Let's fix a UNI-T Power Supply

Power supply is a UNI-T UTP3315TFL-11 30v 5 amp Linear.
Part that failed is a LM1458M SOP-8.

[@MartynDavies]

Great to see things fixed and not just thrown away.

[@Tycowiz]

Sadly a lot of stuff gets binned nowadays.

[@markopopov8291]

I'm not sure but ,if anyone else wants to uncover electronics repair parts try Saankramer Electronic Magazine System ( search on google ) ? Ive heard some super things about it and my neighbor got amazing results with it.

[@JohnnyCab]

Nice job

[@rickowens4397]

"Holy Cow !!! It's actually working! " You sound surprised that you can fix electronic devices. That's wonderful 😁

[@wallybe2946]

Awesome appreciate how you walk us through as you go,really enjoy your videos Thank-you for your time and effort

[@AP9311]

Wow, very nice video, Jeff! Enjoyed every bit on diagnosing the problem! Great fix! I learned something :)

[@rickolson9011]

Nice flow of troubleshooting logic!

[@galegregory97comcast]

He'll fix it guy and put it out on the market someone would love to have it. I love watching you work on that it's interesting and fun

[@thegsmsolution1]

You are great brother such solution really a mean for the technician that is the daily uses tool on repair.Only they know how importance that is.

[@rickchowsr2532]

I’ll take it off your hands if you don’t want it. Lol. Great repair !!👊🏼👊🏼👊🏼

[@dirtydon8661]

Thanks for the good video Jeff!

[@stanghp1]

Nice video, keep them coming!!

[@blagzster6255]

Good fix and a new sub for it:)

[@zx8401ztv]

Smashing diag and repair :-D On most of the basic op amp psu's the current/voltage limiting op amps grounds the pre driver transistor base, the base is pulled up via a resistor. I suspect that one of the op amps had a hairline solder fracture on one input so the op amp was slammed into full conduction. But i could be wrong, i often are lol. it's well worth fitting two new opamps just for peace of mind :-D. You can never have enough power supplys, or meters, or mugs of coffee/tea lol.

[@jeffescortlx]

Good point, can't really have too many power supplies! Although this one is going to a buddy that is having a birthday this weekend.

[@zx8401ztv]

@@jeffescortlx What a loverly idea :-D

[@radius.indrawan]

@@zx8401ztv "you can never have enough power supplies, meters, ..." ok i need to show this comment to my wife to prove that i didn't make up all these things.

[@zx8401ztv]

@@radius.indrawan The trick is to call them ' tools', but be careful as she might expect you to do some useful work with them ha ha :-D.

[@radius.indrawan]

@@zx8401ztv worth to try 👍😂

[@EasyOne]

Nicely done

[@aicisha]

A very cheap, quick and clever fix! 9:25 I was thinking that I'm the only weirdo out there, but it seems I'm not :D

[@Mikton2509]

Nice fix!

[@m80116]

You're right about Uni-T. I have the same meter and I've got several products from them, they've become my go to reliable manufacturer with nice quality standard. I've tried products from Lilliput/Owon and while the concepts are good, their implementation is usually wonky: unstable, not accurate, slow, prog. PSU with hard fan noise even when off, even their multimeter whines like crazy. Some I had to return. Uni-T? Absolute charm... I've bought a 100 MHz oscilloscope going against bad press and it's very comprehensive and pleasing to use, I reckon pretty close to Rigol and nothing like the bad reviews suggested, which chiefly concentrated on missing interface features on earlier models which is now revamped and quite stuffed.

[@LZ1SSA]

Радиоклуб за деца с училище по изкуствата, занаяти и интереси набира средства. Благодаря

[@t1d100]

I liked your strategy of swapping the op amps. Good thinking... I'm thinking it was just a bad solder joint.

[@jeffescortlx]

The board was inspected for bad joints before hand off camera.

[@devttyUSB0]

Would've been cool to scope out the opamps perhaps. Heh. Great fix.

[@annierenard5954]

thank you for this video

[@ahmedalshalchi]

This shows that you should check the biasing of the o/p stage first before going to OP Amps and also do thorough visual checking for PCB assembly since what you had done was to resolder those ICs or probably other components aside and nothing were faulty component... By the way , not good idea to supply back the linear PSUs since this could damage the o/p power transistors because you may supply higher voltage than the max VBE of those transistors and damage them if they were not....

