Sound on vibrato channel only on T400

[PhilipS]

I've just bought a T400 spinet on Ebay - Andy Gilbert has been incredibly helpful in allowing me to cannibalise his old T for spares.
There is one problem though. There is sound with the vibrato tab down, but none with it up - so you can't really enjoy the pure sound of the internal Leslie accelerating and decelerating.
Andy suggests posting a question on what it might be: what should you look at in the non-vibrato line? Any suggestions on where to start to solve it methodically?
The symptoms were that the Leslie sound was beginning to sound quite distorted, when the whole thing packed up.
Thanks for any help.

[PhilipS]

Sorted! It was a dusty contact on the back of the vibrato tab.
That's one thing about this "new" organ - full of dust - amplifier in particular covered with it. Question is whether to leave it, or create a new problem by trying to clean it all of.

[JonathanP]

Sorted! It was a dusty contact on the back of the vibrato tab.
That's one thing about this "new" organ - full of dust - amplifier in particular covered with it. Question is whether to leave it, or create a new problem by trying to clean it all of.

I strongly recommend you clean it all out. My T500 was also covered in it (I couldn't even see some boards/components) and it created a lot of problems. I think some hum/hiss/pop from the amplifier was also dust related. Just get a vacuum in the back and clean it all out!

[indianajo]

After the mains plug is out, power is off a long time and the voltages are well discharged, I use a damp paper towel to clean old electronics. If the dirt is sticky I use a little non-chlorine bathroom cleanser, a cheap clone of scrubbing bubbles. i spray this on the paper towel instead of the electronics, and I rinse the electronis later with a damp towel. I use a steel pick to force the paper towel in around small crevices like around resistors and capacitors and things. I let things dry for a few days in dry weather before turning on again. I do not run the central heat in my house , so it is not that dry in here in the winter. I run AC in one room in the summer to keep the humidity down and prevent mold.
Inside tab switches, if I can get access through a hole, I stick the nozzle of a can of contact cleaner and blow them out. I do not use home generated compressed air, as this usually contains oil, which is bad for electronics. The T series is bipolar semiconductors and should be safe around a vacuum cleaner even in dry weather. later generations of organs with MOS semiconductors are not.

[andyg]

I like a clean T! As indie says, there's nothing sensitive in there, so gently brush with a vac nozzle close in. I got a brilliant 1/4" nozzle at a Poundland store a while back! Took a bit of Gaffa tape to make it fully airtight but works a treat. I''m lucky, the T400 came very clean, apart from the boards on the lower deck near the 'kennel'.

There is some dust on the digital boards of my SR6, and there was dust on the boards I removed from my second SR6. On the advice of my local engineer, I left this well alone. And yes, in case anyone's wondering, antistatic precautions were taken when removing and handling the digital boards. On an old organ with no CMOS or sensitive stuff - no problem.