[Elecraft] RE: Help, I think I've killed my K1

[Jack Brindle]

At 9:18 PM -0600 2/19/03, Stuart Rohre wrote:
>Good news for Mike if it is the regulator.
>Might see if there is room to bypass the input of the regulator with a disc
>cap of say 0.01 for RF protection.  Just place it voltage bus to ground,
>flat on the back of the board or where convenient.

I know Wayne better than that. The linear regulators he uses require 
bypass caps on both sides of the regulator close to the leads. So, 
I'd bet there are already 0.01uF or .1uF bypass caps there.

One thing to look for, and the K2 could be susceptible to this also - 
the protection diode on the power input would do a great job of 
rectifying high power RF signals, and could cause rather high 
voltages to be applied to the input regulator. The power input should 
be well bypassed (I bet it is) at the input connector and maybe close 
to the diode. It also might be worth while to add a 16-V or 18-V 
zener between the protection diode and the regulator. These values 
would not ordinarily do much except when a voltage that would 
ordinarily pop the regulator shows up. Remember, the max 
specification for the input voltage to the radios is 16 volts.

Interestingly, this problem is probably not seen when radio power is 
turned on because of filtering by the power supply and any batteries 
that may be in-circuit. It also would probably not be seen when using 
a large linear power supply since the output capacitors are always 
in-circuit, even when the supply is off. Switcher supplies tend not 
to have the large caps that linear supplies do...

When Wayne quits practicing the words "He's guilty, your honor" he 
might have a chance to comment...   ;-)

-Jack Brindle, WA4FIB
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