Vestel based 16" LCD: PSU ticking

[bbjunkie]

Not been able to figure this one, it's basically a Vestel TV (both power and AV boards) with CHI MEI LCD panel. PSU board is 17ips16-3

Have found the following symptoms:

Standby LED flashing at approx 1hz and very quiet ticking that sounds like it's coming from the primary side of the PSU and in time with the standby LED flashing.

With everything disconnected from the PSU this noise is still there.

Checked caps on both primary and secondary side, all seemed ok -

Mains filter caps 18uF 400v both reading 17uF one with 1.6 ohms ESR and one with 1.7 ohms ESR

302VDC across the filter caps (a pair in parallel)

Startup cap 33uF 50V reading 31uF with an ESR of 0.6 Ohms

Charge resistor 96K ohms in circuit (is this a bit low - should I pull it and check?)

Current sense resistor ~ 1 Ohm in circuit

Q802 chopper transistor is recognised properly by the DCA55 tester so assume it is ok.

303.2VDC at centre pin (Drain) of chopper transistor

D810 not shorted, forward voltage of approx 0.45v measured with DMM

D815 D817 and D818 not shorted, forward voltage of 0.25v with DCA55 tester

SMPS transformer (details shown below)

30065656
SMP-C2331

Primary (Pin4 NC)

1-2 1.3 Ohms
1-3 0.L
1-5 O.L
2-3 O.L
2-5 O.L
3-5 1.4 Ohms

Secondary

1-2 0.6 Ohms
1-3 O.L
1-4 O.L
1-5 O.L
2-3 O.L
2-4 O.L
2-5 O.L
3-4 O.L
3-5 0.6 Ohms
4-5 O.L

No sign of a short on the PSU at the transformer secondary pads with transformer out of circuit.

All component tests done out of circuit unless stated otherwise.

(DMM leads connected together show 0.6 ohms)

Pics of primary side attached, can post others if needed.

[tom66]

Re: Vestel based 16" LCD: PSU ticking

Of these snubber components (RCD clamp), are any failed?

If none are, my bets are on the tiny 6-pin SMPS controller.

[tom66]

Re: Vestel based 16" LCD: PSU ticking

Also check D608 (D808?) on bottom of the board and the three SMD resistors near it.

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

D808 has a forward voltage drop of 0.488v the three SMD resistors are checking at 50 ohms each which ties up as they are 150 ohms each and in parallel. All those were measured in circuit

C852 marked 101 measures 200pf
C873 measures 4.7nf

Both cap tests done out of circui

The diode on the left side of the circle is D810 already checked above.

[tom66]

Re: Vestel based 16" LCD: PSU ticking

Schematic: http://www.4shared.com/office/YtDotRyO/17IPS163.html

Check Vcc across C807.

Check for any shorted output caps (not just ESR.) Check for shorts on any rail.

[Toasty]

Re: Vestel based 16" LCD: PSU ticking

Unfortunately, and again, that is not the schematic for this PSU as I said in the original thread:

https://www.badcaps.net/forum/showthread.php?t=18837

This is for the 17IPS16-2 & a piece of the 17IPS16-1

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

Check Vcc across C807.

Something not quite right here I think.. I'm measuring 10-16VAC jumping around all over the place.

Pulled C807 to check again, 31.59uF and 0.59 ohms ESR

[PlainBill]

Re: Vestel based 16" LCD: PSU ticking

Something not quite right here I think.. I'm measuring 10-16VAC jumping around all over the place.

Pulled C807 to check again, 31.59uF and 0.59 ohms ESR

Voltage jumping like that is often caused by an excessive load. Since the power LED is flashing, I would suspect a problem with the inverter.

PlainBill

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

I have everything disconnected and the fault is still there.

I guess the inverter shouldnt be starting without a PSON signal?

[Toasty]

Re: Vestel based 16" LCD: PSU ticking

Recap it.

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

What would this achieve? I have checked ESR and value of all caps?

[Toasty]

Re: Vestel based 16" LCD: PSU ticking

It eliminates the caps from the equation. Ticking indicates the SMPS controller trying to start and failing. If not the caps, then the controller may be bad as tom66 suspects. If you're going to replace the controller, then replacing the caps is also a good idea as the failure of the controller can come from failed caps. Vicious circle.

Have you compared the caps measured ESR to their respective datasheets?

What is the standby voltage? Is it correct?

