af.2.5. Heathkit SB-102 Transceiver LMO Stability Fix
Source: unknown
I noticed many SB-102 solid state VFOs become unstable over the years. In most cases
a light bump or tap on the radio will cause it to jump frequency, excessive random
mechanical instability especially during warm-up. I have found late SB-series LMOs that
jump from lightly closing a desk draw.
In most SB-102 radios I worked on this problem was attributed to a plate on the bottom
of the LMO being warped possibly by the 2 screws securing the crystal filter bracket. In
some of the late SB-102 kits shipped these screws were cheap, not machined as
precise nor perfectly flat headed. On some chasses they can press on the bottom of the
LMO
Remove the LMO from the radio, then the 4 small Phillips screws securing its cover
plate. At this time while the LMO is open check for any dried up glue securing any disk
capacitors to the side wall of the LMO. Re-glue if necessary (I use red TV Radio
cement)
Inspect the cover plate, clean and re-tension grounding tangs. When re-installing re-
bend any tabs and grounding tangs so it fits back on snugly, tighten its 4 mounting
screws equally and pack the side “seams” with 6 strips of some copper braid. (folded
copper de-soldering wick fits perfect just clean the flux off first with alcohol or lacquer
thinner first) Then press in a thin bead of silicone over your pack (into the seam) this is
for added mechanical stability.
Testing prior to installation
Power the LMO up on a bench supply and tune it to a receiver tuned to around 5.250
MHz (BFO ON). You should note rock solid stability (give it a couple hard taps) When
re-installing the LMO I like to use 4 thin washers to slightly lift it of off the chassis
(NOTE: no more than index card thickness or the calibration knob wont line up) This is
so the LMO is secured by 4 equal points rather than just randomly pressing to the
chassis.
Heathkit Linear Master Oscillators (LMOs) Page 132
To Next Page
Loading...
Need help?
General
