then have to swap it back to see if its reading ohms. Its wearing my patience.EDIT: actually do get 3.6M across c7 pads with no cap there, polarity dictates.Hmm.

author: algorithm
author_rank: Regular Contributor
timestamp: August 09, 2022, 02:55:14 pm
content: Measured the cap c7 and it measured right repeatedly. So I put it back in.Hmm. I ran around this so much its hard to recall what order, its all muddled like a cold stone creamery concoction. but I tested nearly every part on board to my best ability. Aside from slight discrepancies nothing was wrong upon closer inspection.I tested c13. It was not the same. (Having the fluke 12 I was looking through a resistance eyepiece to try to find the problem as that fluke is limited to 10nf iirc) I took it out thinking I surely found it now.Dug through junk pcbs to try to find a proper cap. A poopshow it was.in the end I took at least 20 smd caps so small a sudden deep breath could suck a few righf up thd ol nostril! Out before I found 1. But double checking with tc1 tester said 31picofarad, no 300... so what meter did I believe the tc1? Or other ut61e lacking r36a-d? Neither.I put the cap from it back in. Which tc1 said was 301pF actually.Then with nothing but a prayer I just went old school, relied on my sweet peepers, did my best to pretty joints up, used (or tried to use) deduction to my best ability. And ad some lucky guesses perhaps. And now shes up and running proper. "Calibrated" lol winkWhat ITHINKhappened was bad solder joint. Maybe on c13/c7?Also r28...So this whole time r28 acted weird. Sometimes showing 2ohms.Which thats the thick solid bar , might be bent square, the older version I have hss a 3 hump sine bend.Anyway, it would flash high resistNce intermittently.As in a whole ohm or 2.I reflowed that with a beefwad weller 900w. Used needler nose pliers to compress spring.See when I got that meter I noticed the solder was only on 1 side of pcb pad so I touched bare sides with solder where I thought it might help.But I think that the r28 almost fell out it was still connected on front side, bug on rear the solder was there but the leg was not protruding. Merely level with bottom surfCe I think.Weird thing is if that was the problem it worked for years before it showed ghost ohmsAnyway somehow between prettying up joints and r28, replacing c15, reflowing c7/13. Oh also prettied up the joints on caps c31-34, and c21.Not sure what I did but im happy. Now my main meter works and has a orange backlight with min/max rear 6mm button in hollow ir receiver hole. (I guess thTs for a receiver?)Ill update with a picture if I ever manage to get a setup instead of janky library solution.So all in all, replaced q1,q5,q6,q8, r36a-d at 200k 1% 1206 smd. Replaced c15. Also the 4 electrolytics on the rear top left by the r8 resistor array/pack.And just was getting random values of Megs, as high as 107 1 day.AnywayMuch thanks againOnto the next projectOh yeah, and on capacitance, it doesnt zero but shows 0.047nf. Im happy with that. On that newer version model board it always has .300nf which very well might be a clue to a problem. Like I mentioned I have no idea if thats normal since the cyrustek es51922 mentions something about zeroing and capacitance iirc.