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Post by vanlifeson on Aug 5, 2020 12:59:04 GMT -5
So, I have read a lot about the meter pegging with modulation on a Mark three. What causes this? I have read that it could be the mode selector switch. I have inspected mine and I do not see any signs of traces, such as the carbon deposits people talk about. Doesn’t mean they are not there, but I don’t believe this radio was used very much and the switch looks to be in very good condition. But, my needle does peg violently when I have the switch set to modulation. Why does this do this? Thanks
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Post by 2600 on Aug 7, 2020 0:36:20 GMT -5
But, my needle does peg violently when I have the switch set to modulation. Why does this do this? Thanks If it only pegs when you modulate the transmitter, that's par for the course. If it does this in receive mode, the mode selector has a carbon track between two adjacent rivets that hold the fixed contacts to the insulating ring. They're a 32nd of an inch apart, more or less. Are you sure you looked at it THAT closely? The most-common circuit on the selector to break down first will overheat or simply burn out the half-Watt resistor R51, attached to the main 3-section filter cap "can" towards the rear of the chassis. Just the same, if you see the meter peg WHILE RECEIVING when 'Mod' is selected, shut it off right away, and move the meter selector to 'ma'. Any time you see the meter peg in 'mod' while receiving, you're just one step away from burning out the coil in the meter. And that part is not cheap. 73
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