Heathkit Service Bulletins - SB-104 [Part One]
Joseph W Lutz
joelutz at JUNO.COM
Wed Oct 8 00:03:38 EDT 1997
January 3, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-1
Receiver Desensing Noticed In Cw Mode
Disconnect R19 from E14 and reconnect to G15.
Transmitted Voice Heard In Speaker
Add a .001 capacitor [PN 21-14] from F15 to F13.
-----------------------------------------------------------------------------------------------------------------
January 13, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-2
OutputTransistor Replacement
After power has been applied and an output transistor has been found
electrically damaged, all four output transistors should be changed.
In cases where physical damage has occurred such as the stud being broken
off during construction and power has not been applied, only the one
damaged transistor can be replaced. It must be replaced with one from
the same vendor. No other matching considerations are required.
This information is not for general customer distribution.
-------------------------------------------------------------------------------------------------------------------
January 24, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-3
Beat Note Heard In Transmitted Signal
In CW and Tune Mode
The USB generator may not be completely disabled during transmit in the
CW or Tune mode. The result would be two signals being transmitted
approximately 700 cycles apart. This can be detected either by listening
to it in a receiver or by watching it on an oscilloscope. IT looks much
like a low level tone modulated signal.
Change R625 27K 1/4 watt resistor to a 22K 1/4 watt resistor, [PN
1-45-12]. Change C622 from 10 mfd to 15 mfd, [PN 25-252].
--------------------------------------------------------------------------------------------------------------------
January 27, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-4
No T/R Frequency Shift Using The Remote
VFO While In Low Power
A change is needed in the transceiver to allow the remote VFO to shift
transmit and receive frequencies while in low power.
SB-104:
1) Add a wire from the RX IF/Audio circuit board pin F-7 to lug 3 of the
accessory socket.
SB-644:
2) Disconnect the wire going to the jumper wire between pins 2 and 5 in
the 11 pin accessory plug and reconnect it to pin 3.
--------------------------------------------------------------------------------------------------------------------
January 29, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-5
Excessive Noise With The RF Control Down
And The AF Gain Control Up
Remove R569 330K from the Receiver IF/Audio circuit board. This will
allow section A of IC502 to operate quieter.
---------------------------------------------------------------------------------------------------------------
February 27, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-6
Service Hints - Low Power
The output power specification is 100W +/- 1db, which means output power
can be from 80W to 125W and be within specs.
If the output powr is below specs, check the following:
1. SWR The output reduces as the SWR increases. Check
the Cantenna dummy load with an ohmmeter. It should
measure 50 ohms.
All coax cables should be checked for good connections.
NOTE: A monitor scope in the line causes some SWR at the
higher
frequencies, enough to cause the SB-104 to reduce in
output
power (particularly on 10 meters).
2. Power supply voltage should be 13.8VDC under load, at the
transceiver.
3. Check the 11 volt regulator. It should be at least 11 volts.
A slight change in value (within 10 %) of R254 and R255
causes
the output to change considerably.
4. Check ALC filter board wiring. The loop through the toroid
must go
through in the proper direction. If not, power will be only
approxi -
mately 10%. Interchange the in and out cables for a check.
If
power returns or comes up, the toroid or wire loop are
miswired.
5. IC-301 also affects power output. Interchange IC-301 with
other
442-18 IC's located in the kit, or select one from stock.
6. The gain of Q-301 affects full power output. If needed,
select the
lowest gain transistor for the power output closest to
100W. (NOTE:
NOT THE HIGHEST OUTPUT, THE ONE CLOSEST TO 100W!)
Power can be lost for two main reasons. 1) Not enough amplifier gain,
and 2) too much ALC cutoff. Momentarily shorting Q303 from B-C will
disable the ALC circuit causing the transmitter to operate at full power
when in tune position (Approximately 150W output). If obtained, this
will indicate the condition of the amplifier circuits being good. If the
power does not come up, there is an amplifier gain problem.
If full operating power cannot be restored after checking the above,
replace each transmitter circuit board with known operating ones to
isolate the problem.
