Zenith plasma bad thermal resistor on Power supply

[Nick's Tvs]

General question on thermal resistors, please see my scenario below.

Zenith (Really all LG inside) plasma tv wouldn't stay on. Panel would prime, and then the set would shut off immediately after.
Did some basic troubleshooting and decided bad PSB. Then started testing all components when I found 2 thermal resistor labeled 5w 22ohms next to eachother. One measured 22ohms, the other open. I don't have any 22ohms 5w thermal resistors laying around, but I do have a few 4.7ohm 5w. I replaced the open one with a 4.7ohm one. My thoughts were (its such low ohms, can't really think it would make a difference at this point since its more of a fuse than anything else at this point right) I boot up the set and it works for 5 seconds, then shuts back off to same symptoms. So I take the board out, and come to find out, the one I replaced is fine, but the second one that was fine before is now open. So I replace that one as well with the same 4.7ohm 5 watt thermal resistor and boot it up.

TV has been working fine for about 5 hours straight, turned it on and off several times with out a problem. Now I just don't know enough about these to know if it actually makes a big difference. I bought a few extras of these 22ohm 5w thermal resistors online to do a proper replacement, but for general knowledge, does that matter when we are looking at such low ohms? Is it better to go with more ohms less ohms or not ok at all and need an exact replacement.

Thanks for the info!

-Nick

[dick_barton]

Re: Zenith plasma bad thermal resistor on Power supply

I would attempt to repair it back to factory setting and reinstall the two 22 ohm resistors.

[CapLeaker]

Re: Zenith plasma bad thermal resistor on Power supply

As a professional tech you should know the answer what it the 4.7 Ohm thermal resistor does in a place that had 22 Ohm ones in it as inrush current protection.

So with lower Ohms on the inrush current resistors, the main cap(s) are going to charge faster. They may charge that fast, it could blow the fuse.

[R_J]

Re: Zenith plasma bad thermal resistor on Power supply

Not sure exactly what circuit this is in but sometimes there is a relay that shorts out the current limiting resitors once the caps. have charged. if the relay is bad ie: burnt contacts, current constantly flows through the resistors, heating them up and they open.
This may not be the case here but something to check.
leaving the 4.7 ohm in place of the 22ohm may work but if the tv is left off for a while (day or two) and the caps drain down, when first turned on the fuse could blow or sometimes will weaken and after a few turn ons will open.