Compellor Shows Meter Activity With No Signal

[Info-warrior]

Got a question for the experts.

I have a Compellor 320A that started showing activity on the channel 1 meters even with no signal present. The meter lights up at least 5, sometimes more of the segments regardles of what mode it's in. I've disconnected all cables from the unit, switched it on and off several times, but it still persists. I'm probably going to send it off to Aphex at some point, but is there anything I should look at first that might save a trip to Aphex and some money as well?

Thanks

 

[Tom Wells]

False meter deflections are generally the ever-popular leaky electrolytic capacitor unless there are any switches to suspect.
I doubt the Compellor has any hardware switching in the VU circuit.

If no accompanying noise is present with the indication, it is likely only in the VU indicator circuit.
Any card edge connectors could also do this if they are in the VU circuit.

Was it suddenly at this level, or has it come on slowly and gradually?
Every time or intermittant? Immediately upon power-up or after a while?
Is it normally always-on or off at night? Have you let it cool completely off to see if it's the same when stone cold?

Continuous or showing amplitude variations? If so, how fast?

Have you tried the old-time engineer's shock alignment? (Even cornered drop from experience-dictated height)?
Okay so it's in a rack, but I'm not kidding.
Internal connections become noisy in permanently-on devices not maintained.
Wiggling or reseating such connectors may be in order. ( The above drop procedure addresses most of these in .125 second )

 

[Studio1]

I'm with Tom on this one.

It's time to take the lid off and have a look. If you are not a tech then send it off to Aphex.

If you are, then re-cap it starting at the VU board and working backwards.

Could be a dodgy connector (internal), an IC that needs re-seating or such.

Something in the audio chain that feeds the VU meter or the meter electronics itself has become "noisy".

If you can "hear" this noise on the output then it's in the audio chain.

 

[TomT]

Had a 9000 that did this. Little meters wiggled like crazy, but I couldn't hear any music.

The exorcist was busy so I replaced the by-pass caps on the +/- 15 rails and everything returned to normal.

 

[CW]

Had a 9000 that did this. Little meters wiggled like crazy, but I couldn't hear any music.

The exorcist was busy so I replaced the by-pass caps on the +/- 15 rails and everything returned to normal.

Caps in audio circuits are usually the culprits (especially tantalums).....after so many years, they dry out and either become shorts or act as a total open or high resistance with no filtering effect. I had to change out a lot of 47uF in Rockwell Collins microwave gear years ago...this one size cap was used in their multiplex equipment a lot and on several cards in the RF chassis (AGC, Power Supplies, etc); even though they were mil speced, they starting LEAKING and some of them corroded the PC boards! Others, if one lead was desoldered, the cap fell off the board leaving the other lead by itself! We went through several DOZEN BOXES of caps (~250 per box) once the entire system of microwave stations were done...and then we had to turn DOWN the levels because they had all increased as much as 10db on the baseband (the mux was SSB cards...and SSB 10db hot does not sound good!)

I also recall there being a cap on one of the AM Optimods that, when shorted, will shut down the power supply AND the LED metering on the front...and its a PAIN to get to...just removing the LED metering from the circuit restored operation....and I never bothered to replace the cap (Orban tech guys offered to send a replacement metering but it was our only Optimod at the time on the station..Didnt touch the controls and it worked fine..

 

[Info-warrior]

Thanks for the replies, some good info there.

I don't hear an increase in the noise floor or any distortion in the audio.

It just started doing it the other day and there is a little variation in amplitude when switched to either input or output metering, the sixth segment flickers on and off.

I've owned the compellor for about a year now and it spends most of it's life off as I only use it when running my low power transmitter. I don't know it's full history as I bought it used from a dealer. The date on the side of the unit is August of 1996, so it's a bit over 11 years old.

I'm running it now as I type this and for the last 40 minutes or so the metering was operationg correctly, then it just sudden lit up all the segments on channel one while in gain reduction mode, when switched to input or output mode, the leds seemed slightly brighter than normal with audio present.

I'm not a tech, but I dabble in electronics as a hobby. I'll take the cover off and reseat the connectors and socketed ICs (carefully so as to avoid static discharge). If that doesn't cure it, then it will go off to Aphex at some point.

 

[tjm_pro]

I have a Compellor the same age (1996) and I have had the opposite happen. The left channel LED's work Intermittently but the unit still operates properly and passes clean audio. It's been in use for 11 years now (24/7) and doesn't owe us a dime.. I've budgeted for a new one (the digital AES I/O version) this year.

 

[Tom Wells]

I have a Compellor the same age (1996) and I have had the opposite happen. The left channel LED's work Intermittently but the unit still operates properly and passes clean audio. It's been in use for 11 years now (24/7) and doesn't owe us a dime.. I've budgeted for a new one (the digital AES I/O version) this year.

This almost points to two different failure modes for what is likely the first coupling cap into the VU circuit.
If it fails open, there's no indication.
If it leaks, DC is probably causing the continuous reading and the variation.

But not necessarily. No never.