intermittent tsjirping sound Neufunk TV model 2180

[berre]

Hi,

I have a Neufunk TV model 2180 which suddenly died.

Screen and sound gone, the only thing I hear is an intermittent tsjirping sound... sounds a bit like a capacitor just before blowing up but it is intermittent...

anybody encountered this before?

cheers

berre

[Morrowrj]

The intermittent chirping from my tv turned out to be the result of a shorted horizontal output transistor. same thing , no picture/sound. Hope this helps.

[Guest]

[berre]

Hi,

I've checked the printboard (unfortunatly I don't have the schematics) and I've found the word "horizontal" printed on it... very nearby I found a transistor type BU808DF... could this be the HOT?

Thx

Berre

[Morrowrj]

Yes, i just replaced thr transistor to fix. As to how to locate it, i had the benefit of a similiar schematic. Perhaps someone else could offer insight on how to be certain. I would say you are definitley in the right area however. Did you try checking the trans with a meter ?

also you can check this out http://www.highlandelectrix.fsnet.co.uk/repair/safety.html

perhaps it will help

[berre]

thx for the info, I did some more research: the BU808DF seems to be a Line Output Transistor (LOPTR ) so my question: is a HOT a type of LOPTR or is it just a synonym?

(I googled but found only a few times an association between BU808DF and HOT)

Unfortunatly nobody seems to have the schematics of my model so I'm not 100% sure but I think I have the right one....

I've tested it with my multimeter on diode test and BC, BE and CE (while it was still on the board) were beeping all over the place so I assume it's shorted (or should I take it out of the board to make sure?).

PS I've also read that the reason for a shorted HOT can be a broken flyback transformer, anybody any idea how I can test this one?

Cheers

Berre

[Morrowrj]

Well first of all, yes; HOT , line output transistor(LOPTR), flyback transistor are all names for the same part. I would say if you got a passing continuity test in all configurations then it is defeinitely shorted. As for Flyback testing, i personally skipped it, but if you are ambitious, you can check out this : http://repairfaq.ece.drexel.edu/sam/flytest.htm

Good luck

[berre]

Just bought a BU808DFI for 3ˆ... I'll replace it hopefully tomorrow...

Let's hope it solves the problem!

Cheers

Berre

[berre]

Hi,

I've replaced the HOT and the problem is solved... let's hope it stays that way...

My guess is that the transistor died because it isn't cooled enough. All other transistors on the board have a metal back that's connected to the cooling-plate but this one has a plastic back which doesn't conduct the heat as well as metal.

Anyway, thank you very much for the help!! If you ever come to Belgium I'll buy you a beer

Cheers

Berre

[Al_Dodge_Bundy]

Hello Berre,

You might wanto consider to ad some "therminal conductive grease" ("koel-pasta" in Dutch) between the TOR and the cooling-plate!!

This way the heat is tranfered, from the TOR to the cooling plate, much better!

Grtz Mark