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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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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. |
#2
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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. |
#3
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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. |
#4
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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? |
#5
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| 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 |
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