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

Sat Feb 22 11:40:03 2003

Hi John,

If the only remaining problem is the voltage on the microprocessor, that can
probably be fixed (temporarily) by dropping the 6.2V down to around 5.5V by
putting a rectifier diode in series with the output of the NTE988.

You can use any of the 1N400x family of diodes. Or any other power diode
that you might have on hand.  Disconnect the Output lead of the NTE988 and
put the diode in series with it; it can be stuck up in the air for now since
this is not a high frequency circuit and lead length is not critical.  The
end of the diode with the band on it should be pointed Away from the NTE988.
Then the current will still flow normally but the rest of the circuits will
see a voltage that is one diode drop less than the NTE988, that is, about
5.5V. This is well within the operating range of the microprocessor.  This
voltage will not be regulated as well as before but it will be good enough
for testing the functionality.  It shouldn't vary more than 0.2-0.3V from
the initial nominal value.

The relays will probably still work, although there is a small chance they
might not.  If they are conservatively rated, they should still work with
5.5V.  All the other functions involving the microprocessor should work, if
there are no other hardware problems.

73/ Bob - AG5Q

----- Original Message -----
From: "John Webster" <[email protected]>
To: "Bob - AG5Q" <[email protected]>
Cc: <[email protected]>; "Morrow, Michael A." <[email protected]>
Sent: Saturday, February 22, 2003 4:26 AM
Subject: Re: [Elecraft] Re: Help, I think I've killed my K1

> Thanks for your input Bob and Mike.  Once again I marvel
> at the level of expertise this list provides!  Here's what I
> found.
>
> I picked up a NTE988 regulator this afternoon from
> a local supplier.  It was a bit of a battle to get the blown
> chip un-soldered and out, but fortunately the NTE988 is an
> exact fit and same pin out.  I quickly went through the
> applicable DC resistance checks on the FP board just to
> make sure, and all was OK.  With some trepidation, I put
> everything back together and fired up the rig.  I used the
> internal 8 cell NiMH battery pack (about 10.2 volts at the
> time) just to keep voltages down a bit for initial checkout.
>
> Well, the LED's come on, the relays clicked and the LCD
> read the band and frequency.  So far so good.  An antenna
> soon proved the RX was working, with sweet CW on 40m.
> I have not tried to transmit.  For I quickly began to find
> anomalies occurring:  1. A distinct hum on each press of the
> front panel press-switches; 2. An internal volt-meter that now
> displayed the battery pack voltage as 14.4volts!; 3. And
> eventually I found that pressing the "switch filters" button
> caused the MCU to go into hang up mode.  I can switch
> off and on again and it comes to back to life.
>
> So it seems that Bob was EXACTLY right.  The 6.2 volts
> of the NTE988 causes some spooky stuff to happen with
> the MCU.  So it seems that I will just have to wait to get
> a proper ZR78L06C from Elecraft or elsewhere.  At least
> I think I have shown that it WAS indeed the 6v regulator that
> blew, and hopefully nothing else.
>
> Again thanks for all the help.
>
> 73 John, N6JW
>
> ----- Original Message -----
> From: Bob - AG5Q <[email protected]>
> To: Morrow, Michael A. <[email protected]>; John Webster
> <[email protected]>; <[email protected]>
> Sent: Friday, February 21, 2003 5:30 PM
> Subject: Re: [Elecraft] Re: Help, I think I've killed my K1
>
>
> > The 7.5V spec means the device can survive that much voltage without
> damage
> > but it's only guaranteed to work like a microprocessor up to 6.0V.
> >
> > The 78L06 can be as much as 6.15V and there are a lot of  K1s and K2s
that
> > get by with that, so I wouldn't be surprised it yours works at 6.2V.
For
> > non-critical applications, that's okay, but sometimes the problems that
> are
> > caused by the voltage being out-of tolerance can be very tough to
> determine.
> > "Is it the micro itself or is it some random input causing the problem?"
> >
> > I just mentioned the possibility, so if you do see irregular operation,
> you
> > can switch back to the 78L06.
> >
> > 73/ Bob - AG5Q
> >
> >
> > ----- Original Message -----
> > From: "Morrow, Michael A." <[email protected]>
> > To: "'Bob - AG5Q'" <[email protected]>; "John Webster"
<[email protected]>;
> > <[email protected]>
> > Sent: Friday, February 21, 2003 7:13 PM
> > Subject: RE: [Elecraft] Re: Help, I think I've killed my K1
> >
> >
> > >
> > > Bob / AG5Q wrote:
> > >
> > > > The NTE-988 is speced at 6.2V rather than 6.0V like the ZR78L06.
> > > >
> > > > This will mean running the 16C77 at 6.2V which is slightly
> > > > higher than it's spec limit of 6.0.
> > >
> > > I think it would be OK.  The max. voltage rating spec for 16C7x
devices
> on
> > > Vdd above Vss (logic ground) is 7.5 volts.
> > >
> > > 73,
> > > Mike / KK5F
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