Faulty Vestel 17PW06-2 power supply (dropping voltages, no picture)

[Dannyx]

Re: Faulty Vestel 17PW06-2 power supply (dropping voltages, no picture)

There is only one transistor on the power supply board which controls the Backlight On/Off (Q206).

I think you have a fault on the backlight board which is heavily loading the 24V supply when switched on and this is dragging down the other voltages.

Can you run the set without the backlight connected and use two 12V car bulbs in series as a load to test it.

Edit
May also be worth checking diodes D201, D206,D207 & D208

I believe I mentioned somewhere in one of my earlier posts that all of the test so far have been performed "on the bench", with just the power board and nothing else attached to it, so if it's not stable like this, with no load, it's highly unlikely it will do so under load. On that topic, I've been thinking: if 24V are present at the LED output at all times (even when the BL pin is not connected to 5v) and so are 12v and 5v at the main board connector, why do we need that BL signal on the power board ? What exactly is it switching on on the PSU board. I know the BL signal goes through the LED connector to the LED driver board and switches that on, but what does it do to the power board ? I'm starting to think there's a fault somewhere which keeps the board on at all times (namely that Q306). I think the volts should drop when BL is removed (at least the 24v bus, otherwise WHY would it be on at all times) ? So goddamn confusing >_>

[Dannyx]

Re: Faulty Vestel 17PW06-2 power supply (dropping voltages, no picture)

There is only one transistor on the power supply board which controls the Backlight On/Off (Q206).

I think you have a fault on the backlight board which is heavily loading the 24V supply when switched on and this is dragging down the other voltages.

Can you run the set without the backlight connected and use two 12V car bulbs in series as a load to test it.

Edit
May also be worth checking diodes D201, D206,D207 & D208

Forgot to mention those 3 diodes (yes, 3 on my board - one is not installed) are fine - even desoldered them and checked them. My meter didn't beep to signal a dead-short and also they had the same voltage drop when forward biased and no "leakage" when reversed biased.

[dick_barton]

Re: Faulty Vestel 17PW06-2 power supply (dropping voltages, no picture)

So to recap. With the power supply disconnected from the main board you have 5V, 12V and 24V all stable until you connect BL_On/Off to 5v via a jumper resistor at which point your supplies become unstable?

[Dannyx]

Re: Faulty Vestel 17PW06-2 power supply (dropping voltages, no picture)

So to recap. With the power supply disconnected from the main board you have 5V, 12V and 24V all stable until you connect BL_On/Off to 5v via a jumper resistor at which point your supplies become unstable?

That is correct. Which again brings me back to the question about WHY that BL pin needs to be attached at all - to my mind, it should only go to the LED board straight from the PSU, considering the LED board always has 24v present and only needs the start signal.

[dick_barton]

Re: Faulty Vestel 17PW06-2 power supply (dropping voltages, no picture)

The backlight circuit on the power supply is minimal components as shown in the diagram so I cannot see how it can have any effect on the supplies. The worse case scenario is that the transistor is short circuit.

[Dannyx]

Re: Faulty Vestel 17PW06-2 power supply (dropping voltages, no picture)

The backlight circuit on the power supply is minimal components as shown in the diagram so I cannot see how it can have any effect on the supplies. The worse case scenario is that the transistor is short circuit.

Ok, I've just discovered I've been a dumbass this entire time: remember the connector PL200 ? Well, looking at the schematic, it's not clear AT ALL how those pins are labeled, so I soldered my jumper wire to pin 5 by mistake, thinking that pin 1 is SW_SWITCH and pin 5 is BL ON, when in fact the first pin is ground and pin 5 is STBY, while pin 7 is the "real" BL pin. Essentially, instead of sending 5v into BL, I was sending it to STBY.....still, that wouldn't explain why the voltages drop when I do so. That BL pin actually has nothing to do with the power board - it just goes straight through it and into the LED board, confirming my earlier doubts about it serving no purpose. What's next now ? Damn, sorry for the confusion