There should be a picture of the board with the components
labelled in your service manual.
On 06/12/2024 22:26, Ned Lucas via
groups.io wrote:
Thanks. I¡¯ll check the transistor voltages but how do I know what
transistor on the schematic is which transistor on the board?
?
The transistors you've labelled 1 & 2 are part of the
reverb drive amplifier. They provide the signal fed into the
input end of the reverb springs. As such, they have no
direct connection with the main organ signal, but a fault
here could affect power supplies common to the reverb drive
and main amplifiers. They might get warm when the organ is
operating, but should not get hot enough to be
uncomfortable, or even painful to touch. The transistor in
the black heat sink (#3) is the driver for the output
transistors of the main amp. Them"2111 etc. part number is
the Hammond part number for these transistors, the one in
the heat sink is a similar transistor. Resistance checks
around the transistors really won't tell us much. Measuring
the voltages at the emitter, base and collector pins with
the organ powered up, and comparing these voltages with the
voltages given on the schematic will be much more helpful.
Take great care when measuring not to short the transistor
leads to each other or anything else with your meter probes.
The highest voltage on the amplifier board is about 25
volts. This won't hurt you, but could easily destroy
transistors or other components if you accidentally create a
short circuit.
On 06/12/2024 00:40, Ned Lucas
via groups.io wrote:
Hi Chris,
I¡¯ve checked all the transistors on the pwr &
reverb amp board (with the organ off) using an analog
multimeter on the 1x ohm setting. All check out ¡°ok¡±
except the 2 metal can ones and the large black one. On
those I got ?some leakage when connecting to the emitter
and common. I noticed that with the organ running, can #1
got very hot to the touch. The metal cans (1&2) look
like they have ¡°2111-1 6847¡± on them. No idea what the
black (#3) is. Also, when testing #3 across E - C, the
speaker made a little crackling sound.?
Am I heading in the right direction?
?
If I recall, you said that the loud background hum
wasn't affected by the swell pedal. The signal at
pin 8 goes through the swell before going to the
actual input of the amplifier. As the hum level is
unaffected by the swell pedal, this suggests that
the source of the hum, (possibly also the cause of
the loss of wanted signal) is somewhere on the
amplifier board. The signal after the swell pedal
goes in turn through Q6021, Q602, Q603 and 604 to
the driver transformer, and then to the output
transistors Q605 and 606. Checking the voltages
around the first four transistors may give us a
clue.
On 04/12/2024 14:54, Ned
Lucas via groups.io wrote:
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.?
?
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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