-----------------------------------------------------------------------------------------------------------------
January 29, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-7
SB-104 Circuit Improvements
"Pop" Heard In The Transmitted Signal When The VOX "Drops Out".
Change C1 .1 mfd to 10 mfd [PN 25-54, + end to Pin 7]. This cap may not
appear in the schematic. It goes from connector pin C7 to ground.
NOTE: The .1 cap can be left in and the 10 mfd added across.
Better Noise Blanker Performance
Add a 390 ohm resistor [PN 1-48] from the center arm to ground of the RF
gain control (rear section).
10 Meter Oscillations During Alignment
Solder a ground clip [PN 258-95] to the 10 meter shield on the TX/IF
circuit board. The ground clib must touch the compartment shield in
front of the circuit board when plugged in.
Other Improvements
The following will be made in future SB-104 runs and have come about
through design and evaluation of new products. It is not necessary to
make these changes in existing kits.
- - Add a 500 mfd capacitor [PN 25-157] from terminal J-1 to ground
(ground lug on the receiver antenna jack for improved driver B+
decoupling).
- - Change R903 on the driver circuit board from 100 ohms 2 watt to 220
ohms 2 watts [PN 1-13-2] for improved intermodulation distortion.
NOTE: Although this change may contribute to cooler operation of
the driver transistors, if overheating is a problem, check first for
broken transistor studs. If the plastic part of the transistor case
"feels" considerably hotter than the heat sink, suspect broken studs.
There are instructions in the kit manual to prevent this type of
damage for which Heath will not be liable if it occurs.
- - Add a 39 pf capacitor across R-314 on the Transmitter If circuit
board to improve harmonic suppression of the IF signal.
- - Change C227 from .05 mfd to 47 mfd [PN 25-223] on the Transmitter
Audio/Regulator circuit board to improve the 11 volt regulator filtering.
--------------------------------------------------------------------------------------------------------------------
February 10, 1975
SB-104 Bulletin No:
Solid State Transciever SB-104-8
Incorrect Diodes
An undetermined amount of diodes may have been shipped to be used in D306
to D309 which are the four diodes in the balance mixer on the transmitter
IF circuit board. The incorrect diodes we have seen so far have a blue
colored body. The correct diodes are clear glass, and may not have a
part number printed on them.
Check for the proper diodes in each SB-104 serviced. Incorrect diodes
may cause spurious radiation.
The correct part number is 56-87. The INCORRECT part you may see is
56-78.
-------------------------------------------------------------------------------------------------------------------
February 21, 1975
SB-104 Bulletin No:
Solid State Transciever SB-104-9
Heterodyne Oscillator Coil Interaction
Adjacent heterodyne oscillator coils may be interactive to the point
where one band may be completely inoperative.
If one heterodyne oscillator is not operative, be sure to first check the
adjacent band coil settings.
------------------------------------------------------------------------------------------------------------------
March 21, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-10
VFO Drift and USB/LSB Shift
L1201 is supplied preset on the lower peak with the slug near the back of
the VFO. If this coil is not adjusted on the peak near the front of the
VFO, a shift problem and VFO instability will occur. The display between
USB and LSB will not adjust correctly to read the same frequency when
switched. The VFO may also tend to drift. Be sure the slug is at the
front of the VFO when aligning as stated in the manual alignment
procedures.
--------------------------------------------------------------------------------------------------------------------
April11, 1975
SB-104 Bulletin No:
Solid State Transceiver SB-104-11
Check Out And Alignment Procedures
TEST EQUIPMENT REQUIREMENTS:
Oscilloscope: 15 Mhz vertical bandpass; triggered [IO-4510 or
better.]
RF Generator: Calibrated output attenuator; Frequency Range
3 to 30 Mhz [Radiometer MS-27G or equivalent.]
Augio Generator: 100 to 3000 Hz sine wave output; adjustable
output level [IG-18 or equivalent.]
100 Khz Crystal Calibrator: Harmonic output 100 Khz to 30 Mhz
[HD-20 or equivalent.]
VTVM: High input impedance [IM-18 or equivalent.]
