Toshiba 19BL502B replaced diode worked, now not working

[David-OLW]

Hi all,
Toshiba 19BL502B replaced diode worked, now not working

Toshiba 19BL502B Main Board 23039106 PSU Vestel 17pw05-3 150411/23020632

Was Dead, found D709 centre diode shorted, removed put on briefly on and worked ok. Replaced all 3 diodes, RS did not have UF5408 in stock so used G1751. Worked ok for couple of days, then not working green light on but no picture. There was a smell of burning. Found the 3 diodes very hot and 2 Capacitors were warm C729, C730. Replaced the 3 16 volt 1000µ capacitors C729, C730, C731, but still not working, goes from standby to ON green steady light but no picture.

With Main Board disconnected Volts on PSU 11.5 DC Volts/24 DC volts, with Main Board connected in standby volts on PSU 8.69 DC Volts/20.8 DC Volts, turning it on 11.8/33 DC volts, and the 3 diode get very hot. To me this would suggest the Main Board is drawing a lot of current, although the 12v DC is low, and why does the 24 volts go up to 33 volts.

Any advice would be greatly appreciated.

Thanks David.

[dick_barton]

Re: Toshiba 19BL502B replaced diode worked, now not working

The diodes do not looks like suitable replacements. The UF are ultra fast switching diodes and the G is a general purpose diode, You need to replace with suitable ultrafast diodes.

Also check and or replace C734, C735

[ReeceyBurger123]

Re: Toshiba 19BL502B replaced diode worked, now not working

As the Psu gives 12v and 24 it is wokring, however the mb should not be causing it to over heat meaning its faulty likely tripping psu into protect mode. If you have a 12v Psu put it into the mb and see what smokes or use a dmm to see if you can find anything thats SC but this can take time. Also Psu raises to 24v for the Led driver, tried disconncting that to see if works.

[vinceroger69]

Re: Toshiba 19BL502B replaced diode worked, now not working

not the cheapest of places but delivery is quick as used this seller myself
http://www.ebay.co.uk/itm/Vishay-UF5...UAAOSwcLxYC9wJ

[petehall347]

Re: Toshiba 19BL502B replaced diode worked, now not working

farnell have them
cpc have them as well
if you speak to rs nicely they might get some flown in for you .

[ReeceyBurger123]

Re: Toshiba 19BL502B replaced diode worked, now not working

Also on these you can use UF5404 they will run at a good temp. Check ebay as well.

[budm]

Re: Toshiba 19BL502B replaced diode worked, now not working

The diodes do not looks like suitable replacements. The UF are ultra fast switching diodes and the G is a general purpose diode, You need to replace with suitable ultrafast diodes.

Also check and or replace C734, C735

+1, wrong type of replacement.

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

OK have replaced diodes with UF5408 and have replaced one capacitor C734/C735, there is only one position for a capacitor here, although marked C734 C735 see picture.

I still have only 11.29 DC volts and 23.89 dc volts but the diodes are not getting hot now, green on light comes on ok but still no picture.

How do I now trace the fault.
Thanks for all your help.

David.

[ReeceyBurger123]

Re: Toshiba 19BL502B replaced diode worked, now not working

Led driver test.

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

Led driver test.

How do I do That?

David

[dick_barton]

Re: Toshiba 19BL502B replaced diode worked, now not working

Do you have stby_5V on pin 11 of PL703. You mention 12V & 24V but not 5V

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

Do you have stby_5V on pin 11 of PL703. You mention 12V & 24V but not 5V

Yes the red standby light comes and then using remote turns on to give green steady light.

[vinceroger69]

Re: Toshiba 19BL502B replaced diode worked, now not working

on plug pl706 on pin 4 what voltage do you get on there with the set turned on as its for the bk lights

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

on plug pl706 on pin 4 what voltage do you get on there with the set turned on as its for the bk lights

On Pin 4 I have 0.23 volts, I am only measuring this with a multi meter, if it is PWM should I look at it the scope, should this be higher.

On the Diagram the only other place PWM_DIM is shown is on the Pin !3 on Main Board connector, does this signal come from the main Board.

Pin 1 and 2 27 volts
Pin 3 3.04 volts
Pin 4 0.23 volts
Pin 5 and 6 Ground

Thanks for your help

David

[vinceroger69]

Re: Toshiba 19BL502B replaced diode worked, now not working

that seems low to me for a back light command voltage i wonder if you have a mainboard issue?
Edit just found this thread
this toshiba thread may help his back light voltage was 2.3 volts so maybe you do have a bad mainboard
https://www.badcaps.net/forum/showth...estel+17pw05-3

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

that seems low to me for a back light command voltage i wonder if you have a mainboard issue?
Edit just found this thread
this toshiba thread may help his back light voltage was 2.3 volts so maybe you do have a bad mainboard
https://www.badcaps.net/forum/showth...estel+17pw05-3

Yes I had read that thread.
Is there any where I can get the schematic diagram for the Main Board 23039106? Anyone know what components could be faulty. Is there any way to apply a voltage to Pin 4 on T-Con to check Backlight?

Thanks David

[vinceroger69]

Re: Toshiba 19BL502B replaced diode worked, now not working

im not 100% sure myself so i will let a more experienced member advise you. mainboard schematics are very hard to find a lot of the time there not available at all

[dick_barton]

Re: Toshiba 19BL502B replaced diode worked, now not working

Using a bright light shine it at an angle on the screen while switching the menu on and off using your remote and see if it can be seen on the screen.

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

Using a bright light shine it at an angle on the screen while switching the menu on and off using your remote and see if it can be seen on the screen.

Yes using a bright light I can see the Menu.

Thanks for your help

David

[dick_barton]

Re: Toshiba 19BL502B replaced diode worked, now not working

You appear to have an inverter fault. Will be interested in what other's think.
I suspect that when the voltage was rising to 33V it may well have damaged some of the components / IC's on that circuit board by going over voltage.