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Panasonic ct-27g5b no turn on no low voltage    
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-3db



Joined: 02 Nov 2014
Posts: 5

PostPosted: Sun Nov 02, 2014 3:46 pm    Post subject: Panasonic ct-27g5b no turn on no low voltage Reply with quote

A little background info here. This set started out with verticle ic solder joint issues.

Upon repairing said joints, I though set was working fine. Returned tools to proper places and went to turn the set of I would not turn off. It would not turn off with either the remote or front panel button. None of the others would work as well.

Thinking I may have had the pc board askew I pulled it and checked all good. Tried again same result. Then totally removed the board to check for stray solder or such. Found none.

Returned pc to proper place to try again.

Now no turn on, no relay click.

Out again to check voltages.

Tpb8. .46
Tpd9. .0
C552. .11
Ic551. .11

At this point I stopped checking voltages as I knew what was happening.

How does this thing develope the 13 volt supply.
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JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Sun Nov 02, 2014 5:23 pm    Post subject: Reply with quote

If vertical ic solder joints were solved by resoldering same, what are the chances that you may have missed other bad joints on the same board?

-3db wrote:
How does this thing develope the 13 volt supply.

Scan derived D551 cathode (from flyback).
C552 = 19 Volt supply for audio. Also scan derived.
TPD9 = 13 volt scan derived
TPD8 = 26 volt scan derived
-3db



Joined: 02 Nov 2014
Posts: 5

PostPosted: Sun Nov 02, 2014 6:14 pm    Post subject: Reply with quote

It certainly could be another joint as I've found serval in the past and repaired same. However I don't believe so, it's my belief that my discharging the CRT to remove the chassis killed it. Something or another got whacked by the discharge voltage.


Maybe I'm wrong here but my actual problem is lack of 12 volt standby voltage. I had felt it was pulled from the 13 volt line. Now not sure that's so.

If that is so how could I have 13 line without scan taking place. Need to look further into this drawing to find 12 volt source for turn on.
JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Sun Nov 02, 2014 6:31 pm    Post subject: Reply with quote

Standby 12v comes from across C022.
5 volt Q002 emitter. IC002 EEPROM pin 8. IC001 pin 22 & 61. Also to remote receiver.

Discharge to metal braided strap on CRT.
-3db



Joined: 02 Nov 2014
Posts: 5

PostPosted: Sun Nov 02, 2014 6:59 pm    Post subject: Reply with quote

Yes sir if found it. Small transformer across a/c line.
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JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Sun Nov 02, 2014 7:09 pm    Post subject: Reply with quote

T001 TLP16297
-3db



Joined: 02 Nov 2014
Posts: 5

PostPosted: Sun Nov 02, 2014 8:25 pm    Post subject: Reply with quote

IC 001 pulling 5volt regulated line down to approx 1 volt. 5 volt line is taken off of 12 volt standby.

Pulled jumper lead supplying 5 volts to IC 001
5 volt supply and 12 volt standby returned to normal.

Needs IC 001 replaced.
JTS1957



Joined: 21 Jan 2009
Posts: 2324
Location: Far, Far Away

PostPosted: Sun Nov 02, 2014 8:46 pm    Post subject: Reply with quote

As long as you read near zero ohms from ground to the 'floating' VCC pin of IC001 and a much larger resistance to the 'foil' (with the jumper wire you disconnected reinstalled), I'll agree. I've seen 6.3V and 10V lytics short, just sayin'.
-3db



Joined: 02 Nov 2014
Posts: 5

PostPosted: Sun Nov 02, 2014 8:58 pm    Post subject: Reply with quote

I did check the caps that where across the 5 volt line. The only thing I may check further is Q004 to make certain it's not causing something odd.


Like I've said I killed it shorting the CRT. That's my story. Worked well before hand. Just needed a little wack along side every now and again.


I'll do that a little differently next time.
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