Heathkit Service Bulletins - SB104 [Part Three]
Joseph W Lutz
joelutz at JUNO.COM
Tue Oct 28 21:31:08 EST 1997
February 23, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-22
Harmonics And Suprious Radiations Near The Output Signal
The following changes to correct for undesired radiations should be made
to all units received for service:
Change: R955 .51
ohm to 475-12 Ferrite Bead
R956 .51 ohm to 475-12
Ferrite Bead
R329 4700 ohm to 12K ohm [See
SB-104-26]
L952 5 Turns to 4 Turns
L953 5 Turns to 4 Turns
To remove one turn from L952 and L953 (refer to Pictorial 11-7 in the
Assembly Manual), unsolder the leads at AB and AA, pull the wire end
through LF/LE and LA/LB, cut the wire to proper length, and resolder to
the foil at AB and AA.
To install the ferrite beads at R955 and R956 use lengths of buss wire
equivalent to 1 watt resistor leads.
------------------------------------------------------------------------------------------------------------------
February 23, 1976
SB-104 Bulletin No.
Solid State Transceiver SB-104-23
AC Hum With AF Gain AT Minimum
The hum coming from the speaker with the AF gain control at minimum can
be reduced by removing the blue and violet wires from the wiring harness
to the ON-OFF switch, and repositioning them as shown in the illustration
below.
The wires must be positioned as shown, and as close to the chassis as
possible. If a hum is still faintly audible, re-position the violet lead
as neeeded to eliminate the hum.
[[NOTE: The illustrations shows the Violet and Blue wires pulled out of
the harness/do NOT cut cable lacing/ 3" from the ON/OFF switch. The Blue
wire is positioned around [to the right] of the terminal strip and
connected to pin 6 then 5. The Violet wire is positioned under the
harness [to the right], then back again under the harness [to the left]
to be connected to pin 3 then 4.]]
-------------------------------------------------------------------------------------------------------------------
February 25, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-24
Spurious Radiation on 40 and 20
Meters
The following change should be made to all SB-104's received for service
to prevent RF being fed back into IF amplifier IC 301 through the ALC
line.
ADD: .01 uf [PN 21-176] from chassis pin C4 to nearest
ground lug.
" " " from chassis pin C5 to nearest ground
lug.
----------------------------------------------------------------------------------------------------------------
March 2, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-25
Power Drop-Off On 20 Meters
If power drops off on the 20 Meter band after a period of on-and-off
keying, and then returns again after the unit has been shut down for a
while, the problem may be caused by dielectric heating of the ferrite
bead at the junction of L316 and anode of D328.
If this problem occurs, change the ferrite bewad to a 100 ohm [PN 1-1-12]
resistor.
-------------------------------------------------------------------------------------------------------------------
March 9, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-26
Harmonics and Spurious Radiations Near The Output
Signal
Bulletin SB-104-22 called for changing R329 on the "C" board from 4.7K to
15K. This value has been changed to 12K [PN 1-14-12].
--------------------------------------------------------------------------------------------------------------------
March 9, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-27
High Level 3395 Khz Spur on 80 Meters
A high level spur at 3395khz may be present in some units due to
incorrect tuning of the 3.395Mhz trap on the transmit IF board. This
problem can be avoided by removing the old 3.395 trap on the transmit IF
"C" board, and installing a new trap as follows:
1. Remove and discard L321 and C348.
2. In the Le21 circuit board holes near the top edge of the
board install an 8-40 pf [PN 31-76] with the slotted side toward the top
edge of the board.
3. In the next lower set of holes, install a 150 pf [PN 20-149]
capacitor. Do NOT use the holes screened for C348.
4. Next, install a 13.25 uH [PN 40-1877] coil at C348.
5. Remove circuit board D, and pre-set the front panel controls
to the 3.5 mhz band, MIC/CW Level control full counterclockwise.
6. Put the meter in the POWER position, depress the HI and TUNE
pushbuttons.
7. Turn the MIC/CW Level control full clockwise. Adjust the
8-40pF trimmer for a minimu [null] on the power meter.
