Need to canibalize

[Tridaddy]

I have a 110v power supply which was plugged into a 220 source.
When I opened the brick up, the first thing I noticed was a piece of charcoal which used to be a thermistor. From what I can tell following the PCB traces, line comes in and goes into F1 which is labeled T6.3A250V then proceeds into the second component labeled VAR1 which when I removed the component had a symbol for a thermistor under it. The only marking on the thermistor is 125deg C.
I have not removed F1 to check impedance yet.
My questions are:
1. What are the chances that the thermistor blowing up prevented further damage to the power supply?
2. More importantly if the damage is limited to F1 and VAR1, what other circuitry could I find these components?
I am currently deployed overseas and need to get the pwr supply up and running. Ordering components on-line is an option but a 2 to 3 week turnaround will not cut it.
3. Would pwr supplies from computers have the components I need, or where would be the best place to look?

Thanks for any help.

Todd

[goontron]

Re: Need to canibalize

hello from littleton! being that it was a switching supply you can expect possible damage to the rectifier, main filter cap, primary switcher, etc. i would start out replacing the varistor and fuse(if blown), posting pics, and building a dim bulb tester.

[Tridaddy]

Re: Need to canibalize

Goontron, thanks for the assist.
How do I build a dim bulb tester, and what is it used for?

I will pull the fuse today to check it. I will be looking for a thermistor amongst pwr supplies from old computers and any other electronics I can get my hands on. It would be so much easier if I were home. I could get the components quickly and have access to a real soldering station.

[goontron]

Re: Need to canibalize

Goontron, thanks for the assist.
How do I build a dim bulb tester, and what is it used for?

I will pull the fuse today to check it. I will be looking for a thermistor amongst pwr supplies from old computers and any other electronics I can get my hands on. It would be so much easier if I were home. I could get the components quickly and have access to a real soldering station.

here is a nice writeup on dim-bulb testers http://antiqueradio.org/dimbulb.htm
though being that this is not a radio i would start with a 100 watt bulb since switch modes need a lot of current on startup.

an NTC thermistor from a computer might be a little big but should work.
also check for a shorted MOV.

pics?

[budm]

Re: Need to canibalize

Pictures of both sides of the board will also help.
Is one end of the VAR1 (VARISTOR (MOV)?) connected to the Neutral.

[Tridaddy]

Re: Need to canibalize

My first attempt at pictures.

[budm]

Re: Need to canibalize

That is the MOV, the black shrink tubing encasing the MOV is rated at 125C for the shrink temperature.
For 120VAC power line, the typical rating for the MOV will be 150V, you need to measure the diameter of the MOV, it looks line 10mm dia.
The circuit will function without MOV.
So check the bridge and the MOSFETs mounted on the heatsinks to see if they are damaged.
The fuse is TIME-DELAYED fuse type.
Hopefully the MOV is tripped first and blow the fuse before the other damages occur.

[Tridaddy]

Re: Need to canibalize

budm,
Is a MOV and thermistor the same? How do I check the bridge and the MOSFETs? DO they need to be removed from the PCB to be checked?
If all else is good, do I just add a jumper wire where the MOV was?

Thank you

[budm]

Re: Need to canibalize

"Is a MOV and thermistor the same?" No.
Thermistor: http://www.ussensor.com/technical-in...s-a-thermistor

MOV: http://www.bourns.com/ProductLine.as...xide_varistors
http://www.electroschematics.com/522...xide-varistor/

"If all else is good, do I just add a jumper wire where the MOV was?" A BIG NO! NO! once you understand how the MOV functions and how it works.

"How do I check the bridge and the MOSFETs?"
Just do the search on how to test bridge rectifier and MOSFET.

[Tridaddy]

Re: Need to canibalize

The MOV does connect to the neutral lead. I have to find a square fuse. The markings said T6.3AL/250V
when I do a google search there are all kinds of hits which makes me confused. Is it a 6.3 Amp fuse or a 3amp fuse
I found an MOV which was 10mm and soldered it into place. It was labeled as a GNR 14D214K. The old MOV was to badly damaged to read any writings.

[stj]

Re: Need to canibalize

6.3amp Time-delay or Slow-blow fuse.
NOT a Fast or Quickblow fuse.

[budm]

Re: Need to canibalize

http://www.mouser.com/ProductDetail/...2fGrr1hA%3d%3d

[Tridaddy]

Re: Need to canibalize

stj/budm,

Thank you, I have resigned myself to having to wait to get the power supply working. I did have one on order, but now I am committed to fixing this one. I have ordered several fuses, and capacitors. Since I am ordering some components I have ordered a couple extra items to help with replacing the components once they come in, soldering wick, solder suckered some flux.
I do have a concern, which is not knowing what the proper MOV is. Without the old one being burned up, I can not read any writing if it was there in the first place.

