TSP

In this episode Shahriar investigates the failure of a GW Instek 1080W power supply capable of providing up to 80V and 40A of programmable output voltage and current respectively. The power supply does not power on. However, relay noises can be heard inside the instrument during power on.
Teardown of the unit reveals a modular design with PCBs on all sides. The instrument comprises 6 different modules and 3 complete power supplies in parallel. The controller circuit is powered from the middle power supply module. Examination of the boards reveals three separate failed devices. The in-rush power resistor which prevents the main supply board from startup, a damaged MOS power transistor on the supply output and surface mount resistors. All components are replaced. The instrument's performance is verified with a BK Precision 8601 electronic load.
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[@mohinderkaur6671]

Transistor blows to protect fuse...

[@MCSGproject]

It failed short tho..

[@davidv1289]

More like transistor fails, resistors blow to protect fuse!

[@bugrobotics]

It's a beautiful thing watching someone knowledgeable troubleshoot. Thanks for sharing!

[@PeregrineBF]

Browsing youtube's recommendations, I saw your Keysight UXR 110GHz scope teardown in an autogenerated "consumer electronics" playlist. That's an interesting definition of consumer electronics...

[@RambozoClown]

As usual, components die to protect the fuse. I bet even the cat knows that.

[@modrobert]

Thanks for an interesting repair. I used to dislike power supplies but after many repairs it's like visiting an old friend.

[@thomasleerriem6872]

A switching power supply that fails. What a surprise...I hate these switching turds. Thanks for the interesting troubleshooting!

[@BruceNitroxpro]

Thomas Leerierm , Switchers are so noisy that I wouldn't allow one in a lab setting. This one looks miserable, too.

[@valordk]

Great video as usual. These series don't look awfully old. It's gonna be a nice addition to your lab :)

[@splashman63]

Thank You for this video. Your trouble shooting is incredible and a inspiration to someone like myself when I get stuck on something and looking for some insight

[@rogeronslow1498]

Very nice video. I have found that the cement resistors as used in that PSU inrush limiter don't have a good overload capability. If you break open the failed resistor you'll probably find the resistance wire wound on a tiny glass fibre former. Resistors wound on a ceramic former (like Welwyn) offer far better inrush current handling capability. Basically not the best component choice. Interestingly, the aluminum housed resistors also can't handle a high inrush current even though their steady state rating is ok.

[@SeanBZA]

Designed as a fusible resistor, so will have a thin film resistor inside the body, so it will fail open circuit under overload.

[@rogeronslow1498]

@@SeanBZA That may be a possibility. I remember the vertical cement resistors in TV's had a low temp solder that would melt and break the circuit. The aluminum housed resistors spew their guts when overloaded. It can be a very dangerous situation with a foot or two of resistance wire all over the PC board at mains potential. What happens is the air trapped inside heats and expands and blows them apart.

[@SolidStateWorkshop]

What Welwyn series? I'm trying to look for an example of a resistor with a ceramic former.

[@rogeronslow1498]

No sure which series. I'd have to go to the website. It's not just Welwyn. Other makes also use a ceramic former.

[@rogeronslow1498]

@@SolidStateWorkshop They don't make that line anymore it seems. They were green glazed vitreous bodied and quite fragile actually. TT Electronics probably eliminated the range after the takeover.

[@richardgray8593]

A teardown AND a special guest? How great is that?

[@SeanBZA]

Going to bet somebody tried to charge a battery with it, and did not realise it has a 2 quadrant capability, and it then blew out the downprogrammer trying to discharge the battery. Power supply kept on working, just probably gave an error on startup about the current sink being disabled on the one channel, but otherwise kept on running, with only a long turn off time on power off or dropping voltage. The resistor on the input side failing was probably coincidental, or the central power supply is the one which always powers on first, and the repetitive surges through this resistor finally caught up with it.

[@BruceNitroxpro]

SeanBZA, Sounds like you know that failure mode well!

[@ovalwingnut]

[🌟🌟🌟🌟🌟] 9 out of 10 Techs prefer T.S.P. 👍😁

[@tonysfun]

Another nice video! Love your logical troubleshooting!

[@RoGeorgeRoGeorge]

All the instruments you opened look brand new on the inside, even the cooling fans are clean. Did you dedust and clean the inside of the instruments before start filming, please? If so, maybe it would be interesting to show how can this be made so well.

