JMB JTC0122003b/01 FLASHING LED

[london-freddie]

just got this tv given a 22" JMB LED/TV/DVD was going in the skip
power board 17IPS61-3
main board 17MB82-2
When power applied, LED on front flashes several times, backlights come on for a couple of seconds then set powers off, no picture or sound. TV then tries to restart the same flashing led, backlights on for a couple of seconds then powers off again, this continues until removed from the power.
I have changed the 3 diodes on the power board D9, D10, D25, no change nothing visible, caps look ok ?, 339v at big cap
Any ideas where to start on this one, if not a power board or led problem, I am thinking software, but am probably wrong, I usually am
thanks in advance

[london-freddie]

Re: JMB JTC0122003b/01 FLASHING LED

pics of boards

[dick_barton]

Re: JMB JTC0122003b/01 FLASHING LED

With the mainboard disconnected and using jumper resistors do you have all the secondary supplies.

[london-freddie]

Re: JMB JTC0122003b/01 FLASHING LED

hi thanks for that dick-barton
not sure what you mean by jumper resistors, but checking secondary supplies with mainboard removed, the only supply there is 12v on I think was pins 13 and 14, no 24v or 5v

[dick_barton]

Re: JMB JTC0122003b/01 FLASHING LED

Do you have the stby_5v at CN2 pin 3. If you have 12V then the stby_5v is derived from this 12V via Q5, Q10, D17
If you have the 12V then there should also be 24V at CN2 pin 15 since they are derived from the same transformer. Did you replace the diodes with ultrafast diodes or general purpose?

[dskall]

Re: JMB JTC0122003b/01 FLASHING LED

Might want to check black connector between power and main for broken solder joints. What is voltage of main cap when it tries to power on?

[london-freddie]

Re: JMB JTC0122003b/01 FLASHING LED

hi thanks for that guys, have 324v to 334v on main cap when trying to power on
replaced diodes with general purpose, which I had in my box of bits.
With main board connected to power board on starting I seem to have all outputs except No 24v at pin 15

[london-freddie]

Re: JMB JTC0122003b/01 FLASHING LED

will check later, the solder joints on the black connector, I did look at them yesterday and did not notice any bad joints, but will look a lot closer at them later with a x10 glass

[dick_barton]

Re: JMB JTC0122003b/01 FLASHING LED

hi thanks for that guys, have 324v to 334v on main cap when trying to power on
replaced diodes with general purpose, which I had in my box of bits.
With main board connected to power board on starting I seem to have all outputs except No 24v at pin 15

I thought you said earlier that you only had the 12V supply and none of the others but you now say it's only the 24V missing.
Replace the diode with an ultrafast schottky and that should solve the problem.

You must replace the diodes if ultra fast with likewise and not general purpose or the supply it's intending to rectify will not happen. So look up the spec for the diodes you took out and replace with correct type.

[london-freddie]

Re: JMB JTC0122003b/01 FLASHING LED

with mainboard removed only 12v output on power board, with mainboard connected to power board all outputs except the 24v which is not there.
now have a big problem with mainboard, took boards out of the chassis placed them on worktop upside down, with intention of checking outputs at solder joints on underside of black sockets on boards, powered boards up and mainboard started smoking, at I think U23 next to the scart socket, now no flashing led, so looks like I have now killed the mainboard, whoops

[dick_barton]

Re: JMB JTC0122003b/01 FLASHING LED

Oooop. Is it your tv or a customers?

[london-freddie]

Re: JMB JTC0122003b/01 FLASHING LED

no its mine, was going in a skip, dont know how or why there was nothing around that could cause a short, maybe just coincidence dont know, but something has died on the mainboard, not sure of the chances of finding a mainboard for this