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 ...
--
--
--