Measuring anything in the circuit past the primary caps/rectifiers for AC is incorrect. DC is all that would be in the circuit from the mains caps forward.

Toast

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

It eliminates the caps from the equation. Ticking indicates the SMPS controller trying to start and failing. If not the caps, then the controller may be bad as tom66 suspects. If you're going to replace the controller, then replacing the caps is also a good idea as the failure of the controller can come from failed caps. Vicious circle.

Ok, all noted.

Have you compared the caps measured ESR to their respective datasheets?

No, compared with other caps I have seen in psu's like this. Not such a good idea i'll admit. I'll look their datasheets up and see. Apart from the low value high voltage caps such as C807 and the mains filter caps all electrolytic caps were lower than 0.1 ohms, cant recall measurements now but i'll start again and write them down. (then recap if they are out of spec)

What is the standby voltage? Is it correct?

I cant recall, will check that again tomorrow.

Measuring anything in the circuit past the primary caps/rectifiers for AC is incorrect. DC is all that would be in the circuit from the mains caps forward.

I thought that was the case myself and have always used DC for voltage measurements south of the rectifier. However, when I measured C807 for a DC voltage I saw a reading which resembled AC, so switched and found a much more stable reading.

(Still no isolation transformer so didnt scope it)

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

What is the standby voltage? Is it correct?

Been quite busy with life stuff, not had much time 'til today.

OK, on the pins (they arent numbered, so I have numbered them 1-10 and 11-20 when looking at the board upside down with the power connector closest to me)

I measured:

Pin 4: 5.04VDC
Pin 5: 5.32VDC
Pin 6: 5.32VDC
Pin 9: -2.55VDC
Pin 10: GND
Pin 14: 5.02VDC
Pin 18: 5.32VDC

The other pins had zero or less than 1v

These were taken with the board totally disconnected from the tv (due to the mechanics it's near impossible to measure 1 row of power out pins in situ) - the SSB plugs into the power board directly, (socket on SSB plug on PSU) no wires with plugs on them.

[tom66]

Re: Vestel based 16" LCD: PSU ticking

Are you sure pin 9 is negative?

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

100% sure on pin9. Unless the pin im using for ground isn't ground - it measures less than 1 ohm to chassis though.

I have just pulled most of the caps and re-measured ESR:

C830 2200uF 10v Epcos B41827 85c 2156uF ESR 0.06
C850 2200uF 10v Epcos B41827 85c 2076uF ESR 0.04
C833 2200uF 10v Chang CD110 85c 2236uF ESR 0.02
C829 1000uF 25v Samxon YDA 110c 949.8uF ESR 0.06
C841 1000uF 35v HEC ZP 105c 931.1uF ESR 0.02
C831 1000uF 35v HEC ZP 105C 931uF ESR 0.04
C905 1000uF 25v HEC ZR 85c 926.6uF ESR 0.03

These values are OK, right?

Some sort of a lookup table for ESR values would be very useful. I understand the lower the voltage the higher the ESR tends to be, and similar for the capacitance value.

Therefore a low voltage low value cap will have a higher ESR than a high voltage high value cap.

Is there a formula for working out a rough ballpark acceptable value?

<edit> found a chart, would this be ok? https://www.badcaps.net/forum/attach...5&d=1300287950

[tom66]

Re: Vestel based 16" LCD: PSU ticking

My gut feeling tells me that C830 and C829 are going out, but they're not failed yet.

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

I'll replace C829 and C830 then.

Anything else I should check before ordering the switch mode controller?

Although we dont have a schematic for this particular revision the controller appears to have stayed the same throughout. This one is labelled AAJF X which ties up with the SG6859A in previous variations.

My usual parts supplier stocks these, so I guess it's worth a try.

[bbjunkie]

Re: Vestel based 16" LCD: PSU ticking

Ok, ordered a new controller IC on Tuesday, should be here soon.

Got a low resistance on the SENSE pin, not sure if there's a problem there. Will investigate before I swap the chip.

[giagiuf]

Re: Vestel based 16" LCD: PSU ticking

Hello to all Forum Users.

I'm writing from Italy and I have the same problem to a Vestel 17IPS16-3 V1 (240906), do You have some solutions to repair IT?

I have changed the SG6859A controller with a new one, the Power Mosfet and some broken diode and resistors.

It is possible to have a HIGH resolution photo of the board.
I had found the schematics but the parts value on the board are not the same with schematics.

Please let me know as soon as possible,

Best Regards,

Gianluca Giuffrida.