AC VTVM: Calibrated in decibels [IM-38 or equivalent.]
Bench Supply: 13.8 VDC; less than 2% regulation, no load to 20
amps
[HP-1144 or equivalent.]
DC Voltage Supply: 0 to 11 V. at 1 amp [IP-28 or equivalent.]
Wattmeter: 150 watts at 50 ohms [HM-102 or equivalent.]
Dummy load: 150 watts; 50 ohms resistive load [HN-31 or
equivalent.]
PTT Microphone: High impedance, approximately 25K ohms
[HDP-21A or equivalent.]
2 ea. Speaker: 8 ohms impedance [HS-24 or equivalent.]
Probes: 10:1 LC Probe [PKW-101 or equivalent.]
RF Probe [PK-3 or equivalent.]
VTVM Probe [PKW-4 or equivalent.]
Receiver: Monitor [SB-303 or equivalent.]
Monitor Scope: SB-614 ((Do not use SB-610)).
Assorted cables: See attached sheet for cables and test lead
needed
for interconecting test equipment and UUT.
SB-104 TRANSCEIVER AND TEST EQUIPMENT INTERCONNECTING CABLES
Part numbers of connectors, wire and cables needed to make the test
cables are listed at each part. the 134- part numbers are cable
assemblies and it is only necessary to add the specified connector to one
end ot complete these cables.
Make about 6 "jumper leads" of various lengths to use for temporarily
connecting circuit points together during troubleshooting. Install an
insulator on each alligator clip.
Cable Assembly No: 134-237 'REC Jack to RF Generator'
[other end
of cable has PN 438-4]
Cable Assembly No: 134-36 (2ea) 1. AC VTVM to Patch Out Jack
2. Audio Gen. to Patch in Jack
[other end of these cables has PN 438-30]
Cable Assembly No: 134-36 'HD-20 Xtal Cal. to REC Jack'
[other end of cable has PN 438-47/70-11 (on
center conductor) & PN 260-16 with 73-34
insulator (on braid)]
Piece of cable [PN 343-2] 4' long 'Ant Jack to Wattmeter'
One end with connector 438-9 & insert 438-12, the
other end with connector PN 438-4]
Piece of cable [PN 343-2] less than 5' 'Wattmeter to Dummy Load'
Both ends with connector 438-9 & insert 438-12.
Piece of red wire [PN 341-2] 4' long & black wire [PN 341-1] 4' long
(IP-27 leads)
one end of the wires has alligator clips [PN 260-16/insulator
73-34] and
the other ends are crossed into a (dual banana plug) [PN
438-30].
SB-104 ALIGNMENT PROCEDURE
The following checks and alignment of the SB-104 transceiver is made with
all circuit boards plugged in. Always turn the unit off when you remove
or insert a circuit board.
INITIAL CHECKS
1. Depress the on button. Release all other buttons.
- Pilot lamp lights.
- Display lights.
2. Check for 4.5 volts DC [plus or minus .5 volts] at terminal
B4 and
10.5 volts DC [plus or minus .5 volts] at B1.
3. Set bandswitch to 3.5: Lift COUNTER Board [A] from connector
pins.
- Display reads F FFF.F
4. Switch BAND switch through all positions, starting at 3.5.
First digit
should light in the following sequence:
BANDSWITCH FIRST DIGIT
3.5 Blank
7. Blank
14. 1
21. 2
WWV 1
28. 2
28.5 2
29 2
29.5 2
5. Depress the 100 Hz buttor.
- Digit on the right end of display extinguishes.
6. Plug in COUNTER board [A] and set BAND switch to 3.5. Lift
the
HFO/PRE-MIXER board [D] from conenctor pins.
- Release all pushbuttons except ON.
- Display reads 6600.0
- Depress USB switch; display reads 6603.6.
- Depress LSB switch; display reads 6606.4.
- Depress CW switch; display reads 6604.3.
- Plug in HFO/PRE-MIXER board [D].
7. Lift TX IF/PRE-DRIVER board [C] from conenector pins.
- Check that the tips of choke L-311 on board C are not shorting
against
the shield.
