This time, folks, I have news of a major setback – and an interesting discovery. First, allow me to tell you about the setback.

Remember my test jig I threw together to try out the 37-116 RF unit I had intended to use as a “standby” unit for this 38-690? Well, Murphy’s Law seems to rule with this radio and anything having to do with it. I had previously noticed that it was playing, but at extremely low volume. So I made some changes to my 38-116 chassis test jig, and tried the whole thing together again.

Not only was I hearing nothing at all now, but what I was hearing was the sick sound of sizzling somewhere inside the rebuilt 37-116 RF unit! This indicated that this RF unit was likely also burning a carbon track in a switch wafer. When it rains, it pours. So I won’t be sending this RF unit to my friend. I resisted the temptation to take the whole thing outside and destroy it with my sledgehammer. Instead, common sense prevailed, and I simply set it aside.

Pulling the 38-690 upper chassis back out later on, before I did anything else, I flipped the chassis over and did a resistance check between the end of resistor (64) which leads into the RF unit and ground. A properly working 38-690 would have read infinite resistance. But instead, the multimeter was reading 643 ohms!

AHA! I was right – there is a partial short to ground inside the RF unit! To confirm this, I unsoldered the wire which carries B+ into the suspect part of the circuit inside the RF unit. I measured the resistance between the now disconnected wire and ground. Once again – 643 ohms.

I measured resistance again between the end of resistor (64), now disconnected from the RF unit, and ground. I found infinite resistance, as I expected. This confirms that the issue is inside the RF unit.