[Elecraft] Re: PLL Reference Oscillator problem

[John C. Henry]

I have checked a few more things, and (incorrectly) determined it was a bad
xtal.  I replaced it and still have the same issues, so aside from feeling
REALLY dumb, I still have a dead radio...

I checked the DC voltages on the ICs and found several out of spec.
Unfortunately, I don't know which part these issues point to, so I am hoping
someone can help.  Obviously I have problems with U4 and U5, and the Q19
doesn't look too good either.  But how to tell if the chips are working and
are trying to correct for the frequency problem, or if they are broken?

Here is the table:

IC    | Pin | Spec | Read
------|-----|------|------
Q19   |  G  |  0   | .615
      |  S  |  .8  | 2.20
      |  D  |  8   | 8.05

U4    |  1  | 2.1  | 2.26
      |  2  | 2.4  | 2.294
      |  3  |  0   | .005
      |  4  | 2.3  | 2.255
      |  5  | 5.0  | 5.11
      |  6  | 5.0  | 5.11
      |  7  |  0   | 5.11
      |  8  |  .1  |  .09
      |  9  |  0   | 0
      | 10  |  0   | 0
      | 11  |  0   | 0
      | 12  |  0   | 0
      | 13  |  4   | 5.05
      | 14  |  5   | 5.05
      | 15  |  5   | 5.05
      | 16  |  5   | 5.05

U5    |  1  |  0   | 0
      |  2  |  5   | 4.0
      |  3  |  5   | 4.07
      |  4  |  5   | 0
      |  5  |  0   | 4.02
      |  6  | 2.0  | 2.05
      |  7  | 0-4  | 4.07
      |  8  |  5   | 5.07

U6    |  1  | 0-8  | 8.01
      |  2  | 0-4  | 4.0
      |  3  | 0-4  | 4.07
      |  4  |  0   | 0
      |  5  |  4   | 4.02
      |  6  |  4   | 5.04
      |  7  | 0-8  | .01
      |  8  |  8   | 8.05

Thanks,
John
AC7LC
----- Original Message -----
From: John C. Henry
To: elecraft@mailman.qth.net
Sent: Tuesday, March 11, 2003 7:41 PM
Subject: PLL Reference Oscillator problem


Greetings fellow Elecrafters,

I am building K2 #3318
Page 57, step 4
The frequency counter is hopping rapidly from around 478 through around
482 instead of showing around 12090.
I checked the connection and the probe.  When the probe is connected to
TP1, it shows 11965 fairly stable even when adjusting the tuning.  I
checked this with an external frequency counter and got the same
results

I sent mail to Gary (not thinking to send to the reflector first) and got
some helpful suggestions.
The xtal is not shorted (checked with a DMM).
Re-checked and re-soldered T5.
Checked the VCO voltage and got .01v for all bands at both ends and no
change with L30 adjustment.
The probe works at TP1 & 2, and I checked with another probe and counter
just to be sure.

I suspect I cooked the xtal while grounding it, but I am looking for a
method to be sure.
I am unfortunately unfamilliar with the circut ( beyond it looking like an
oscillator :) and don't know what I am looking for to troubleshoot it.  The
schematic doesn't have any reference voltages listed (not a complaint, just
an observation).
Any suggestions would be appreciated.  I'd really like to make sure I didn't
wipe out anything else.

thanks,
john
AC7LC

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Never attribute to malice what can be explained by stupidity.