January 3, 1975SB-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 TuneMode 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:Soli