techwood 37722hd faulty psu 17pw15-8

[gary19610]

I have a techwood 37722hd with a 17pw15-8 psu I have change 4 caps 1000uf 16v what was bulging but no look tv still not working.when you plug tv on blue light comes on and when you press button blue light go of and screen is still black with no picture no back lights psu is buzzing a bit to.any help please

Gary

[Clydeuk]

Re: techwood 37722hd faulty psu 17pw15-8

Vestel power supply, I'd take a punt at the 15nF capacitors on the primary, there are 2 of them near the heatsink top left by the 2 FET's (which may also be short-circuited). Those caps fail frequently and are always worth replacing with a better quality component, they also cause random faults when they start to fail. These are polyester type caps not electrolytics, you might see a bulge in the side, but equally maybe not. If the FET's have failed you'll probably have an open resistor or fuse as well (i forget now as its been a while since I worked on one of these)

The standby power circuit is separate if I remember correctly so a standby light is no indication of a working power supply.

[gary19610]

Re: techwood 37722hd faulty psu 17pw15-8

I have changed 15nf,s and fets seem ok but still get the same plug tv in blue light comes on press power button blue light gos of and nothing just buzzing coming from the power supply and the other buttons do nothing on front of the tv

[Clydeuk]

Re: techwood 37722hd faulty psu 17pw15-8

I've got a diagram for this if it helps. You may have one already. Sounds like the main voltage rails aren't coming up so we need to know if the ST-BY on signal is reaching the main SMPS controller. I'm trying to pick my brain as I did a lot of work on one of these last year with several faults. A quick look at the diagram looks like the optocoupler IC8 is responsible for relaying to on signal to the main primary. There's an LM317T regulator involved there as well that supplies the primary SMPS controller I.C. I've heard mention of failure there but never had one gone, might be worth checking it's pins for voltage.

[gary19610]

Re: techwood 37722hd faulty psu 17pw15-8

could you send me the diagram please. I can see if I can work it out with the diagram my email is gary19610'live.co.uk

thank you

[gary19610]

Re: techwood 37722hd faulty psu 17pw15-8

mine gary19610@live.co.uk for diagram

[tom66]

Re: techwood 37722hd faulty psu 17pw15-8

Diagram:
http://www.tgohome.com/ServiceManual...&Search=Submit

Good luck decoding Vestel schematics... they're, uh, "special".

[gary19610]

Re: techwood 37722hd faulty psu 17pw15-8

think its down to the mainboard because the voltage on plug 803 the 34v stars dropping down and the 12v drops to 11v but unplug from mainboard and the voltages stay at 34v and 12v

[tom66]

Re: techwood 37722hd faulty psu 17pw15-8

Unlikely -- more like bad power board -- bad main boards are rare on this generation of Vestel and wouldn't usually cause that fault.

If you connect a car brake light to 12V and two 60W car headlights in series to 24V you should see same effect.

When first plugged in the power supply undergoes self test from main board: voltages rise for a couple of seconds then fall. Main board goes into standby mode. Then press power butotn, they should come up and stay steady. Or, the main board will shut down if fault detected giving a continuously flashing LED.

[gary19610]

Re: techwood 37722hd faulty psu 17pw15-8

I get no flashing led and only get steady voltages when I disconnect plug 803 from mainboard. If connect plug 803 to mainboard and press power button for TV to come on the 34v on plug 803 starts dropping like 34 33 32 31 and so on and 12v go's to 11v and this is my 2nd psu with same tv fault so both psu are giving me the same fault on the tv

[gary19610]

Re: techwood 37722hd faulty psu 17pw15-8

and I still get the buzzing out of both psu when I tried them one at a time the 2nd one is supposed to be fully working. The buzzing only starts when I press power button for the tv to come on. I have disconnect both back lights and still get the buzzing to.when I disconnect plug 803 buzzing go,s away

[tom66]

Re: techwood 37722hd faulty psu 17pw15-8

Check the voltage across the big 450V capacitor as it powers up: should be about 390V run, 330~350V standby. If faulty, will give around 330~350V continuously.

99% of these Vestels have power board faults: don't rule out the chance that you got the same fault across both models. They do have the odd inverter/t-con fault, but that causes other symptoms. I've never seen a main board on one of these go bad.

[gary19610]

Re: techwood 37722hd faulty psu 17pw15-8

Check the voltage across the big 450V capacitor as it powers up: should be about 390V run, 330~350V standby. If faulty, will give around 330~350V continuously.

99% of these Vestels have power board faults: don't rule out the chance that you got the same fault across both models. They do have the odd inverter/t-con fault, but that causes other symptoms. I've never seen a main board on one of these go bad.

just wondering on the plug 803 going to the mainboard if number 4 pin yellow wire is ground because its reading ground with the black wires.it just reading ground on the mainboard but not on psu board.on the diagram psu its saying number 4 pin is AC-DIM-SEL

[gary19610]

Re: techwood 37722hd faulty psu 17pw15-8

just put a new mainboard in and working ok hope fully will Carrie on that way thanks everybody for their help

[badcaphunter]

Re: techwood 37722hd faulty psu 17pw15-8

I had the same issue, unplugged the eeprom and it fired up.