Vestel 17PW26-4 No Standby

[TechWizard.Support]

Just some quick background, I'm a computer technician with very basic soldering experience, and I'm looking to learn more about component level repair. I own a multimeter with diode mode & continuity, an ESR meter and an Antex 760RWK Rework station. I have some basic knowledge about electronics.

My client has a Technika LCD32-229 with a Vestel 17PW26-4 Power Board and there is no standby power. I said that I mainly deal with computers, but I'd take a look and could replace the capacitors if they were the issue. Upon inspection, these looked OK, and just to be sure, I confirmed with my ESR meter.

The inside of the TV and the board were thick with dust, the vents were completely blocked and I'm guessing some components may have overheated. Once cleaned, I noticed a lot of burn marks on the board, quite extensively around C903, D800, D882/3, Q813 and minor signs around the transformers and various other components. Do you think this board is too extensively damaged? Or is it worth troubleshooting further? I have included images of the front and back of the board and a schematic I found.

Thank you for taking the time to read my post, your support will be greatly appreciated!

Richard.

[vinceroger69]

Re: Vestel 17PW26-4 No Standby

This is whats in the repair kits for no standby faults so maybe start with checking these first
F800
Q813
Q814
IC830
D894
R860
R8661
R971
C840
FAN7711

[TechWizard.Support]

Re: Vestel 17PW26-4 No Standby

Thanks Vince, here are my results:

F800 - OK
Q813 - OK, no shorts
Q814 - OK, no shorts
D894 - OK
R860 - 32.8 (33) Ohms
R861 - 32.8 (33) Ohms - Can't see an 8661, I presume you meant 861
R971 - 0.26 (0.22) Ohms
C840 - 30.78 (33) uf, 0.82 Ohms ESR
IC830 / FAN7711 - Not sure how to test this

*Expected value in brackets.

Is it best to remove the MOSFETs and test the switching out of circuit? I just tested for shorts. Excuse my lack of knowledge, this is a new area for me!

[diif]

Re: Vestel 17PW26-4 No Standby

You can give MOSFETs a test in circuit with your meter in diode mode.
https://www.utm.edu/staff/leeb/mostest.htm
If they show a short then I remove and test out of circuit.

[TechWizard.Support]

Re: Vestel 17PW26-4 No Standby

Thanks for that Diif, I did take a look on that page myself, but didn't test further as there was no short. I bought a replacement board for my clients TV, but I'd still like to work on this board myself as a project to develop my understanding.

When I get chance in the new year, I'll come back to this board and work my way through it. So any guidance regarding a troubleshooting process to follow would be greatly appreciated. I watched a few videos from MrReeceyburger123 which have been helpful, so I certainly appreciate the time he and others have committed to help people new to the area such as myself.

[R_J]

Re: Vestel 17PW26-4 No Standby

If you have no standby voltage I suspect IC806 has failed.
Check the resistance of R1012, You can also check the fet inside the ic, check the resistance between pins (6,7,8) and ground, if there is a short the ic is bad.
It could also be as simple as a bad C801 (33/50v) or C892 (10/50v)

[tom66]

Re: Vestel 17PW26-4 No Standby

While the set is plugged in you should check the standby voltage on the connectors going to the main board. If unsure just check all voltages and see if anything is active.

[TechWizard.Support]

Re: Vestel 17PW26-4 No Standby

Thanks R_J, I'll check that IC806 & R1012. Regarding the caps, they tested ok with my ESR meter.

Tom, I'm getting nothing on that connector, sorry, I should have mentioned this in my original post.

[tom66]

Re: Vestel 17PW26-4 No Standby

Schematic:


Check points:
F800: check ok
C802, C934: expect ~320V DC across either
D879, IC831 (dual diode): check not shorted
D823, D884: check not shorted
5V/3.3V standby outputs - check each to ground, not shorted
C817: check for 12V when set connected to mains
C892: Vcc, check for 7~18V when connected to mains
C801: Vcc, check as above
D807, D862: check not shorted
Measure resistance across C892: should be high (>100k)

If Vcc is present but oscillating: Replace C892, C801 and D866 (5.1V zener).
If Vcc is DEAD and no shorts are visible, OR Vcc line has short, then IC806 is probably bad.

[K_i_t_c_h]

Re: Vestel 17PW26-4 No Standby

If you have no standby voltage I suspect IC806 has failed.
Check the resistance of R1012, You can also check the fet inside the ic, check the resistance between pins (6,7,8) and ground, if there is a short the ic is bad.
It could also be as simple as a bad C801 (33/50v) or C892 (10/50v)

Changed all the faulty capacitors still no joy, found ic806 was faulty replaced and now working TV!!! R1012 and c801 was okay in this repair

Original fault for me was turn the power button on and stand by voltage would drop and would loose voltage to the standby and would give me voltage again and turn of again, thanks for this suggestion and taking the time to reapond!!