Dead Sony KV-T25SZ8 TV

On Sat, 12 Mar 2011 22:18:42 +1100, Sylvia Else put finger to keyboard and composed:

There appears to be a short on one of the SMPS outputs.

Service Manual for Sony BG-1S Chassis:

- Franc Zabkar

--
Please remove one 'i' from my address when replying by email.

Thanks for the reference.

The horizontal deflection output transistor measures 5.7 omhs from emitter to base in either direction. It would certainly show as a short on the SMPS output.

I can source a replacement for $15 (possibly!), but is it the cause, or just a symptom?

Time for a new TV, I think, as suggested by by David.

Damnation - now I have to choose one - I hate doing that.

Sylvia

"Sylvia Else"

** Probably normal.

There is an inbuilt resistor from B to E in nearly all HOTs of 20 ohms or less.

** Bollocks.

.... Phil

Er, yes, I meant emitter to collector.

Probably true, for the emitter to base.

I found what appears to be the correct schematic. The transistor's collector emitter junction is in series with an EHT transformer primary winding, and together they sit across the HT output from the SMPS, with just a small inductor in the way. I must admit it doesn't look to me as if it's performing a horizontal deflection output role - that's just how the transistor is described in the data sheet.

Sylvia.

I've bitten the bullet, and bought a new television.

Still, I'm puzzled by the failure in the old one. The transistor has clearly failed, as far as I can see. Removing the small inductor mentioned above stops the clicking noise, which is consistent with there no longer being a short across the SMPS.

I'd have expected the set to now turn on and produce sound. But it doesn't.

The SMPS uses a quasi-resonant circuit, and disconnecting the inductor has a side effect of removing the feedback for the SMPS. But on my, admittedly limited, understanding of such circuits, it should still work.

Sylvia.

It's been a long time since I dealt with CRT horiz output sections/transistors, and the latter ones were in VGA monitors.

In the Repair FAQ there are safety, testing and troubleshooting procedures for horiz section faults, including the lightbulb in series with the HOT B+ setup, IIRC.

The HOTs (transistors) are fairly rugged semis, but operating at 15+kHZ and high peak/fast risetime conduction cycles.

FWIW section..

A few conditions wrt HOT failures that I can recall at the moment include bad/cold/broken solder connections, loss of horiz drive and drifting values/faults in the tuning capacitors (the small value 1 and 2kV caps).

Small low voltage/battery powered testers aren't very reliable, IMO, for testing/evaluating HOTs, since reliable leakage testing at higher voltages than most small testers are capable of, should be performed to determine the junction's performance compared to the datasheet published specs.

The above point being that one rarely knows for sure if they're receiving genuine exact replacement parts nowadays, and testing before installation is likely the best way to find out if the part are bogus.

My recommendations (and many other archived repair recommendations) for Sony TVs and monitors, is to research the failure and buy all the recommended repair parts from a Sony authorized distributor, especially for PSU and H,V sweep faults.

-- Cheers, WB .............

"Wild_Bull"

** Not to forget arcing inside the CRT or the horizontal transformer.

** 99 % of them cannot do any test on them at all.

** Pure gobbledegook.

** Instead of what - fakes ??

** Absolute bullshit.

No simple test will reveal a device that is merely sub-standard or of a similar but cheaper type to the original.

The only way is to deal with reliable suppliers ONLY.

** Wear a belt and braces too - do you ??

.... Phil

In a vacuum?

or the horizontal transformer.

Sylvia.

"Stupider than Anyone Else.

** One of the most common causes of HOT failures.

Dumbass.

.... Phil

Arcing, shorts and HV leakage can all take place within a CRT. I've seen several CRTs that had HV leakage to the Focus element (didn't damage the HOT though).. there may be some examples in the Repair FAQ of this type of fault and other CRT faults.

-- Cheers, WB .............

******Bollocks.

Most horiz output internal resistors are between 25 and 50 ohms. Besides, 20 ohms isn't 5.7ohms. In circuit, E to B reads an ohm or under as the secondary of the horiz driver transformer is directly across it.. Out of circuit, a reading of 5.7 ohms E to B is a bad transistor. It's not common in horizontal outputs, but an E to B short does happen.

**** More likely a stupid answer.

A common problem in Sonys is a bad solder connection on the secondary of the horiz driver transformer, so instead of reading under an ohm, the cold solder causes a reading of several ohms up to the internal resistor value. Simply resoldering the horiz driver will restore proper reading if the output is otherwise OK.