8. Turn off the unit, and reinstall circuit board "D".
--------------------------------------------------------------------------------------------------------------------
March 9, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-28
Skewed Receiver Response On 80 Meters
A number of units tested by Engineering have shown the 80 meter bandpass
response to be skewed toward the low end because of the tuning response
of the tuned circuits and trimmer capacitors. To correct for this skewed
response, make the following changes:
FROM TO
Change: C703 130 pF 105 pF [PN 20-162]
C707 130 pF 105 pF [PN 20-162]
C764 1-8 pF trimmer 8-40 pF [PN 31-76]
C769 1-8 pF trimmer 8-40 pF [PN 31-76]
Remove and discard: C763 5pF
Realign the receiver according to the manual.
--------------------------------------------------------------------------------------------------------------------
March 18, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-29
Springs Simplify Cabinet Installation
An often encountered problem after servicing SB-104's and other units
using the two-piece wrap-around cabinet with side rails is keeping the
side rails and the #10 flat washers separated.
If the PN 258-53 springs are cut in half and slipped over the threads of
the #10 mounting screws, the #10 flat washer wil be compressed against
the cabinet sides and the cabinet halves can be easily installed.
If the cabinet retainer does not clamp the cabinet halves securely,
remove turns from the spring until a good fit is made.
-----------------------------------------------------------------------------------------------------------------
March 23, 1976
SB/HW-104 Bulletin No:
Solid State Transceiver SB-104-30
Spurious Responses on Ten Meters
Some of the high level spurious responses found on ten meters is due to
the high VFO injection which occurs when the VFO attenuator pad is
bypassed on transmit. This should be corrected in all SB-104's received
for service by clipping out the 1000 ohm resistor at R1251.
This change keeps the attenuator pad and VFO filter in the circuit at all
band switch settings by disabling switch transistor Q1251.
In addition to this change, put four large ferrite beads [PN 475-12] on
the grey lead from chassis connector pin K5 to lug 8 of the relay. Glue
ferrite beads to chassis with PN 350-12.
------------------------------------------------------------------------------------------------------------------
March 24, 1976
SB/HW-104 Bulletin No:
Solid State Transceiver SB-104-31
Improved Sensitivity
The following change should be made to all SB-104's received for service:
Remove and discard L733
Remove and discard C787
This change eliminates the series resonant circuit from the colector of
Q703 to ground, and improves the performance of the PN 40-1875 coil at
L734.
-------------------------------------------------------------------------------------------------------------------
March 24, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-32
Improved +11 Volt Regulation
The 680 oh, 5% resistor at R254 [See Bulletin No. SB-104-12] may not work
well in all cases. When the +11 volt buss is found to be low, R254
should be replaced with a 750 ohm, 5% resistor [PN 1-96].
This bulletin does not apply to the HW-104, since all production units
have the 750 ohm resistor installed at R254.
-------------------------------------------------------------------------------------------------------------------
April 9, 1976
SB-104/HW-104 Bulletin No:
Solid State Transceiver SB-104-33
Product Improvements
Low Power On All Bands
Select R-332 with a D.V.M. to 1.2K 1% or slightly higher. Future runs
will use a 1% resistor. The part when speced in will be assigned a new
number. Keep in mind, the power spec is 80-125 watts. Too much power
can cause additional problems. An ideal performance would be 100 W on all
bands.
Carrier Suppression
Carrier suppression can be improved, if there's ample power on all
bands, by lowering the value of R314[1K] to as low as 390 ohm.
The carrier balance adjustment can be accurately made by watching the "S"
meter on another receiver tune to frequency and adjusting for minimum
reading. Couple the receive antenna to the SB-104 to provide an adequate
reading. Also, see Bulletin No. SB-104-19.
Unstable And Excessive Harmonic And Spurs 15 & 10 Meters
ALC Board
If the SB-104 has been oscillating for some reason, theres a
possibility coils L801, L802 and L803 have been overheating. There will
be no physical sign of this now. Direct replacement cures the problem.
Driver Board
The Driver Board mounting holes (3) do not have the solder resist
cleared for secure grounding when the hardware is installed. Each board
must be disassembled, solder resist cleaned from around the holes, tinned
and reassembled. If the transistors have been oscillating on this board
they will probably be getting hot as a sign now. They must be replaced.
