Hardware Fix
-h-

AEA has announced that free replacement capacitors are available for
certain PK-232s which my have defective capacitors at C-58 in the tone
adjust circuit.  Symptoms are that you cannot hold 1200 Hzc
calibration.  The faulty part C-58, is tiny, b lue, numbered 223J X7R
and located directly behind the bar-graph tuning display.  the correct
capacitor is a 0.022 uF NPO ceramic and is buff or yellow in colour.

Affected PK-232 serial numbers are 13,815-14,156 (but possibly not all
in that sequence), 14,175-14,235, 14,261-14,600, 14,614-14,710, 16,800,
16,821-17,240 and 17,341-17,424.

The frequency can be adjusted to 1200 Hz with the bad capacitor, but
will drift because the capacitor has the wrong electrolyte and
dielectric constant.  After replacing the capacitor, the tone frequency
potentiometers must be readjusted: R-167 to 1200 Hz, R-165 to 2200 Hz,
R-164 to 2310 Hz, R-168 to 2110 Hz.  R-167 and R-168 interact.  R-167
must always be adjusted first and R-168 adjusted last.  After adjusting
R-168, then re-adjust R-167 and, then, R-168 again.

By Dave Tyler N6DRT @ W6CUS.

Copied from Gateway Vol.4 Number 17 dated May 13th 1988 by Dick, G4BBH @
G4BBH

Following information received from Wolf ZS6KE
concerning new Eproms for the PK-232 plus a mod to eliminate
noise from the op-amps.

Hello Pat, just want to let you know that I have obtained a new set of prom's
for this PK-232 of mine. The release date is Feb. 88 and it comes in 2
27C256 proms. It has some of the old bugs ironed out and also a few new
features for FAX and NAVTEX etc. Otherwise no change.
On recommendation of OM Piet, ZS6AQC I checked the noise on the power bus
to the MC34074P op-amps and found (just like he said) that there is a lot of
rubbish between the pins 4 and 11 of U23, 26, 28, 30, 32 and 34. So I placed
some MKF 1 uF cap's across them and my receive noise (measured on a mark-space
scope cross-display) is MUCH MUCH less. In fact, I can now even copy some
steady signals that don't even raise the S-meter needle. Hope you can improve
yours also!
Cheers, hope we can chat again soon! Wolf

-g-

The proposed changes :1 uF blocking cap's across the Op'amps (TL084C in my unit)
and replacement of C58 (near U40 XR2206 the FSK chip) by a Styroflex capacitor
have lowered the noise level and improved the frequency stability of the FSK
tones.
ADDITIONAL CHANGES to the PK-232:
- In order to improve the stability of the TNC aginst RF interference a choke
(few 10 uH's) has been introduced directly in the power supply line in the
back of the unit between the connector J1 and the fuse F1.
- The stability of the FSK tones can be further improved by removing the the
5-Volts regulator U21 (LM317T) from the circuit board and thus preventing it
from heating the frequency adjusting potmeters R164, R165, R167, and R168.
The regulator should be mounted to the bottom of the housing in order to be
heatsinked.