I have a Panasonic Tx-28DK1 TV (Euro4 chassis).

when attempting to switch on, the standby LED switches from red to
green, but after about 4 secs a relay clicks and it reverts to standby.

Before the fault became permanent, it was intermittent - would
eventually switch after several attempts.

The Line Output Transistor had gone low resistance between base and
emitter (22ohms both ways), but replacing it didn't fix the problem. I
have removed and checked all the large high voltage electrolytics for
value and leakage at up to 50Vdc on a bench PSU, but they're all OK.

Any ideas where I might look next?

Tony

PS. Does anyone have a complete schematic they'd be prepared to share? I
bought a manual online, but it's obviously dodgy because the (badly)
scanned schematics are very incomplete. The parts list is complete though.

On Sat, 13 Sep 2008 19:26:20 +0100, Tony Casey
put finger to keyboard and composed:

I have a Panasonic Tx-28DK1 TV (Euro4 chassis).

when attempting to switch on, the standby LED switches from red to
green, but after about 4 secs a relay clicks and it reverts to standby.

Before the fault became permanent, it was intermittent - would
eventually switch after several attempts.

The Line Output Transistor had gone low resistance between base and
emitter (22ohms both ways), but replacing it didn't fix the problem. I
have removed and checked all the large high voltage electrolytics for
value and leakage at up to 50Vdc on a bench PSU, but they're all OK.

Any ideas where I might look next?

Tony

PS. Does anyone have a complete schematic they'd be prepared to share? I
bought a manual online, but it's obviously dodgy because the (badly)
scanned schematics are very incomplete. The parts list is complete though.

Original Euro4 circuits are available FOC he

http://www.eserviceinfo.com/download...X-21%20MD.html
http://www.eserviceinfo.com/download...c_TXW28R4.html
http://www.eserviceinfo.com/download...TX-28MD4C.html
http://www.eserviceinfo.com/download...TX-28MD4C.html

I'm not familiar with this chassis, but it appears that the main uP
(SDA5450) has two protection pins (VPROT and PROT1) which you should
verify. The Video Display Processor chip (VDP3108) also has its own
protection pins.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Franc Zabkar wrote:
On Sat, 13 Sep 2008 19:26:20 +0100, Tony Casey
put finger to keyboard and composed:

I have a Panasonic Tx-28DK1 TV (Euro4 chassis).

when attempting to switch on, the standby LED switches from red to
green, but after about 4 secs a relay clicks and it reverts to standby.

Before the fault became permanent, it was intermittent - would
eventually switch after several attempts.

The Line Output Transistor had gone low resistance between base and
emitter (22ohms both ways), but replacing it didn't fix the problem. I
have removed and checked all the large high voltage electrolytics for
value and leakage at up to 50Vdc on a bench PSU, but they're all OK.

Any ideas where I might look next?

Tony

PS. Does anyone have a complete schematic they'd be prepared to share? I
bought a manual online, but it's obviously dodgy because the (badly)
scanned schematics are very incomplete. The parts list is complete though.

Original Euro4 circuits are available FOC he

http://www.eserviceinfo.com/download...X-21%20MD.html
http://www.eserviceinfo.com/download...c_TXW28R4.html
http://www.eserviceinfo.com/download...TX-28MD4C.html
http://www.eserviceinfo.com/download...TX-28MD4C.html

I'm not familiar with this chassis, but it appears that the main uP
(SDA5450) has two protection pins (VPROT and PROT1) which you should
verify. The Video Display Processor chip (VDP3108) also has its own
protection pins.

- Franc Zabkar

Thanks Franc - this is a useful (free) resource.

I checked these out, but they don't exactly cover the model I have.

Tony