Watkins-Johnson Company WJ-8718A Owner's manual

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This document and the subject matter
disclosed herein are proprietary items to
which Watkins-Johnson Company retains the
exclusive right of dissemination, reproduction,
manufacture and sale.
This document is provided to the individual or
using organization for their use alone in the
direct support of the associated equipment
unless permission for further disclosure is
expressly granted in writing.
WATKINS-JOHNSON COMPANY
700 QUINCE ORCHARD ROAD
GAITHERSBURG MARYLAND 20878
INSTRUCTION SUPPLEMENT
FOR
WJ-8718A AND WJ-8718A/MFP
1-Hz READOUT OPTION
(TENTATIVE MANUAL)

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WARNING
This equipment employs dangerous voltages
which may be fatal if contacted. Exercise
extreme caution in working with this
equipment with any of the protective covers
removed.
NOTICE
This is not the original Instruction Manual for the 1-
Hz Option for the WJ-8718A Receiver Series, it is only
an attempt to write one from scratch.
It is based upon visual inspection and visual circuit
tracing on existing and unmodified WJ-8718A and
WJ-8718A/MFP receivers including this rare option.
The author is Paolo Viappiani of La Spezia, Italy
([email protected]), a radio collector whose only
purpose is to share technical information. It is a no-
profit work and consequently in no way this manual
may be sold and/or made object of commercial
transactions.
The work is still in progress, so any contribution and
suggestion is very welcome. The author also
apologizes for eventual ad unwanted mistakes,
misprints or omissions of which he cannot be held as
responsible.
La Spezia, Italy, June 2017
Revisions:
- Version 1.0 –June 2017

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FIELD MODIFICATIONS INSTRUCTIONS
FOR INSTALLING THE 1-Hz OPTION IN
THE WJ-8718A OR IN THE WJ-8718A/MFP HF RECEIVER
The following tools are necessary to perform the modification steps:
Phillips screwdriver;
Soldering gun and solder.
Perform the following steps to install the 1-Hz Option in the WJ-8718A or in the
WJ-8718A/MFP receiver:
1. Remove power from the unit.
2. Remove top and bottom covers from the unit.
3. For the WJ-8718A:
Remove the six screws mounting the manual front panel to the unit.
Disconnect all cable assemblies from the old manual front panel except
A10P1. Disconnect A10P1 from the Front Panel Interconnect board A6A2.
Remove the manual front panel from the unit.
For the WJ-8718A/MFP:
Remove the six screws mounting the stock MFP front panel to the unit.
Disconnect all cable assemblies from the old MFP front panel (MFP-P12
from MFP-P14, MFP-P13 from MFP-P15, MFP-P1 [16-pin] from J2, MFP-
P2 [14-pin] from J1). Disconnect also the MFP-P6 plug from the J1 socket
on the Front Panel Encoder card A1- 796056-X, unplug that board from the
Front Panel Interconnect small motherboard (MFP-A1, 794310-X) and set it
apart temporarily.
Remove the old MFP front panel from the unit.
4. Place the unit with the bottom side facing up.
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NOTES
- The 1-Hz Option is normally Factory-installed together with the 10-Hz
BFO Option, although this is not mandatory. It is recommended to have at
hand and to read carefully also the 10-Hz Option Manual anyway.
- For the WJ-8718A/MFP: before starting the 1-Hz Option installation,
please check and ascertain that all the Field Modifications considered in the
“WJ-8718A/MFP INSTRUCTION MANUAL REVISION A CHANGE 1”-
February 1991 have been already performed as described.
- This manual can also be used for installing the 1-Hz Option on WJ-8716
and WJ-8716/MFP receivers.
5. Find A6 I/O MB (Type number 791580) location by referring to Figure
5-8 of the WJ-8718A HF Receiver Instruction Manual.

