"Jason D." wrote in message
...
On Tue, 16 May 2006 23:02:28 GMT, "ian field"
wrote:


"sigmma" wrote in message
...

sigmma

Replace the H-transistor, but do not solder the collector terminal - route
this via a 60W bulb which will limit the current if the LOPT has shorted
turns. If this arrangement fails to develop a voltage across the LOPT
primary - don't despair, it could be a S/C rectifier for a scan derived
supply, just follow the tracks away from the LOPT and look for diodes to
test. Another common cause of H-transistor failure is the flybak tuning
capacitor - this is often a disc-ceramic type (normally go S/C and
split/burn!) the regular high voltage wound foil types commonly fail O/C
and
allow the peak flyback voltage to exceed the H-transistor's Vceo!

Caution - examine the flyback tuning caps first - the current limiting
lamp
won't protect the transistor from excessive flyback if it fires up!!!


Good question on that HV caps in horizontal circuit, what is the
method of checking them? I have capacitance meter but I know better
not to trust that, cap could fail under load (even instantly) and pass
a cap meter test?

Cheers, Wizard

Given the cost of the H-transistor, test by replacement is probably the
safer option.