Dead Sony KV-T25SZ8 TV

I'm not expert but ...

Arcing within the PSU?

Examine it really closely and if nothing is obvious it might be worth powering up on your bench with the covers off and the lights turned way down - but you shouldn't completely discount the possibility of internal arcing in a cap or the transformer.

But I will bow to anyone else with experience.

Make sure you have a small, tightly focused torch, earth leakage protection, and don't get yourself electrocuted (keep one hand in your pocket, no loose hair, chains, cloths or anything else, don't touch etc).

If it were me I would balance the cost of a new TV - some of the flat screens are sold at ridiculous prices v. the time, effort and cost of repair including the possibility of spending time and effort to discover you can't get a part - especially if you don't already have good connections for TV parts

"Sylvia Else" wrote

answer is; probably HOT (probably BU or 2SC)

solder it out and check pins for zero ohms....it shouldnt be zero in any way of measuring to locate it, its right beside the HV coil on some heatsink ...beside it is usually some elco 100 - 470uF / 160 or 250V..solder it out too and check the cap and ESR as well....so as the diode nearby

repair will cost you max 5$

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

"Sylvia Else"

** Hey dumbass.

You misspelled "sci.electronics.repair".

... Phil

A friend and I (he very experienced) tries to fix a similar fault in a similar Sony TV a year back. The clicking was coming from a relay in the PSU, which appears to be driven via some circuitry from an opto-isolator from the main board. It would appear that it would try to power up, detect a fault, and shut off again, repeatedly. We never did get to the bottom of it. Really, with so many rather good glass TVs on the nature strip, are you sure it's worth the trouble?

Clifford Heath.

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.

So I did. Now why didn't the server complain?

Sylvia.

Probably not, particulary as I've identified a dud transistor that is moderately expensive to source, and whose failure may only be a symptom. If the problem had been a failed electrolytic capacitor that I could get from my local electronics shop, then it would have been worth having a go at fixing it. As things stand, it's destined for the tip (or something - see below).

But we don't get good glass TVs on the nature strip, at least not in my suburb. The council banned getting rid of them that way (i.e. leaving them out on an official council cleanup day), with the result that one cannot simply go out on such a day, and pick up a TV whose only sin is that it isn't wide-screen.

Sylvia.

I replaced the HOT in this TV also. $9 including shipping from WES. However, HOTs are very strange devices. If you just do the basic two-diode test, you'll probably consider that a good one has failed. That's what I did :)... something to keep in mind.

So drive to the next suburb. Aforementioned friend has picked up half a dozen perfectly functional TVs that way, usually wide-screen versions (he prefers those), and provided them to friends. Must get a few duds, but you can drop those back.

Clifford Heath.

t f

ou

We had a nice 2004 vintage Sharp set that failed about a year back. Intermittent, wouldn't turn on sometimes but would other times. had a fast look inside and saw corrosion around one of the IC's. (looked like the CPU).

The set only just fit into the wheely bin, but it did fit. Saved a trip out to the (isolated) main road to leave it for someone to take home.

"Phil Allison" wrote

was that really nesecarry?!?!? you really enjoy it, dont you :P

show some attitude at least toward ladies FFS :)))

"Gagi-9a6aag" "Phil Allison"

** You are new here and know nothing of the past.

Sylvia is no lady.

.... Phil

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.

"Phil Allison" wrote

ok, then SilviO

"Clifford Heath"

** You need a " Power Transistor Tester" - published as a full construction article in EA magazine back in May of 1988 by me. Altronics and Jaycar had kits for it at one time.

It will reasonably accurately test the beta (or Hfe) of any power transistor OR power Darlington pair OR horizontal deflection transistor. Very cheap to make - uses only a few passives, a couple of red LEDs and a WW pot.

No PCB was used as it take only minutes to wire up the bits once they are all fitted into a small jiffy box.

It will also allow close matching ( ie Vbe match) of groups of power transistors that must operate in parallel.

Requires an external 12 volt DC source.

I would post the schem on ABSE, but like so many others I no longer have access to the site.

..... Phil

"Gagi-9a6aag"

** ROTFL !!

.... Phil

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 .............