Bush LCD27TV006HD 2 secs to black

[tom66]

Re: Bush LCD27TV006HD 2 secs to black

Pin 1 of the OZ960GN should have a small capacitor attached to it. Put a bridge across this so it is shorted out. This should set the start timer to never expire. Run the set for a maximum of 30 seconds in this mode. Connect a computer and generate a full white frame, see if the panel is evenly lit. If not you have a bad bulb.

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

OK tried that but still '2 secs to black'.

[tom66]

Re: Bush LCD27TV006HD 2 secs to black

Hmm, looks like they may have multiple protections. What do you measure on pin #3 of the OZ960GN?

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

Pin 3 - ENA - 2.46v

[tom66]

Re: Bush LCD27TV006HD 2 secs to black

Working and not working? Same?

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

In standby 0v, switch on 0v until lamps light then rises to 2.46v and stays constant even after lamps go out, can't leave it on for too long as still have the jumper across Pin 1 and GndA.

Would a logic probe be of use here?

[tom66]

Re: Bush LCD27TV006HD 2 secs to black

Logic probe may be useful later, but at the moment a multimeter is more usable.

Pin 2 and pin 7 readings please.

I'm trying to figure out what is causing shut down.

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

Ok, just thought it worth mentioning that I had one if needed.

Pin 2 - OVP - 0v stby, quickly peaks to 0.9v, drops to 0v when lamps extinguish
Pin 7 - REF - 0v stby, 1.46v when lamps lit, drops to 0v when lamps extinguish

[tom66]

Re: Bush LCD27TV006HD 2 secs to black

Hmm... REF should be 2.5V +/-10% please recheck otherwise the OZ960GN may be bad.

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

Did check it a couple of times and it jumps quickly up to 1.46v briefly before dropping to 0v, hard to see an exact reading but its definately no more than 1.5v.

Well, 1.7v at the most with the DMM set to 2volt range. Never goes out of scale.
Checked a few more times and its reading different every time, 1.4, 1.3 1.9v.

Pin 5 - VDDA - 4.96v so the source voltage looks good

[tom66]

Re: Bush LCD27TV006HD 2 secs to black

I would consider that as being a potential fault. That voltage determines the bulb voltage. If it is too low, the bulbs will strike (2 second period) but then go out because the voltage isn't high enough to sustain light.

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

OK, so replacement board then, just wanted extra reassurance it wasn't the lamps.

Another Darfon board I have has an OZ960G, I wonder.

[tom66]

Re: Bush LCD27TV006HD 2 secs to black

If it were an open bulb you'd see OVP hitting around 2~3V, though it's not impossible that you have a leaky-to-chassis wire or bulb causing this issue, just relatively unlikely given the REF voltage looks dodgy.

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

Think I shall just get a replacement board, 20pins to unsolder and resolder, not likely to be easy for me and its possible the 0Z960 on my spare is shot too though it was a Mosfet blown on that one!

£3.42 for 2 from China, but with my soldering skills and the time it takes for carriage may as well buy a board, £9. Someone in UK but £9 for the I.C, huh.

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

Board ordered.

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

Quick update.
Still awaiting board, missed 1st delivery so waiting for re-delivery. Damn it!

Anyway, got fed up and replaced the OZ960 with one from another spare board, one that was replaced due to a fault, so I know this board was faulty it had a blown mosfet unsure what else or what caused it but replacing the board fixed the tv.

So, swapped the OZ960 and now get a screen showing something but its only lit up half of the screen, right side lit up, left side dim and the screen is flickering. Theres also some noise coming from the inverter board now, sounds like arcing could be poor solder joints where I removed the trannys to test and re-soldered.

Bl-On - 4.1v

OZ960G
Pin 2 - OVP - 0.5v
Pin 3 - ENA - 1.4v
Pin 7 - REF - 1.4v

Could be that this OZ960 is bad too!

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

So thought the new board would solve all my problems, well that was not so!

Back to the original fault with the replacement board.

So I decided to check the 24v rails by removing inverter connectors and wiring up 2 12v bulbs in series, with them connected to Gnd and 24v from the PS b/d they do not light up, but if I connect them when the board is already powered up the lamps glow bright and steady as would be expected from a good 24v supply.

So the question is: why are the lamps not lighting up when connected to PS before powering up?

[budm]

Re: Bush LCD27TV006HD 2 secs to black

The cold resistance of the lamps can trigger the over current shutdown when the power supply is starting up from 0V. Take the resistance reading when lamps are cold, then you can calculate the in-rush current at start up.

[notallbad]

Re: Bush LCD27TV006HD 2 secs to black

Resistance of both lamps in series is 5.6ohm, so a draw of 2.14 amps.

[tom66]

Re: Bush LCD27TV006HD 2 secs to black

Check again: 24V / 5.6 ohm = 4.3A
A little high for a 27" LCD.