8. Connect a microphone and depress the PTT switch.
- Receiver mutes.
9. Depress PTT switch on microphone and depress HI button.
- T/R relay pulls in.
- T/R relay drops out with PTT switch released.
10. Depress VOX and HI buttons; speak into microphone and turn
VOX
GAIN control slowly CW.
- T/R relay pulls in when speaking and drops out when you cease
talking.
11. Turn VOX DELAY CW and speak in microphone.
- T/R relay holds for a length of time after you cease talking.
The hold-in
time will decrease as DELAY control is truned CCW.
12. Release VOX button and check the voltage on the foils at
L-952 and
L-953 on the PA board.
- The voltage on these foils is zero.
13. Depress the TUNE button.
- T/R relay pulls in; approximately .6 volts should be measured
at the
indicated foil patterns on the PA board.
14. Release TUNE button.
HFO COIL ADJUSTMENTS
- Install HFO/PRE-MIXER board [D] on extender board.
- Set VTVM to +DC; 1.5V range.
- Connect the positive lead of the voltmeter to TP [free lead of
2200
ohm near Q402; and the negative lead to chassis.
- Adjust each HFO coil as described in the following chart.
Each coil
may peak at two points throughout its tuning range. Use the
peak
that occurs at the bottom of each coil. After the bottom
peak is found,
turn the slug CCW to zero volts. Now, turn the slug CW for
peak
voltage; typically .1V DC to .5V DC.
______________________________________________________________
BAND SWITCH COIL NUMBER ROTATE SLUG FOR PEAK VOLTAGE,
THEN ROTATE SLUG AS DESCRIBED.
-------------------- ------------------- --------------------------------------------------
3.5 L401 1/2 turn CW*
7.0 L402 1 turn CCW**
14.0 L403 1 turn CW
WWV L404 1/2 turn CW
21.0 L405 1 turn CW
28.0 L406 1 turn CW
28.5 L407 1 turn CW
29.0 L408 1 turn CW
29.5 L409 1 turn CW
* = Clockwise
** = Counterclockwise
_______________________________________________________________
- Release ON button and reinstall HFO/PRE-MIXER board (D).
VFO ADJUSTMENT
- Set bandswitch to WWV.
- Depress USB buttons.
- Connect RF probe to VFO connector PL201, pin 1 [coax center
lead]
and adjust VFO LEVEL ADJUST control (R1232), at hole FY, CW
for
.5 volts reading on VTVM.
- Check for a stable display (+/- 1 count) at all positions of
the band-
switch. Turn VFO LEVEL ADJUST CCW, if necessary, to obtain a
stable display.
VFO FREQUENCY AND SHIFT ADJUSTMENTS
- Set Bandswitch to 3.5.
- Turn the MAIN TUNING until the display will go no lower. If
the display is
unstable, repeat VFO output adjustments.
- Remove the MAIN TUNING knob.
- Adjust the VFO FREQUENCY ADJUST control (hole ET) for a
display of
3475.0 or the point which gives the reading closest to
3475.0. This
readout may appear at two positions of the coil slug. The
correct
position is where CCW rotation of the slug causes a lower
frequency
to be displayed.
- Reinstall and tune MAIN TUNING knob for display of 3800 KHZ.
- Remove MAIN TUNING knob.
- Depress USB button and record frequency display.
- Depress LSB button and adjust VFO SHIFT ADJUSTMENT (C1211) at
hole ES with a small screwdriver. Remove the screwdriver
after each
adjustment and check the frequency. Adjust C1211 until the
LSB
frequency is the same as the USB frequency. Check 3500 KHZ
and
4000 KHZ. The side band shift should be less than plus or
minus .5
KHZ at each point.
- Reinstall customer's black tape over holes ES and ET;
reinstall MAIN
TUNING knob and tighten the two set screws.
- Check stability of frequency display at all positions of the
bandswitch.
Turn the VFO LEVEL ADJUST slight CCW to stabilize the display
as
necessary. Adjusting this control beyond the point necessary
for a
stable display will incease noise and birdies.
