[Elecraft] Re: Help, I think I've killed my K1
John Webster
[email protected]
Sat Mar 8 01:44:00 2003
Mike, again thank you very much for your detailed
comments. They are very helpful to someone not
really secure in what they are doing!
Yes, you are quite right. I misread 6B. It is OK,
reads 6.02volts.
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. So your
observation that all problems are due to low output
from the MCU due to low 6volt 6A line, seem spot
on.
I now suspect FP Q1 2N4124 (Counter Amp.)
might have blown. Could this be right? If so what
type of transistor is this? Any common replacement
possibilities?
Here's an update of what I have done, with help from
Bob, AG5Q:
> Hi John,
>
> Since the MCU is in a socket, you can remove it and check the 6A line
again.
Done. 6A is still too low (4.3v). So I hope that means the
MCU is OK.
>
> Also check the 6B line voltage.
On rechecking this more carefully, 6B is OK. 6.02volts.
>
> Is U1 on the Filter board in a socket? If so, try removing it too.
I've removed the Filter board, so this is not causing the problem.
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.
I've not pulled the regulator (U4) from the circuit, or lifted its
output leg, since it is quite hard to unsolder in there and I fear
damaging it. I did, however, check the NTE988 I pulled and
with 10 volts in it gives 6.19 volts out. This is just using clips
to its leads, i.e. out of any circuit. This chip was giving the same
symptoms while it was in circuit, so I suspect it is not a problem
with the regulator itself.
The only candidates I can see as causing the problem are:
1. The EEPROM (FP U3) 6A goes to pin 8 VCC. But the rig
did work, mostly, so not likely, to my mind.
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.
4. Via C5 .01 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.]
6. Via R12 2.7K to the collector of Q1 a 2N4124
transistor (Counter Amp). Could Q1 be shorted or
leaking?
That's all that I can see could be effecting 6A with the
MCU out.
Any comments and further hints toward a solution would be
greatly appreciated.
Thanks again,
John, N6JW
----- Original Message -----
From: Morrow, Michael A. <[email protected]>
To: 'John Webster' <[email protected]>; <[email protected]>
Sent: Friday, March 07, 2003 9:56 PM
Subject: RE: [Elecraft] Re: Help, I think I've killed my K1
> 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
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