Nuclear Comms (RS-501)

EdSavoie

Well-Known Member
We seem to be having a systematic problem with comms. This Clearcom RS-501 pack has failed by carbonizing a resistor, and burning the talk LED (the lamp wasn't illuminated to my knowledge, reverse voltage?)

After a four hour run for this evening rehearsal, the box went dead. I suspected the cable was at fault, so we fetched another XLR of similar length and patched it in. At this time, I talk successfully for about 45 seconds, unlatch talk, and put it down.

Fast forward about a minute, the musical director has the headset on, and the unit on her lap. She then proceeds to panic and flip s*** as the box starts smoking.

(I've been told this is the same behavior as some other packs we've had.)

I'll add images after I crop them down, this new phone spits out massive images...
 
A couple that's not good at all.

It sounds like your Base Station is sending voltage down the line that it shouldn't be.

I would meter what it's sending out and compare that to the spec sheet.
 
Mind you, other packs were plugged in at the same time this occurred. I will be checking the PSU, which is a CS-222 if I'm not mistaken.

20 minutes after, one of our hard to reach FOH lights failed by strobing at about 15hz "Seriously?" >_<
 
Mind you, other packs were plugged in at the same time this occurred. I will be checking the PSU, which is a CS-222 if I'm not mistaken.

20 minutes after, one of our hard to reach FOH lights failed by strobing at about 15hz "Seriously?" >_<

PARDON?! Neither should be happening... If you weren't so many hours drive away I'd want to have a look myself just to know what is going on.
Clearcom packs are quite reliable, however even when failing this should not happen. If the power supply is sending over voltage and that beltpack had a fault than the catastrophic failure could be explained.

Really suspicious as you mentioned multiple packs have failed this way.
 
Good timing, I got an alert you responded as I was writing this.

Odd. I metered the CS-222 base station (date code 1992 on the PCB) and the voltage is spot on. I couldn't get the voltage to go above ot below that. It would seem this unit has had some work on it, because there is no way the beefy PSU caps are that old, judging by the almost new state they appear to be in.

Right on power on, the red fault LED lights up for a split second, but It would be reasonable to attribute that to building the magnetic field in the transformer / filling caps, as it only does this when the unit has been off long enough for the voltage to drift down to 0.

I also checked continuity and resistance, the common pin for the XLR is directly referenced to mains earth pin, and nothing really seems strange. The isolation on the transformer may be a tad iffy, as gently passing probes around the outer winding gets the occasional 0.2-0.5 megohm reading.
 
Put a load on the power supply, let it cook for awhile, then measure it again. I'd be looking for two modes of failure. A series pass regulator that is shorting, which would make the output voltage go several volts high. Or, the regulator is oscillating, which might be hard to see with a meter. You can try by measuring AC. The ripple should be down in the milliVolts.

A common failure mode with three terminal regulator chips is the deterioration of the pair of small bypass capacitors located right next to the regulator. They are typically electrolytics of around 1 uF. The regulator and heatsink is hot, so they die young. When they go, the regulator becomes unstable. When in doubt, just replace them.
 

Users who are viewing this thread

Back