LCD Monitor inverter gets way too hot

[CudaDave70]

I realize these ccfl inverters make some heat . But this one you can smell it getting hot and you cannot touch either one of the two transistors underneath (c5706) or the inductor coil on top.
I checked it with an infared
heat gun and it is 250 degrees and climbing . Odd thing is ,it looks like a brand new inverter that someone replaced. I replaced the two aluminum caps just to be sure they were not causing the problem,that didn't help at all.Coul it be that one or both transistors is causing this .
It also looks like brand new light tubes were put in the screen .The voltages going in to the inverter are good ,I can't figure this out without some expert advice ,whaddaya think it could be . I will post a pic here soon of the inverter

[CudaDave70]

Re: LCD Monitor inverter gets way too hot

Some pictures of the inverter board that thinks it is a heating element.

[PCBONEZ]

Re: LCD Monitor inverter gets way too hot

Maybe new tubes and new inverter are not a good match.
- I dunno how to check that. Someone else might.
Just thinking that if the tubes pull more current at inverter's volts than the inverter is designed for it's gonna overheat.
.

[CudaDave70]

Re: LCD Monitor inverter gets way too hot

Good thought ,I did try some othet lamps I had and they are a bit smaller than the correct ones ,same result ,I dunno I never saw this before I may try changing those two transistors ,still cheaper than another board for forty buck and shipping charges.
Dave

[Toasty]

Re: LCD Monitor inverter gets way too hot

Do the tubes light?

[PlainBill]

Re: LCD Monitor inverter gets way too hot

I realize these ccfl inverters make some heat . But this one you can smell it getting hot and you cannot touch either one of the two transistors underneath (c5706) or the inductor coil on top.
I checked it with an infared
heat gun and it is 250 degrees and climbing . Odd thing is ,it looks like a brand new inverter that someone replaced. I replaced the two aluminum caps just to be sure they were not causing the problem,that didn't help at all.Coul it be that one or both transistors is causing this .
It also looks like brand new light tubes were put in the screen .The voltages going in to the inverter are good ,I can't figure this out without some expert advice ,whaddaya think it could be . I will post a pic here soon of the inverter

If I analyzed an inverter circuit properly this is a tuned circuit. It's not possible to arbitrarily choose a transformer and expect it to work. I suspect the other guy made that mistake. That toroidal transformer doesn't look real healthy, either (that might be the lighting or some glue). And the inverter and lamps are usually matched (even this newbie knows that). I'm not sure of the consequences of using lamps with a lower voltage rating, or a transformer that puts out too high a voltage, but it can't be good.

This might be the time to start looking for a new (or used) inverter.

PlainBill

[Toasty]

Re: LCD Monitor inverter gets way too hot

This strikes me as a single tube inverter, not 2 tube. Can you remove one tube and see if it works and cools down?

Particulars of the display it's in, plz.

[PlainBill]

Re: LCD Monitor inverter gets way too hot

This strikes me as a single tube inverter, not 2 tube. Can you remove one tube and see if it works and cools down?

Particulars of the display it's in, plz.

It's an inverter for two tubes. Both tubes driven by a single transformer. Look at the back of the circuit board. Not sure I think too much of the layout, tho.

PlainBill

[EGuevarae]

Re: LCD Monitor inverter gets way too hot

You say the Voltages getting to the inverter are good. What voltage reaches the transistors?
And what monitor/display is being discussed here?

[Toasty]

Re: LCD Monitor inverter gets way too hot

It's an inverter for two tubes. Both tubes driven by a single transformer. Look at the back of the circuit board. Not sure I think too much of the layout, tho

Okay. Are there any that do use a single lamp?

It's the first time I've seen a circuit with the secondary of the transformer deliberately shorted.

[PCBONEZ]

Re: LCD Monitor inverter gets way too hot

I don't think that's a winding.
More like a center tap with two terminals.

[CudaDave70]

Re: LCD Monitor inverter gets way too hot

OK, lots of feed back and questions to answer,that's good .Not as much worried about fixing this as I am just trying to understand this situation.
First it is a15" LCD TV with a Chunghwa claa150xp screen . A single tube lamp on the top and bottom,they do light and stay lit, the main transformer gets warm but not hot (unusually cool I think).
The toroidal transformer looks OK almost like new and still has a cellophane looking cover on the outside with a part #.
I did not check the voltage at the transistors , I will do that but I am not too sure what it is supposed to be.

I am about 90% certain that someone replaced this inverter, at least it looks brand new and the TV has been apart (rounded out phillips screws and foil tape cut apart).

When I got this it had the classic bad inverter or bad lamps symptoms ,it would come on for a few seconds then the backlight went out .
I took it apart disconnected the lamps and plugged in the spare lamps I had (not exactly the correct ones but real close) to test the inverter out and they stayed lit .

