Vestel 17PW01-4 PS board stuck in standby

[Nevillet]

Hi All,

I'm looking at a Finlux (Vestel) TV which is stuck in standby. On inspection, the power board had 3 bulging caps (C851, 970,969) which were replaced with Rubycon ZL series. (they are a strange angles at the moment to ensure I have a decent lead length if they are removed) The standby problem did not resolve it self.


Off the TV i've measured the voltages of the PL816 connector that goes to the main logic board. The readings are below:



The original capacitors are Samxon brand. I've measured the ESR and capacitance and all apear within 'normal limits'. (I had to desolder them as some of them were in parallel and I was getting skewed results)

Similarly. I desoldered the big power diodes which were all fine.

As a general question, on a normally functioning PS board what kind of voltage variance would you expect on the +5V & +3.3V lines?

Any pointers would be most welcome.

[R_J]

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

It could be that the board only supplies 3.3v standby. to turn on the power supply board (disconnected from main) connect the 3.3VSTBY to pin 6 ST_BY. this should turn on the power supply. You can use a 1k resistor to be safe in case you connect to a wrong pin but a 47K resistor (r828) is already in place in Q804 base so no external resistor is needed.
Look at the trace side of the board, the +5VSTBY may not be used or may be connected to the +3.3VSTBY
The standby voltage could be a bit high due to no load when disconnected from the main. Also the voltage could be off due the the pfc circuit not operating in standby mode.

[Nevillet]

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

Hi Both,

I bridged the pins 6 and 16 as suggested and remeasured the voltages on the PL816 connector. The results are below:



The other multipin connectors PL801 & PL802 also show no voltages.

The RL5 Relay also switches when the PL816 6&16 are joined.

Please let me know your thoughts and next steps.

Many thanks.

[R_J]

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

When you say THE relay switches, which one are you talking about? If you look at the schematic you will see more than one relay.

[Nevillet]

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

When the PS board is connected to mains power there is a relay that switches on the primary side.

After powering the board and when the 6-16 pins are joined the RL5 relay engages on the secondry side.

[R_J]

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

Relay5 is powered by +12 volts, the source for that is the secondary of TR817, so that circuit must be working. Are you sure you don't have +12 and +24 volts?

[Nevillet]

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

CORRECTION:

When the PCB is powered initially you hear the click of a relay. When you jumper pin 6 to 16 you hear another relay click.

I falsly thought this click was RL5 on the low power side. It was not, it was RL4 on the high power side.

RL5 is not energised at all. I've tested RL5 off the board and it works fine when energised with 12V.

[R_J]

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

Explain HOW relay5, Quote from post #7: "After powering the board and when the 6-16 pins are joined the RL5 relay engages on the secondry side" gets energized if you have NO voltage going to it?

[Nevillet]

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

#7 post was a mistake, sorry.

To clarify:

RL4 energises when the board is powered.

RL4 de-energises when pin 6-16 are jumpered.

RL5 does not energise in any condition.

[R_J]

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

What is the voltage on VF_MAIN? When the board is tured ON what is the voltage on VCC1 and VCC2? VCC1 supplies the voltage for IC500, this is the ic that drives Q13/14 so you can get the secondary +12/24 volts
Does the voltage across the main filter (C962) increase when the board is powerd on?

[Nevillet]

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

Hi Again,

I've taken the measurements you asked for, table below:



When I measured the voltage across the C962 I noticed a lot of ripple on the meter (Fluke 85). I then connected a scope lead to the + leg of C962. The grounding point being PL846. The first trace is with the board not switched on:



The next trace is with the board switched on:



I'm not sure if this helps or hinders but:

In trying to locate the voltages I looked at a few IC's e.g.

IC500 (FAN7711)
Measuring the supply voltage between pin 1 VDD & pin 4 GND was 14.79V when switched off and 0v when switched on.

IC830 (NCP1653)
Measuring the supply voltage between pin 8 VDD & pin 6 GND was 15.01V when switched off and 0v when switched on.

Many thanks

[R_J]

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

VF_MAIN voltage comes from the standby ic circuit, You measure 9.6v, when you turn ON the power supply that voltage droped to 0. This could be caused by a bad C801 or it could be due to a short on either VCC1 or VCC2
If C801 is bad, it can't maintain the voltage to keep the circuit working

[Nevillet]

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

C801 (100uF,50V) measured off the board is 100.8uF with an ESR of 0.26 ohms.

I compared these measurements with new stock caps and C801 scored better.

[Nevillet]

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

Not sure if this helps matters, but this is the plastic insulation from behind the power board and gives an indication of the areas of excessive heat:



I'm at a bit of a loss to find any shorted parts of VCC1 or VCC2.

[R_J]

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

I think the voltages you are measuring are backwards, VDD 15 volts on ic500 and ic830. will be there when the tv is turned ON not OFF
This is how ic500 & ic830 circuits are controlled. in standby the VDD is OFF, when the tv is turned ON, Q844 supplies VCC1 and VCC2 to the VDD pins of ic500 & ic830.
Check the voltage across the main filter capacitor (C962,C963 etc.) In standby it will be about 340vdc, when the tv is turned ON (VDD 15v) that voltage should be close to 400vdc. If it does then the PFC circuit IS working.

[Nevillet]

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

So when pins 6>16 is joined the board is off, when 6>16 is open circuit the board in on. That makes a lot more sense.

So the default state of the board, when not connected to the logic board, is that it's powered on. (effectively the 6>16 jumper is open)

Yes I have VCC of approx 15v on IC500 & IC830 and the voltage across C962-964 is 379v.

I tried to measure the voltage on VDD on IC832 and realised it was not a DC or sinusoidal AC signal so put the scope on it:



With the board on I measured all the DC voltages across the large electrolytics laying on their sides:

C965 378.9v
C958 353v
C967 0v
C911 0v
C852 0v
C850 0v
C851 0v
C970 0v
C969 0v
C962 378v
C964 379v
C963 378v

[dick_barton]

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

At switch on Pin 5 (Vstr) of IC806 (FSDL321) connected to the 400V line via a 10K resistor should charge C892 to 12V at which point the VCC supply (Pin 2) is switched over to the supply provided by D807, C801. I would check C892.

[Nevillet]

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

C892 on the schematic states its a (10uF,50v)

Off board inspection reveals it's marked as 100uF,25V,85C and measures:

93.69uF, ESR 0.51 (Peak ESR70 meter)

Should I replace it with a 10 or 100uF? or put the old one back?

[R_J]

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

It is hard to say, does it look like it was changed before? I dont' think the original would have been a 85c, it would have been a 100c. try a 10µf and see if works better.

[Nevillet]

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

it looked original.
Swapped for a 10uF,50V no change.
swapped for a 100uF,25V no change.