[TechAssist] Re: Rca PTV P46770CK PTK169PAAS chassis No contrast update FIX

Well I found it. I worked my way back from the micro to see why the contrast
Voltage was being held at 4.5V. disconnected parts one at a time to see if
the voltage would go high. When I disconnected the beam limit transistor the
voltage went high. Back tracking I found that when I took out R2721 27K 1/2w
it broke in half. Replaced this and same thing. Went back further and found
a 10V pulse on R2721. Checked R4713 and it was 58K was supposed to be 68K.
Changed that no help. Checked C4701 and when I got it out the one leg came
out. Replacing this cut the pulses to nothing and the 8.3V that was on R2721
went up to 9.5 volts and the contrast voltage went high. I replaced R4703 a
3.3ohm 3W resistor because when I moved it that one broke in half too. Also
I replaced C4755 1mf 250V on the high voltage regulator board for high ESR
and C4758 for good measure on the beam limit line. So there you have it,
there is no pulse on R2721 and the voltage on this has to be 9.5 for the
circuit to work. WHOOPEE!!!!!
Al Marquardt
ampm@xxxxxxx
Al Marquardt Electronic Repair
206 W Main
Girardville Pa. 17935
----- Original Message ----- 
From: "al m" <ampm@xxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Wednesday, April 28, 2004 5:46 PM
Subject: [TechAssist] Rca PTV P46770CK PTK169PAAS chassis No contrast update


> this PTV the contrast will not adjust. I have found that if I disconnect
the
> Beam limit transistor the contrast adjusts.checked all parts in that
circuit
> and all check OK. Now the big question. Does anyone know what waveform
> should be on the line that comes from the high voltage Regulator board to
> the main board on E25? I have checked the voltages on the transistors and
> the transformer waveform looks good on pin 2. It must have something to do
> with the amplitude of the signal going back to the beam circuit. Can weak
> picture tubes cause this to happen? Have very little experience with these
> beam circuits. Thanks.
> Al Marquardt
> ampm@xxxxxxx
> Al Marquardt Electronic Repair
> 206 W Main
> Girardville Pa. 17935
>
>
>
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