If you lost ground on the PBT/REF board is seems likely that you would have many more problems. More likely perhaps that you have lost something on the PS board. There are two independent grounds on the PS. What do you see if you measure directly on the pots? The passband control voltages are switched by U1001 on the PBT/REF board. Switch control voltages to U1001 are selected by the PBT and filter switches, Mode switch, and T/R switching. Follow the DC.
On Tue, 25 Feb 2025 03:12:50 -0800
"Craig W8CS via groups.io" <craig_severson@...> wrote:
Thanks as always, Jim.
I should be able to bypass all of the fixed passband values from the PS board (at least on RX) by using the PBT control.
Same problem; the PBT control does not alter the 5.645MHz signal. I've tried shotgunning in a spare PBT board with no change. The unit "receives" but it's what you'd expect with the passband being off-center.
This is a strange one; it's almost like the +10V has lost ground reference to the PBT board. The PBT control is just a voltage divider between +10V and gnd and the signal into the PBT board never goes below about +7.5V.
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Craig/W8CS
Greenville, SC
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73
-Jim
NU0C
Jim Shorney