On Fri, 02 May 2008 14:11:40 +0200, Wiebe Cazemier
wrote:

On Friday 02 May 2008 03:44, John-Del wrote:


Hmm, there seems to be some disagreement over whether a H-K short can be fixed.
Will the filament also be killed if you tie its pins together? That way, a
current path other than through the entire filament always exists.

Floating might work, but not in this case, because the problem exists in two
guns. Additionally, it would decrease image quality (at least when the short
exists; it might clear up when the short disappears when it's warm), and the
reason I want to fix this monitor is because of it's high quality; a quality
that not even other T766 models have/had.

Another thing; if I measure the filament voltage, it's 5V. Is that normal
deviation from the 6.3 which is common? And, when isolating, is it useful to
use some kind of regulation, like with a couple of diodes and an LM317, to
make sure the voltage is exactly what it should be?

Floating the heater in a monitor is not usually possible because they
run the heaters on a regulated DC supply instead of using AC from the
flyback. DC obviously won't work with a CRT heater isolation
transformer. I have seen other Sony monitor CRTs with 5v heaters, so
it may be fine. If your monitor does use AC heaters, then you need a
true RMS meter to measure this voltage.

I've seen more H-K shorts than anything else. K-G1 shorts can usually
be blown out, but H-K shorts are harder to remove reliably. The
problem with fixing a H-K short is that the heater is coated with
insulation. If this insulation cracks, then the heater will short to
the cathode. Attempting to blow out the short can blow the heater.
Also, even if the short goes away, the heater still has damaged
insulation and could short again at any time.

A CRT with two shorted guns is probably past hope. If you really want
to fix the monitor, start looking for a compatible replacement CRT.
Almost any 19" Trinitron monitor CRT should work.
Andy Cuffe