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?
toggle quoted message
Show quoted text
On Dec 4, 2024, at 10:27 AM, Chris Clifton via groups.io <clifton.christopher@...> wrote:
?
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 ...
--
--