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For receivers with Manual Tuning Module only (WJ-8718A etc.):
a. Install A6JW5 by wire wrapping one end of a wire to A6X9, pin 42
and the other end to A6X8, pin 42.
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b. Install A6JW6 by wire wrapping one end of a wire to A6X9, pin 44
and the other end to A6X8, pin 44.
c. Install A6JW7 by wire wrapping one end of a wire to A6X9, pin 46
and the other end to A6X8, pin 46.
d. Install A6JW8 by wire wrapping one end of a wire to A6X9, pin 48
and the other end to A6X8, pin 48.
For receivers already having a MFP front panel (WJ-8718A/MFP, etc.):
a. Install A6JW5 by wire wrapping one end of a wire to A6X9, pin 42
and the other end to A6X8, pin 7.
b. Install A6JW6 by wire wrapping one end of a wire to A6X9, pin 44
and the other end to A6X8, pin 12.
c. Install A6JW7 by wire wrapping one end of a wire to A6X9, pin 46
and the other end to A6X8, pin 14.
d. Install A6JW8 by wire wrapping one end of a wire to A6X9, pin 48
and the other end to A6X8, pin 54.
For all receivers:
e. Carefully remove the coaxial bridge (W6) that connects J7 to J9
(both placed on the aluminium chassis sides) unscrewing its P10
and P9 connectors. Set the bridge apart for possible future use.
f. Install the following coaxial leads:
1Hz-W1 (from J7 to A6X9, pins 5 [signal] and 6 [ground shield]);
1Hz-W2 (from J9 to A6X9, pins 3 [signal] and 4 [ground shield]).
6. Place the unit with the top side facing up..
7. Carefully insert the 796022 (1-Hz Option) card into the X9 socket of the A6
I/O mainboard (with the card rear facing the A6 I/O MB right edge).
NOTES
- Figures 1a, 1b and 2 (on this Manual) show the bottom side of the A6 I/O
mainboard (on a WJ-8718A and on a WJ-8718A/MFP respectively) with all
the above-mentioned modifications already performed, while in Figure 3 is
shown the bottom side of a NOS A6 I/O mainboard that had been already
Factory set up for installation of the 1-Hz Option.
- Instead of using wire-wrapping technique, all the required wire connections
can be installed by using PTFE-insulated stranded wires and standard strip-line
female connectors that have to be inserted into the proper socket pins. In this
case, two four-pole female connectors are required for the WJ-8718A, a four-
pole and three two-pole female connectors are required for the WJ-
8718A/MFP (as shown in Figure 4).

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Figure 1a: A6 I/O mainboard of a WJ-8718A 1-Hz resolution receiver (bottom side).
Figure 1b: Further details of the same WJ-8718A receiver (A6 I/O MB, bottom side).

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Figure 2: A6 I/O mainboard of a WJ-8718A/MFP 1-Hz resolution receiver (bottom side).
Figure 3: Factory-installed wire-wrap wiring for the 1-Hz Option in a WJ-8718A/MFP
radio (A6 I/O mainboard partial view, bottom side).

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Figure 4: Alternative wiring on the A6 I/O MB for the 1-Hz option in a WJ-8718A and in a
WJ-8718A/MFP. Some strip-line female connectors and stranded wires are used.
8. Final steps:
For receivers with Manual Tuning Module only (WJ-8718A etc.):
a. Locate the A6A1 Manual Tuning Up-Down Counter card (791575-X) on
the A6 I/O mainboard, sockets XA1 (X7 and X8); unplug and remove it,
replacing with the 796014 type (see Figures 4a-4b).
b. Place the new manual front panel (with an 8-digit frequency display and also
with a 4-section BFO thumbwheel switch eventually) in the front of the
receiver, taking care not to break the power switch shaft.
c. Reconnect to the proper front panel sockets all the plugs that had been
disconnected: the ones coming from J4 (A7P1 to manual tuning board), J2
(A8P1 to display), and J3 (A9P1 to BFO thumbwheel switch) on the new
A6A1 board (796014).
Reconnect also the A10P1 plug to J1 (on the A6A2 Front Panel
Interconnect 791828-X card).

