Vestel 17PW01-4 PS board stuck in standby

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

I think we crossed posts..

D909 was backwards??? I can't quite understand that because to test them I cut one leg rather than desolder the whole diode..

Anyway, it's now round the correct way. Out of circuit the drop was 0.135. (the same as the other 2)

Voltage across C970 is 0.000v

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

0.00v

see above edited post

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

The dc voltage on the anode side of D908-9-10 is 0.123v

I have some new UF5402's in stock. Is there any benefit to swapping them?

IC500 FAN7711
1 - VDD 14.93v
2 - RT 0.001v
3 - CPH 0.001v
4 - GND
5 - LO 0.542v
6 - VS 13.18v
7 - HO 13.57v
8 - VB 14.91v

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

Have you since tried to power up the set with power supply and mainboard reconnected?

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

No. I will and report back.

Same as before: The front of the set blue LED lights and the buttons on the front of the set cause a bleep to be emitted from the logic board with each button press.

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

I'm at a loss here. With the power to the set off what's the resistance reading across the two legs of C851.

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

After charging it reads 375 ohms.

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

So no short problem on the 12V line.

Can you initially visually check both Q813 & Q814 for any damage which I think are under the heatsink. There is a possibility that they may have been damaged due to the diode in the secondary circuit being backwards.

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

I've desoldered the heatsink and both mosfets.

In off state I have o/c between D & S
In on state I have continuity between D & S

I've compared the results to a new n-mosfet and the results are the same.

I have a very cheap eBay component tester & here are it's results:

Q813
Vt3.4v
Cg3.00nF
RDS0.7 ohm
Vf 565mV

Q814
Vt3.4v
Cg3.06nF
RDS0.5 ohm
Vf 564mV

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

What are the part numbers on the mosfets.?
The set should not be powered up when taking the measurements. If they are MTP6N60E mosfets then with your meter set to diode mode there should be a reading one way but not when you reverse the meter leads since those devices have a diode between Drain and Source.

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

So the mosfets check out OK. At this point I cannot think of what else to check out next.

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

The part numbers on both are:

1K28AB
FQPF
13N50C

With - lead on the Source and + lead on the Drain i'm reading OL on the Fluke
With +lead on the Source and - lead on the Drain i'm reading 0.515V drop on the Fluke

This is the same on both.

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

Time to pull the plug me thinks..

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

IC500 FAN7711
1 - VDD 14.93v
2 - RT 0.001v
3 - CPH 0.001v
4 - GND
5 - LO 0.542v
6 - VS 13.18v
7 - HO 13.57v
8 - VB 14.91v

Check C928, 1uF 25V

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

One last thought:

When the owner brought the tv round they reported that the set came on for a few seconds then went into standby. I confirmed this behaviour.

When I opened the back I spotted and replaced C851, C969 & C970 which were bulging and had very high ESR readings.

From that point forward the set has not come out of standby.

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

C928 is a SMD, measuring in circuit gives spurious results. Shall I desolder to measure?

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

Make a note of which way around it is soldered in and be careful not to lose it.

[Nevillet]

Re: Vestel 17PW01-4 PS board stuck in standby

Its measures 11.19uF. The schm states 1uF..

I've marked it but is doesn't appear polarised.

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

One last thought:

When the owner brought the tv round they reported that the set came on for a few seconds then went into standby. I confirmed this behaviour.

When I opened the back I spotted and replaced C851, C969 & C970 which were bulging and had very high ESR readings.

From that point forward the set has not come out of standby.

And you would have thought that replacing the bulging caps would have resolve the problem and often would have. Unfortuanely it appears to be more than that.

[dick_barton]

Re: Vestel 17PW01-4 PS board stuck in standby

As a quick test do you have an 1uF, 25V electrolytic cap you could put in it's place. Negative of cap to ground and positive connects to pin 3.