I then suspected that one or both of the lamps failed,so I took the screen apart and was surprised to see that the lamps appeared to be new (no black spots on the ends like old ones look ).
I plugged the same lamps in that were removed from the screen and they lit and stayed on now.
That is when I smelled something getting hot (we all know this oder means trouble) and noticed it was the toroidal coil on top and both transistors on the bottom getting real hot.
I grabbed the heat gun and got 250 degrees off of it .
Before I elect to get a new one I would like to know why .I am asking some of the great brains on here their opinions because I know someone out there knows. There it is. Thanks for all your interest ,support and suggestions.
Dave

[Toasty]

Re: LCD Monitor inverter gets way too hot

Okay. From what I've read that is the correct inverter. This is a generic unit rebranded into the likes of Phillips/Magnavox.

You probably had the overcurrent problem when you first got the unit. Your replacement tubes ran at less draw and reduced the load to where the unit would stay on.

I think the problem existed and continued to deteriorate until the second time. Now you're left with an expensive space heater.

Most likely suspect is the output transformer. You'd have to remove that completely and shoot us some resistance readings and a pic of the underside plz. Is there a part number stamped on the end?

@PC -
It seemed odd because it looks like the XFMR (fried resistors) that we were yakkin about in this thread with eguevarae: https://www.badcaps.net/forum/showthread.php?t=6644

[Toasty]

Re: LCD Monitor inverter gets way too hot

PS: What is the two-leaded, rectangular white component next to the transformer?

[Wizard]

Re: LCD Monitor inverter gets way too hot

poly (not polymer) box capacitor. aluminum/plastic sheet layers wrapped up into a brundle with 2 leads and inserted into a plastic box, potted with epoxy & vacuum to pull bubbles out. Then left alone for epoxy to cure. For some reason the HV capacitors (around 250V to 2,000V) of these box capacitors have fair number of failures.

Cheers, Wizard

[PlainBill]

Re: LCD Monitor inverter gets way too hot

PS: What is the two-leaded, rectangular white component next to the transformer?

That would appear to be an Arcotronics RSB series capacitor. Designed for EMI control in lighting applications.

Good catch, that will affect the tuning of the circuit.

PlainBill

[Toasty]

Re: LCD Monitor inverter gets way too hot

@Wizard - Thank you. I thought as much, but I haven't seen enough of these circuits to be sure.
@PlainBill - Wow! Nice. TY. ...another walking database.

Poly = polystyrene, correct?

It is connected to both driver transistors collectors. If it is failing, it could be the problem. But, I'd expect no or dim lights then, as it would be shorting their output to the transformer.

Are there different wattages of these tubes at the same length? Could this be a case of 20w tubes in a 12w inverter?

FYI- Inverter p/n is: 715T1537-4

[EGuevarae]

Re: LCD Monitor inverter gets way too hot

@PC -
It seemed odd because it looks like the XFMR (fried resistors) that we were yakkin about in this thread with eguevarae: https://www.badcaps.net/forum/showthread.php?t=6644

That was the thing I was thinking when I asked about the Voltage reading the transformers. I guess I should have asked for current. The idea behind the question is that the transistors are either receiving more that they can take, or overworking and would end up frying R13~R16 in this case. And I have some two output inverter that use only I transformer to feed both lights, but the output is separated, not "Shorted", as Toasty says (they are, indeed, shorted on purpose)

[CudaDave70]

Re: LCD Monitor inverter gets way too hot

Wow ,lots of info, some of course goes right over my bald head. I am starting to believe that the transformer is possibly bad as it started to get pretty hot and started to smell pretty bad.
I did replace the two transistors ,mostly because I had some and I can use the practice on something might end up in the scrap eventually .I had it close to smoking while checking voltage at the transistors, it is around 9.4 volts. There is some numbers on the transformer, looks like 80LL15T-7-H G0611,means absolutely nothing to the untrained brain. I feel pretty sure this inverter would melt down if left on more than 3 minutes . It kind of bothers me that something like this has no safety feature to shut it down, built into it for overtemp situation.
I think I gonna start hunting for a replacement and use this as an experimental specimen .
I also think this is possibly a bad replacement inverter that never worked properly from the get go,and is exactly why I ended up with it of Ebay.I did locate a missing resistor at R7 on the back side but This could be intentional ,for who knows what or why.I thank you all for your input I am still open for suggestions because I am into learning something new for future knowledge down the road.
Dave

[EGuevarae]

Re: LCD Monitor inverter gets way too hot

Wow ,lots of info, some of course goes right over my bald head.

Is good to know that I'm not the only bald guy around here....