That's an interesting case. You should be aware that an oscillation will most likely be anywhere else but where you are listening. The 40 Meter instability that surfaces in some rigs actually occurs around 9.5 MHz and is at the full power level that the SWR protection circuit will allow on that frequency. That does not sound like what you have. Have you tried adjusting the anti-vox lever? It is not used for CW of course but that doesn't mean it does not do anything.
The IF/Audio board has had some changes over the production life. Several in the case of the Version 1 and one known change on the Version 2 board. Your A model *should* have the Version 2 board. From Joe KC9LAD: "On version 2 of the 2nd IF/Audio board there was a mistake in the foil layout which creates a direct short across R1187 10k resistor. The fix was to cut the trace on the bottom of the board to put R1187 back in the circuit. This will stop the pop when switching to CW." Again, that doesn't sound like what you have but worth checkign. I would do a thorough visual inspection of the IF/Audio board to see if you spot any anomalies. I you happen to have a Version 1 board then someone may have been playing letter games with that radio.
I wonder if the RX is just coming back too fast. You might check C324, R362, and CR309 on the Transmit Exciter board.
On Fri, 25 Apr 2025 19:12:01 +0000
"Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote:
The situation:
When I transmit on CW and let up the key, the meter goes to the power out during key-down, as normal. When I let up the key at the end of sending, the meter swings hard to the right when using shorter delay settings, controlled by the CW delay "knobette". If I use a longer delay, there's nothing unusual happening with the meter.
Listening on my IC-7610, and watching the spectrum, there is no RF being indicated by either the receive audio or by the spectrum display. This set has always worked like this since I've owned it. I would think that if this was a real spike, I would see RF out. Listening on two other receivers, not a peep when key is opened.
Could something in the receiver be putting a voltage onto the receiver's meter circuit, which gets switched on when the TR7A returns to receive?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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--
73
-Jim
NU0C
Jim Shorney