Thanks. When I tested these points the schematic said to have key #25 down with upper drawbar 8¡¯ out and expression pedal down. Also, I wondered if my multimeter was unable to read mv since I was looking for p-p. My lowest scale on the meter is 0-25 vac. Don¡¯t have an oscilloscope. I was able to hear a very slight sound of notes ?(under the electrical hum) if I held a full chord down with all the drawbars out. I guess I try reading component values going through the power amp board since I think the TWG is delivering a signal to it.?
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On Dec 3, 2024, at 3:19 PM, Chris Clifton via groups.io <clifton.christopher@...> wrote:
?
I shouldn't worry too much about voltages at the percussion board
to start with, a fault here would only affect the percussion
voices.
Pin 8 on the power amp board is signal input to the amplifier.
Somewhere in the service manual there will be a set of conditions,
(Something like U/M drawbar tab down, certain drawbars pulled out
and particular key or keys played). If all is well playing the
organ as specified for the test should give a signal at this point
which can be observed on an oscilloscope. Note that the voltage is
specified as peak to peak, which can only be measured on a 'scope,
a meter reading RMS AC volts will read something less than half
the P~P voltage. Pin 6 is return from the reverb tabs, there will
only be signal here with reverb tabs down, and notes being played
on the organ. Pin 19 is output to the speaker system, again, there
will only be an AC signal voltage here if the organ is being
played. There should never be a significant DC voltage here. Pin 2
on the power amp is DC power to part of the amplifier. Nominally
+15 volts, I wouldn't worry if it isn't exactly +15.
I'm struggling a bit here, I no longer have the library of paper
manuals that I used when I was working. I only have some
downloaded scans which seem to be missing a lot of the useful
text.
On 02/12/2024 22:34, Ned Lucas via
groups.io wrote:
Hi Chris - I've started to check different voltages of 2 of
the boards.? I started looking at the Percussion board.?
?
At pin 10 with the perc. tab down I get 16 vdc? ? should be
16 vdc? ? ? ? ? ? INPUT VOLTAGE FROM PRESET TABS
At pin 7? ? ? "? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? I get 2.5
vdc? (it should be 14 vdc)? ? ? ? ?INPUT FROM REITERATION TAB
At pin 2? ? ?"? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?I get 14.5
vdc? should be 14.5 vdc? ? ? ? ?TO PERCUSSION KEYING
?
On the power amp board:
?
#8 = 0 mv should be 800 mv? ? (FROM PIN #3 RECOVERY &
NON-VIBRATO 800MV P-P)
#2 = 16 v? should be 15v? ? ? ? ??
#6 = 0 mv should be 500 mv
#19 = 0 v? should be 15v
?
So somethings not right ...
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