TV/Monitor: Protecting HOT from secondary breakdown

[L.Chung]

Hi,

After replacing the HOT and doing power up check, its usual to put in
series a lamp bulb to limit the current. The problem comes after the
lamp bulb is removed and full working voltage is fed to the circuit.

There is the possibility of HOT damaged instantly via HV secondary
breakdown if there is some remaining fault in the rest of the circuit.
As I understand from surfing the net, the HOT is usually operates at
some 80% of its highest breakdown voltage Vceo.

I was wondering is it possible to put in parallel a string of
varistors (or a series of neon bulbs with voltage grading resistors)
from HOT collector to 0V so as to act as HV protection during the
final test. After the max. coillector flyback pulse amplitute have
been measured and confirmed using a 100:1 probe, the varistors can be
removed.

In addition, if I can build a device which impose a fixed(settable)
voltage drop with current limit, would it be possible to use it in
series with the horizontal B+ to bring up the voltage to the Horiz.
stage gradually?

Thanks in advance for your reply.

Regards

L.Chung

 

[Rich Grise]

Hi,

After replacing the HOT and doing power up check, its usual to put in
series a lamp bulb to limit the current. The problem comes after the
lamp bulb is removed and full working voltage is fed to the circuit.

I have no idea where you got this idea. When you replace the defective
part, the circuit is supposed to operate normally.

What you need to do is diagnose the actual problem that is causing your
HOT to let the magic smoke out, then when the rest of the circuit is
repaired (and the HOT replaced for the last time), your new HOT will work
just fine.

Good Luck!
Rich

 

[j.b. miller]

I've given up trying to fix monitors. ANything out of warranty isn't worth a
penny and the really new ones only have SMT on board. The garbage guys just
left with 10 SVGA types, all 15 or 17".
Sign of the times.
As to TVs, heck I don't even bother taking a look. the rest of the consumer
stuff is the same. hace 2 'offshore,what isn't ?) DVD players, less than 1
year old(90 day war), both need new transports. Let's see $30 for the parts,
$50 for labour,$20 taxes and some gas = $100. For $50 you can get another
New DVD player with 'more features', OK, more landfill.....Ok I've
ranted....
Some things just aren't worth fixin'..