[@davesage9190]

Both good points. I blew up the output transistors on a supply once by charging a battery and reducing the supply to lower than the battery was at. Since then I always put a high current capable diode in series with the output to eliminate current flow from the battery back into to the supply.

[@robinsattahip2376]

Miss you, KZbin stopped sending me your videos for some reason.

[@Ped0772]

Not wise to short out a psu while it's running at full voltage output, even if it is current limited. Great diag & repair.

[@MegaMarclar]

One of these days we need to arrange for me to send you my dads old 80s radio shack rc truck for repair. I think I know what's wrong with it, may make a good video..

[@SDS-1]

Cool

[@davesage9190]

I'm surprised you didn't check it a bit further for basic operation. Like apply a known load to see if it would supply the correct current and regulate it. Same for the voltage. Oh well.

[@jeffescortlx]

The current was tested at 7:58 and had no trouble getting to the rated 5 amps and the voltage reading was confirmed at 8:39

[@davesage9190]

@@jeffescortlx Not really. Shorting it out to observe maximum current doesn't really check for current regulation. Nor does observing that the output is variable prove that it will regulate voltage. That's what the opamps are probably for (regulation feedback). For voltage you need to set the voltage somewhere and apply a variable load to see that it will maintain the voltage at the chosen setting regardless of load. And for current you need to load the supply, put it in CC mode and be sure it regulates to that current regardless of a varying voltage pot setting. Just saying a bit more proof of it working properly would have been good.

[@jeffescortlx]

@@davesage9190 shorting it out IS testing it's current regulation, it doesn't get any more CC than that. You can see at 7:58 running the current pot from a low 300mA to over 5 amps. The voltage pot is also run from minimum to maximum and giving expected values. This power supply was used to test a 24v rail on a TV power supply and worked exactly as expected. I guess I don't see any evidence to assume somthing is wrong with it after the op-amp was switched out. If you are seeing something I'm not seeing I would be happy to make a part 2 going over the issue.

[@davesage9190]

@@jeffescortlx Point taken on the short and you winding the current up and down. I guess that proves that part of it good enough. I didn't really catch on to what you were doing while you were declaring it was working. No need for another video. Thanks

[@Ender_Wiggin]

I defiantly agree that it at least needs some independent reading of current to make sure it was not regulated at higher or lower values. It was a lackluster send it its fixed

[@thisnicklldo]

I must be mishearing - do Tektronix really use UNI-T bench power supplies? Nice fix.

[@jeffescortlx]

It came from a fellow cluster repair techinition, tachtronics.

[@phillipzan2005]

I have a quick question as a newer guy to circuit board repair. I believe I have this same model I'll have to look when I get back into town but when I turn the voltage up on mine nothing happen s till I turn the current up. And then I can only turn mine up till like one Amp. Which at that point I can set my voltage. Is that normal? The instructions were not very useful. Also what is an op Amp?

[@jeffescortlx]

Some switching style power supplies need a little current to start. But definitely needed one amp is too high. .01 amp should be enough for the voltage to adjust.

[@phillipzan2005]

@@jeffescortlx sorry I meant if I give it at least some amps the voltage control will start working. I meant I can't turn the amps up till say say 5 amps. I'll only go to. 700 mah. I think I have your email so when I get home latter I'll make sure what model I have and retest it since I haven't really used since the pendamic and just send u my results. Then u can tell me if it's normal. If not I think this might be a real good learning experience for me to get it to work right.

[@jeffescortlx]

@@phillipzan2005 that behavior isn't normal for a good bench power supply, but is normal for the inexpensive switching power supplies, like the $45 and under range.

[@nixxonnor]

Nice fix & superb cow. And it was a nice touch to see you peel off that protective screen protection at the end. How can you know for shure that the power supply (DUT) can handle external voltages (and reverse current) coming in through the outputs? I am a bit concerned about this if I charge a battery, and when the charge is complete, I turn the output of my power supply off. Then the battery will supply a pretty high voltage with a lot of current ready to kill something inside the power supply that has just finished charging the battery.

[@jeffescortlx]

I'm not an engineer, or claim to know everything but my understanding is when the power supply is off, and power back fed through the posts, the power will make it to the main power transistor and than stop at that point because the transistor is off and open.