RECEIVER ALIGNMENT
Preselector BPF And 8.65 BPF Alignment
- Set transceiver controls as follows:
Bandswitch - 3.5
RF Gain - FCW
ALC Button - IN
USB Button - IN
AGC - OFF
ANT Switch - SEP
LEVEL - FCCW
- Install RECEIVER FRONT END board (G) on an extender board.
- Connect 100 KHZ crystal calibrator ro REC antenna jack.
- Connect AC VTVM to PATCH OUT jack.
- Set AC VTVM range switch to .1 V.
- Adjust AF gain control for a -10 dB reading on the meter scale
(noise output).
- Turn transceiver to calibrator harmonic at 3800 KHZ. Turn to
the high
side of receiver bandpass (high pitched beat note) until AC
VTVM
indicates -5 dB.
- Adjust the three PRESELECTOR BPF trimmers for maximum
indication
on AC VTVM.
- Tune transceiver to calibrator harmonic at 3500 KHZ and adjust
LOW
END trimmer for maximum output.
- Adjust trimmers at coils L725 and L726 (8.65 BPF) for maximum
output. Adjust these trimmers for the most uniform response
across
the 80 meter band.
- Follow the same procedure and adjust the PRESELECTOR BPF's for
the 40 through 10 meter bands. Refer to the chart below for
the
location of thetrimmers and the three frequencies used for the
adjustment of each filter. Do not adjust the trimmers at
coils L725
and L726.
[[Looking at component side of Board G, where coils L725 and L726 are in
the
upper left-hand corner of the board, there is shown (5) rows of
3-trimmers on the
right 2/3 of the board. Trimmer L704 is shown at the extreme lower
left corner of
the board. Again looking at the board - component side - the 3
trimmers are,
reading from top to bottom::
MATCHING HIGH END LOW
END BAND
TRIMMER TRIMMER TRIMMER SWITCH
29.0-29.5
28.0-28.5
21.0
14.0
7.0
3.5 ]]
[[The next chart shows mid-band adjustments for the 3 trimmers:
| F R E Q U E N C I E S
________|________________________________________________
| MID-BAND | | |
BAND | (ADJ. 3 TRIMMERS | LOW END | HIGH
END |
_______ |________________|_______________|________________|
29.0 | | | |
29.5 | 29400 | 29000 |
29700 |
---------------------------------------------------------------------------------------------------
28.0 | | | |
28.5 | 28400 | 28000 |
29000 |
---------------------------------------------------------------------------------------------------
21.0 | 21100 | 21000 |
21400 |
---------------------------------------------------------------------------------------------------
14.0 | 14200 | 14000 |
14400 |
---------------------------------------------------------------------------------------------------
7.0 | 7100 | 7000 |
7300 |
---------------------------------------------------------------------------------------------------
3.5 | 3800 | 3500 |
4000 |
---------------------------------------------------------------------------------------------------
[[ Hope this can be followed, please advise if not]]
3.395 MHZ Receiver Trap Adjustment
- Connect RF generator to REC antenna jack and AC VTVM to PATCH
OUT jack.
- Tune generator to 3.395 MHZ and tune transceiver to 3.5 MHZ.
- Adjust trimmer capacitor at L704 of RECEIVER FRONT END board
(G)
for minimum output.
NOTE: Due to the location of the 3.395 trimmer, this adjustment
is hard
to get at. The board (G) will have to be removed and the trimmer
adjusted in increments until the correct setting is reached. The
position of the trimmer of L704 will be changed in future runs
for easier
access to the adjustment.
- Reinstall FRONT END board (G).
S Meter Adjustment
- Set the generator and transceiver to 3800 KHZ.
- Set AGC switch to FAST.
- Set the generator output for 50 uV and tune the receiver for
maximum
output.
- Adjust the S Meter LEVEL ADJUST on the RECEIVER IF/AUDIO board
(F) for an S-9 reading on the S meter.
Receiver Sensitivity Measurement
The receiver sensitivity is specified at less than 1 uV for 10 dB
signal
plus noise-to-noise ratio.
