Toshiba 21N21B2 PSU fails once a week.

[Mark 1948]

I have a Toshiba here (TMC572B Chasis) that keeps knocking out the Line Output transistor a 2SD2499. The PSU then trips for a few seconds and pops the FET 2SK2499 and various other compnents. The PSU type is SOPS

It popped for the 3rd time this morning and I am at a loss, I have rebuilt it again and it runs fine but have turned it off as I am clearly missing something.

What has been done:

1) Changes the Line Output transistor 2SD2499 and block soldered for dry joints
2) The PSU needed 2SK2651, 0.22 Ohm 1W feed resistor, 18v Zenor. I have changed the 1.2 Ohm resistor between Source and ground even tho it measured OK.

The failure of the Line Output transistor could be down to a cap or something else but when it fails the PSU should trip not got pop????

Oh and the HT is at 125v which for a 21" seems about right.

[minnie]

If the line out put transistor is the horizontal out put transistor off the flyback I'd say change the flyback/trippler/doubler. I call it a flyback. The transformer that has the red lead that goes to the picture tube.