[@redtails]

I could imagine most of these instruments come from labs and not from people's homes. Lab environments are already a lot cleaner than your typical home, as far as dust is concerned.

[@vincei4252]

All the eBay equipment I've ever bought have been pretty clean on the inside. It's possible the sellers dust them off to make them more presentable but if they do come a lab environment they're unlikely to be full of fluff. The labs I've worked in are very clean. Automotive & Healthcare.

[@brainndamage]

The labs typically have HVAC systems with filters that filter the dust out of the ai

[@redtails]

@@brainndamage Also I back this up. I currently work in a biomedical lab, and I have horrible hayfever. Once inside, zero hayfever. The outside air, and probably also the inside air, is filtered nonstop.

[@topherteardowns4679]

Another beautiful video. Thank you again!

[@yunanliu1876]

Thanks for you and your high quality video. I have learned a lot from it.

[@CATA20034]

WOOOW, don't use that kind of resistors for current limiting during start-up. They tend to explode when are overheated (that polimer is melting on the wire and is vaporized creating pressure....than it burst trough lateral leads.....I have seen one exploding). Use ceramic resistors this can handle high peak power dissipation without any failures.

[@BruceNitroxpro]

Gatea Catalin, Failure mode is a critical thing to know, regardless. It comes with experience for good engineers. If you fail to heed that data, you destroy good equipment for no practical reason.

[@inductorbackemf7204]

Amazing video as always thanks friend! Alex.

[@mazenl7139]

another great video, thank you!

[@WillArtie]

Thanks again mate!

[@Darieee]

Love these types of videos!!!

[@Club_JT]

I wonder if you would ever do any 'beginner' videos with an Arduino or similar ..... I feel like you would be a wonderful teacher for starting the path toward a career or interest in EE .... I wish I could have met someone like you when I was a student ...

[@buzdarbaloch1871]

Good Repair ,This power supply has lack of protection circuit

[@andypalm7061]

Interesting repair. I wonder if that unit would be a good power supply for radio/receiver bench work?

[@t1d100]

I would think that, even after cleaning the carbon off of the plastic shield, some carbon might remain embedded in the plastic. I thought that covering the remnant with Kapton tape might be helpful. It seems that it would be better than nothing...

[@li0201]

Losing screws is so classic lmao

[@johncloar1692]

Another grate video.

[@leozendo3500]

Wow. It's all real engineers here. Where can you find something like this though?

[@jaa93997]

Jbctools rework station...... Very nice!

[@ukaszsmoa8416]

How are you getting 400VDC from rectified us mains voltage? Don't you guys have 120VAC? We don't get that from 240VAC.

[@pa4tim]

probably voltage dubbeling. That way I make over 500Vdc from 230Vac for a leakage tester

[@ukaszsmoa8416]

@@pa4tim Thanks. I don't remember anything about his isolation transformer, maybe it can output wider range of voltages.

[@SuperZylar]

I'st because of a power factor correction, www.ti.com/lit/an/slua144/slua144.pdf

[@SeanBZA]

Looks like this has power factor correction on each blade, so the voltage will be 395V irrespective of mains input being from 60 to 265VAC. This means the main control has one less thing to compensate for, as input voltage is constant across the world. Also means the power devices can be simplified, and you can run them closer to the edge. Bonus is also reduced noise on the input and it is much easier to filter, plus reduced ripple on the main DC bus as well.

[@MCSGproject]

PFC is boosting the voltage after rectification to ~400VDC.

[@dtiydr]

13:02 I was wondering why you didn't check the resistor first. Without it no current can get into the system and not a single thing will happen, you really should have seen that.

[@tommihommi1]

isn't it an incredibly bad idea for the output to be on when you turn the device itself on?

[@hermannschaefer4777]

Yeah, but I guess it's optional and the last owner prob. programmed it that way for an unknown reason.

[@BruceNitroxpro]

@@hermannschaefer4777, Poor design, I'd say. Of course... that is an arguable point!

[@endrestory4345]

this was Nice, long time sins i se one off Your video. i love them, but those are allitel over knowlage. butt i Learning something ewery day. tanks for the Nice videos. Greetings from norway

[@superciliousdude]

Can you please link to where you got those needle point gold plated probes you were using with your Fluke 289?

