[SignalOne] CX7 Screen Sensing

[jerry]

Hello!

    Another little discovery on my "INOP" CX7A.  Scanning the power 
supply, I noticed a missing resistor.  This is a VERY IMPORTANT 
resistor.  It is the current sense resistor in the negative leg of the 
300V screen supply.  How could the radio transmit at all without that 
resistor?  Powering down, I ohmed from that point to ground.  192 ohms.  
Where did that come from?  Leakage in the transformer windings?  
Something tacked on the back?  I popped the power supply board off the 
chassis and looked underneath.
Sure enough, there was a 1/2W carbon comp resistor tacked under the 
board.  I ohmed it out - sure enough, 192 ohms.  Obviously, a hard 
working resistor, and its value had drifted up.

   I got two 5% 200 ohm 1/2W resistors out of the junkbox, paralleled 
them and tacked them in place of the bad one.  Two in parallel, twice 
the dissipation, they should last.

   Fired up the radio... and what's this?  144W on 40M?  Yes!

                   - Jerry, KF6VB