[stj]

Re: Need to canibalize

the mov needs to be rated above running voltage.

in eurpoe where mains is 230v we usually use 270v mov's for example.
your power is 115 roughly, so a 150v mov would be o.k.

what a mov does is short out when you hit the marked voltage.
if the spike is short enough you will never know, but a long spike or what you did wil blow the mov and fuse.
hopefully saving everything after it.

[Tridaddy]

Re: Need to canibalize

I think I am good on the MOV then. It looks like the path was the fuse, MOV, and a capacitor and it took all three. Looking for a place to order the parts now. The first place was out of the fuses.

[budm]

Re: Need to canibalize

More fuse choices:
http://www.mouser.com/ProductDetail/...%252bpNOuvE%3d

http://www.mouser.com/ProductDetail/...9uWCeownW80%3d

[momaka]

Re: Need to canibalize

Just to recap (no pun intended) some of the answers.

THERMISTOR: a resistor who's resistance varies based on it's temperature. There are two types: NTC and PTC. For NTC, resistance goes down when temperature goes up. For PTC, resistance goes up when temperature goes up.
Power supplies have NTC on the input. The NTC is "cold" when the PSU is not plugged in. This makes the input resistance of the PSU appear high. Once you plug in the power supply and current starts flowing through the NTC, its temperature goes up and so its resistance goes down. The idea here is to limit the current inrush when the PSU is plugged in.

MOV (Metal Oxide Varistor): a component commonly used for protection from over-voltage (like you just saw with your PSU). If the applied voltage on the terminals of the MOV is higher than its voltage rating, the MOV will short out and prevent the voltage from going any higher. As stj mentioned, if the spike is small and quick, the MOV will survive. But if the spike has a very long duration, the MOV will short out permanently. The idea here is for the MOV to short out and not let the abnormally high voltage get to other more expensive components in the rest of the device.

With that said, you *don't* need an MOV right now if you want to test if the PSU is working (just leave the spot for the MOV on the board unpopulated - NO JUMPERS!). Just be careful to plug it in the correct voltage, because without an MOV, you can do a lot of damage if you plug it in the wrong voltage again.

That means all you really have to do is just replace the fuse (to test the PSU). However, since we don't know whether anything else has been damaged, put a incandescent light bulb in series with the PSU's live input. Here's how to set up that:
https://www.badcaps.net/forum/showpo...4&postcount=70

When you do the above configuration and plug in the PSU in the wall, the bulb should light up quickly and then dim down or even go out (note: do NOT put a load on the power supply). If there are any shorted components on the primary side of the PSU, the bulb will light up and stay lit - if that happens, *don't* leave the PSU plugged in for more than 5-10 seconds.

If the PSU turns out to be working fine, then you just need to replace the MOV, and that's it.

By the way, I am glad you decided to repair this power supply. It is made by Chicony (HiPro), as evident by the transformer markings. Generally, they make pretty good power supplies.

*edit*
In regards to finding an MOV replacement... that "125C" you see on it is just a rubber sleeve to keep it from blowing into pieces when it becomes shorted. If you remove the rubber sleeve, you should (hopefully) see more marks on it - that is, if they didn't get burned or smoked out.

[Tridaddy]

Re: Need to canibalize

I had to go to Digi-key for my parts. It was a one stop shop for everything. I have five fuses, five capacitors, solder removal braid, and a desoldering pump on the way. Momaka, you are correct it is a Chicony power supply, and the more everyone has given me to read, the more excited/determined I am to make it work. From what I can tell and I may be wrong, but power comes into the power supply circuitry through the fuse, MOV, and cap which are in parallel, it looks like it then goes into inductors, I believe they are also in parallel with the afore mentioned components.
The fuse, MOV and Cap are all bad, so I hope the damage ended there.
When I removed the rubber sleeve, the MOV pretty blackened but reading what markings I could, this is what I think they are:
141271K
and at the bottom it is either 420+ or 4204 it is a 10mm MOV.

I am trying to google the numbers, but any help is appreciated.

Todd

[Tridaddy]

Re: Need to canibalize

Looking up part numbers, I am thinking it is a MOV-14D271K. The blown MOV is 14mm not 10mm. After looking up numbers 14D271K makes sense. Here is the data sheet: http://www.digikey.com/product-detai...71K-ND/2799115
What do you all think?

Todd

[budm]

Re: Need to canibalize

I would use 150VAC (241) in stead of 175VAC (271).
http://www.digikey.com/product-detai...41K-ND/2799114