Volume reduced when the B preset is depressed

[Dkvandal]

The volume on my B-3 drops by about half when the B preset is depressed on the upper manual. This happens whether or not the percussion switch is enabled.
I've checked the signal from the drawbars and it is ok (the same whether the A# or B preset is depressed. The only thing I can figure is that the button under the B preset key is changing something when that preset key is depressed. Possibly in the matching transformer?
All other presets upper and manual are ok.
Clues anyone? I'm going to dive into the matching transformer to see if anything is shorted there.

[muckelroy]

Here is what the service manual says in regards to the Preset Percussion Switch (below the B preset):

The Preset Percussion Switch is not part of the control tablet assembly or percussion on-off tablet, but functions as an interlock with it. It is located under the upper manual B adjust key. This switch insures that the full upper manual signal is restored by shorting out series resistor R1 introduced by the percussion on tablet when any other upper manual preset or adjust key is pressed. The Volume Tablet in soft position shunts resistor R46 across the percussion output transformer, reducing percussion signal, and also shorts out upper manual matching transformer compensating resistor RI thus restoring upper manual signal strength to provide proper balance between the manuals.

That being said, if that switch was not making proper contact when B preset is depressed, it will have the effect of keeping R1 at play at all times, I think whether percussion is on or off. I could be wrong, but that's how I'm interpreting it.

[muckelroy]

On second thought, I misinterpreted it. The switch is "normally closed", and only opens when B preset is pressed. When you press B preset, R1 is "in play" and not shorted to ground, if percussion is on, AND perc volume is normal.

In your situation, if you have normal volume on other preset keys, the preset percussion switch is doing its job.

However, since B preset might be behaving in a that R1 is always at play (not grounded) regardless of the percussion settings, this implies there is an issue either with the percussion on/off switch, or the percussion soft/normal switch.
-- The percussion on/off switch is supposed to ground R1 when percussion is off.
-- The percussion soft/normal switch is supposed to ground R1 when set to "soft".

One brute force method to fix this problem is to short R1 inside the matching transformer, but then it's always shorted, end of story, regardless of your percussion settings.

If your problem is not due to R1 "not shorting ever" then I have no idea where else to look for the cause of this. (at least not right this second.)

[enor]

Sounds like a fault in the percussion switch assembly. My guess: missing ground to the "normal-soft" switch, or the switch itself might be broken somehow.