Cobra 29 NW ST WT.. No static

Check the SWR and if fine then you know likely it is in the radio. With volume midway and squelch fully CCW (down all the way - wide open receive), try rotating the RF gain slowly from 12:00 to fully up CW, back and forth. Notice if there are any spots where RX tries to return. Being an old radio it could be simple cleaning of the control can save it or it must be replaced. Of course this is if you notice any lively spots indicating it is the control with the trouble. Also possible is a bad first RF transistor (TR7), or the two protect diodes (D1,2) or some combination. Especially true if some tweaknician clipped R55. If one studied the schematic the antenna line coming in is coupled through capacitors, floating to DC except for the static drain resistor R55. The antenna builds up charge in stormy weather since it is floating DC-wise, insulated from ground from the mount all the way into the radio. If the static buildup exceeds the breakdown of one of the capacitors it will arc over. This can be either the RX front end or the final itself, neither is safe and yes I have seen finals blown due to this. To answer your question yes a bad final can sometimes knock the receive sensitivity down severely but not so common. Besides all you need do is check if the radio is putting out normal power to know to discount this possibility. R55 is by the back of the antenna connector next to the final heat sink wall (S angled Aluminum piece inside). Sounds like you were talking about Ray at your shop and he is good so certainly worth running it by him to find out. Never toss a dead radio it is still valuable as parts to many out here and of course if the repair is reasonable have him fix it for you. First and foremost make sure some antenna system problem is not the cause. One last thought - never overlook a bad wire in the microphone (RX line) stopping your RX audio (if you do not have talk-back in it RX must have the microphone working or there will be no sound).

Also FYI yes this static induced failure can and will occur even with the radio off, truck parked in the yard and you home for the weekend. All that is required is the radio be connected to the antenna via the coax.

 

If he sees R55 missing or clipped make sure he replaces it especially if indeed this is what happened. Or after he repairs it this can easily happen again any time there is a lot of electrical activity is in the air. All R55 does is bleed static from the antenna preventing a dangerous buildup. There are so called 'tune up' books out there which say clip it for more power and the 'tweaks' know no better. Nor did the authors obviously. 1,000 ohms across the 50 ohm (impedance) output barely affects power and only fools clip it. An analogy: going down the Grapevine with 80,000 lbs in neutral* as you put your bare feet through the hole in the floorboard against the road to slow you down (Fred Flinstone brakes). Your feet will slow the truck about as much as R55 lowers the output power of the radio. Conclusion: anyone who clips it should not be doing radio work.

*Before the days of PC we called the situation Chi---e overdrive (not neutral).