May 20, 1971 HD-10 Bulletin No: Electronic Keyer HD-10-1F A vender change on this four-pin socket make it unusable. All units in stock are being corrected - - but a run of HD-10 units has been shipped with this incorrect socket. An insert is being prepared advising the customer to solder the transistors directly to the circuit board---eliminating the need for this part. Any future production will not use this part. Please advise any customer purchasing an HD-10 to discard the sockets & install transistors directly on the circuit board. Also, watch for this problem when servicing the HD-10. ------------------------------------------------------------------------------------------------------------------ MAY 23, 1974 HD-10 Bulletin No: Electronic Keyer HD-10-1 Service Guide HD-10 Keyer The following steps are a troubleshooting sequence you can use to isolate each stage of the keyer and check its operation. It is difficult to check circuits when the keyer is in operation because voltages change rapidly. With this troubleshooting sequence, you can stop the keyer action in each state of operation to check voltages and other circuit conditions. After you pinpoint the area of trouble, check all parts and connections in the associated circuitry. 1. Measure voltages at the points shown in figure 9 on page 32 of the manual. This checks the circuits for proper bias voltages while they are at rest. In this condition, each multivibrator has one transistor cut off and the other saturated, the clamp transistors are all saturated, and the switch tansistor and its driver are both cut off. The following transistors will be saturated while the circuits are at rest: Q1, Q3, Q5, Q6, Q9 and Q11. The following conditions exist when a transistor is cut off: No collector current flows; the collector voltage will be nearly at the supply voltage; and the base will be biased negatively with respect to the emittor for NPN transistors [2N2712], or positively for PNP transistors [2N407 and 2N398A]. The following conditions exist when a transistor is saturated: its collector voltage will be nearly the same as its emitter voltage; if the voltage between the emitter and base is measured, the base will be biased toward the supply voltage, silightly positive for NPN transistors, and slightly negative for PNP transistors. 2. Remove Q11. Now the audio tone should be on, indicating that the audio circuitry works. Replace Q11. 3. Ground the hand key terminal. A tone should be heard, showing that Q1 is working, and the transmitter should key, indicating that Q8 is working. Remove the ground. 4. Remove Q5. A tone indicates that Q7 is working. 5. Measure the emitter-to-base voltage of Q6. A base reading of about 2 volts negative to the emitter indicates that Q6 is receiving the dash-completion voltage. 6. Ground the base of Q2. Measure the base-to-emitter voltage of Q3. A reading that shows the base is about 1 volt negative with respect to the emitter indicates proper dash-completion voltage from Q5 to Q3. Replace Q5. 7. Ground the base of Q2. Momentarily ground the base of Q5: This should cause the tone to go on and stay on until the base of Q4 is momentarily grounded. This indicates that the flip-flop multivibrator is working. Remove the ground from the base of Q2. 8. Momentarily ground the base of Q5. A short-duration tone signal indicates that the completion circuitry is working. 9. Remove Q1. the tone should be heard, indicating that the dot signal is reaching Q7. 10. Measure the base-to-emitter voltage of Q3. a reading that shows the base is about 2 volts negative with respect to the emitter indicates that proper dot-completion voltage is reaching Q3. Replae Q1. 11. Remove Q3. Dots should be heard, indicating that the dot generator is working. 12. Remove Q6. Dashes should be heard, indicating that the multivibrators are all working. Replace Q3 and Q6. 13. Measure the base-to-emitter voltge of Q3, with the paddle at the dots position. This voltage should show that the base is about 4 volts negative, indicating proper dot keying. 14. Measure the base-to-emitter voltage of Q6, with the paddle at dots. the base voltage should remain positive with respect to the emitter. 15. Measure the base-to-emitter voltage of Q6, with the paddle at dashes. The base voltages at both Q6 and Q3 should show that these bases are about 5 volts negative with respect to their emitters, 16. Note: It may also be helpful to refer to the oscilloscope waveforms in the circuit description, Similar waveforms would be obtained in your keyer if an oscilloscope with good low-frequencey response is available. The oscilloscope must be capable of fast rise-time to see the trigger pulse shown in figure 14, since this pulse is extremely short. A 10:1 divider probe should be used with the oscilloscope to avoid loading the trigger pulses with cable capacitance. ----------------------------------------------------------------------------------------------------------------- January 24, 1975 HD-10 Bulletin No: Keyer HD-10-2 Improper Grounding When servicing a keyer that is inoperative, check for proper grounding at: 1. The on-off switch. 2. The two ground lugs on the chassis rear panel. 3. The phone jack on chassis rear panel. Be sure all hardware at these points is secure. ------------------------------------------------------------------------------------------------------------------- Thats everything I hold up to 1985 that covers the HD-10 Keyer. -------------------------------------------------------------------------------------------------------------------