ghosts in the machine

why is it whenever there is an issue and a unit is sent in to the tech it works as designed and there is no issue?

I have a few units in front of me where sworn to not work but the moment I plug in, they work as designed. this is with test tones and  program material(music) in fact there isn't a problem at all.

You have a hammer on your bench............
Best,
Bruno2000

bruno buddy you back?

I'm attending a theatre stage play with just one singer and a piano, a nice and minimalist show, this Saturday as the singer started the second song his mic started to make loud pops, really annoying, so I ran down to the stage as soon as he gets out of it for a dressing change to check if everything was ok (I was thinking in the minijack connecting the mic to the bodypack being loose), all connections looked good, I go back to my control room and the show goes nicely till the closing song, where the pops came back...

The next day I was almost 2 hours checking the mic, moving, singing really loud, forcing a bit the connectors, getting far of the receiver, everything was ok.... till the closing song, again... 

I took the mic to my home after the show, and can't get it to fail, those damned ghosts are tricky...

Had a ghastly one recently - a G10 compressor that was claimed to suddenly stop compressing after some heat-up time. Checked everything MANY times, had it in burn-in-oven at 80C overnight, pushed around every component.

It compressed alright - no wrongdoing whatsoever...

Then, after a week or so of observation, I noticed that the meter behaved unevenly after heat-up - and here was the fault: The internal meter light bulb was so close to the needle movement that occasionally it would stop the needle exactly at 0VU/NoGR - which would somehow persuade the user that no gain reduction was going on....

My error-tracing fault was that I was listening the whole time, not paying attention to the behavior of the meter.

Some times, don't use your ears....

Jakob E.

well that's just it, in this case there is no metering other then  stereo buss meters and the signal would be going as follows from the monitor input jack  on the mixer  through the monitor path which has a volume pot and a pan pot. If it was not working as claimed I would have heard it as well as seen it or the case of not working would not have seen the meters move or heard any signal. I ran it all day and over night and no drop outs for the 8 hours I was in the shop, let it on over night and came in the next day with tone still going and nothing to indicate it ever was not working.

pucho812 said:

bruno buddy you back?

Click to expand...

Limited participation for now.  I couldn't pass up the opportunity.  Thank you!
Best,
Bruno2000

Also in actual conditions in case there is interaction with something
for rf  mics time of day could provide a competing frequency from someone , somewhere else
that is close enough to  cause problems, not usually that high power but the interfering one could be.

For chasing ghosts a can of spray cold, and an iron or small hot air tip can selectively heat or cool individual components to recreate thermal cycles.  Tapping with a pencil eraser can sometimes reveal a faulty component or solder joint.

JR

We have one desk with four intermittant faults. Since more than one year every fault disappears as soon as I enter the room with measurement gear and enough time to actually have a chance to find or narrow down the problem. Next day in production they´ll be back - sometimes.

jensenmann said:

We have one desk with four intermittant faults. Since more than one year every fault disappears as soon as I enter the room with measurement gear and enough time to actually have a chance to find or narrow down the problem. Next day in production they´ll be back - sometimes.

Click to expand...

You need to sneak up on them... pretend you aren't performing an exorcism.

JR

I already told the desk that I love it and won´t do no harm. But it still doesn´t want to be cured.

jensenmann said:

I already told the desk that I love it and won´t do no harm. But it still doesn´t want to be cured.

Click to expand...

The problem isn't the desk, but the ghost(s)...

JR

have you tried candle light dinner with a lil wine.  ;D

No, unfortunately I´m a bit shy with spilling wax and wine into faders.

Funny I was cleaning candle waxout of faders on a pm-700 this past weekend.  Lucky for me it was just on the mechnicals so everything worked was just sticky faders.

jensenmann said:

We have one desk with four intermittant faults. Since more than one year every fault disappears as soon as I enter the room with measurement gear and enough time to actually have a chance to find or narrow down the problem. Next day in production they´ll be back - sometimes.

Click to expand...

Next time, try leaving a large hammer in the room when you leave.  Maintenance by intimidation.........
(why is the solution always a hammer?)
Best,
Bruno2000

because sometimes the only real solution is to break it permanently

bruno2000 said:

jensenmann said:

We have one desk with four intermittant faults. Since more than one year every fault disappears as soon as I enter the room with measurement gear and enough time to actually have a chance to find or narrow down the problem. Next day in production they´ll be back - sometimes.

Click to expand...

Next time, try leaving a large hammer in the room when you leave.  Maintenance by intimidation.........
(why is the solution always a hammer?)
Best,
Bruno2000

Click to expand...

Something like that happened accidently last week. At one point I had to leave the CR and forgot to take my DMM and screwdriver with me. They were sitting on the desk for a week. Since then it works. Now I´m a bit hesitant to remove these from the board.....  :

I strongly believe there are techs and anti-techs.. Gear always works just fine for me, but I have friends who can make brand-new gear fail just by being nearby. Every tech needs to employ an anti-tech for testing purposes.