Quick question on what part this is

tom66 · Jun 15, 2011

JJS1234 said:
I dont know if this is any different than above but perhaps another symptom??

I had the lights off and I could see mini sparks in the defective resistors.

And the voltimeter I was using could detect these, fluctuating I believe (don't remember)75-120v.

EDIT: Ok just purchased both resistors and a cap, I have one in my stereo that seems a little corroded on the top. :O

Sparks are bad, probably means the resistors are open circuit and something else has gone bad.

JJS1234 · Jun 15, 2011

tom66 said:
Sparks are bad, probably means the resistors are open circuit and something else has gone bad.

I don't believe I detected any voltage past the resistors. Any idea what you think has gone bad? Ill take a look.

I ordered 10 of each which gives me about 3 chances to find it. Assuming it will fry the chips again (over some time).

SgtWookie · Jun 15, 2011

In a properly designed circuit, resistors very seldom fail by themselves.

If you simply replace the failed resistors and power it up, the new resistors will likely be destroyed in moments.

tom66 · Jun 15, 2011

SgtWookie said:
In a properly designed circuit, resistors very seldom fail by themselves.

If you simply replace the failed resistors and power it up, the new resistors will likely be destroyed in moments.

That's a good point.

Unless these resistors were under a continuous overload then they wouldn't fail. Resistors are dirt cheap. In my product a 1206 1/3W resistor costs only 10% more than an 0603 resistor (1/10W - 1/16W), it's not really worth cheapening it. From the looks of the circuit, it appears to limit current (or control a current mode PWM controller); so something down the line failed, leading to a gross overload. I'd look elsewhere. Have you measured the resistance of them yet?

JJS1234 · Jun 15, 2011

tom66 said:
That's a good point.

Unless these resistors were under a continuous overload then they wouldn't fail. Resistors are dirt cheap. In my product a 1206 1/3W resistor costs only 10% more than an 0603 resistor (1/10W - 1/16W), it's not really worth cheapening it. From the looks of the circuit, it appears to limit current (or control a current mode PWM controller); so something down the line failed, leading to a gross overload. I'd look elsewhere. Have you measured the resistance of them yet?

One moment checking now...

I assume its the x1 setting?

Ok odd, I thought resistors could go in any way polarity but when I switch the Pos and Neg sides of resistor I get different readings.

First off: When the numbers of the resistor are facing me I get on ALL: 15ohm then rapidly increasing to about 50ohms.

If I do it where the numbers are upside down I get:

RS1-RS3 (Chip number on the picture) .5ohms.
the R1 resistor is reading about 6ohms.

tom66 · Jun 15, 2011

JJS1234 said:
One moment checking now...

I assume its the x1 setting?

Ok odd, I thought resistors could go in any way polarity but when I switch the Pos and Neg sides of resistor I get different readings.

First off: When the numbers of the resistor are facing me I get on ALL: 15ohm then rapidly increasing to about 50ohms.

If I do it where the numbers are upside down I get:

RS1-RS3 (Chip number on the picture) .5ohms.
the R1 resistor is reading about 6ohms.

Well if anything it proves the semiconductor is good (probably an NPN), and that there is a capacitor on the board somewhere. Those resistors need to be removed and tested individually. Resistors are nonpolar, but the circuit may not necessarily be so.

I think you need to give us detailed pics of the top and bottom of the board. I think more has failed than those resistors.

JJS1234 · Jun 15, 2011

tom66 said:
Well if anything it proves the semiconductor is good (probably an NPN), and that there is a capacitor on the board somewhere. Those resistors need to be removed and tested individually. Resistors are nonpolar, but the circuit may not necessarily be so.

I think you need to give us detailed pics of the top and bottom of the board. I think more has failed than those resistors.

tom66 · Jun 16, 2011

Pictures are okay - but not detailed enough to see all the parts.

Never mind about the pics of the whole board as your camera probably isn't made for macro. I found my Coolpix does it well but it isn't perfect. Anyway I want you to take a picture of the secondary side components which look like three leaded transistors on the heat sinks. I'm thinking one of them has popped. Usually though that is pretty bad, as it can damage the control (main) board. If one of the ASICs is gone it is next to impossible to repair, at least not economically.

JJS1234 · Jun 16, 2011

tom66 said:
Pictures are okay - but not detailed enough to see all the parts.

Never mind about the pics of the whole board as your camera probably isn't made for macro. I found my Coolpix does it well but it isn't perfect. Anyway I want you to take a picture of the secondary side components which look like three leaded transistors on the heat sinks. I'm thinking one of them has popped. Usually though that is pretty bad, as it can damage the control (main) board. If one of the ASICs is gone it is next to impossible to repair, at least not economically.

The three transistors to the left of this picture...

http://i79.photobucket.com/albums/j160/RISEOFNATIONSFRK/DSCN2355.jpg

right?

tom66 · Jun 16, 2011

JJS1234 said:
The three transistors to the left of this picture...

http://i79.photobucket.com/albums/j160/RISEOFNATIONSFRK/DSCN2355.jpg

right?

Yep. Can I see pics of the face of the devices? Also pics of any other devices which look similar. Make part numbers clear in the pics, if not possible, note them down in your post.

JJS1234 · Jun 17, 2011

SgtWookie · Jun 17, 2011

<snip>I heard a POP sound when I was testing voltage the top busted off this, I dont know if it is bad or not...

If an electronic component goes POP, parts fly off, smoke exits, or there is a bright flash, you are virtually guaranteed that the part in question will no longer perform to its' original specifications. So, if something goes "BANG" and the lid flies off, it is dead.

tom66 · Jun 17, 2011

All diodes are good but you killed that little IC.

Don't power up a board and test it at the same time unless you know what you are doing! You can easily kill yourself doing this. A 400V capacitor will very likely kill you if it is energised.

I'd note down the part number of the PSU board and buy a new one, which should be around $50. Repairing this one will be next to impossible without a schematic, and it's likely that some of the parts are proprietary, especially on cheaper TVs.

Or look for another TV... one just with a click of death or "shuts down after 5 minutes" or has standby but no main power... etc. Not completely dead...

JJS1234 · Jun 17, 2011

I see. Well, Ill just sell it for parts then.

JJS1234 · Jun 17, 2011

Thanks for the help. I was wearing latex gloves while doing it. Though I wonder if they help?...

Anyway, Ill try to get another one just taking into effect what I have learned.

tom66 · Jun 18, 2011

JJS1234 said:
Thanks for the help. I was wearing latex gloves while doing it. Though I wonder if they help?...

Anyway, Ill try to get another one just taking into effect what I have learned.

Latex gloves will absolutely not help when dealing with high voltage electricity because they will break down easily.

You will kill yourself if you try stupid things like that. I didn't have my TV powered up while I was repairing it. I removed the PSU board and repaired it separately, then replaced it.

Please be careful.

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