Tait Limited TEL0024 用户手册

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Programming and 

serial bus OK?

Check programming.

Check serial bus

when programming

i.e. clock/data/enable 

activity (IC740 pins

18, 19 & 17).

N

Check loop filter components

R775, C774, C776, R510,

C505, IC750. Is the supply

to IC750 +20V +4, -2V?

Check regulator circuitry.

Check C772, R774, R772,

C770, R763 & Q790.

Check Q760, Q780,

R766 & C765.

Check charge pump components

(Q775 & Q780) and Q790. 

Check R762 & C762.

Check the signal path from 

the VCO to synthesiser. 

Measure the frequency from

the VCO at IC740 pin 11 using

a frequency counter.

Is the level >-10dBm?

Does the frequency adjust

as the VCO trimmer is 

adjusted (out of lock)?

Check VCO.

Y

Y

Y

Signal

Y

Y

Y

No signal

Replace synthesiser

(IC740).

Y

N

Y

Y

N

N

N

N

Check phase detector output

pins (IC740 pins 3 & 4).

Are there very narrow pulses

(~50ns) at the reference frequency?

(i.e. 5kHz : 200µs period

   6.25kHz : 160µs period)

*See Note below.

Is the charge pump bias

voltage at the base of 

Q760 & Q780 between 

3.5 and 5V? (5V when locked)

N

Is the voltage on C762,

R760, and R758 9V ±0.2V?

Is the loop filter reference 

voltage at C772 (+) 6.5V ±0.2V?

N

Check divider buffer

circuit (Q795) and bias

voltages on Q795 emitter

(1.3V ±0.2V).

*Note:
When locked, both of these
are very narrow (~50ns).
If unlocked, one will be
very narrow (~50ns),
and the other wide (>15µs).

Replace synthesiser

(IC740).

Continued from previous page

   B

Is the charge pump voltage

on Q790 gate between 

3 and 8.5V? (6.5V ±0.2V locked)

Is reference

clock present

at IC740 pin 20

(200kHz >4.5Vpp)?

Check microcontroller

section (IC810).

N

Is reference

clock present

at IC730 pin 12

(200kHz >4.5Vpp)?

Is reference

clock present

at IC730 pin 1

(12.8MHz >4.0Vpp)?

Check TCXO (IC700)

and buffers (IC710).

N

N

Y

Y

Check phase

modulator sections:

IC720, Q710, Q720,

D710, Q730, Q740,

D720.

Check divider

IC730.