Problem: At turn on, repeatable, periodic buzz in the RX on 10m and to a
lesser extent on 12m. Also noticeable when engaging the RX Ant switch. A
bang or two to the case with the palm of the hand can make it stop - and
come back.
Cure: This can be done with all of the radio's cables attached and in a
matter of minutes. Leave the AC plugged in at your own risk.
1) Remove 8 screws and the radio top cover.
2) Pop the shield off of the LPF board. It's the large silver cover. Turn
the shield towards the back of the radio being careful with the strap
attached at the rear left corner.
3) Locate the open frame relay with a clear cover, RL 7217, towards the
right front side. Remove the RCA connector directly in front of the short
side of the relay. Use an Xacto fine blade hobby knife and a small screw
driver to carefully pry the cover up. Take your time. Don't force anything.
4) The relay is DPDT. I cleaned the contacts first with a burnishing tool
and then with a strip of index card soaked in contact cleaner. Apply the
lightest pressure with a stick while wiping the contacts.
While this helped, the problem still persisted. With the radio on (try at
your own risk!), I tapped the LFP board and recreated the problem as the
board flexed.
5) Tighten the four corner screws holding the board down. I also tightened
the three screws holding down the shield case. ALL of these screws easily
turned at least 1/8 turn in my radio. They were definitely loose.
6) For good measure, pull all of the RCA RF connections and reseat.
7) Replace theplastic relay cover, LFP board shield and radio top cover.
Result: Problem solved! No amount of cabinet pounding causes any audible
change. There remains a extremely low level hiss on 10m but only when the
RX Antenna switch is engaged. (My radio has SW 1001 set to R-ANT, not
E-BPF.) I have nothing terminating the RX Ant input. 160m through 12m is
absolutely quiet with the RX Ant Sw ON.
My thanks to Jim, W6YA, for his suggestion to clean the relay contacts.
This led me to find the "screws loose" problem.
73, Steve WB6RSE
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