[@nixxonnor]

@@jeffescortlx But power (W) equals effect. And power/effect creates corresponding heat and damage. How can you tell if one power supply unit (PSU) can withstand reverse voltage at potentially high amps at the outputs without being toasted inside? And Volts x Amps = Watt (effect and heat)

[@jeffescortlx]

@@nixxonnor if the power supply is off, the base of the transistor can't be turned on. If the transistor is off, it's going to be open and not allow current to flow.

[@nixxonnor]

@@jeffescortlx But if the power supply is still on, but solely the output is off? What then? And, in such a state, what if there is a low resistanse component connecting the two output connectors?

[@jeffescortlx]

@@nixxonnor if the output is off, then current isn't going to flow past or in any direction with the open contacts, assuming it uses some sort of relay or switch for output control.

[@mira5751]

Althought I didn:t like your start on servicing this PS you did manage by luck to find out by swapping the op amps that you probably had a dry solder joint on one of the pins ,so it worked

[@jeffescortlx]

2:57 I commented that the front boards were inspected, (off camera). Just because it wasn't filmed, doesn't mean it didn't happen. The solder joints were good before swapping the op-amps. If it had questionable joints I would have covered it in the video.

[@mira5751]

@@jeffescortlx I am sorry Jeffe ,but what you do off camera has nothing to do with the video you made.At least it would have been much more constructive if you had mentioned it in the video.then I wouldn't have commented.

[@jeffescortlx]

@@mira5751 I did mention it in the video, that why I gave you a time stamp of 2:57 that's where I mention no manufacturer defects were found.

[@mira5751]

@@jeffescortlx Yes you did my apologies I missed that Thanks

[@Peter_Riis_DK]

Randy at Tektronix? You from Portland, OR?

[@Ender_Wiggin]

What Lab power supply leads do you use? I have been looking for some good sets for a while on the cheap.

[@jeffescortlx]

Just some eBay banana plug test wires, advertised as silicone insulation.

[@hansslob6749]

Now I bought this kind of power supply of AliExpress which works but both displays are way of what the actual current and voltages are measured on a Fluke. I tried to adjust this but I can’t get it right. Is there a way you can make a video of how to adjust these displays so I can use this power supply without constantly having my Fluke connected? Thanks in advance!

[@jeffescortlx]

If the trim pots on the front panel are not allowing you to dial it in, than it is defective and you should open a claim with the person you bought it from.

[@hansslob6749]

jeffescortlx well, since sending it back to China is on my cost and is 60% of the price I paid I decided to keep it. It is functional and usable but I’m looking for an option to get the displays right. Does you answer mean that I have to experiment with an other (higher) value for those trim pots?

[@FIXDIY]

Continue

[@SwapnilV]

How did you remove the knobs on the front panel? Mine seem to be stuck hard. I tried pulling them.

[@jeffescortlx]

Mine just pull off.

[@SwapnilV]

@@jeffescortlx yeah pulled it. Used excessive force. The fit is too tight.

[@mimeanalytics4331]

Hi, just came about your video. How is this power supply regarding the output HF noise? Have you ever measured that?

[@jeffescortlx]

HF as in high frequency noise? It's a linear power supply so I wouldn't expect that to be an issue.

[@jimmy8653]

I would say bad solderjoint

[@jeffescortlx]

Solder joints were inspected before op-amp swapping and were fine as covered at 2:58

[@lidiovalencia6195]

Do you openly take on new jobs. I have a 2003 Chevy Silverado, and the back lighting on the instrument cluster doesn't work anymore

[@jeffescortlx]

Yes. Contact information is here: kzbin.info/www/bejne/ipCViKGAgtiNl7c

[@himeysales]

I know this is off topic.. but how do I email you to get a correspondence going with you on a repair.

[@jeffescortlx]

kzbin.info/www/bejne/ipCViKGAgtiNl7c

[@paramj4287]

Helllo, I know its kind of very unprofessional question. I want to know if this powersupply can be connected to power strip? or it must be plugged into wall outlet for proper function. I hope to get a reply soon. I am not technical person. Thank you.

[@jeffescortlx]

Power strip or extension cord is just fine. It's only about 120 watts max, similar to a bright incandescent lamp.

