17PW25-4 found in 26" Vestel "Digihome" fixed

[tom66]

Another free TV from a friend. Fault blown fuse, no power -- same as 42" Vestel I am working on.

Found one shorted diode plus blown FET and associated driver components.

The bank of 8x3A through hole diodes were for the 24V. These diodes are all in parallel, a very bad idea. The diodes are not thermally matched, so if one gets hotter than the other, its forward voltage will drop, causing it to take more current, causing it to get hotter, causing it to take more current... This cycle is destructive to the diode. The poorly designed current limiting of the power supply means this damages the FET and other components. Only one was failed, but I elected to replace all 8.

The power supply is rather bizarre. It does not have a large 400V capacitor. Instead, it uses a transition-mode PFC controller in a flyback configuration. The main 24V output capacitors (3x3300uF) are the bulk for the PFC, plus the 12V. The measured output ripple is in excess of 1Vp-p.

This PSU is also used in the rebadge Toshiba 32BV501/502/701/702 sets. It is an unworthy pile of rubbish.

[Ralph Green]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

Hi Tom66. I got Toshiba 32BV501B with 17PW25-4. TV is just blinking orange diode so I think is PSU. Checked Q935 and is fine (not shorted). What else can I check to repair this TV?
Thank you.

[selldoor]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

As Tom said it is rather an unusual power supply. Can you post good clear pictures of your board and also of the main board.
Perhaps next test with it all connected up would be to work along that big connector to the main board and list the voltages. I dont suppose that the expected results are listed on the board - front or back of either board?
If you struggle to get probes to metal with the connector in place then get
a sewing needle and insert alongside the wire and test to that.

With the power off you could test all those diodes

[vinceroger69]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

wrong post sorry

[tom66]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

Blinking orange is PSU or main, if you have no voltages from PSU then it is PSU, otherwise it is the main board.

[vinceroger69]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

tom have you a scheme for this psu i have one here but not sure if the output voltages are ok.

[Ralph Green]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

It's not easy to check voltage because outputs are not marked on pcb. I think I will need schematic for this PSU. Attached pictures. There is one diode D927 missing. I've found this one faulty, it's not shorted just not giving anything while testing.

[vinceroger69]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed


you can get 2 free downloads a day i have used my limit today.

[tom66]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

SCH:

[Ralph Green]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

Thank you tom66 for schematic. Weird thing just happened. I put PSU back to TV and is working now Was it diode I've removed? Now there is only 2 instead of 3. Just ordered diodes on ebay so I will put 3rd diode back.

[tom66]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

That could be, if that diode was shorted. You are very lucky it did not blow the FET. Maybe that only happens on 24V. I've found tons of Vestel PSUs with bad diodes... crazy how common this failure is.

[Ralph Green]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

That diode wasn't shorted. Just won't give any reading from multimeter like others did.

[vinceroger69]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

was it open circuit did you have a reading at all?

[Ralph Green]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

Sorry guys. This one was shorted.

[mesersmith]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

SCH:

Hi, Tom!
Can you tell me with what software you created your web database?

[tom66]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

Hi, Tom!
Can you tell me with what software you created your web database?

Custom PHP scripts, about a day's work to put together. Based internally on text databases, would you believe it. I didn't want to use MySQL because I had just finished a huge MySQL project and was getting a bit bored of it.

[vinceroger69]

Re: 17PW25-4 found in 26" Vestel "Digihome" fixed

Tom a bit of a old thread but can you remember how to force on the psu by itself as we want to check all the output voltages on one of these psu s in another thread thanks.