Heathkit Service Bulletins: HW-104 [1966-1989] Complete
Joseph W Lutz
joelutz at JUNO.COM
Wed Jan 27 21:28:05 EST 1999
December 4, 1975
HW-104 Bulletin No:
Solid State Transceiver HW-104-1
Receiver Inoperative
Check for and remove the shorting wire at FET's Q701 and Q704. These
part number 417-274 FET's are now being shipped with a shorting wire on
the leads.
--------------------------------------------------------------------------------------------------------------------
January 29, 1976
HW-104 Bulletin No:
Solid State Transceiver HW-104-2
Low Sensitivity and Spurious Products
Complaints of low sensitivity and/or spurious products may be due to [PN
56-56] diodes being supplied in the kit instead of the [PN 56-24]. The
[PN 56-24] diode is Blue, and may have "56-24" stamped on the diode body.
The [PN 56-56] is Orange-Red and usually has "1N4149" stamped on the
diode body, or a small "H'.
A quick inspection of the receiver front-end board can determine if
incorrect diodes were supplied in the kit; all the diodes on the board
should be Blue [PN 56-24].
This problem may occur in other kits, and should be watched for.
--------------------------------------------------------------------------------------------------------------------
February 23, 1976
HW-104 Bulletin No:
Solid State Transceiver HW-104-3
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.
((Illustration shows blue and violet wires broken out of the wiring
harness approx 3" from the ON-OFF switch. The Blue wire is positioned
going to the right where it will go around the terminal strip and then
directly to pin 6 of the switch. The violet wire is taken UNDER the
wiring harness then brought back [in a 'S' fashion to where it will be
connected to 3&4 of the switch.]))
The wires must be positioned as close to the chassis as possible. If hum
is still faintly audible, re-position the violet lead as needed to
eliminate the hum.
((Note: When taking the violet and blue wires from the harness, DO NOT
cut cable lacing - just pull from the harness.))
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February 23, 1976
HW-104 Bulletin No:
Solid State Transceiver HW-104-4
Harmonics & Spurious 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
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 25, 1976
HW-104 Bulletin No:
Solid State Transceiver HW-104-5
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.
.01 uf [PN 21-176] from chassis pin C5 to nearest ground
lug.
See Bulletin No. SB-104-24 dated February 25, 1976.
------------------------------------------------------------------------------------------------------------------
March 2, 1976
HW-104 Bulletin No:
Solid State Transceiver HW-104-6
Power Drop-Off on 20 Meters
If power frops 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 bead to a 100 ohm [PN 1-1-12]
resistor.
--------------------------------------------------------------------------------------------------------------------
March 16, 1976
HW-104 Bulletin No:
Solid State Transceiver HW-104-7
Harmonics & Spurious Radiations Near the Output Signal
Bulletin HW-104-4 called for changing R329 on the "C" board from 4.7K to
15K. This value has been changed to 12K [PN 1-14-12].
//Note: I have already corrected the 104-4 value//
-------------------------------------------------------------------------------------------------------------------
March 16, 1976
HW-104 Bulletin No:
Solid State Transceiver HW-104-8
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 L321 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 minimum (null) on the power meter.
8. Turn off the unit, and reinstall circuit board "D".
-----------------------------------------------------------------------------------------------------------------
March 16, 1976
HW-104 Bulletin No:
Solid State Transceiver HW-104-9
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 130pF 105 pF [PN 29-162]
C707 130pF 105 pF [PN 29-162]
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.
----------------------------------------------------------------------------------------------------------------
October 10, 1977
HW-104 Bulletin No:
Solid State Transceiver HW-104-10
Audio Level Control of Receiver Does Not Completely Reduce
Volume
Volume is reduced but still quite audible with fully CCW setting. This
is usually accompanied by moderate talkback through the speaker when
transmitting with reactive termination. This is usually caused by
fracturing or warping of the Volume control when the control is mounted
to the front panel. A control solder lug is soldered to a control pin
before mounting; as the control is tightened to the front panel, this pin
flexes-facturing the resistor element. The control lug should be
soldered after mounting to prevent this when replacement is required.
------------------------------------------------------------------------------------------------------------------
November 9, 1984
HW-104 Bulletin No:
Solid State Transceiver HW-104-11
Power Drops Off On 20 Meters While Transmitting
If the power drops off while transmitting, especially in the CW mode,
make the following change.
On the driver board, change:
C909 from a .01 uF capacitor to a .002 uF capacitor [PN 21-36].
-----------------------------------------------------------------------------------------------------------------
April 28, 1989
HW-104 Bulletin No:
Solid State Transceiver HW-104-12
Sidetone Modulates Carrier
When the sidetone modulates the carrier, especially when the VOX control
is FCCW, check for a shorted diode at D3 [PN 56-56] on the chassis.
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*******ATTENTION**************ATTENTION************ATTENTION*******
After 3/16/76 all bulletins which are applicable to both the SB-104 and
the HW-104 will be listed only in the SB-104 Bulletin Section. The model
number at the upper left corner will be written as SB/HW-104 when the
Bulletin applies to both models. Bulletins that apply only to the HW-104
will be in this section.
Because of the similarity of circuits used in the HW-104 and SB-104, you
should refer to previously issued bulletins on the SB-104 when servicing
the HW-104. Many of the service hints and modifications listed are
applicable to the HW-104.
------------------------------------------------------------------------------------------------------------------
That's all that is shown for HW-104 [1966-89]. Enjoy!
------------------------------------------------------------------------------------------------------------------
73 de Joe W7LPF/4 [NNN0KUU]
QWCA - SOWP - NCVA - FISTS - RCC
Gordonsville, Va 22942 [Orange Co]
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