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

[John Webster]

Elecrafters:

Wow! One simply has to experience it for oneself.  Help arrived
within minutes of posting.  It was spot on.  It raised important
considerations for a wider audience.  And it made me learn quite
a bit more about the circuit of the K1.

Thank you Michael, Stuart, Robert, Jack, Stephen and Jessie!

In fact, Mike's response to my over hasty comment:
>> 2. +6v and +8v regulated power supplies seem OK.

>Are you absolutely sure the front panel board 6 volt regulator U4 is
>working?  Are there 12 volts in and 6 volts out at FP U4?  Symptoms 4, 5,
>and 6 below could be due to no output voltage from FP U4.

. . . was not only spot on, it arrived even before my original post
appeared on the list!  I had measured the 6 and 8 volt signals on
the RF board and incorrectly assumed that all regulators were OK.
U4 is in fact dead--12 volts in, nothing out.

The discussion of the bypass protection question is interesting:

> > 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.
>
> The front panel PCB 6 volt regulator FP-U4, the likely failed component in
> John's case, has FP-C4 and FP-C5 as RF bypass caps on the output.  Its 12V
> input side has a bypass cap, **BUT** it is located on the RF PCB (RF-C34).

C5 is also placed near FP-U1 some distance from FP-U4.  Not sure if this
is adequate?

> Perhaps a cap similar to RF-C34 installed on the front panel PCB would be
> more effective for RF bypass of the input to FP-U4.  The assumption here
is
> that, in the presence of a strong RF field, the front panel metal may not
be
> at RF ground potential with respect to the rest of the K1 case and
> circuitry.  I was not satisfied with the possibility of my K1's front
panel
> metal "RF floating" with respect to the remainder of the K1 case.  There
was
> quite a lot of paint covering the points where it joined the rest of the
> case.  Therefore, I used a Dremel tool steel brush to remove the paint
from
> the inside of the case metalwork at *all* points, on all pieces of the K1
> case, where there is a fastener to hold that piece to some other case
part.
> This made several bare metal patches on each piece in addition to the
> several that were originally provided inside the K1 case.
>
> The only K1 regulator which seems not to have an input RF bypass cap is
the
> input to the VFO 6V regulator RF-U6, which is the output of 8V regulator
> RF-U5.  I suspect adding a bypass cap there wouldn't hurt, but I doubt
that
> had anything to do with John's K1 problem.

And Stuart's prudent warning is well taken:

>Do not place rigs atop each other if  they have aluminum or plastic cases
>and antenna tuners, as there may be considerable magnetic field coupling of
>the tuned circuits leading to overload of the standby rig.
>Do not even place an ATU atop a rig, for the same reason if the ATU has
>solenoid rather than toroid coils.  Some field even escapes toroid coils so
>having space between rig tuned circuits and Transmatch circuits is
>desirable.

Although, in my case, the antenna tuner (a British made K.W. E-Zee Match)
is in an all metal enclosure, it was only an inch or two from the K1 which
was
probably the reason for the overload.  I'll err on the side of caution in
the
future.

Particularly, given Jessie's account of a near identical mishap:

>The K1 was near the transmatch and antenna cables.  It was powered
>up, but not connected to the antenna. . . the little K1 started flashing
and
>clicking. . . .  On inspection, the regulator was actually cracked.  My
guess
>is that the RF got in and confused the regulator. . .  I replaced it, and
the
>rig has been running fine ever since!

Perhaps, given two near identical experiences, Wayne or Eric might wish
to comment on the desirability of adding a bypass cap or two around
FP-U4 6v regulator, for added protection?

Again, thanks so much for the quick, helpful responses.  Radio Shack (my
only source of parts locally) does not have the 78L06 just a 7805 in the
wrong package, so I will have to wait for a replacement part from Elecraft
to find out if that was the only damage done.

73
John, N6JW