Testing SMPS

I am finally getting back to working on this Plasma TV that occasionally shuts down.

I would like to isolate the power supply to be certain that it is where the problem lies. I have tried powering it up using 2 100V light bulbs as a load on the 60v and 80v rails to no avail. It doesnt attempt to power up unless it is attached to the Y-sus board.

Im guessing it gets some kind of ok signal from the VSS line?? Or is the

150W light bulb not enough of a load?
Reply to
Michael Kennedy
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Usually with a ticking problem, I will pull the cathodes of each diode one at a time that are located on the secondary side of the SMPS xfmr, and power up. When the ticking stops, then you have found the DC line causing the problem.

Reply to
circuit

You do realize that a cold light bulb's resistane is very low... Lightbulbs are not terribly good as a dummy load--use power resistors instead.

Probably the light bulb, cold, is too much of a load. Check the cold resistance of your light bulb, the apply ohms law, and you'll find the current--bet it is much more than the PS is capable of delivering.

Reply to
PeterD

"circuit" wrote in news:i9r2tp$igr$ snipped-for-privacy@speranza.aioe.org:

that works except for the supply that provides feedback,part of the control loop.

or you could scope each line,see which one isn't coming up properly.

you have to have a load on the supply that the PS regulates from. Otherwise,the control circuit sees that supply rail come up too quick,and shuts the PS down. Many PC supplies regulate on the +5v logic rail.

Also,-some- switchers have a "balance node",where all the supply rails are summed by sense resistors,and there's a "window" of operation and outside that,it triggers a shutdown.That way,if one rail is too low or too high,the balance node is outside the window(might only be a few 100 mv) and the PS shuts down.

--
Jim Yanik
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Reply to
Jim Yanik

Well actually the problem is the SMPS comes up but sometimes shuts down right away. After it heats up it USUALLY works fine, but occasionally will still shutdown..

After hearing that the X-sus board may be drawing too much current, I wanted to see if I could test the PSU with a dummy load and see if it still shuts down.. As a simple trail I hooked up some 100v 150W light bulbs to the 80V and 60V supply.. Unfortunately it doesnt supply power unless connected to the x-sus board. I'm guessing it is something to do with the low voltage VCC supply providing some kind of OK signal.

Reply to
Michael Kennedy

Well the PSU will start with them as well as the X-sus board connected. So I think the problem is related to something else. But I had that same thought..

I am actually wondering if they are not enough of a load. Power resistors would be the best route, and I will be getting some soon, as soon as I can. I'm kind of short supply here of everything.. I'm used to having a workshop full of tools at my disposal. Here all I have is a DMM soldering iorn and my Bob Parker ESR meter. I guess one of the prices to pay for living abroad for a while..

Reply to
Michael Kennedy

That's fairly typical of high ESR/dried out electrolytics.

Some visual signs to inspect for are any electros with bulged tops. Very occasionally the electros can have slightly concave tops - the cap overheats and vents some of its electrolyte, when it cools there becomes a vacuum that sucks the top in just perceptibly.

A failing electro invariably runs too hot, so look for discolouration or shrinkage of the plastic sleeve - of course you could feel if any electros are running hot, but the aluminium can isn't isolated so if the circuits live - so is the capacitor can!

Going over the soldering can be enlightening - sometimes electros corrode one of the lead wires and leak on the PCB, heating the lead cooks the leaked electrolyte which makes an evil smell.

Reply to
Ian Field

I'd say the extreme variability of the light bulbs resistance makes trying to accurately match them to a given load condition is going to be difficult--hence the suggestion for resistors.

If nothing else, oil-cooled wirewound would work, as long as you can keep the temperature stable.

Reply to
PeterD

PeterD wrote in news: snipped-for-privacy@4ax.com:

don't forget you can parallel resistors to get higher wattages. I've seen double-sided copperclad used to build dummy loads of considerable wattages from 2W carbon comp resistors,and immersed in tin cans full of mineral oil for cooling.

