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Maybe the 4049 at IC1 isn't switching voltage for the following diode/capacitor multiplier section. Or, the voltage
could be shorting to appear near zero volts dc as would be the case with a shorted PP On/off switch. Trouble
with the switch is something you could just "eye" before setting things up for further checks/tests. The terminals
can tilt or misalign if there is tension on them during soldering and this can result in contact with the metal
threaded mounting bushing in contact with the chassis which is in contact with the circuit-ground/common/0vdc
circuit originating at circuit-board-wiring-points G / SG. If this looks like a possibility, an ohms measurement will
tell (confirm the 9407 power switch is set to Off for this test). There should not be zero ohms between the
terminal with wire from E and the outer, metal part of the switch.
-0-0-0-0-
IC1 alternately puts about Vcc voltage or 0v to the diode and capacitor voltage multiplier circuit that follows it.
Measurement of the dc of this post-audio-rate pulsing should show a reading between 0 and about 15, but not a
steady 0 or 15. It outputs from pins 10 and 12, parallel connected stages on this IC. The pulsing should cause
an increasing voltage from capacitor to capacitor on Cs 7, 9, and 11. The reading on the + end of each
capacitor should be an increase of an amount about the same as the Vcc voltage to the part or 18v or so, for
about 18, 36, and 54 volts.
DC oltage tests.
DC voltage tests can be made at IC1, first, at the power supply pins 1 for voltage and 8 for ground/common, and
then at the output pins 10 and 12. The pin 1 dc power supply voltage should be about 16 to 18 vdc. This will
surely be there, but if not the most likely cause would be a solder connection that didn't flow at pin 1 or 8. Pins
10 and 12 are outputs of paralleled IC sections and the dc voltage reading here is an average of the 0 to 16-18
volt, 60kHz ''on"/'off" switching, and in a 4-12 vdc range--a near zero or Vcc (16 to 18 vdc) reading would point to
no switching action that could be due to a failed IC or soldering trouble in the area of sections IC1:A through
IC1:D/E looking at the schematic and on the board.
-0-0-0-
It is best to measure the dc power supplies right at IC pins. The power supply voltages should be getting into the
eight pin dual op-amp ICs on pin 8 (+ 12 to 15 v dc) and pin 4 ( - 12 to 15v dc). Viewed from the top of the
board, the pins count-up, going ccw from the notch. Select negative DC polarity or swap the probes used to test
the pin 4 voltages when using a tester with a meter movement that swings to the right from zero. The sixteen pin
hex inverter IC originates at a point earlier in the positive dc power supply circuit and is a couple of volts more.
Measure for this voltage shown as Vcc on the schematic at pin 1 of IC1.
-0-0-0-
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Tube path.
The fully post setting on the Blend control adjustment is 100% of the tube signal, so, if nothing gets through on
this setting it is trouble in the tube path. Maybe it's just the control twisted so the terminal with the tube signal on
it (the solid-state path is on one end and the tube path is on the other with ground in the middle to shunt one side
or the other according to the setting) is touching the grounded case. Be sure the tube is seated all the way in it's
socket. The bottom of the tube should be against the surface of the socket base. Look through an opening in
the side of the base to see this. The Symmetry trim is in-line between the tube stages and maybe it's adjusting
disk is loose or the part cracked or broken.
... shorts to ground and the shielded cable. Look for shorts where the shield separates from the internal wire.
Heat from soldering can cause the shield to melt the insulation of the internal wire and if there is tension, it can
pull on through against the internal wire. Or, a stray strand of the shield might be extending over and contacting
an adjacent point. A test can be made to confirm resistance between these points in the circuit with the power to