- Set the controls of the transceiver as follows:
Bandswitch - 3.5
RF Gain - FCW
USB Switch - IN
AGC - OFF
ON Switch - IN
- Connect AC VTVM to PATCH OUT jack.
- Connect generator to REC Antenna jack.
- Set generator for unmodulated RF to 50 uV output.
- Tune generator and transceiver to center of band [3800 KHZ].
- Reduce generator output to zero.
- Set AC VTVM range switch to .1 V.
- Adjust AF GAIN control for a -10 dB reading on the meter scale
[noise output].
- Increase generator output and tune the receiver for a maximum
indication of 0 dB on the AC VTVM [signal plus noise output].
- If the output of the generator is 1 uV or less, the receiver
is within
specifictions.
- Check the sensitivity of the remaining bands.
NOTE: The sensitivity of the receiver on the 20 meter band can
be
improved by a slight toughup adjustment of HFO coil L405. This
is
the only band that a noticeable increase in sensitivity is
achieved
by a touch of the HFO couls.
8.64 MHZ IF Rejection Check
The IF rejection is specified at -60 dB.
- Set bandswitch to 7.
- Connect RF generator to REC antenna jack and AC VTVM to PATCH
OUT jack.
- Tune receiver and generator to 7.25 MHZ.
- Make sensitivity measurements and note generator output
reading
for a 10 dB S+N/N.
- Tune generator to 8.65 MHZ and incrase generator output until
the
VTVM reading is the same as obtained in the sensitivity
measurement.
- If the generator output was inceased 60 dB or more to obtain
the same
VTVM reading, the IF rejection of the receiver is within
specifications.
NOTE: If on 50 dB of rejection is obtained during this test,
check that
coils L1 or L3 are not shorted to the chassis or across the lugs
of
terminal strip AE. To prevent a short at these points, dress the
coils
away from the lugs of the terminal strip and place a piece of
fish paper
between each coil and chassis.
COUNTER CLOCK CALIBRATION
- Connnect antenna to REC antenna jack.
- Set bandswitch to WWV (15000 KHZ) or 7 (CHU, Canada, 7335
KHZ).
- Tune to zero beat station selected.
- Adjust the MAIN TUNING until the voice announcements sound
natural.
- Adjust the TIME BASE TRIMMER capacitor on the upper right hand
corner of COUNTER board (A) for a readout of 15000.0 or
7335.0.
TRANSMITTER ALIGNMENT
Low Power Transmitter Check
- Check that the coil slug of L321 on the TX IF/PREDRIVER board
(C)
is flush with the bottom of the coil form and reinstall this
board.
- Connect a wattmeter and a 100 watt dummy load to ANT jack.
- Set controls as follows:
BANDSWITCH - 3.5
LEVEL - FCCW
SIDETONE - FCCW
ANTI-VOX - FCCW
PWR, TUNE and ON button - IN
All Other Buttons - OUT
CAUTION: Never change bands when the TUNE button is IN.
- Advance LEVEL control and check for power output at the middle
of
the band and within 25 KHZ of the lower and upper band edges.
Panel
meter will read about 1 on the relative power scale; 1 watt
or greater
on the wattmeter. The meter should not deflect when the band-
switch is set to WWV.
- Release TUNE button and set the bandswitch to the next higher
band.
Check the output at the middle and each edge of all bands.
- Depress the ALC button and advance the MIC/CW LEVEL control.
The
ALC meter should show a full scale indication as the LEVEL
control
is advanced on all bands.
- Turn AF GAIN control to 9 o'clock and advance SIDETONE control
for
a confortable listening level.
10 Meter IF/PREDRIVER Filters Adjustments
- Set transceiver controls as follows:
BANDSWITCH - 28
ALC BUTTON - IN
- Connect dummy load to ANT jack.
- Tune the transceiver to 28.1 MHZ.
- During the following coil adjustments, the ALC indication will
vary
with the setting of the LEVEL control. Keep the meter reading
at
mid-range.
- After each coil is adjusted, turn the LEVEL control FCCW. The
ALC
meter indication must drop to zero.