[@vineshpv816]

hi friend my utp1306s got microcontroller ( n76e003at20) getting heated up when power on and not working it I have replaced all other ic s on the motherboard but no hope at all till now is there any fix for this issue? I can't find any uni-t service centre in our location in India yet. may I get a programmed microcontroller for this power supply unit? any help are highly appreciated thank you

[@jeffescortlx]

I sorry but I don't have a spare microcontroller to sell. Have you tried to find a front panel for parts or a entire parts unit on ebay?

[@vineshpv816]

I can't find it on Ebay thank you

[@snipersquad100]

Could have been a bad solder joint.

[@elon524]

The power supply was made in china and it's very cheap! The bad op amps means 运算放大器

[@jeffescortlx]

In my opinion the uni-t is some of the better power supplies to come out of China. China is flooded with cheap power supplies, but uni-t can be trusted as a step above the bottom.

[@shahilkumar4200]

I am from india , how can i contact you. i have problem with this power supply voltage is fluctuating and fine and coarse is not working properly

[@jeffescortlx]

What question do you have? I'll try my best to help.

[@johnmayer2635]

Mine became ruined after the red probe touched a 300V. I tried your trick but mine is still not working. It only displays 00.00V and 0.000A. I would appreciate any help.

[@jeffescortlx]

You'll need to do some deeper trouble shooting. Start at the output and work backwards.

[@johnmayer2635]

@@jeffescortlx I resoldered the two chips back to their original places. Now it's working fine showing voltage correct values. When I try to adjust the amps, values remain 0.000. I did further troubleshooting, and I found this surface mount voltage regulator (S3M) being bulged with tiny cracks on top. It is not shorted. Could it be that the voltage regulator lost some of its value? I don't have correct tools to know for sure. I have been looking for the regulator replacement but all in vain. What can I do? I really love this linear power supply. Thank you.

[@jeffescortlx]

@@johnmayer2635 I would order 2 (or more, they are cheap) new op-amps and voltage regulators. Closely check any semiconductor on that path of high voltage destruction.

[@johnmayer2635]

@@jeffescortlx I live in Kenya and the probability of me getting those chips is an 8 out of 10 by mining them out of other devices. I don't know anyone who ships chips here. May be bridge rectifiers an some basic diodes. Anyway thanks again at least I know where to start.

[@jeffescortlx]

@@johnmayer2635 is eBay available at your location?

[@andymouse]

Maybe one of the op amps wasn't soldered correctly.

[@jeffescortlx]

The board was inspected for bad joints before hand off camera.

[@lamwaikow]

Sir you should press the knob bebore you turn the knob am i right😂

[@marcelocmj6680]

Jeff! or anyone, Mine identical device, is showing and outputing around 44.33v constantly , values are real comparing with my tester... current seems to be fine if could be tested passing CC to CV as usual, rotating knov volt does not change values at all.... always arround 44 vol, PLEASE what to test?? all is clean at 100%!! not blown components or traces of exploded caps or anything... most diodes are ok and transistors too i think..caps are good shape

[@jeffescortlx]

Typically when a power supply is stuck at maximum volts it's because the main mosfet that controls the voltage is shorted.

[@marcelocmj6680]

@@jeffescortlx can you please guide me to which one is it? where the mosfet/ transistor is located in this device?

[@marcelocmj6680]

@@jeffescortlx it started to work fine again by itself, maybe the relay stucked or similar due to its sounds...tks for your help, and if you can confirm that a relay might have affected to generate this issue you are welcome..

[@calvending1588]

Hi I have a 2004 Chevy Silverado and my odometer says odometer error

[@jeffescortlx]

Yes sometimes that happens.

[@calvending1588]

How much do you charge to fix my instrument cluster

[@jeffescortlx]

@@calvending1588 my contact information can be found here: kzbin.info/www/bejne/ipCViKGAgtiNl7c

[@giselltarrio6557]

Hello bro,Help not power :(

[@ustadrakha786]

Sir i have same suply can you show me number both 2 transistors who change you sir please i from Pakistan🇵🇰 please 🙏 sir tell me Suply Uni-t utp3315tfl

[@jeffescortlx]

The part number is listed in this video at around the 10 minute mark: kzbin.info/www/bejne/aGqzYaZ8qNyDjKc