MSF-5000 Horrible noise...

[kk6rq]

Let me first say we're going to properly troubleshoot this with a knowledgeable technician shortly; I just want
to see if what I describe sounds to anyone here as something inherent in the product or stands out as something obvious; ..So....

We have a 110w VHF MSF-5000; arrived from halfway across the country. When you plug it in it make the most godawful loud 60 Hz grind (or super-loud vibrating hum)

We've think we've isolated it as relating to the RF deck/tray, since when we unplug it the noise stops.

The Control tray self-checks fine.

Unplugging the amplifier has no effect on the noise. The cable to it properly (I assume properly) tests at 30v.

The fan doesn't work, though there's voltage on the cable going to it (15-17v or whatever it was without a load). Put an independent 13.8v to the fan and it doesn't function or make a peep.

We also tried completely disconnecting the power supply from the repeater and hooking the 15v side to a 35w mobile radio; it works fine, even when we key it

The travel cams are now in the "OPERATE" position on the RF tray. The plastic cover on the bottom of the cabinet is intact so I can't imagine the distribution board down there got munched or anything.

The only thing I can think of that I haven't gotten to yet is to hook a separate 12v power supply or battery into the side of the thing. Probably I'll try that next.

So, as I said we're going to properly troubleshoot it with the right equipment and someone who knows what they're
doing; I'm just hoping something I've described pops out as something one of you lot has heard about previously, thereby saving some effort perhaps... Thanks.

[Jim202]

You have sort of indicated that the power supply is groaning from some sort of a heavy load.
Just what may be causing the problem is up to you to locate. You seem to be on the right
track with what you have done so far.

If you can locate a clamp on DC amp meter, it might make narrowing down the problem
a bit faster. Find out what is pulling the high current. You should not be pulling much
at all in RX. Even with all the control stuff and audio. I wouldn't expect it to be much
more than an amp or so for the whole cabinet. TX is a different story. That will take
you up into the range of 20 to 25 amps depending on the PA settings.

Jim

Let me first say we're going to properly troubleshoot this with a knowledgeable technician shortly;

We have a 110w VHF MSF-5000; arrived from halfway across the country. When you plug it in it make the most godawful loud 60 Hz grind (or super-loud vibrating hum)

We've think we've isolated it as relating to the RF deck/tray, since when we unplug it the noise stops.

Thanks.

[kk6rq]

So it turns out I had the ID of the plugs backwards in my head- it wasn't the
cable to the RF tray that we unplugged; it was the cable going to the big capacitors.
to make a long story short, we isolated the problem to the battery charging board.
Disconnected it, problem solved for now. Thanks for the help.

[bernie]

My two bits worth:
The battery charger board has been a problem from the beginning. Last production MSF was available with an after market battery charger.
Be sure to change the transformer taps when disconnecting the charger board. The terminal strip is to the right of the charger board.