"z" wrote in message
ps.com...

boardjunkie wrote:
z wrote:
Anyone knows which circuit in a tv set is resposible for the
brief delay between switching the set on and the appearance
of an image on the screen?

Tube cathodes heating up via the filament (heater).

O.k. so what conclusion could one draw if this warm up
period is taking very long (15 minures)?


One possible cause is high value start up resistors in the PSU going very
high, this can mean the PSU doesn't start immediately but can be got going
by a random mains spike.

Some designs use the charging current through a small high voltage
electrolytic to kick-start the PSU.

Another capacitor related problem is whichever electrolytic holds the PSU
error feedback voltage goes high ESR giving a false excess voltage error
voltage - this causes the PSU to idle at too low O/P to start the set - in
both capacitor related faults, the capacitor in question gradually warms up
causing the ESR to decrease, at some point the capacitor may then get close
enough to normal operation for the set to start.