Hi all,

I've got hold of a projector which is immediately blowing the main internal fuse. I'm certain the fault lies with the power supply and i have located some possible components right next to the mains input.

I don't have my multimeter with me so can't do a great deal but an obvious clue is a black cylindrical component which looks like this has exploded:

I've taken it out and there's practically no resistance between the legs, and after removing it the fuse no longer blows (but it still doesn't work).

At first i thought it was a varistor but looking at the symbol on the PCB below i'm not sure. It looks like this:

Anyone know what it is?

Thanks very much in advance,
Doug

 

If it helps the component is labelled TH101, thermistor?

 

Just going by the reference designation alone (TH101) I would hazard a guess that the component in your jpeg is a thermistor.

A thermistor comes in two flavors, a negative temperature coefficient or a positive temperature coefficient.

A typical datasheet for an NTC thermistor would look like this.

The resistance of an NTC thermistor decreases as the temperature increase. In the case of a PTC thermistor the resistance increases with increasing temperature.

The writing that appears on the body of the component would lead me to guess that is has a value of 281Kohms at 25 degrees Celsius.

You would need to track down the manufacturer's datasheet for the specific part to get an accurate picture of the behavour of this particular component with temperature.

hgmjr

 

I'm thinking MOV. Metal Oxide Varistor
http://en.wikipedia.org/wiki/Varistor

 

Can you take a picture of the other side of the component and post it also? There may be some useful information there like a manufacturer's logo.

hgmjr

 

If that picture is not the one in the set then you will need to trace back the solder points for the device. If the device is across the AC line it's a MOV. one lead goes to the one leg of the AC and the other goes to a bridge diode it's a surge current limit thermistor.

An example of both is here and convieniently TH101 is the thermistor...

http://www.intersil.com/data/an/an139.pdf

 

Using the Intersil link provided by mrmeval I was able to locate the manufacturer's website. The device appears to be a NTC made by Thermometrics. The K in the number indicates that the part is a negative temperature coefficient device. The T with a circle around it is the logo for Thermometrics. The 281 indicates that the resistance at 25 degrees Celsius is 280 ohm (not 281 Kohms as I previously guessed).

I suspect that the device that actually was damaged is most likely the MOV. This is a metal-oxide varistor device that protects the circuit from overvoltage. I am guessing that the destroyed device either was exposed to too much line voltage or more likely was the victim of a power surge due to lightening strike.

hgmjr

 

Here is the datasheet for the MOV. It is made by Panasonic. You can thank mrmeval for his link to the Intersil website. There is a typo in the parts list on the Intersil website. It calls out MOV101 as a EZR-V07D431. The correct part number is ERZ-V07D431.

Digikey catalog page

hgmjr

 

A big thank you to all who replied, you've given me a fair bit more information to go on.

I feel bad that i have unintentionally mislead you, the picture i posted is not of the actual component, just a component which looks the same but has different writing.

I just borrowed the g/fs camera as mine is hopeless for macro shots, here's the part that blew off the real one with the writing on.

I have looked at the circuit and one lead from this component is connected to the negative output from a rectifier and the other lead to the T1 terminal of a triac.

I can see two varistors across the input to the rectifier, so going on this and what's been said above it's a thermistor?

Thanks again in advance.

 

Yep. It appears to be a Power Thermistor part number 16D-13. It is made by Semitec.

hgmjr

 

Thanks hgmjr, i found the data sheet, not sure why i didn't see before!

So what would usually cause that to blow? It was shorted, i presume maybe a power surge? The varistors all seem to be ok, there are about 6 before the AC gets to this board..

 

Thanks hgmjr, i found the data sheet, not sure why i didn't see before!

So what would usually cause that to blow? It was shorted, i presume maybe a power surge? The varistors all seem to be ok, there are about 6 before the AC gets to this board..

I'm afraid that without a complete schematic, any attempt to go beyond your reasonable assessment of the root-cause would be fruitless speculation.

hgmjr

 

Yes you're right, i'm going to order a multimeter and do some testing.

In addition to the vast amount of information on this site i have found the link below extremley helpful, especially for a newb like me...

http://www.repairfaq.org/sam/smpsfaq.htm

 

Based on your circuit tracing it's a surge limiting imput thermistor. Based on hgmjr's findings I found the datasheet, it's a 16 ohm+-5% power thermistor, NTC.

http://www.datasheetarchive.com/search.php?q=16D-13

I don't know where to get one. I used to have stacks of catalogs to look for substitutes. You may have to contact the manufacturer and order one based on model and the reference designator TH101.

 

Thanks mrmeval. I agree with your suggestion that is a surge limiting NTC thermistor. I actually made a mistake in my earlier circuit trace. It is connected across the T2 and T1 terminals of the triac.

Now i just need to figure out why it would have blown and what else could have got damaged.

Doug

 

Ok, i finally got a multimeter (Fluke 110) cheap off eBay and have done some testing.

From what i understand the NTC thermistor is an in-rush supressor, initially current flows through it which powers some control circuit, which turns on the triac and the NTC cools down.

I have tested the rectifier and the triac and they seem fine. Previously with the NTC attached to the PCB the fuse would blow immediately, but with it removed it doesn't blow at all, i presume because the triac doesn't switch on. The NTC measured 21 ohms in it's cold state which seemed normal given the spec sheet.

I measure 4 ohms between the T2 triac terminal (negative) and positive output of the rectifier. I presume this is why the NTC was burnt to hell!

So now i look for the short. The only thing between the flyback transformer appears to be a plastic coated capacitor. I really hope this is shorted!

Is it usual for the flyback transformer to short? I figure if it has i'm screwed for a replacement.

Thanks!

 

Did you ever find a solution to this problem?
I'm asking because I have an Epson 8150 with exactly the same fault, I found the 16D-13 thermistor burnt-out so replaced it with an equivalent from RS, it blew the hell out of the new one.
When I started fault finding I also found I have 0.4 ohms at the same points as you show on your schematic. I even have 0.4 ohms between the thermistor and the heatsink, but I can't find what's pulling it down.

 

If the cap's OK, disconnect one flyback primary lead & see where the 0.4 ohm reading is. From the drawing, it could well be the flyback, they run at high voltage & the insulation could fail although I haven't seen this happen a lot, but then, I'm not a TV repairman.

 

The caps fine so I did what you suggested and disconnected one side of the primary and secondary windings, problem is there is a lot of taps off it and I'm not sure what connects to what.
One breakthrough though is that I found a MOSFET (2SK2370) that's short on the output from the flyback, I've ordered some today so will let you know the outcome.

 

Hi all,

I should have updated this thread, i too found a single shorted 2SK2370 near the ballast output, the other one was ok. I also ordered a new one yesterday. I should mention the circuit diagram above is wrong, the flyback transformer in the above diagram is actually an inductor, stupid me!

Anyway, with the 2SK2370 removed there is no short circuit and every other component tests well up to the FET so i'm hoping it will be OK. Even the burnt apart NTC still appeared to work but i got a new one anyway.

I'm not sure i understand what those FETs are doing. It seems they are maybe some sort of overvoltage protection? As far as i can see when the gate is switched on it creates a short between the negative and positive output from the rectifier.

Are you in the UK by any chance? I saw an 8150 go on eBay the other day with the same fault?