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

[Morrow, Michael A.]

John Webster / N6JW wrote:

> I did not check the NTE988 while in circuit.  But
> have done so now (using clip leads) with it out of
> circuit.  No problem.  Output is 6.19volts.

I bet that it would be pulled low were it installed on the FP PCB.

It sounds like you'd already tried everything I later suggested.

> I now suspect FP Q1 2N4124 (Counter Amp.)
> might have blown.  Could this be right?

I don't think so.  The counter was working and displaying frequency.  In
addition, were it shorted collector-to-emitter, R12 (2.7K) would limit
current flow to about 2 mA, which would never pull down the output of a
78LC06C.

> In fact, I have been able to isolate the problem to the FP board.
> I removed it (FP) and connected 10volts to the 12volt input side
> of the regulator (FP U4) and get the low output.  This is with the
> FP board disconnected from the rest of the K1 and U1 (the MCU)
> pulled from the socket.  So it seems to me it is something pulling
> the voltage down on the FP board.
 
> 1. The EEPROM (FP U3) 6A goes to pin 8 VCC.  But the rig
> did work, mostly, so not likely, to my mind.

I agree.

> 2. The D/A Converter (FP U2) 6A goes to pin 7 VDD
> 
> 3. Via R16 2.7K to U3 pin 5 SDA, and U2 pin 4 SDA.

May be the D/A converter, BUT if you were able to change the receiver filter
bandwidth while you still had the rig together, it's probably OK.

> 4. Via C5 .01 cap to ground.

Also, C4 .047 cap to ground.

> 5. Via R13 470, D2 (ATTN LED) to pins 7 and 6 of
> U5B part of a LM358.  [Note ATTN LED seemed to
> work normally when I had the whole K1 together.]
> That's all that I can see could be effecting 6A with the
> MCU out.

Seems to rule out problems with U5.  Yet of all the solid-state devices on
the FP board, that would be my first suspect (short from pin 8 to ground).
Yet U5B ATTN LED wouldn't likely work OK.  Were you able to get the XIT
orange LED color to come on when the rig was all together (U5A working OK)?

I'd lift C4 and check 6A, followed by C5, followed by separating U5 pin 8
from 6A.

Any chance that you might have created a low resistance path to ground on
the 6A line (it would probably be 40 ohms or less) when replacing U4 the
first time?

Good hunting!

73,
Mike / KK5F