Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

[televizora]

I have a problem with my Crown 32" LCD TV with chassis 17MB08P-5 and 17PW15-6 power supply.
4 days ago the TV suddenly turned itself off(we had some momentarily power outages here). Now the set is stuck in standby with only red light on the front panel on. The set is reacting neither to the keypad, nor to the remote.
I measured the capacitance of the C878 and C877 - both read as 14.5-14.8 nF. I replaced all the electrolytic capacitors with brand new. I bought new 5V IC voltage regulator.. I replaced the capacitors near the standby transformer - C801 and C892.
Now - to the point - I have 5V and 3.3V standby voltages(PL806). When I plug the TV to the mains, the 3.3V shows up for 1-2 seconds on the PL805 and then disappears. Then the yellow wire of the PL803(StandBy state) goes from low(0V) to high state(2.89V)
I'll be very glad if someone could give me some advice how to proceed from this point.

[ReeceyBurger123]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Images of boards ?

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Images of boards ?

Okay, I made some photos for you...

[ReeceyBurger123]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Esred the smaller caps ? Also what voltages do you get with the mb out and osu plugged in ?

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Esred the smaller caps ? Also what voltages do you get with the mb out and osu plugged in ?

I replaced the caps with numbers C801, C892, C857, C815, C817, C863, C852, C850, C851, C812. I have the rest in stock, but i havent replaced them all. I checked the two diodes - D846, D845.
I don't own a ESR meter, only a capacitance meter from 2000pF up to the 200uF.
With board unplugged, I only have 3.3V and 5V. - 5.13V and 3.37V to be exact.
p.s I have to add, that I also have 3.2V on the white wire of the PL805.

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Leave the main board disconnected and connect PL803 pin 6 (Standby) to +5Vstby then see what voltages you have. +12, +33, +24 etc

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

2.4V on PL805, 1.1V on the blue wire of the PL804(pin3) - have to be due induction.. Nothing more, except the 3.3V and 5V standby.

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

2.4V on PL805, 1.1V on the blue wire of the PL804(pin3) - have to be due induction.. Nothing more, except the 3.3V and 5V standby.

These are the voltages you read when +5Vstby is connected to PL803 pin 6, standby, yes?

What dc voltage do you have across the two pins of the large capacitor laying on its side before you connect +5vstby to Stby Pin6 PL803 and after you connect the two pins. Remember to disconnect the power supply from the mainboard first. DC voltage should be approximately 400V so set your meter accordingly.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

389V with no 5VStb connected to the PL803 - PIN3(Yellow wire). 308V when 5Vstb connected to the PL803 - PIN3(Yellow wire)
When 5Vstb wire is connected to the pin3 of the pl803 - no voltages of any kind, except 5Vstb, 3Vstb and 2.4V on the PL805(instead of 3.3V specified in the documentation)
And...I have the full schematic of this chassis(Main board and PSU) Just seems that I cannot diagnose the fault in the PSU myself.
Should I try to replace the 15nF capacitors(brown ones) with 630V 33nF MKT capacitors, which I have in stock?

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

That looks fine. I have it backwards. It looks like the power supply is already on and making the connection I suggested is putting it into standby mode.
The 389V means that IC802 is working.

What dc voltage do you have with the red meter lead on pin 13 (VCC) of IC807 and the black lead of your meter on the negative lead of that large capacitor?

I would also check mosfets Q813 & Q814

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

wait a minute.
...
10volts on the IC807 leg 13 relative to the negative of the big capacitor. I measured it with PSU in standby(no connection between 5Vstb and STANDBY wire)

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

The data sheet says the min voltage for the IC to run is 8V but the capacitors around it are rated at 50V so I would expect a higher voltage than 10V.

What is the DC voltage on D807. Use the black lead connected to the negative lead of the large capacitor as ground as you did above.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

11volts on the D807. On the side where tD807 is connected to the transformer - 0V.

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Can you check C384 & C835 in case something is loading VCC and making it drop to the lower value of 10V.
I would also check all the diodes and mosfets around IC807 as well as Q813 & Q814.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Do you think that voltage drop of 1V has any significant meaning, related to the issue with the PSU as a whole?
Is it required to change the MOSFET-s with exactly the same or their equivalent or just any MOSFET will do the trick?
I don't have the same MOSFETS-s. Will be required to order them and wait god knows how long.
On the PCB I see that there are SMD resistors between the Gate and Source, so the resistance between this legs as very low(35Ohms).

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

The 1V drop is not a problem. I think the voltage to start with may be lower than it should be but I am not 100% certain.
Don't change the mosfets unless they are faulty and it is best to change them for the same part number.
You can use you meter set to ohms (with the TV powered off) and just check there is no short circuit (zero ohms) between any of the 3 legs on each.

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Google for a repair kit for this power supply and see what components they mention which you could check yourself.


http://www.ohmsupplies.co.uk/17PW15-...EL-POWER-BOARD

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

I checked the MOSFET-s. No short circuit between any 2 legs. Between G and S - 35Ohms(there is SMD resistor between G and S legs)
I Googled for repair kit, but most of the kits have only capacitors - to be specific the capacitors near the IC806, and some have optocouplers, more capacitors and the two capacitors near the MOSFETS.

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

I checked the MOSFET-s. No short circuit between any 2 legs. Between G and S - 35Ohms(there is SMD resistor between G and S legs)

What mosfet was that (Q??) and can you read the marking on the smd resistor.

Edit
The circuit does show 10 ohms in series with each gate going through a transformer and then back to the source, so 35 ohms looks OK

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

When they go short it's 0 ohms so that looks OK.

The link to the kit you posted doesn't match the description of my problem. No blown fuses. No problems with the diodes. No problems with the power resistors. I have standby voltages.