Model 1220 Frequency Jump Fix

From the Ten-Tec Reflector January 4, 2003

While visiting Ten-Tec a while back, I mentioned the above problem and was given a "Fix", which works for me on the 1220 and the 1230, 220 MHz Version, as well.

Just add (Solder) an Electrolytic Capacitor, from about 1uF to 4.7 uF, 15VDC or more, across Resistor R32 (In parallel). The Positive end of the Capacitor goes toward the Base of Q8, the 2N4124 Transistor. This is the side of R32 away from the Front Panel.

Evidently, when you let up on the PTT switch, the supply voltage jumps, causing a power-on reset to the microprocessor. The processor then retains the old transmit frequency as the current receive frequency. Ten-Tec suggests several ways to try to correct this problem, including using heavier wire from the power supply and shorter lengths, to prevent voltage drops, and also adding a capacitor in the space labeled C86, on the PC Board. This capacitor should be an Electrolytic in the range of 1,000 to 4,700uF, rated at least 16VDC or more. The Positive end should be oriented as shown on the PC Board. You may have to look around for a capacitor small enough to fit on the space available on the board. I had to use one with both leads coming out the bottom, and adding a piece of wire and insulation, to get a cap small enough to fit in the space.

I found that adding the capacitor across R32 is what cured the problem for me. Adding C86 helped when the rig was used in mobile operation.

Carl Morris, WN3DUG