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May 20, 1971

HD-10 Electronic Keyer

Bulletin No: HD-10-1F

Transistor Socket Problem

A vender change on stock are being co with this incorrec

this four-pin socket makes it unusable. All units in rrected - - but a run of HD-10 units has been shipped t socket.

An insert is being

transistors

direct

this part.

Any fu

prepared advising the customer to solder the ly to the circuit board---eliminating the need for ture production will not use this part.

Please advise any install transistor problem when servi ------------------

customer purchasing an HD-10 to discard the sockets & s directly on the circuit board. Also, watch for this cing the HD-10. ------------------------------------------------------

HD-10 Electronic Keyer

MAY 23, 1974 Bulletin No: 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 are at rest.

checks the circuits for In this condition, each

proper bias voltages while they multivibrator has one transistor

cut off and the other saturated, the clamp transistors are all

saturated, and the switch The following transistors

rest:

Q1,

Q3,

Q5,

Q6,

Q9

tansistor and its will be saturated and Q11.

driver are both cut off. while the circuits are at

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 emitter 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, slightly positive for NPN transistors, and slightly negative for PNP transistors.

2. Remove Q11. audio circuitry

Now the audio tone should

works.

Replace

Q11.

be

on,

indicating

that

the

3. Ground the hand key terminal. Q1 is working, and the transmitter

A tone should

should be heard, showing that key, indicating that Q8 is

working.

Remove

the

ground.

4.

Remove

Q5.

A

tone

indicates

that

Q7

is

working.

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