[Icom] A Weird IC-756Pro2 Glitch and its Resolution

[Adam Farson]

Whilst tuning my Pro2 across the 17-metre band, I observed some strange
behaviour in the COMP scale on the analogue meter.

I had USB mode, COMP meter scale and COMP-ON-MID selected. When
transmitting, the COMP scale normally reads zero without audio input, and
deflects to the preset value on voice peaks. The weird glitch manifested
itself as follows:

I selected RTTY mode to set up the Quadra amplifier on 18.160 MHz. I then
selected USB, and tuned the VFO above the band-edge (beep at 18.168 MHz). To
verify that the radio would not transmit, I keyed the mic; as expected,
there was no output. However, the COMP meter rose to 20 dB and stayed
steadily at that reading until I unkeyed. When I tuned the VFO back below
the band-edge and keyed up, the COMP meter remained at zero, and deflected
normally when I spoke into the mic.

The glitch was reproducible by executing either of the following sequences:

In-band freq -> Select RTTY or CW -> Select LSB or USB -> out-of-band
freq -> key TX -> COMP meter rises -> in-band freq -> key TX -> COMP meter =
0

or: In-band freq -> out-of-band freq -> Select RTTY or CW -> Select LSB or
USB ->  COMP meter rises -> in-band freq -> key TX -> COMP meter = 0

I performed a CPU Reset (756Pro2 user manual, p. 21). This resolved the
glitch, and I was no longer able to reproduce it. Apparently a condition had
arisen which left "garbage" data in dynamic buffer associated with the COMP
meter. If another Pro2 owner encounters this condition, a CPU Reset appears
to fix it.

My understanding is that  buffers (registers) in the main processor's
dynamic RAM store the various meter readings. The CPU presents the buffer
contents to a DAC which drives the analogue meter, and to a bar-graph driver
which drives the on-screen digital meter.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Icom FAQ site:
http://www.qsl.net/icom/