Twit.

Hey, this is fun!!!!!

Sony tvs are notorious for being picky about spares. I dislike them for that reason, as they usually get repair estimates rejected due to cost grounds.And that's assuming spares availability...

I recently dumped a 25" CRT set (FE2 chassis I think) - shorted horizontal output stage. Common fault with the chassis - the transformer fails, killing the line o/p transistor and damages the micro. Unless you replace the lot in one go, with genuine sony bits, you're back to square one... plus the uPc is NLA and an awkward smd type. Set was BER, a shame considering it was barely 8 years old.

-B

"Stroonz is a SHITHEAD "

** I have seen them with 20 ohms and less.

You need to get out more.

** The OP corrected her error in the next post - which like a total s*****ad you have not bothered to even read.

The 5.7 ohms was actually measured from C to B.

And the bitch gave no clue about the use of in or out of circuit testing.

** Not all HOT drive circuits are like that.

Many have a low value R in series with the base with a diode across it.

** Why don't you go f*ck a dead donkey ?

...... Phil

ng.

.

Im very annoyed now, I was sipping coffee when I read that, and some got sprayed from laughing ;)

On Mar 14, 9:38=A0pm, "Phil Allison" blathered:

******* Doesn't matter if she corrected it or not. You were INCORRECT when you believed a 5.7 ohm E to B reading was normal in HER SONY.

On Mar 14, 9:38 pm, "Phil Allison" blathered:

** I have seen them with 20 ohms and less.

Yes, and they were shorted. OTOH, if you can cite a transistor that was actually used as a horiz output that has an emitter-base resistor of less than 20 ohms, I'll happily concede.

On Mar 14, 9:38 pm, "Phil Allison" droned:

******** Read above ^

ng.

******** We don't know if she's a bitch or not. She might be quiet pleasant.....

No one said all HOT drive circuits are like that. But again, she wasn't interested in every conceivable version of the drive circuit, she was interested in HER Sony. Her Sony doesn't have a "low value resistor in series with the base". If you don't know what you're talking about or can't offer correct specific information, you really should pipe down, or at least qualify your opinions as just that.

Common Phil, where does one find a dead donkey, even if one was so inclined to be intimate with it. You may not be the smartest guy on the web, but you are a riot!!!

Oh, and the quiet above is a typo: reverse the "e" and "t"

"Stroonz is a PSYCHOTIC SHITHEAD "

** I have seen them with 20 ohms and less.

You need to get out of that asylum more.

** The OP corrected her error in the next post - which like a total s*****ad you have not bothered to even read.

The 5.7 ohms was actually measured from C to B.

And the mad bitch gave no clue about the use of in or out of circuit testing.

** Not all HOT drive circuits are like that.

Many have a low value R in series with the base with a diode across it.

The original exchange was:

" > The horizontal deflection output transistor measures 5.7 omhs from > emitter to base in either direction.

** Probably normal. "

See - no reference is made to any particular set in my remark .

** Why don't you go f*ck two dead donkeys ?

...... Phil

****** Yes, the OP did correct her error, something you refuse to do. You said a 5.7 ohm reading was "probably normal" for her Sony. You were wrong and can't admit it. Nice character flaw Phil.

It's hard to explain this to someone who is unfamiliar with Sonys, but I'll try again: If everything in her Sony is normal, the E to B resistance reading will be under an ohm in circuit. If the secondary of the horiz drive trans in her Sony is open or the connection is bad, it will read the internal emitter to base resistor directly, if the transistor is so equipped. (some Sonys of this era use no e to be resistor). If the transistor is measured out of circuit, it will read approx 35 ohms e to b if it's not shorted. Under NO CIRCUMSTANCES will this TV show 5.7 ohms across the e to b junction. Such a reading is ABNORMAL. Perhaps you left the "ab" out of your reply.

And I know you'll requote her correcting her reading, but it doesn't change the fact that you believed and proclaimed as fact that an E to B reading of 5.7 ohms in HER SONY was normal.

You know, vile, classless folk take all the fun out of a debate.

Enjoy your last word Phil......

"Stroonz is a LYING PSYCHOPATH "

You said a 5.7 ohm reading was "probably normal" for her Sony.

** Wrong.

** Why don't you go f*ck two dead donkeys ?