[LAU] Delta 66 woes

Tim termtech at rogers.com
Fri Dec 20 07:14:48 CET 2019

On 12/19/19 4:36 PM, Dave Phillips wrote:
> Greetings,
> Great thanks for the help, folks ! I've switched out the Omni I/O for 
> the simpler box, audio is back on track now. Clearly the Omni is the 
> culprit, it lit up when there was nothing connected to it. It's a handy 
> unit, I'd like to keep it so I'll see about getting it fixed.
> Ah, warmth and noise, it's all good again.
> Best regards,
> dp

If the lights, and others, are as bright as they usually are,
  and are not flickering or cutting out, the power supplies are
  likely mostly OK since the lights are powered from a low voltage,
  meaning voltages that are higher such as the ones powering
  the operational amplifiers driving the LEDs and processing
  input are likely OK too.
Also, op-amp power supplies can vary quite a bit, being low or
  having moderate ripple, before they start to do nasty
  things like that. I note that it does this with no input,
  so lack of supply headroom wouldn't likely be a problem here.

Always good to replace some power supply capacitors, but...

The immediate problem may be one or more small electrolytic
  input coupling capacitors to the op-amps, leaky or weak,
  passing Direct Current to the sensitive op-amp inputs,
  slamming their outputs full on, lighting the lights.
Very easy to check with a can of freeze spray or compressed
  air duster turned upside down, with the plastic 'straw' given.
Leave the unit on until working (or speed up the process with
  a hair dryer on the caps).
Then give the caps near the op-amps a short freeze blast,
  as if the unit was starting from 'cold'. If the caps are
  the problem, you'll soon notice if those lights come on again.
No physical contact required.

Anything else unusual to report?

Good luck with the venerable unit. Hope it's not expensive
  if you take it somewhere. It should be repairable, trust me.
Virtually all symptoms like that are.

Send it to me if no-one else will touch it. Canada, eh?

"Don't fear the repair"

And may your noise always have warmth ;-)

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