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Figure 4a: A 796014 card that replaces the stock 791575-X board (front view).
Figure 4b: Rear view of a 796014 card.
For receivers already having an MFP front panel (WJ-8718A/MFP, etc.):
a. Locate the MFP-A4 Synthesizer Interface/Memory card (794275-X) on
the A6 I/O mainboard, sockets XA1 (X7 and X8); unplug and remove it,
replacing with the new one that is also provided with U17 IC and two
proper EPROMS (U1 and U2) containing the software for the 1-Hz Option
too (see Figures 5 and 6 for some more card details).
b. Place the new MFP front panel (with an 8-digit frequency display) in the front
of the receiver, taking care not to damage the power switch shaft.
c. Reconnect to the proper front panel sockets all the cable assemblies that had
been disconnected, using a reverse process: MFP-P12 to MFP-P14, MFP-P13
to MFP-P15, MFP-P1 (16-pin) to J2, MFP-P2 (14-pin) to J1. Reconnect also
the Line Audio cable coming from the A4 IF motherboard to the Line Audio
potentiometer on the front panel. Re-insert the Front Panel Encoder card A1-
796056-X into the Front Panel Interconnect small motherboard (MFP-A1,
794310-X).

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Figures 5(a-b): A 794275-X MFP-A4 card suitable for the 1-Hz Option: notice the
presence of U17 (normally missing) and of two EPROMS (U1 and
U2) that include the 1-Hz software (front and rear views).
Figure 5c: Details of U17 connections (wire bridges in the front of the MFP-A4 card)

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Figure 5d: Details of U17 connections (wire bridge in the rear of the MFP-A4 card)
Figure 6: Schematic detail of the PCB bridges near U17
For all receivers:
d. Install the new front panel using the same six screws removed in step (3)
above;
e. Replace the top and bottom covers using the same screws removed in step
(2) above.
f. Apply power to the receiver and check it for proper operation.
NOTES
- Figures 7 (a and b) show the front and the rear sides of a 796022 1-Hz Option card
(that has to be inserted into the A6X9 socket on the A6 I/o mainboard after having
performed all the above listed modifications). This enables the 1-Hz tuning and readout
resolution.

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Figure 7a: The 796022 1-Hz Option card for the WJ-8718 Series of receivers (front side).

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Figure 7b: The rear (shielded) side of the same 796022 1-Hz Option card.

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WJ-8718A & WJ-8718A/MFP 1-Hz OPTION
PRINCIPLES OF OPERATION AND CIRCUIT DESCRIPTION
In stock receivers (10-Hz tuning resolution) the coaxial cable bridge named W6 and placed on
the bottom side of the receiver - towards the rear of the unit and in correspondence of the A6
I/O mainboard - leads the 11.155,000 MHz signal coming from the third L.O. to the third
mixer (U1 on the A4A2 card) in order it is mixed with the 10.7 MHz 2nd IF signal and
produces a 3rd IF of 455 kHz. The 3rd L.O. output signal is applied to J9 (P8 on W6) and the
3rd mixer input corresponds to J7 (P10 on W6).
Installing the 1-Hz Option implies that the coaxial bridge W6 is removed and that the 3rd
L.O. signal is applied to pin 3 of the X9 socket that corresponds to the new 796022 1-Hz
Option card instead (1Hz-W2 cable starting at P4/J9). Then a signal coming from pin 5 of the
same X9 socket (1-Hz card) is applied to the 3rd mixer input (1Hz-W1 cable coming to
P1/J7).
So it is evident that the 796022 1-Hz Option card produces 1-Hz shifts (from -9 Hz to + 9 Hz)
in the 11.155 MHz signal that comes to the 3rd mixer, so that the tuning resolution becomes 1
Hz. Obviously the 1-Hz shifts depend from the tuning encoder (and from the numeric
keyboard in the /MFP receivers) and are also sensed by the tuning display.