Hitachi shut down
 

Same problem, just more info to post. Hitachi 50EX10B, press power
button, led comes on, set shuts off. Stand by power OK. Kept blowing B+
fuses after replacing the HOT. I disconnected the anode of the green
CRT, and it doesn't blow fuses anymore. Other tubes OK. But, the dang
thing still will not power up. Same symptom above except not blowing
fuse with green tube disconnected. Flyback checked good. Resoldered the
drive transformer posts as was suggested, but no luck. I believe I have
a 2 part problem. Probable bad green tube blowing fuse, and something
else sending set into shutdown at power up. Have to unplug, and plug
back in to get power led to light. Otherwise the power button will
still cycle the relay, but no light from power led. Hope someone has
experience with a similiar problem. Thanks group.

How did you check the flyback???

--

Jerry G.
======


wrote in message
oups.com...
Same problem, just more info to post. Hitachi 50EX10B, press power
button, led comes on, set shuts off. Stand by power OK. Kept blowing B+
fuses after replacing the HOT. I disconnected the anode of the green
CRT, and it doesn't blow fuses anymore. Other tubes OK. But, the dang
thing still will not power up. Same symptom above except not blowing
fuse with green tube disconnected. Flyback checked good. Resoldered the
drive transformer posts as was suggested, but no luck. I believe I have
a 2 part problem. Probable bad green tube blowing fuse, and something
else sending set into shutdown at power up. Have to unplug, and plug
back in to get power led to light. Otherwise the power button will
still cycle the relay, but no light from power led. Hope someone has
experience with a similiar problem. Thanks group.

wrote in message
oups.com...
Same problem, just more info to post. Hitachi 50EX10B, press power
button, led comes on, set shuts off. Stand by power OK. Kept blowing B+
fuses after replacing the HOT. I disconnected the anode of the green
CRT, and it doesn't blow fuses anymore. Other tubes OK. But, the dang
thing still will not power up. Same symptom above except not blowing
fuse with green tube disconnected. Flyback checked good. Resoldered the
drive transformer posts as was suggested, but no luck. I believe I have
a 2 part problem. Probable bad green tube blowing fuse, and something
else sending set into shutdown at power up. Have to unplug, and plug
back in to get power led to light. Otherwise the power button will
still cycle the relay, but no light from power led. Hope someone has
experience with a similiar problem. Thanks group.


If the set has too much HV the green crt is the first to break as an arc
snaps thru the glass. The set should have gone into shutdown fast enough to
not have broken the green crt.

Someone probably defeated shutdown for diagnostic purposes. The only safe
way to service the set is to disconnect the picture tubes first then confirm
with a HV meter that the HV is not going too high. The Switching regulator
is probably outputting too much voltage. Other circuits can be damaged if
you defeat the shutdown.

I replaced the switching regulator already, and 2 other transistors
that were suspect in the power supply. All with Hitachi replacements. I
wasn't getting steady voltage readings, they were cycling slightly
above to almost zero compared to the schematic. I'm not sure though how
to check Q702 which I think is an SCR (part of protective circuit). I
have read that someone with similiar symptom replaced a leaky one that
repaired the set. There are also 2 IC's - 902, 903, protective and
regulator respectively. Both are exact same circuit wise, but don't
check the same with diode/ohm check. Thanks for the info, any other
ideas?

| Thanks for the info, any other ideas?


The Flyback is part No. 2436493 subbed to a 2436493/A , NLA from Hitachi
but its a high fail common problem in this chassis that does cause shutdown.
Originals can be purchased online he
http://www.technotronic-dimensions.com/Products2.html