[@ukaszsmoa8416]

Try brymen leads off of ebay, gold plated, silicone isolation. Very cheap and quite good. www.ebay.com/itm/Brymen-Silicone-Gold-Plated-Test-Leads-Probes-for-Multimeters-CAT-IV-1000V/171162377470?epid=2063657290&hash=item27da129cfe:g:uSQAAOxyTjNShpch:rk:1:pf:0

[@Sloxx701]

Probemaster also sells micro tip leads, American company, good stuff. There's lots of cheapo micro tip leads on ebay and amazon too. If you want the real Fluke ones, they're a bit pricey. www.amazon.com/Fluke-TL910-Electronic-Test-Probes/dp/B000VRJH0G/ref=cm_cr_arp_d_product_top?ie=UTF8 I use these as they serve the same function and are also extended. www.amazon.com/Fluke-8845A-EFPT-Extended-Point-Adapter/dp/B000VRFKPW/ref=sr_1_1?s=industrial&ie=UTF8&qid=1543002744&sr=1-1&keywords=fluke+tp88

[@sincerelyyours7538]

I use a pair made by probemaster.com/. A bit more expensive than the Chinese made probes but they have the sharpest gold plated probe tips in the industry. You can easily poke them into insulated wires to read a voltage without damaging the insulation, the cheaper ones are generally too blunt to do that easily. They're so sharp, in fact, I have to be careful not to poke myself with them as I work. They can also elevate a budget priced test instrument into a near lab quality instrument by getting around the manufacturer's habit of cutting corners on the probes in order to reduce the sale price, as long as the instrument itself is of good quality.

[@superciliousdude]

​@@sincerelyyours7538 I own some probemaster probes (the 8043S kit) and I hate them. They are too big and clunky in the hand. Their only redeeming feature is that they are sharp, but but the tip is too big and clunky. With the CatIV cover on them the tip is too far recessed and with the cover off its too big for my liking. The handle is huge too and feels too distanced from the tip. I have just ordered the brymen probes Łukasz Smoła recommended but I really like the look of the needle-point ones being used in this video. I know the probemaster ones get rave reviews on youtube, that's why I ordered them, but I find them to be awful as general purpose probes. The point is too big for fine stuff, they are more like automotive probes.

[@mangeshmahure8039]

kindly share back panel wiring

[@electronic7979]

👍👍

[@DeeegerD]

Nice problem tracing. I checked their site and no service manual or schematic. They do have a user manual but it too doesn't contain a schematic. We need to start insisting on these or not buy their equipment. Same is happening in the HAM radio world. I can understand their view if it's a cheap toss away unit, but expensive equipment such as power supplies, transceivers, etc... should have service manuals.

[@robertw1871]

So much stuff is sourced from China these days probably down to google translate not being able to cope, and the designs are probably copied from any source available, patented or not, and good service manuals are expensive to produce so I wouldn’t hold my breath.

[@yaghiyahbrenner8902]

A blackfin processor seems overkill ?

[@robertw1871]

Yaghiyah Brenner, they probably had a bizillion in stock from a product that undersold and also already had the development gear setup when starting the project, seen overkill happen like this. Especially when marketing is already taking orders for gear that is still on paper lol...

[@yaghiyahbrenner8902]

@@robertw1871 yeah probably true, BF chips are cheaper 400MHz cost 9$ for 1k MOQ

[@diatomsaus]

A zap from this wouldn't be fun.

[@shana_dmr]

With 80V DC you'd really have to try;) Unless you regularly work with wet hands or open wounds. Much more "fun" comes from accidental insulation testing your skin instead of DUT using a megger.

[@BruceNitroxpro]

@@shana_dmr, Don't use your tongue as a circuit tester! LOL

[@douro20]

I used to have a Flextronics power supply a little smaller than a loaf of bread which could handle 145 amps continuously at 12VDC with a 240V supply input.

[@andrewmorton9683]

"Used to have ... PSU ... a little smaller than a loaf of bread..." - is it now toast?

[@douro20]

@@andrewmorton9683 No I tore it apart.

[@shazam6274]

Looks very, very, very similar to a Tektronix / Keithly 2260B-80-40 I had at work. More Info Here: www.tek.com/dc-power-supply/series-2260b-360w-720w-1080W-dc-power-supplies . Can you ask your buddies at Tek about it?

[@gacherumburu9958]

👍👍