- Refer to the pictorial below for the location of each coil on
the
TRANSMITTER IF/PREDRIVER board (C).
[[[Looking down at the this board, the 3.395 MHZ coil (L321) is at the
top of the board, far righthand side. The other coils are [reading from
left to right:
L309 [29.6], L310 [28.1]. L320 [29.6], L319 [29.1] and then and the
extreme right
edge, L321 [3.395 MHZ] ]]]
- Depress TUNE button and peak coil L310 [28.1 MHZ].
- Release TUNE button.
- Set bandswitch to 29 and tune to 29.1 MHZ.
- Depress TUNE button and peak coil L319 [29.1 MHZ].
- Release TUNE button.
- Set bandswitch to 29.5 and tune to 29.6 MHZ.
- Depress TUNE button and peak coils L309 and L320 [29.6 MHZ].
- Repeat the preceding steps until maximum output is obtained
across the 10 meter band.
- Release TUNE button.
CW Check
- Connect wattmeter and dummy load to ANT jack.
- Connect speaker to SPKR jack.
- Plug key into KEY jack. A positive voltage is present at this
jack so
the leads of any "grid block keyer" must be reversed.
- Set the controls as follows:
BANDSWITCH - 7
LEVEL - FCCW
PWR, VOX, CW and ON BUTTON - Depressed.
All Other Buttons - Released.
- Tune to 7000 KHZ.
- Close the key. The panel meter should read between 1/2 and 1
as
the LEVEL control is advanced.
- Adjust SIDETONE Control for a comfortable volume level.
P. A. Circuit Board Check
CAUTIONS:
1. Check that all five cables in the P.A. compartment are
properly
connected. If an error is make at this point, you may have to
replace
the four power transistors.
2. Whenever the transceiver is operated in both HI power and
TUNE,
the duty cycle requires an OFF period [receive mode] of five
times the
TUNE time. [Example: 10 seconds TUNED followed by 50 seconds
with
TUNE button released]. This must be carefully observed in the
following steps. Complete duty cycle information is given in the
"Operations" section of the SB-104 Operations Manual, Page 261.
3. Do not exceed 30 seconds in the HI power and TUNE modes.
4. Read the following nine steps before preoceeding to make the
P.A.
circuit board check.
- Set front panel controls as follows:
LEVEL - FCCW
BANDSWITCH - 7
VOX DELAY - FCCW
PWR, USB, HI and ON BUTTONS - Depressed
All Other Buttons - Released
- Connect a wattmeter and dummy load to the Ant Jack.
- Depress the TUNE button.
- In the following steps, turn the LEVEL control FCW only when
making a
check. Return the LEVEL control to the FCCW position after a
check is
made.
- Advance the LEVEL control. The panel meter should read above
12 on
the upper scale. The wattmeter should read 80 to 125 watts.
- Depress the ALC button. The panel meter should read not less
than
full scale.
- Rotate LEVEL control FCCW; ALC meter should read between no
deflection and 3.
- Release the TUNE button.
- Perform the preceding five steps at 20 through 10 meter
positios of
the band switch, being careful to observe the duty cycle. There
should
be no output at the WWV position.
- Perform the following 3.395 trap adjustment. Then, repeat the
last
five steps of the P.A. check at the 80M position.
3.395 Trap Adjustment
- Set the bandswitch to 3.5 and tune transceiver to 3500 KHZ.
- Depress PWR, HI and TUNE buttons.
- Turn the MIC/CW LEVEL FCW.
- Adjust coil L321 on the right side of the TRANSMITTER
IF/PREDRIVER
board (C) for a dip in the power output. Then adjust the coil
CCW until
the power output is 80 watts.
SWR "Power Down" Check
- Turn unit off.
- Interchange the IN and OUT plugs on the ALC/FILTER board (K).
- Depress the TUNE and ON buttons.
- Turn the LEVEL control CW.
- Output should be "powered down" considerably (Wattmeter should
indicate approximately 15 watts output).
- Reinstall the IN and OUT plugs in their proper jacks.
