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Crumbtrail TV Forums: TV Equipment: TV Repair Forum:
Panasonic CT-20G12V No Picture - Relay Click, hi-pitched scream

 

 


trinidex
New User

Feb 7, 2003, 11:40 AM

Post #1 of 7 (3178 views)
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Panasonic CT-20G12V No Picture - Relay Click, hi-pitched scream Can't Post

I have the above set, recently the picture would take a long time to come up, and would fade. Finally, the other day, I switched it on, there is a relay click, and then a high-pitched scream (possibly from the flyback TX?) and you cannot turn the set off with the power button, you have to pull the power. I'm thinking it could be flyback TX or flyback Transistor?

Help and advice greatly appreciated.

Thankyou



BL_Thompson
TV Repair Authority

Feb 7, 2003, 9:14 PM

Post #2 of 7 (3167 views)
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Re: [trinidex] Panasonic CT-20G12V No Picture - Relay Click, hi-pitched scream [In reply to] Can't Post

trinidex, it sounds like your flyback is arcing. Turn all the lights off and look carefully around the flyback for arcing. A shorted HOT could also cause the high pitched "scream"... some switched mode power supplies complain loudly when there is a short on the B+ line. You can test for high voltage with an NE2 neon bulb attached to an insulated stick (such as a pen housing). I assume your set is shutting down, so hold the NE2 bulb against the body of the flyback while you turn the set on. If the bulb lights, your HOT is ok, and your flyback is probably the cause of the problem. One other possibility is that the CRT is shorted to HV. If all else fails, remove the CRT socket & see if the symptoms change... just steer clear of the CRT pins. If the CRT is shorted to HV, you'll have 20KV on those pins!

BLT
-----------------------
Bryan Thompson
Spyder Byte Services
Albuquerque, NM


trinidex
New User

Feb 8, 2003, 3:17 PM

Post #3 of 7 (3160 views)
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Re: [BL_Thompson] Panasonic CT-20G12V No Picture - Relay Click, hi-pitched scream [In reply to] Can't Post

BLT - Thanks for the advice - this is what I've done....

Unplugged the CRT neck board and switched on - same thing, upon further investigation I do not think the flyback is screaming, seems to be the relay itself?

Anyway, I unsoldered the flyback and switched the set on, no scream this time, tried a *similar* flyback, scream returns

Any further thoughts greatly appreciated - thanks again


trinidex
New User

Feb 8, 2003, 3:42 PM

Post #4 of 7 (3157 views)
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Re: [BL_Thompson] Panasonic CT-20G12V No Picture - Relay Click, hi-pitched scream [In reply to] Can't Post

Quick update (set still not working) - I pulled the STR-58041 (voltage reg apparently), I powered on the set, no scream. Problem is, I am unsure on how to test the STR-58041 and do not have a handy one - any thoughts?


BL_Thompson
TV Repair Authority

Feb 8, 2003, 7:02 PM

Post #5 of 7 (3154 views)
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Re: [trinidex] Panasonic CT-20G12V No Picture - Relay Click, hi-pitched scream [In reply to] Can't Post

trinidex, you probably have a shorted HOT (Horizontal Output Transistor). The noise you're hearing is most likely from the switching regulator transformer... I seriously doubt it's the relay. Check the HOT with a DMM.
-----------------------
Bryan Thompson
Spyder Byte Services
Albuquerque, NM


trinidex
New User

Feb 8, 2003, 8:54 PM

Post #6 of 7 (3149 views)
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Re: [BL_Thompson] Panasonic CT-20G12V No Picture - Relay Click, hi-pitched scream [In reply to] Can't Post

BL_Thompson - forgive my ignorance, (I am not a TV technician by profession), is the HOT the transistor located near the LOPT? if it is, then you are correct, this appears to be the problem. It is a BU2506DF, I swapped it with a Panasonic branded C5622 and the set came on - I did however turn it off quickly, as I do not know if the C5622 is a suitable replacement for the BU unit.

Thank you again for your help, it is nice to be able to get help when you're lost!


BL_Thompson
TV Repair Authority

Feb 8, 2003, 9:02 PM

Post #7 of 7 (3148 views)
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Re: [trinidex] Panasonic CT-20G12V No Picture - Relay Click, hi-pitched scream [In reply to] Can't Post

Happy to help. Do us both a favor and replace the HOT with the original part.
-----------------------
Bryan Thompson
Spyder Byte Services
Albuquerque, NM

 
 
 


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