Slightly Different Vestel 17PW26-4 Problem

[John949]

I have searched the archives but I can't find one quite like this.
As the set comes out of standby the backlight flashes briefly and then the set goes back into standby. I'm 99% certain it's the power supply because the set works fine if I power the backlight with an external 24V supply.
Looking at the supplies as the backlight flashes, the 24V dips to about 19V then recovers for a while before shutting down. The 3.3V & 5V run supplies seem to collapse as the backlight flashes - I asume this is what turns the backlight off and puts the set back into standby. Standby supplies are fine.

When I started trying to repair this set the usual FETs (Q813 & 814) were blown, so I replaced these and IC 830. I've also looked at which components are in several 'repair kits' for the board and checked these as best I can but found nothing wrong.

I'm trying to repair this TV (Sanyo CE37FD47) for a friend and as a challenge for me, but I've run out of talent.

BTW I had convinced myself it was the inverter board so I bought another one - no different.

Thanks

[tom66]

Re: Slightly Different Vestel 17PW26-4 Problem

Check and replace the poly capacitor on the primary. Post a picture if you need it pointed out. You will need a capacitance meter (not an esr meter) to test it.

[John949]

Re: Slightly Different Vestel 17PW26-4 Problem

I think this is C878 (22nF 630V), which is in many of the repair kits. I was a bit suspicious of this one so I have already replaced it. My skill level isn't up to working out what this cap does but I'll check other components around this area.

Thanks

[John949]

Re: Slightly Different Vestel 17PW26-4 Problem

Turned out to the PCF controller IC806. Pin 8 had a resistance of about 25 ohms to ground.
Spent a lot of time chasing red herrings as my board has many changes to the circuit diagram I found on the web.

[tom66]

Re: Slightly Different Vestel 17PW26-4 Problem

Thanks for posting the fix back. It will help others. Enjoy the TV.

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

I have a sharp lcd with the exact same fault , the tv switches on for a few seconds then it switches back off to standby. I replaced the power board but still the fault is there any tips tom. Thepower board is vestel 17pw 26 -4.
Main board 17MB 38-1. TV MODEL SHARP LC42 CT2E.

[vinceroger69]

Re: Slightly Different Vestel 17PW26-4 Problem

I have a sharp lcd with the exact same fault , the tv switches on for a few seconds then it switches back off to standby. I replaced the power board but still the fault is there any tips tom. Thepower board is vestel 17pw 26 -4.
Main board 17MB 38-1. TV MODEL SHARP LC42 CT2E.

not sure if effects you sharp model or not? but is in the sharp data base on another forum

Goes to standby after a few seconds
A few seconds after switching on the TV reverts to standby.
Cause is the Lamp failure protection circuit on the PWR board. If any lamp fails to strike after 2 seconds the TV reverts to standby. After 5 failures the TV goes into failure mode and does not even try to light the lamps.

The cause of the failure is often the 10pF 3kV ceramic capacitor adjacent to the lamp sockets. One capacitor for each lamp. This is a common enough failure that Ohm supplies Ltd sells a repair kit containing 10 replacement capacitors, although they can be bought a lot more cheaply elsewhere.
Once the capacitor(s) have been replaced it is necessary to put the TV into service mode to clear the lamp error.
To enter service mode power on while holding down Volume - and input select until a 'K' appears on screen. Then press vol- and prog- to enter service mode.
Using the remote use the down button to select page 10/11 then use the prog button to select clear lamp error and right button to clear it.
To exit service mode power on again with Vol- and Input Select held down

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

Thanks for the advice vince. So you are saying the lamps will probably be fine just a faulty cap on the inverter. Some times the tv will be on 20 -30 seconds before going off but i will test these caps tomorrow.

[vinceroger69]

Re: Slightly Different Vestel 17PW26-4 Problem

not sure at all 20-30 seconds is a long time just saw this on another forum whilst on google looking at another sharp fault worth checking though and the lamp error reset is a good tip i never heard of that before.tom or budm may have more ideas to what the fault could be.

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

I think i will power each and every back light up tomorrow with my back light
tester to prove all of the lamps are lighting, it#s not always easy to see if a single lamp is out, they do all seem working- looking through the holes in the back of the panel but some are out of sight. Then i will test the inverter transformers and high viltage caps you suggested. I will post back once i have done some tests on the inverter board , i need an handset too for this tv that i will have to order.

I was hoping this was going to be a simple power board problem but not to be .

[tom66]

Re: Slightly Different Vestel 17PW26-4 Problem

Check the power supply voltages. If they're dropping out then the PSU may be at fault, but if they're stable consider the inverter.

I have a very, very broken 17PW26-4 (as in physically damaged, from that 32" Polaroid, but most components are intact.) If you need a component read off, let me know.

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

Ok thanks for the offer tom. I did notice the 12 volt line from the power board fell to 11.7 volts as the tv powered down. I did suspect a power board problem and i did extensive checks doing board comparison tests with another working 26 -4 board, nothing amiss. The replacement board has been fitted too but still the same so i am pretty confident the power board is probably working ok. The replacement board is a version 1.1 same as the board in the tv but a couple of minor differences , just an extra component mounted on an heat sink on the replacement board plus the replacement board has a single mains lead socket, the original in the tv has 2 mains sockets the second just going to an on off switch on the back of tv.
I am hoping the inverter is the problem, a main board could be more expensive. I have a full service manual for this if needed by the way.

[tom66]

Re: Slightly Different Vestel 17PW26-4 Problem

I may have a suitable main board, but I am not sure if it is OK, as it is very slightly warped, I would sell it to you for very little.

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

I am willing to try anything :-) , thanks for the offer. I will test the inverter
out tomorrow and the lamps and let you know.

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

The backlights all test ok and the inverter transformers read good.
Does any one have any ideas.

[tom66]

Re: Slightly Different Vestel 17PW26-4 Problem

Check BLON pin. Pics of chassis would help us help you.

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

Ok tom thanks i will have a look tomorrow and post some pics.

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

Tom i am thinking of forcing the power board to stay on , how would you your self do this. Do i need to snip the wire that goes to the PS_ON pin and supply a voltage to the pin on the power board. Maybe if the tv stays on it would then be easier to do more tests.

[tom66]

Re: Slightly Different Vestel 17PW26-4 Problem

Yes, if you can locate PSON that may work. However be ware the main board may just shut down anyway meaning it will cut power to T-con and turn BLON low.

[Techstar]

Re: Slightly Different Vestel 17PW26-4 Problem

Ok thanks , another job for tomorrow.