HEATHKIT SERVICE BULLETINS - CONT.
Joseph W Lutz
joelutz at JUNO.COM
Wed Jun 18 20:59:49 EDT 1997
May 20, 1971
HD-10 Bulletin No:
Electronic Keyer HD-10-1F
A vender change on this four-pin socket make it unuable. 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.
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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 cehck 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 prober 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 Q1!. Now the audio tone whould be on, indicating that the
audio circuitry works. Replace Q11.
3. Ground teh 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.
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Thats everything on the fiche I hold that covers the HD-10 Keyer.
--
73 de JOE
- - - - - - - - - - -W7LPF/4 (NNN0KUU)- - - - - - - - - - - - - - -
QWCA - NCVA - SOWP - FISTS
Gordonsville, Va 22942 (Orange County)
Looking for: Heathkit HR/HX-20, MR/MT-1,
Collins 516F-2, 312B-4, EFJ TR Switch
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