Hitachi 42PD5200 PSU query?

[quaduplex]

Hi all,

My first post on this forum. It seems a very active and helpful place to be. I'm a bit of a newbie to the TV side of electronics but learning fast.

I have a Hitachi 42PD5200 that was exhibiting all the signs of the infamous 10 ohm resistor failure. Pulled the PSU, both 10ohm resistors were o/c. Q201 was also shorted. Q220 seemed ok. Replace transistors and both resistors.

Checked IC201 as per the KIT54 guidance as it seemed fine with no apparent shorts. Daughter board was removed from board and checked - transistors were still in circuit however but no shorts apparent.

Assembled it all back together and power on. Within 2 seconds of switch on and with a relay click, Q201 blows in a big way

I am wondering if I've missed something on the Q201 daughter board or as per the faults list on here -

"42PD5200/5300-dead -check and repaced R005(10oM),R003(10oM),C111(10n) beside T101 5v PS and Optocouple PC101,PC001 and check Transistor for short circuit -Q201(2sk2843)"

if the photocouplers could cause this? How are photocouplers checked?

Any help or guidance is much appreciated.

[quaduplex]

UPDATE!

Revisited the daughter board this morning. One of the SMD transistors has blown its top. They're idented 'CQ' - any ideas? There seems to be about 4 or 5 possibles!! One is a darlington.

I've checked everything associated with Q201 according to the circuit in the manual on the downloads link on this site.

[thevolatile1]

hi there, i have problems with a 42pd5200e,, resisters were blown - replaced & they blew again, found the mosfet to be shorted (q201) also checked daughter board as suggested in service data & removed the smd transistor to check - ok.. replaced mosfet & tried again - this time the fuses blew in the mains plug, on the power filter board & the resistor again.
once again the mosfet had died.. so i replaced the mosfet & resistors.... again..
state of play now is that the set holds power - no more blowing !! standby red light on,, turn on with remote & green led lights but no sound or display. also the diagnostic doesnt work (holding stdby & down  for 5 secs).
took the board off again & metered every diode on the board (especialy d581) - all ok,, no signs of damage on any components anywhere, so i got the service manual & looked at the fault finder flowchart. first part to chgeck was CN68 pin 6 - should be 5v - i get zero in standby & when green led is on.. doesnt seem to be power accross most of the board.. any suggestions anybody ??

[thevolatile1]

...oh and on a further note - the service data indicates c111 as 10n - incorrect.. mine has an electrolytic capacitor at this position, not a small ceramic 10n !!!

[thevolatile1]

,,had another go at this today,, had a dry joint on the main rectifier - d001.. plugged it in & it went CRACK.. Q201 exploded & IC201 smd transistor blew.. nearly papped my pants,, lol,, all resistors & fuses still okay !! anyway.. i have a spare mosfet so thats good,, but the smd transistor on ic201.. seems to be marked 'CQ' - i used this site to identify - http://www.marsport.org.uk/smd/mainframe.htm (sorry if im not supposed to post links),, that page says that 'CQ' is either 2SC2411K NPN 32v 500ma ROHM darlington smd transistor sot23 (2.9mm x 1.6mm)  or  MSD710Q pnp sot346 25v 150ma by Motorola (2.7mm x 1.3mm case).
the smd marked 'CQ' measured roughly 1.6mm  x 1.0mm so there isn't a match there based on the dimensions of the thing.. BUT based on the service diagram ic201/q201 supply 30v, 12v, 10v i.e max of 30v.
so, before i blow it to bits again, would it be a safe assumption that the correct part for the 'CQ' replacement is a  2SC2411K NPN as it is rated at 32v - even though the dimensions aren't quite right ???
any suggestions anybody ????

[thevolatile1]

,,ritey people - the illusive transistor on the daughter board marked 'CQ' - i've used a BC848 as a direct replacement - done !!! this could do with stickying to all post with power supply issues using the MPF7409 power supply where the standard fixes didnt work & you were suffering from exploding mosfets !!!
hope this helps some of you out !!!

[magikbilly]

on the daughter board what are the capacitor values

thanks