Vestel 17PW16-2 troubleshooting

[vitasik]

Hi Guys

Today I am playing with a funny behaving power supply board.

Somebody recapped it before, but by the looks of things couldn't get it going as it was popping the fuse. Q803 was to blame. So replaced it with something I had with similar data. Good news - it doesn't pop the fuse, has stand by 3.3v and 5v. But nothing more. Did look at the manual for it and it appears that when its in stand by it gets 3.3 v back from main board. When in full power it should get 0 at the stand-by pin? Am I wrong? tried unplugging main board and bridging controls to see if 24v for inverters would go up. Answer is - NO. Whatever I did with the control pin ( both grounding it and pulling to 3.3v) PSU wouldn't give +24,+12,+5 and +3.3 v (later 2 not the stand by ones).

Does anyone have experience with this junk and if so what are the common problems. I will find the problem eventually, but wanted to see if someone could help out to cut the time a bit.

[ReeceyBurger123]

Re: Vestel 17PW16-2 troubleshooting

God I hate these when they blow up, what is Q803 part of ? Also did you check things like the controller for it and other related parts ?

[vitasik]

Re: Vestel 17PW16-2 troubleshooting

Q803 is a switching power MOSFET for some sort of active PFC. On the Schematic diagram its noted as RESONANT PFC. Its driving part looks ok with no short circus to the driver. Besides this part is OK as all other parts are taking power supply from here. If this was gone I would think that stand by would be gone as well.

See the attached file. The only control from mainboard is to pin 6 of the PL803 connector. This gets from main board +3.3v. I presume this is in OFF state due to the arrangement ( see the attachment).

[dick_barton]

Re: Vestel 17PW16-2 troubleshooting

The 3.3v & 5V standby are derived from a different circuit. IC806 & TR807.
Do you have 400v dc cross C819?

Edit.
Use a 1K resistor between 5Vstby and st_by with main board disconnected and then check for 400 across C819.

[ReeceyBurger123]

Re: Vestel 17PW16-2 troubleshooting

You dont need to bridge ps on to get these to run just unplug the Mb completely and plug supply into mains. You should bave 400v across the cap.

[vitasik]

Re: Vestel 17PW16-2 troubleshooting

Hm... its 324v.... weird.

EDIT: R830 is gone. Well at least I think so. Its the only one fitted there ( there should be R829 as well, but its not here from factory). its 2 reds and a silver strip, which should be 0.22 Ohms???? Nope - multimeter wont even register it.

[ReeceyBurger123]

Re: Vestel 17PW16-2 troubleshooting

Yeah thats deffo a problem, replace it and let us know.

[vitasik]

Re: Vestel 17PW16-2 troubleshooting

Hm
It did absolutely nothing, same voltage. Initially I thought that maybe it has popped again, but no. It was not even warm, so not overloaded. So I am facing 2 options in my opinion - IC802 or... my choice of the Mosfet

It had P9NK50ZFP, but I had 15N65C3. Both N - channel power FETS

Old vs New
V ds 500 650
I ds 7.2 15
R ds (ON) .72 0.28

For full datasheet see attachments

Any bright Ideas???

[dick_barton]

Re: Vestel 17PW16-2 troubleshooting

Can you check what voltage you have at D807 (VF_Main).
VF_Main feeds IC828 to provide VCC1.
VCC1 feeds R953 & C881 which feeds VCC2.
VCC2 feeds IC802 pin8.
Can you check what voltage you have for VF_Main, VCC1 & VCC2

[vitasik]

Re: Vestel 17PW16-2 troubleshooting

Yes - all of the voltages are present as follows:
Vf_main - 14.7v
VCC1 - 12.98v
Vcc2-12.8v

EDIT:

Been messing around with it. R823 that is between IC802 and the Q803- Mosfet I changed before was blown. After replacing it (had 11 ohms instead of 15) Mosfet blew again as well as the fuse.

[dick_barton]

Re: Vestel 17PW16-2 troubleshooting

The mosfets are not interchangeable. The original mosfet STP9NK50Z has zener diode voltage limiting gate drive protection which the substitute mosfet does not have.

[dick_barton]

Re: Vestel 17PW16-2 troubleshooting

Yes - all of the voltages are present as follows:
Vf_main - 14.7v
VCC1 - 12.98v
Vcc2-12.8v

EDIT:

Been messing around with it. R823 that is between IC802 and the Q803- Mosfet I changed before was blown. After replacing it (had 11 ohms instead of 15) Mosfet blew again as well as the fuse.

Those voltages appear fine and is supplying the voltage (VCC2) for IC802 to run that chip.

I would also check that c920 and other components around that circuit have not been damaged due to the mosfets blowing.

[vitasik]

Re: Vestel 17PW16-2 troubleshooting

Have already checked most elements in a IC802 and mosfet's circuit. Didnt check c920 though. Will do when get the original mosfet. The whole repair is put on hold until than.

[llonen]

Re: Vestel 17PW16-2 troubleshooting

I spent ages working on one of those, the 24volt was unstable - intermittent would work for weeks on test and then fail, I ended up having two sets with those supplies come in, one with batch of bad capacitors and the other the screen was broken so one set was repaired and the other supply went into the first one. If you need any values measured for replacement parts I probably still have one of these in the workshop that works.

[dick_barton]

Re: Vestel 17PW16-2 troubleshooting

Have already checked most elements in a IC802 and mosfet's circuit. Didnt check c920 though. Will do when get the original mosfet. The whole repair is put on hold until than.

Let us know how it goes.

[vitasik]

Re: Vestel 17PW16-2 troubleshooting

Hey guys
Time for an update - been busy with other junk - too many projects ( biggest is a recovery truck).

Now replaced mosfet with the correct one and checked c920 - according to my multimeter its 200pF which is off but not enough to be doing this shit. Bare in mind my multimeter is not a pro so could be within speck or even more out of spec. Result- same in 2 secs after switching on fuse blows and mosfet has shorted again. Really puzzled.

Good thing I have 4 more mosfets.
Bad thing i am running out of ideas.

EDIT: brainstorming - IC802(fan7529) doesn't have shorts on any pins, but what would happen if it was either keep mosfet always on or always off?

[vitasik]

Re: Vestel 17PW16-2 troubleshooting

anyone?

[dick_barton]

Re: Vestel 17PW16-2 troubleshooting

brainstorming - IC802(fan7529) doesn't have shorts on any pins, but what would happen if it was either keep mosfet always on or always off?


Transformers work by switching on and off a voltage on one of their windings generally the primary which then produce other voltages on the other windings (secondarys).
This is carried out by switching the mosfet on and off to produce the changing voltage across the primary of the transformer.
No switching of the voltage on the primary results in no secondary voltages.

[dick_barton]

Re: Vestel 17PW16-2 troubleshooting

If you lift out your mosfet Q803 and power on
Does the fuse remain intact
What voltage do you have across C819 pins

[vitasik]

Re: Vestel 17PW16-2 troubleshooting

Right -
I have around 324v on c819, if I lift Mosfet fuse does not blow.

As to the transformer explanation - this is not your most common transformer, but its a single coil(choke) like in boost converter -this "transformer" has only one winding, no secondaries.