Heathkit Service Bulletins - SB-104 (Part 7 & Final)
Joseph W Lutz
joelutz at JUNO.COM
Sun Nov 2 20:57:04 EST 1997
November 20, 1978
SB/HW-104(A) Bulletin No:
Solid State Transceiver SB-104-76
Excessive 15 Meter HFO Signal At Antenna Jack In HI-Power
Mode
Check to see if the ground foil located on the "C" board, between Q-302
and Q-303, is cut. If so, reconnect the cut ground foil. This foil
should not be cut when installing modifications in this unit. Bulletin
SB-104-54 and SBM-104-2 had instructed the technician and customer to cut
the foil on the "C" board. Please cross out this step in SB-104-54.
This step is also being removed from the instructions for mod kit
SBM-104-2.
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November 28, 1978
SB/HW-104(A) Bulletin No:
Solid State Transceiver SB-104-77
Burst Of RF On 10 Meter Band When Transmitter Is Keyed
With PTT On SSB
A burst of 100 watt RF on the 10 meter band exists when the transmitter
is keyed with PTT on SSB. This is caused by Q-601 remaining on too long
due to the long discharge time of C-608. Thus Q-601 is still on when
Q-602 turns on. On 10 meters, a signal of approximately 3395 kHz appears
to be generated at the front end board and is amplified by the still
turned on Q-602, passes through Q-602 to the input of the transmitter IF
board where it is amplified and heterodyned to the 10 meter band. Here
it is amplified again and passed to the driver and PA.
The solution is have Q-601 turn off before Q-602 turns on. To do this,
remove the wire from chassis connector pin E3 to E11. Now, connect a
wire from E3 to C7.
Since the newer SB-104A front end board [G] has higher gain, this problem
may only exist in the "A" model units, but willnot show up in all of
them. It can show up in both high and low power and is dependent on the
gain of the various circuits involved.
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November 28, 1978
SB/HW-104(A) Bulletin No:
Solid State Transceiver SB-104-78
Update Of SBM-104-2 Modification Kit
The instructions given on page 13 of the Modification Manual [PN
595-2016-0 through -03] for cutting the ground foil on the "C" board
should be deleted when installing the PN 830-24 modification kit.
The 360 pF mica capacitors installed on page 19 of the same manual should
not be installed, especially if a clearance problem exists between the
foil side of the circuit board [PA], and the metal heat sink plate. The
-04 edition of the manual [PN 595-2016] has deleted this instruction. If
the capacitors are already installed and no clearance problem exists,
leave them installed.
------------------------------------------------------------------------------------------------------------------
November 28, 1978
SB/HW-104(A) Bulletin No:
Solid State Transceiver SB-104-79
PA Board Oscillations
It has been found that the PA board oscillates at approximately 27 MHz in
high power position on all bands, including 15 MHz withthe microphone
gain turned counterclockwise and in TUNE position.
This is caused by an open connection between the phone plug shield and
the coax cable shield of the power amplifier output cable. Check for
proper connections at these points.
Also, 3.5 MHz and 7.0 MHz bands oscillate at approximately 21 MHz with
the same conditions listed above.
This is caused by open connections from the phone plug shields to the
shields of the coax cables to the ALC/Filter board. Check for proper
connections at these points.
-----------------------------------------------------------------------------------------------------------------
December 11, 1978
SB/HW-104(A) Bulletin No:
Solid State Transceiver SB-104-80
Burst Of RF When PTT Is Released In SSB Mode
This burst of RF when the PTT is released can occur on all bands. Three
causes of this are:
1. A spike on the audio output of board B caused by the +RX mute voltage
applied to pin 2 of IC201B through R212. The solution is to let IC201B
remain active all the time. This is done by connecting R212 to ground
instead of Q-205's collector.
2. The rapid rise of the voltage on the PTT line. This is coupled to
the input of IC201A through the stray capacitance at the MIC connector.
Installing a .05 uF capacitor from B8 to ground slows the rise time
enough to prevent this coupling.
3. The transmitter is keyed for the first time after power is first
applied to the unit. The application of power to the unit causes a
charge to build up on C-646 which, in turn, causes a short burst of
carrier output when the balanced modulator is driven with a signal from
the carrier oscillator. Subsequent keying will not produce the burst.
Installing a 6.8K ohm resistor [PN 6-682-12] across C-646 will allow it
to discharge. Then perform the carrier null adjustments.
To prevent the RF burst, make the following changes:
- Remove the jumper connecting R-212 to Q-205 collector. Connect R-212
to ground.
- Install a .05 uF capacitor [PN 21-143] from B8 to ground.
- Install a 6.8K resistor [PN 6-682-12] across C-646.
--------------------------------------------------------------------------------------------------------------------
March 20, 1979
SB-104A Bulletin No:
Solid State Transceiver SB-104-81
Q-603 Oscillates
If the circuit of Q-603 oscillates, it may be caused by a too-high input
impedance of some of the PN 417-274 FETs at Q-501 on the Receiver IF
circuit board. This problem is apparent when the AGC is off and the RF
gain is varied. To correct the problem, replace Q-501 [PN 417-274].
--------------------------------------------------------------------------------------------------------------------
August 27, 1979
SB-104A Bulletin No:
Solid State Transceiver SB-104-82
Inconsistent Readout On 10 Meters
In November and December of 1978, a number of SB-104As, Series No. 04840,
were produced with a wrong transistor installed. Two hundred "D" boards
may have a 2N2102 instead of a 2N3866 transistor installed.
To correct, replace: 2N2102 with a 2N3866 [PN 417-205].
--------------------------------------------------------------------------------------------------------------------
September 20, 1979
SB-104A Bulletin No:
Solid State Transceiver SB-104-83
21 MHz Bandpass Filters On TX IF Difficult To Bring To Specs
On Edges Of Band
Change C-356 to 5 pF ceramic disc capacitor [PN 21-78]. This will
broaden the response on the bandpass filters before the redrivers. It
will also reduce the spurious compoonents on the output.
Make this change on an "as-needed" basis only.
-------------------------------------------------------------------------------------------------------------------
November 19, 1979
SB-104-84 Bulletin No:
Solid State Transceiver SB-104-84
Obtaining A more Logarithmic S-Meter Response
The S-meter in most units is largely insensitive to plainly audible
signals, while allowing slightly louder signals to peg the meter [with
R-534 set for an S9 meter reading at 50 microvolt signal at the antenna
connector]. To provide a more logarithmic response, perform the
following:
- Replace ZD-502 with a 1N191 signal diode [PN 56-26]. Install this
diode
opposite that shown on the circuit board, so that it is forward-biased
[cathode
towards R-534].
- Set R-534 to S9 with a 30 microvolt signal.
The meter will register slightly more accurately from S9 to =30 but will
have little or no action above +40.
Perform this modification only if the customer specifically complains of
this problem.
-----------------------------------------------------------------------------------------------------------------
Okay gang - that is what I hold on fiche for the SB/HW-104(A). I am
sorry that it has taken me so long in getting it out - I didn't know that
there was such a demand for info on this unit - guess I will have to find
one for my own use now. I will now resume in putting out these rest that
I hold, and re-posting the ones that have been requested. 'Keep those
Greenies Going' Ciao!
73 de Joe W7LPF/4 [NNN0KUU]
QWCA - SOWP - NCVA - FISTS - RCC
Gordonsville, Va 22942 [Orange Co]
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