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

[televizora]

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

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

Q813 and Q814. The resistor between the two legs is 103 - 10K.

[dick_barton]

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

Q813 and Q814. The resistor between the two legs is 103 - 10K.

So as shown in the circuit. The problem does not appear to be to do with the mosfets.

I'm out of idea's but still believe that the voltage to IC807 is too low.

Perhaps others on the Forum can offer some advice at this point.

[televizora]

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

Maybe I need a scope to check the signal on the IC807. Perhaps the IC that controls the MOSFETS has gone out of commission.
Something is definitely wrong. Some backfeed prevents the PSU from starting then.
It's abnormal not to have any voltages when the PSU is in ON state, except the StandBy.

[dick_barton]

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

Unless you have an isolation probe for your scope to check waveforms on the HOT (mains live) side of the power supply, you will damage both your scope, power supply and yourself.

[televizora]

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

Unless you have an isolation probe for your scope to check waveforms on the HOT (mains live) side of the power supply, you will damage both your scope, power supply and yourself.

Indeed, I need a isolation probe. But how else I could diagnose the problem?

[dick_barton]

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

You could at the moment with the power supply disconnected, use your multi-meter in diode mode and check all the diodes, transistors and mosfets to begin with.

[televizora]

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

I did this before posting here. No short circuits. The reason I registered here is to ask for help, because I can't find obvious signs of malfunction, except the fact that all the voltages, except the standby are missing.
The only short I have is on the secondary side of the TR805, on Q829, which is normal, considering the fact that all the pins of the Q829 are somehow connected to the leads of the transformer itself. The inductors and transformers are simple wires for the direct current. When it comes to the direct current, the inductor characterizes itself only with it's ohmic resistance(active resistance)
The whole story is that a working TV set suddenly stopped working - turned itself off, after this moment, the only thing that kept working is the red standby light on the front panel. There wasn't any kind of warning or sign that something goes wrong.

[dick_barton]

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

Q829 may present a short between base and emitter but I would lift it out and check to be certain that it's OK.

[televizora]

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

Q829 is stps10l60cfp which is Schottky rectifier.

[dick_barton]

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

Do you have a schematic that matches your board. Even if it's a diode you could lift it out and check it with your meter.

[televizora]

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

Yes. I did so. Seems like is 2 coupled Schottky diodes in one package. Also - seems like one of the diodes has short circuited. Two of the pins have 0 Ohms resistance between them in both directions. I really wasn't expecting short circuit on the secondary side of the transformer.
If you see the schematic, they use only one of the PN junctions of the transistor(effectively using it as a single DIODE if I am reading this properly). The third trace is not connected to the third pin of the transistor, there is a blank space in the trace to the collector of the Q829.
I can replace the Schottky with any regular Schottky in the same package, right?
I have STPS1545C in stock. It's rated 45V, the original is rated 60V. Is this gonna be a problem?
I also gonna need isolation pad, because the back side of the STPS1545C package is metal and is directly connected to the Cathode.
Is this a Schottky, as I think?

[dick_barton]

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

I would not since the one you suggest is lower rated than the one that's already faulty. I would expect the STPS1545C to also fail. Which pins were shorted together?

They are available from mouser.com

[televizora]

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

I would expect the STPS1545C to also fail. Which pins were shorted together?

The left and the middle pin are shorted together(A1 and K).(when we look at the front side of the shottky).
First of all - IS this a shottky, as I think? Please, look at the photo I have uploaded.
The second one - I think that the problem is perhaps overheating. Because I dont see any voltage on the secondary, that could exceed 33V
The third - Am I correct in my conclusion about the transistor used as diode?
And the last of all..I will have to find this shottky in my local stores or TME. Mouser is too far away from me. So I will have to wait a very long time for the delivery.

[dick_barton]

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

The short circuit diode will stop the secondary voltages coming up.
The 33V is for the tuner and is low current and would not have caused the problem.

I would be patient and try and locate the correct part. Use Ebay and have it sent to you. It would be a pity to end up with more problems than you already have.

Parts do fail for a number of reasons. It could be heat, it could be a short circuit that caused it to fail, it may be operating at its maximum rating.

The STPS10L60CFP is a Schottky diode

[televizora]

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

The STPS10L60CFP is a Schottky diode

So, you confirm that the electronic component on the photo I uploaded is a double shottky diode? And as we saw, it shortcircuited on the side, which is used, not on the side, where the trace is not completed.
p.s Will any double shottky with rating of minimum 5Amps at 60V will suffice?

[dick_barton]

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

Yes, it is a double Schottky diode as show in the image post #32
If the middle and left pin are in use then it is faulty because you have a short circuit.

Are you certain the right pin is not connected to anything???? Can you post a picture of the underside where it is soldered into the board.

[televizora]

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

Yes, it is a double Scottky diode as show in the image post #32

So I am correct that they used transistor as a diode? Why the hell this turkish brainiacs didn't just use simple diode?
And - Will any shottky with the rating of minimum 60V@5A will suffice?

If the middle and left pin are in use then it is faulty because you have a short circuit.

p.s. Do you think that the side, which is in use can be in working condition, but unused side - fried?

Are you certain the right pin is not connected to anything???? Can you post a picture of the underside where it is soldered into the board.

On the schematic - it is not connected to anything. On the board - both anodes are connected to the TR805!
This is why on the schematic the cathode of the transistor is not connected! They have used both of the diodes, connecting them to the TR806!

[dick_barton]

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

If you post a picture of the underside of the board and mark the diode solder connections then that would help.
It needs to be a clear and sharp picture. I do not know the answer because I cannot tell without the board in front of me or at least a good picture of the board.

[televizora]

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

If you post a picture of the underside of the board and mark the diode solder connections then that would help. .

Okay! Here we go. This is as good as I can get. Just my phone sucks, when it comes to taking photos on artificial light.
p.s better try with the second picture - 71.

[dick_barton]

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

Looking at the position of the holes both diodes in that package are required to be working. I've tried to draw it on your photo. It need to be replaced.