Mark,
Analyzing the switch matrix is an iterative process
The first thing to do is to determine which wrong responses are being
sent, and for that you must refer to the schematic. In your case of the
REV button and the STP 60 display, the hold of the REV button is
bringing up the PF1 display.
Check the TAP function of the same button (AGC) to see if it brings up
the RIT announciator (I think it will).
If so, it means that the D1 and D2 lines are somehow being activated at
the same time.
Your first check would be to see if there is continuity between pins 12
and 13 of U2. Also check for continuity to ground for both of those
lines. If you find U2 pins 12 and 13 shorted together, look for the
reason - a solder splash making a bridge or a bit of wire lead stuck
between the pins, look top and bottom of the board.
That is how the process goes - as I indicated, it is not 'nice'.
Hopefully those two buttons are the only ones involved.
At worst, it means removing the pushbuttons and replacing them with
new. If it comes to that, clip the leads on the switch side close to
the switch body and remove the leads one at a time, then troubleshoot
the board.
73,
Don W3FPR
On 6/10/2018 7:15 PM, Mark Petrovic wrote:
Thanks, Don.
Would you mind outlining the approach for analyzing the front panel switch
matrix?
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