C Board
When first keyed a spur occurs due to late ALC action. Remove
C322 on ALL SB-104's serviced.
If one band has more output than others and you suspect spurs,
change any one [or more] of the corresponding output resistors R337,
R339, R343 or R345 to 100 ohms [PN1-1-12]. The most likely one is 40
meter R343.
Chassis
The four ferrite beads in Bulletin No. SB3-104-30 should be
cemented down with the same cement used for the coils [PN 350-12]. This
is for mechanical reason only.
Low Sensitivity
G Board
To improve the 80 meter sensitivity, change L734 to PN 40-1726.
Remove 2 turns before installing this coil. Future runs will have a coil
for this location with its own part number. When it's available, you
will be advised.
In the first 3 runs, the coils were not color coded. We also
find, many of these coils in the B,P,F,S, are below Q spec. If you have
a sensitivity problem change to the new number. 80 to 10 meters is
usually the more difficult ones to meet spec.
New 10 M coil [PN 40-1875 (Red)]
New 80 and 40 M coils [PN 40-1882 (White)]
The new numbers are found in the most recent manuals. Also a
cross reference is in the HW-104 service data book. Also suspect the (3)
8.65 MHz B.P.F. coils [PN 40-1805].
E Board
Remove R613
Change R619 from 560 ohms to 100 ohm [PN 1-1-12].
--------------------------------------------------------------------------------------------------------------------
April 21, 1976
SB-104/HW-104 Bulletin No:
Solid State Transceiver SB-104-34
Trimmer Capacitors Tune Full Open
The 40M and 15M bandpass filter trimmers C718 and C741 usually trim fully
open, preventing proper tuning of the filter and reducing sensitivity.
Make the following changes in all SB-104/HW-104's received for service.
Change: C719 30 pF s.m. to 24 pF s.m. [PN
20-77]
Remove and Discard C742 3.9 pF disc.
The capacitor plates in the square black trimmers are indicated by the
indented and raised spots on the capacitor body -- the capacitor is fully
meshed when the indented and raised spots are closest to each other.
-----------------------------------------------------------------------------------------------------------------
April 21, 1976
SB-104/HW-104 Bulletin No:
Solid State Transceiver SB-104-35
Low Sensitivity On 10M and 15M, Other Bands OK
In cases of reduced sensitivity, bypassing the 8.65 MHz band reject
filter located under the chassis should result in an increase of not more
than 1 db on 10M and 15M. Check the series and shunt torroids by pulling
them slightly away from the terminal strip and re-checking the filter
attenuation. A noticeable improvement in signal-to-noise ratio indicates
the insulating formvar on the torroid windings had been broken at point
of contact.
-----------------------------------------------------------------------------------------------------------------
April 22, 1976
SB-104 Bulletin No:
Solid State Transceiver SB-104-36
Incorrect Wires In Harness
Wiring Harness [PN 134-887] should have a WH/BR/BR wire and a WH/BR wire
coming from BO#1 and BO#4. In kits with series number 05551 harnesses
were found with two WH/BR/BR wires or two WH/BR wires at these breakouts
causing the unit to be wired incorrectly. SB-104 store stock with this
series number should be checked for the correct wires in this harness.
Factory stock is being corrected.
-------------------------------------------------------------------------------------------------------------------
Okay gang - next one is quite long, and it is after 10 - have to get up
at 4AM and didn't get to bed until 5AM this morning - so will continue
this weekend after I get off work. Ciao!
73 de Joe W7LPF/4 [NNN0KUU]
QWCA - SOWP - NCVA - FISTS - RCC
Gordonsville, Va 22942 [Orange Co]
--- --- --- --- --- --- --- --- --- --- --- --- --- --
To subscribe: listserv at listserv.tempe.gov
and in body: subscribe HEATH yourfirstname yourlastname
To unsubscribe: listserv at listserv.tempe.gov
and in body: signoff HEATH
Archives for HEATH: http://www.tempe.gov/archives
--- --- --- --- --- --- --- --- --- --- --- --- --- --
More information about the Heath
mailing list