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Jim Yanik
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Reply to
Jim Yanik

quick,and

outside

PS

overheats

that

leaked

Now I own a 0.1 deg Fahrenheit resolution non-contact IR thermometer , the next problem SMPS I come across will get a scan across before ESRing

18GBP and its already found the awkward problem area of an analogue amp, well worth adding to any repairman's toolkit badged in UK as Maplin N19FR
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it has a scan mode , not mentioned in instructions
Reply to
N_Cook

Hmmm.. I would love to buy one of those. For now though my budget prevents me from doing so..

I guess I will be removing and ESRing all of the caps again. First time around did all in circuit and didnt find anything out of spec.

Reply to
Michael Kennedy

You need *VERY* low ESR for modern SMPSUs.

For some low value electros, like about 1uF or so it isn't too difficult to find non-electrolytics small enough to fit in the space.

In some of the less critical places you can sometimes bolster an average electro by adding multilayer ceramic chip capacitors on the print side - you can get 10uF, maybe more.

Reply to
Ian Field

line

rails

the

is

down

Very

or

circuits

corrode

the

I imagine with .1 deg F resolution , if you could get inside and get some sort of decoded feed (LCD to BCD or whatever) out to a pc plus mount on an X/Z platform driven by geared down pair of stepper motors and a bit of colouring software you could make a poor-mans IR survey camera system. Perhaps a scan taking a few minutes rather than near real time.

Reply to
N_Cook

I have a Sears Craftsman model 50466. It resembles the "Infrared Thermometer" shown below the pocket version in your reference, and has a laser for aiming. "Scan" mode apparently means that it reads continuously as long as you hold the button. When you let go of the button, it holds the last reading for 7 seconds.

I've noticed that a GFCI outlet may be about 8 degrees F higher than room temperature. The doorbell transformer is 7 degrees higher. It has proven quite handy when looking for hot components. However, you need to be aware that the sensor reads a spot that has finite size. You could be reading an adjacent resistor instead of a capacitor!

Fred

Reply to
Fred McKenzie

You want a thermal imager, not a thermometer.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

Here is a video of this thing clicking while warming up and cooling off.

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I have gone through this thing with my ESR meter and havent found any bad caps. I changed some suspect caps because of their location near hot resistors. To make things more difficult the inside of this tv is coated with cigarrette tar... So some caps and things look blackened but in reality its form smoke residue..

by the way thank you everyone who has made a suggestion on this. I am very thankful everyone here is so supportive to amatures like myself..

Reply to
Michael Kennedy

My 32" LCD makes all kind of clicking noises while it warms up and especially when it cools off after it is shut off. But it is mechanical noise from the expansion and contraction of heated surfaces. Are you sure you're not hearing some of this?

--
Live Fast, Die Young and Leave a Pretty Corpse
Reply to
Meat Plow

Hmm.. It is very possible the noise is expansion and contraction noise, although it can be very loud. When I first heard it I thought it was fairly big relay clicking. I was unaware that plasmas usually make noise since this is my first experience with the technology.

Since I became less focused on the clicking and more on looking for the problem I believe that I have solved the problem. After thourghouly checking the PSU and noticing that it wouldnt run without an OK signal from the X-sus board I decided to give the X-sus a once over again.

I found a 1uF 50v mini alunimum cap that had an ESR of 9ohms. It is attached to an M3356 transistor. The board also has solder landing pads for a SMD ceramic cap which was not populated. I think it would have been a better choice becasue IME these small aluminum caps seem to go high in ESR quite easily.

The only bad caps I've found in this thing have been 1uF on the Y-sus board and X-sus. Changed the Y-sus caps before without any improvement.

Anyhow.. I would like to thank everyone for all of their suggestions and advice. I hope that this thing is fixed now. I guess thats the challenging part about intermittant failures.. You don't really know if its fixed or not unitl it stops working again..

- Mike

Reply to
Michael Kennedy

You're right on the money there, the smaller the electro (physical size) the more likely it is to go high ESR - higher voltage types even more so!

Shouldn't be too hard to find a non-electrolytic 1uF that fits in the space, or have a rummage for any forgotten about very old HDDs - they can be a good source of large value multilayer ceramic chip capacitors.

Reply to
Ian Field

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