[BC] RE: FX 50 problems (solved!)

[Tom Taggart]

Couldn't find where the + 20 was going in this unit. Also couldn't find fuses 1, 2, and 3 on the transformer secondary, as well as Plug and jack 401 on the RF amp chassis.  They just didn't exist in my 1990 model FX-50, despite what the circa 1993 schematic claimed.

Indeed, once I figured out which pins did what on the jack into the RF module, the mystery deepened. No voltage reaching the 3 pin regulator (mounted on the RF amp deck) from the power supply board. Indeed, no continuity between the RF board and the input to the 3-pin regulator.

Looked more closely at the plug into the power amp. This is a square, reddish-brown plastic 20 pin plug and jack assembly. Amphenol, I do believe.  The Auditronics 2500 uses dozens of the 15 pin variety. Unregulated 28 volts was supposed to be on pin 17.

Tugged on the wire--came right out.  Someone had popped this pin out of the shell (probably to measure current?) bending the little tabs that hold the pin into the housing.  Gee, no wonder the regulator wouldn't work.  Spread out the locking pins, pushed the connectors back together, and fired it up.

Everything lit up, and the front panel said five watts out.  Which is what I wanted since I only had a 15 watt dummy load.  Have to use the Harris 2.5H as a guinea pig to see if it will make enough power. Need about 25 watts since I am driving the final directly.  Isn't buying used equipment fun??

Now to the next project--used Marti RPT 30 VHF transmitter.  This came in as a rack mount with the back panel mushed in at the fuse. Fusholder smashed.  Bent the chassis back out Replaced the fuseholder, got the right crystals, set them on frequency, nice strong signal into the rpu receiver. Unfortunately, no audio! 

Compressor meter shows some action, though I seem to need a lot of gain. And then there is the mysterious molex connector hanging in mid air behind the preamp board. They didn't have a battery in this thing, did they?

Looks like I dig out my trusty Triplett ohmmeter again. Hopefully it's just a loose connector someplace, not a missing circuit board.

--