How hot should a resistor get?

[parkerbeder]

Okay, there are two of them, and i'm reading 154v across both. 110v supply. sorry about the poor pictures... and thanks so much in advance for helping!

 

[Vizier87]

if the problem's about heating at all then a small 5V DC fan which costs next to nothing would've helped cooled the system.. I suppose when it does really fire up there, the temperature's gonna overkill the cooling anyway.. try that if nothing else works.

 

[tvtech]

OK. So far so good. BTW, what was the original fault on the PSU that you fixed?

 

[Sceadwian]

No Vizier, he should not be just adding another fan, if the power supply is overheating after being repaired the problem needs to be fixed not the symptom. If he can't get it to normal operating conditions then the supply should be recycled and a new one bought.

 

[tvtech]

No Vizier, he should not be just adding another fan, if the power supply is overheating after being repaired the problem needs to be fixed not the symptom. If he can't get it to normal operating conditions then the supply should be recycled and a new one bought.

Exactly what I am thinking. Something has changed. That's why OP must reply and let me/us know what the original fault was that he repaired.

Otherwise, it becomes a guessing game. And that does not help anyone....

 

[Sceadwian]

By the way, what's the thermistor supposed to be? The black disc next to the resistor? I'm not familiar with all the different packages thermistors come in.

 

[tvtech]

By the way, what's the thermistor supposed to be? The black disc next to the resistor? I'm not familiar with all the different packages thermistors come in.

Normally around 2.2 to 4.7 Ohms. Depending on the design.

And it's a Negative Temperature Coefficient resistor. Hence NTC. It's job is to limit inrush current to the PSU. Starts with a higher resistance and falls to around "zero" within a few milliseconds.

In the TV game we have a thing called a PTC.. Just the opposite. It is in charge of the TV's Degauss Coils(s). A PTC starts with very low resistance and it's resistance rises very quickly.

Degauss means circuitry that automatically "de magnetises" your CRT every time you turn it on with the Mains switch. Ever seen crazy mixed up colours on your TV?. That is the Degauss circuit that is not working properly or has not been given a chance to work for a while.

Using the Remote Control does not do it. PSU was always running anyway. TV needs to be manually turned off and then on after a couple of minutes.

I think I have said enough for today.

I hope somebody learn't something here.

 

[Nigel Goodwin]

In the TV game we have a thing called a PTC.. Just the opposite. It is in charge of the TV's Degauss Coils(s). A PTC starts with very low resistance and it's resistance rises very quickly.

Actually it's called a posistor, and the vast majority of them use two thermistors, one NTC and one PTC. A small number of later sets did however did use just a PTC.

 

[tvtech]

Actually it's called a posistor, and the vast majority of them use two thermistors, one NTC and one PTC. A small number of later sets did however did use just a PTC.

Nigel, you are out of your turf. With all due respect please comment on stuff you work with on a daily basis.

Thank you

 

[Speakerguy]

tvtech is correct about the black disc in the picture. It is definitely an NTC thermistor for inrush current limiting. Having it next to a resistor that gets hot during operation probably improves its performance

 

[tvtech]

tvtech is correct about the black disc in the picture. It is definitely an NTC thermistor for inrush current limiting. Having it next to a resistor that gets hot during operation probably improves its performance

Common guys. This is really not a hard problem to fix.

We have the photo's, and we all know what the PSU is supposedly doing....

All we need is for the OP to tell us truthfully what he did to get it working in the first place.

Therein lies the Clue......

 

[Sceadwian]

Nigel according to Google Posistor is a trademark for a particular brand of PTC.

 

[Speakerguy]

Common guys. This is really not a hard problem to fix.
We have the photo's, and we all know what the PSU is supposedly doing....
All we need is for the OP to tell us truthfully what he did to get it working in the first place.
Therein lies the Clue......

I agree, I was just pointing out you were correct about the NTC thermistor in case anyone else had doubts.

 

[parkerbeder]

Hey, sorry for the slow reply. The original problem was that the supply would blink on and off at about 1Hz, when turned on. To fix this, I just replaced all the electrolytic caps with panasonics. I tried to find ones with better ratings, but the ones it had were already all 105C's so I just replaced them with the same rating.

 

[Birdman Adam]

Could by chance have connected two solder joints on accident?

 

[parkerbeder]

I had wondered that too originally, and I can't see anything wrong with any of the joints, though, i may reflow them again, just for posterity.

 

[Sceadwian]

Okay so it was blinking before, and it's blinking now, albiet at a slower rate and you think you fixed it? Apparently not or it wouldn't be blinking at all =) The caps are obviously not your problem. If you reflowed them once don't bother with it a second time as repeating a failed repair step isn't likely to magically start working. Although I do appoligize as I can't think of anything to suggest at this point, except perhaps checking power FETs or resistors associate with them, perhaps one of the main switching FETS got hit too hard one time and now won't go all the way low resistance so the supply is overheating. A non contact IR thermometer will show you what exact part is over heating and might possible help you figure out where to look net. Considering the cost of these types of supplies repair is not generally worth it though., unless you have no possibility of finding a replacement, but it looks like a relativly modern design.

www.mpja.com sells a wide variety of switch mode supplies.

 

[parkerbeder]

I had checked everything with my ir thermometer, and only one of the fets gets a little hot, which is still only about 150F. I may replace it, but otherwise, I don't specifically think that the problem is heat, as I did before. Also, this power supply isn't being produced anymore, even though it is only 6 years old. I'm frustrated about it, but alas it just means it needs to be fixed. This is definitely not the problem it had before, but one probably caused the other. I may just replace the fets, and their resistors, unless tvtech has more troubleshooting advice.

-Parker

 

[Sceadwian]

So the power supply is going into overheating shutdown, yet you don't think the problem is overheating?
It doesn't matter if the power supply is being produced, what is the voltage in/out. There is virtually no such thing as a truly 'unique' supply. By the time you get over the cost of replacing the primary switching FETS you'll be over the cost of a new supply capable of the same current and voltage. If you had a problem before and a problem after nothing was fixed, all you did was change the equation, what is wrong is still wrong.

 

[parkerbeder]

I'm not sure if it is going into overheating shutdown, as that the thermistor is an NTC, so, I'm not 100% sure if the supply even has an overheating shutdown. It is true that it is theoretically doing a similar thing, but why would the 'equation' change, if functional parts were replaced with identical functional parts? I think that there may have been more than one fault to begin with. Also, I will have to check what the output voltages are, but there are no fewer than six wires going in, and twelve wires coming out. it also has to fit inside an enclosure that is not terribly large. There arn't that many components, and the most expensive parts, e.g. fets and the transformer are only 5-10$ a piece. I am pretty tempted to just blindly swap the rest of the components in the unit, but would love to know what is actually wrong, as that upon looking for a solution for this problem, it seems that many other people with the same supply are having the same problem.

Thanks for all the insight and replies!

-Parker