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Post by mrt4d on Apr 28, 2019 16:44:28 GMT -5
I have Browning Mark IVA Was using today turn radio off , Turn radio back on. Went to transmit AM Dead key 4 watts but no rf output powerr. Tried LSB and USB Good rf output power 12 Watts. . Troubleshooting needed, where to start?
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Post by 2600 on Apr 28, 2019 21:57:56 GMT -5
The mode selector (AM/LSB/USB) switch is where I would start. The silver-plated contacts build up a tarnish layer. The plastic hub at the center of each section of this switch is sensitive to the solvents used in many contact cleaners. The solvents in use 40 years ago were based on freon, and would not attack plastics. Those chemicals are outlawed now, and the solvents used in modern spray cleaners can attack this kind of plastic.
Full-strength or 91% isopropyl alcohol is safe for the switch and won't attack plastic.
Just beware that this switch is prone to breakdown problems. The spacing between the rivets that hold the fixed contacts in place is too close for the high voltages being switched. The brown plastic insulation often begins to break down after about 20 years.
Since the radio is over 40 years old, this is a risk.
There is a 3.3k 1/2-Watt resistor R229 that is often the first casualty when the mode-selector switch begins to break down and short across separate circuits. It's on the audio circuit board to the left of V204. If it looks darkened, the mode selector has begun to fail.
Barkett sells a replacement selector. It has ceramic insulation that won't fail like the factory part did. It's not cheap, and installing it is a major pain in the neck.
Have a look at R229 and see if it looks dark or damaged.
73
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