Problem with KV27XBR35
 

Have no schematics, nor service manual, trying to rescue this huge work of
art tv from the dump...
symptoms: picture goes off and on repeatadly once per second, colors are
way off, sound OK. Scoped the RGB signals going to the CRT board and
indeed they all go on and off as the picture does. Checked for poor
solders on the main board and the power supply board, only found one
transistor with weak joints, but the problem persists. I didn't manage to
make the problem go away or get worse by banging all over the place, so it
does not seem to be an intermittant connection, maybe a permanent
disconnect?
Going out of the PS board, one of the supplies (orange wire in the 5 wire
cable) is marked as 24V on the board, but it is actually 20V, yet it is
stable on the scope. When disconnected the connector going to the main
board (removed the load) the voltage rises to 24V, so possibly somthing
oveloads it.
Your help is much appreciated.

In some models of the Sony sets, the AKG bias drive will cycle the CRT
brightness off and on, when the CRT is very weak. If this is the case, you
may be able to frig it a bit, by increasing the screen bias to have more
beam current. Increasing the screen bias will also accelerate the wear of
the cathodes, but it is an old tube anyways.

When you raise the screen bias, you may find that there will be retrace
lines, but the brightness cycling should stop. The fix is to change the CRT.

--

Jerry G.
======


"DavidA" wrote in message
lkaboutelectronicequipment.com...
Have no schematics, nor service manual, trying to rescue this huge work of
art tv from the dump...
symptoms: picture goes off and on repeatadly once per second, colors are
way off, sound OK. Scoped the RGB signals going to the CRT board and
indeed they all go on and off as the picture does. Checked for poor
solders on the main board and the power supply board, only found one
transistor with weak joints, but the problem persists. I didn't manage to
make the problem go away or get worse by banging all over the place, so it
does not seem to be an intermittant connection, maybe a permanent
disconnect?
Going out of the PS board, one of the supplies (orange wire in the 5 wire
cable) is marked as 24V on the board, but it is actually 20V, yet it is
stable on the scope. When disconnected the connector going to the main
board (removed the load) the voltage rises to 24V, so possibly somthing
oveloads it.
Your help is much appreciated.

When you say colors are way off, what do you mean?

The odds are very high the picture tube is simply at the end of its
life and the AKB circuit is blanking the video.

A google groups search will go a long way in your quest for
information.

David