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Old 07-29-2019, 07:27 PM
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StellarTV StellarTV is offline
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Join Date: Jan 2007
Location: Sacramento, CA
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Admiral C-21A1-1A Chassis with low boost voltage

Hello! I'm working with a 1964 Admiral portable that had low/no boost voltage and am at a loss. Here's the current situation:

-Capacitors have been replaced
-The yoke and flyback both ring out OK
-DC Voltages are correct at the horizontal output tube, but the input waveform on pins 9-10 show only about 67v peak to peak instead of 100v
-Plate voltage on the output side of tube V7 (Horizontal oscillator) is only ~83v instead of 120v, and this is tied directly to boost voltage (are these then additive voltages?)
-Cathode voltages at pins 8 and 3 of the same tube are about 3.4v instead of 5v
-B+ voltages are correct at 140v and 145v where required. Actual boost voltage is low at ~200v.
-Boost filter capacitors C62 and C63 have been re-replaced to eliminate the possibility of faulty new components to no avail.
-Horizontal Output and Oscillator tubes have also been replaced with no change.

Does anyone have any suggestions as far as what else to check?

Schematic attached
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