Carrier Suppression
Transceiver carrier suppression specification is 50 dB down from
100 Watts.
- Connect the wattmeter and dummy load to the ANT jack.
- Connect the microphone.
- Turn the bandswitch to 7.
- Turn the MIC/CW LEVEL FCCW.
- Depress the PWR, USB, HI and ON buttons. Other buttons
released.
- Connect an RF probe to the OUT jack of the ALC/FILTER board
(K).
- Key the transmitter with the PTT switch for short periods and
alternately adjust R666 and C649 on the CARRIER GENERATOR/XTAL
FILTER board (E) for the best possible null as indicated on the
VTVM.
Carrier suppression is within specifications if this voltage is
2/10 volts
or less when the power output in the HI power mode is 100 watts.
- Depres the LSB button. If the meter indiction is any higher,
make the
best possible compromise adjustment between USB and LSB.
ALC Metering Check
The operator of the transceiver is instructed to adjust the ALC
meter for
a total change of 6 units on voice peaks. Either low power
output or
sideband 'splatter' will result if 100% modulation does not occur
at the
6 unit difference point.
- Connect monitor scope [SB-614] and dummy load to the ANT jack
of
transceiver.
- Depress the PWR, VOX, CW and ON buttons.
- Depress the HI button and advance the LEVEL control only to
the point
where the meter reading ceases to increase. Note the height of
the CW
pattern on the monitor scope.
- Turn LEVEL control FCCW.
- Depress the HI, ALC, USB and ON buttons.
- Depress PTT switch on microphone.
- Speak into the microphone and advance LEVEL control until
voice
peaks obtain the same height as the CW signal. The peaks of the
signal shold be sharp, [giving a 100% Modulation Voice Pattern].
- The panel meter should indicate the total change of
approximately
6 units on voice peaks. Advancing the LEVEL control beyond this
point
should result in overmodulation [as indicated on the monitor
scope].
SERVICE HINTS
1. When connecting probes to a circuit for tests, connect the
ground lead of the probe as close as possible to the point of mesurement.
THis will minimize the signal pickup in a ground loop.
2. Check all coax cables used in the unit for proper grounding
of the shields. Tighten the hardware used to mount solder lugs on the
chassis and check the solder connection of each coax shield.
3. If the second harmonic content of the output signal in the
high power mode exceeds specifications, check for interchanged 100 ohm
and 10 ohm resistors on the P.A. circuit board.
4. To eliminate or confirm the ALC circuit as a cause of low
power output, connect a jumper wire between pin 5 of the transmitter IF
board and the 5 volt line. This will allow the transmitter amplifier
stages to operate at maximum gain, causing the output power to increase
to 175 watts. If a problem exists in the amplifier stages, the power
output will remain low. If the power output increases to 175 watts, this
would indicate a problem exists in the ALC circuits.
5. If power output is normal on the 10 through 40 meter bands,
but low on the 80 meter band, with the power output deceasing as you tune
from the high to the low end of this band, check for and remove a jumper
wire between lugs 2 and 3 of bandswitch S1C. This wiring error will also
cause C957 and C963 [25 uF electrolytics] on the P.A. board (H) to
overheat.
6. Each "S" unit on the S-Meter is approximately equal to 3 dB.
7. If the VFO frequency shifts when transmitting, check the 11
volt line for proper regulation (10.75 VDC; +/- .5V] and zener diode
ZD1201 for proper type [PN 56-19; 9.1V].
8. The VFO output voltage on 80 meters can be measured directly
with an IM-28 VTVM set to 1.5 VAC range. Approximately .5 RMS can be
measured at PL201, pin 1 (coax center lead).
--------------------------------------------------------------------------------------------------------------------
That's Part I, sorry it has taken so long but one has to work! - Enjoy,
and hope the
rest will follow shortly.
73 de JOE- - - - - - - - - - -W7LPF/4 (NNN0KUU)- - - - - - - - - - - - -
- -QWCA - NCVA - SOWP - FISTSGordonsville, Va 22942 (Orange
County)Looking for: Heathkit HR/HX-20, MR/MT-1,
Central Electronics 100V or 200V- - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - -
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