Question about Panasonic CT-27SC14 27" TV

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Panasonic CT-27SC14 This is a strange problem, or maybe not, the set when turned on appears to start up, I get High Voltage, static on screen and in checking there is indeed high voltage on the CRT around 20-30,000 volts, however there is no raster or picture or sound, no fuses blown and power indicator stays lit, the set does not shut down until turned back off, I suspect a problem on the secondary board, power supply board, any ideas as to what might be defective on this board to cause this? again I have no schematic for this model, any help would be appreciated.

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  • Mark Moore Apr 24, 2007

    HI
    No, I didn't mean the voltage was fluctuating, I meant the voltage had a reading of somewhere between 20 and 30KV probably around the voltage you state. No as far as I can tell no filaments are lit in the CRT, in fact I have checked for heater voltage and have non as far as I can tell, this is why I'm suspecting a problem on the Low voltage supply board, as to what I'm not sure, thats the issue, I have no schematic for this model, any other ideas?

  • Mark Moore Apr 26, 2007

    HI
    Well after doing the checks, I found the CRT at fault, Ohmed out the pins, they were open, now I just have to find a good CRT, thanks for your help:)

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  • Master
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The high voltage should be around 29.5 KV and not fuctuate between 20-30 KV that would indicate a high voltage regulation issue then. Are the filaments lighted up in the neck of the CRT? If so then yes you are probably looking at a low voltage issue such as a 12 volt source or a a/v switching IC issue.

Posted on Apr 23, 2007

  • Don
    Don Apr 24, 2007

    If you have high voltage at 30kv then you should have filaments. The filament voltage comes freom the high voltage transformer and not low voltage. I would check on the CRT board for the two pins marked "F" for filament or "H" for heater and see if there is any kind of A.C. volatge there at all. If there is, disconnect the board and check for continuity between those two pins. Low resistance is normal, open is a bad CRT.

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Assuming there is no deflection and no High Voltage , you either have a low voltage power supply problem, bad startup circuit, or bad horizontal output transistor (HOT) or other bad parts in the horizontal deflection.

Check for bad fuses.

(If you have High Voltage as indicated by static electricity on the front of the screen and you hear the high pitched whine of the horizontal deflection when it is turned on, then the following does not apply).

Use an ohmmeter to test the HOT for shorts. If it is bad, look for open fusable resistors or other fuses you did not catch.

Assuming it is good, measure the voltage on the collector-emitter of the HOT (this is safe if there is no deflection). You should see the B+ - probably between 100 and 150 V.

If there is no voltage, you have a low voltage power supply problem and/or you have not found all the bad/open parts.

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Test the transistors if it is that type with an ohmmeter. If one is shorted, you have a problem. The usual way a TV service person would test for startup problems is to inject a signal to the base of the HOT of about 15.75 kHz. If the TV then starts and runs once this signal is removed, the diagnosis is confirmed. This is risky - you can blow things up if not careful (including yourself). See the section: Bypassing the Startup Circuit for details.

If you hear the high pitched whine of the deflection and/or feel some static on the scree, confirm that the horizontal deflection and high voltage are working by adjusting the SCREEN control (probably on the flyback). If you can get a raster then your problem is probably in the video or chroma circuits, not the deflection or high voltage.
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