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

[Morrow, Michael A.]

John Webster/N6JW wrote:

> A locally purchased NTE988 regulator (6.2v rather than 6v) 
> brought the rig back to life, but with erratic MCU activity.

and

> 1. The new replacement 6v regulator ZR78L06C from Elecraft
> is only putting out 4.3 volts.  Thus FP U1 pin 40 is 4.3v as are all
> other pins on FP U1/2/3 that expect 6v.
> 
> 2. The pins on FP U1 that expect 3v are reading 2.3v.

John, did you happen to measure the output voltage of the NTE988 when you
had it temporarily installed?  I'm betting, based on what you describe, that
it's output was being pulled low also, instead of being too high, and that
the erratic behavior you saw with it installed was **not** due to it putting
out 6.2 vdc instead of 6.0 vdc.  The NTE988 doesn't have as high a current
carrying rating as the part you've got installed now (78L06C), so its output
may have been even lower!

> 1. While the K1 will switch on normally, and the RX seems
> to work well (freq readout is accurate when checked against
> another rig),

and

> 3. A surprise to me is that the RF board 6v regulator (also a
> ZR78L06C,  6B line) is also showing only 4.6 volts, e.g.
> on RF U2 pin 6.  [But the RX works OK?]

I think you've mis-measured voltage 6B.  Try measuring it at FP-P1 pin 15.
I'm sure you'll find that it is normal at a nominal 6 vdc.  Your VFO
frequency tuning range would have shifted up in frequency a great deal if
the 6B voltage were as low as you say.  The 6B line supplies the VFO pot
high side, so you'd see a big effect on the VFO varactor tuning.  The first
paragraph above shows that you have normal VFO tuning, so 6B voltage *must*
be OK.

On the other hand, RF-U2 pin 6 connects to the BFO crystal.  I wouldn't see
much value in measuring DC voltage there.  I think you must have meant pin
8, which is the Vcc supply to U2.  That voltage comes from line 6A (not 6B)
through RFC6, so you would expect that to be nearly the same value as the
output of the regulator you replaced (abnormally low, in this case). 

> any attempt to change bands will cause the K1
> to go into a state where the RIT and ATT lights will flash
> alternately, indefinitely.

and

> 2. The Offset pot (RIT/XIT) works all the time, i.e. it always
> varies the frequency on both receive and transmit, regardless
> of whether RIT or XIT have been switched on or not.

I believe these are a direct consequence of the FP-U1 MCU output signals
DVM/ATTN, /OFFSET, and RA2 being too low in voltage.

> flashing decimal point does NOT appear unless the RIT is
> switched on.  The RIT pushbutton and RIT/XIT LED works 
> as expected.

and

> 3. All menu functions and FP pushbuttons work normally

and

> 4. The transmitter works.  A strong signal (clean sounding) can
> be heard on another receiver...Message buffers work OK

That shows that the MCU firmware is working properly, though obviously the
MCU output signal voltage levels are not.

> 5. The built-in voltmeter, S-meter, and power-out meter does
> not read correctly.  The internal battery pack is at 10.2 volts,
> but the LCD reads 14.2 volts when on voltmeter setting.  The
> bar graph S-meter reads significantly lower (a signal that is 
> clearly S9 or stronger reads only one or two segments).  The
> power-out segment meter reads full scale (6 segments) when
> the power out setting is set to 2 watts.

> 6. The ATU will not function correctly.  It will not find a match
> on an antenna that it has always matched without difficulty before.
> This is probably due to problems noted in 5.

I think you are correct, but 5 and 6 are also attributable to abnormally low
6A voltage going to the MCU Vdd line.

> I removed the filter board and ATU to make
> the voltage readings.  Thus, as expected, on power up the LCD 
> reads E27.

Good start.  6A voltage goes almost everywhere in a K1 system, to all the
PCBs.  If you have the KNB1 installed, you might want to remove it too, then
measure 6A.

I would then recommend trying to narrow the voltage pull-down problem to the
two remaining PCBs, the FP and the RF boards.  I would separate the FP board
from the RF board, use jumper leads to apply positive battery pack voltage
to FP-J1 pin 16, and  negative to the FP case, then measure 6A voltage at
pin 17.  If it is now normal at 6 vdc, then at least the problem has been
narrowed to the RF board 6A lines.  Conversely, if it is still low, then
your trouble lies on the FP board.

> Is it the MCU that has gone?  Or some
> other suspect component?  Should my next step be to pull the 
> MCU chip FP U1 and take readings again?

After that point, all I could suggest is what the manual's troubleshooting
guide recommends for problem number 22 with 6A voltage too low.  I don't
think the MCU is gone.  It seems to be executing its firmware all OK.  But
pulling it may be part of your problem isolation technique, as recommended
in the manual.

73,
Mike / KK5F