[Kenwood] R-5000 displays dots

[Dr. Gerald N. Johnson, electrical engineer]

Maintaining grounds while squeezing compressible boards requires some
springiness. Pure mechanical locking such as loctite or locking nuts
does not accomplish continued electronic operation. The board material,
not being solid strong metal gives way to pressure and that plastic flow
removes the pressure necessary for electrical conductivity. Only the
star or shakeproof lock washers simultaneously supply spring and cutting
action to get through oxidized surfaces.

Radios used in mobile applications (including hand helds) may be
affected by vibration, but many radios of all makes, have been found to
fail in the same way. Its the plastic flow of the board, more than
vibration on those radios that don't travel and that can take longer to
occur.

There could be cures in design, but the best possible thing in the field
is to use the star washers and then plan on tightening the screws at
intervals of a couple years. The designs are deficient in depending on
the mounting screws through compressible material for circuit grounding.
Proper design should have made the grounds independent of the mounting
possibly by using a solderable chassis and soldering straps from circuit
board ground circuits to the chassis and by completing ground circuits
on the board. With die cast chassis soldering is not possible and poor
grounds result that get worse with age.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.