I have a commercial 220 MHz PA manufactured in the mid
1990's by a company in Washington called II Morrow.
They were bought out by UPS and later by Garmin. It's
a 28V linear PA mounted on a plain black heat sink,
using a single push-pull Phillips DU28200 MOSFET (or
PolyFET SH703) for 150W rated Po. It has a single
large multi-pin connector handling A+ and a control
interface. I bought it off E-Bay a year or so ago and
I'm pretty sure it was one of several that were sold -
probably to other hams.
Does anyone have any info on this PA or been
successful in getting one running ?
Here's the issue - Internal to the PA is a control
board, handling (I assume) the PA bias and (I'm told)
power fold-back from a external detector/VSWR sensor
plus a simple interface to the systems original
exciter. There are no switches or controls on the PA,
only red and green LEDs, which I figure is a status
indication. On the control board (among other stuff)
is a big power relay which switches the A+ directly to
the PA board. When A+ is applied to the connector
with the other 8-10 control lines unterminated, the
red status LED flashes for a couple of hundred
milliseconds.....and nothing else happens. The power
relay does not pull in to supply A+ to the PA module.
I'm pretty sure one or several of the control lines
need to be manipulated to convince the control board
all is well and have it power up the PA. None of the
control lines have any solid voltages on them so I
grounded them one by one through a 1K resistor to see
if a logic low might bring it to life - nope. I don't
think I want to try a logic high unless it's a last
resort...
Before someone says 'Just bypass the relay', I'm
concerned that doing so will result in improper (or
no) bias being supplied to the MOSFET. I don't think
these devices are still available, so, again, that's a
last resort. Any info or suggestions would be
appreciated.
Jay W9RM
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