Severe volume loss standard etherwave

Hi all,

I have a problem with my standard Etherwave.  
The volume antennae does nothing. The volume is really low and here is what sounds like a ground hum that covers everything. 

Any ideas?

Thanks,

Samgar

There is a strong possibility that static discharge popped the volume side detector diode or transistor. 
Others are better qualified to guide you through this one.

Christopher

So at this point I have tested the diode at D11 and it seems to work properly.  I have shorted the capacitor at C28 and that behaves as it should.  I metered across node D1/R14/C12 and it reads properly.  I do not have a Oscilliscope to do deeper testing.    I am at a loss as to what to do next, shy of sending it back to Moog.  Any suggestions?

Sorry about the weird font above.  It seems to be a copy/paste thing.

Here are the wise words of Thierry,

There are basically a few things which can provoke that faint remaining tone when the Etherwave should be mute. The most often occurring phenomenons are external:

- grounding problems: Either bad grounding connection between the Etherwave and the amplifier, which happens normally through the shielding of the audio cable, so try with a new and better shielded cable. Or bad grounding of the amplifier on the mains side: Never use amplifiers with an external power supply since these break ground. Only use amplifiers with a three prong wall plug and a corresponding three prong AC inlet (C14) with the Etherwave.

- stray problems: Some amplifiers, even HiFi equipment, might catch the pitch RF radiated from the antenna and demodulate it accidentally. If moving the amplifier closer or more far away from the theremin changes the intensity of the faint tone, or if the faint tone appears still with the audio cable unplugged, trash that amp and get a better one which is appropriate for the theremin.
More rarely occurring causes are internal:

- volume circuit completely out of tune. That doesn‘t come from natural circumstances or slow de-tuning because of aging. So, an attempt to re-tuning will only temporarily reduce the symptoms. If an Etherwave gets suddenly this way out of tune, that means that something in the oscillator or volume processor stages went totally out of specs and will soon die completely.

- damaged volume discriminator, either one of the inductors L7 to L9 broken due to mechanical shock or D1 killed by static discharge when touching the volume antenna.

- damaged volume processor, U3B killed either by static discharge or by accidentally feeding DC into the Audio output, i.e. 48V microphone phantom supply from a connected mixing desk will over-stress the DC blocking capabilities of C25 and damage the LM13700A

But at distance, it’s all only wild guessing. A precise diagnosis can only established while connecting the Etherwave to a known well working amplifier (I’ve a Bose L1 PA for that purpose in my workshop) and using an oscilloscope to systematically trace down the problem.

Back in business.  I sent it off to Moog and they took care of it.  Turns out one of the volume inductors was broken.  Not one of the adjustable ones mind you.  

Hello Samgar,

With turn around shipping and if they charged you for the fix what was the total cost?

Those series antenna inductors are so dam fragile it amazes me.

Thank you

Christopher

$110.00  One hour of bench time plus shipping.  If you have a replacement inductor in mind...

Obviously, my bench time tariff is ways too low... 

"Turns out one of the volume inductors was broken."  - Smagar

It's a veritable epidemic!  The ones I bought some years ago from a reputable parts supplier came all jumbled together in a plastic bag, which killed a couple of them just in shipping.  I'm imagining the parts warehouse with these RF chokes in a pickle barrel, and a pallet of magnetrons on top.  They need a protective coating of some sort if they're going to get man handled.  The wire is so fine and stiffly varnished that you might be able to kill them just by bending the leads too sharply at the base where they connect.