Tait T850 II Series, Service Manual

Page: 272 / 370

D4.8 T858/859 Fault Finding
M850-00
31/09/98 Copyright TEL
4.6 Fault Finding Charts
4.6.1 T858 PA
Key exciter.
Is input power
to PA >0.7W? Repair exciter.
Remove lead #2 of wireline
L19 from PCB and replace
with flying lead into
power meter.
N
N
N
N
Y
Y
Y
Y
Check for shorts on base of Q1,
chips, input matching components
and input pad.
Check for shorts on Q4 base.
Check Q3 collector voltage.
Check CV32.
Check Q4 collector voltage.
Check Q3 & Q4.
>9.6V RF present
at base of Q1?
>3.5V RF present
at base of Q3?
Check for Unelco shorts at base
or around chips. Check CV8.
Check Q3 collector >13V.
Check Q16 & Q15. Check
IC1 pin 8 is high (>12V).
Check input voltages
on IC1 pin 10.
Q4 output
power >20W?
Replace lead #2 of L19.
Remove leads #2 & #4
of wireline L39 and replace
with flying leads: one to a
wattmeter & one to a 50 ohm
load (or second wattmeter).
Replace leads #2 & #4 of L39
PA OK.
N
N
N
Y
Y
Y
Check for shorts on Q6 base,
CV35 & CV51. Check wireline
L19 & Q6.
Check for shorts on Q7 base,
CV34 & CV57. Check wireline
L19 & Q7.
Q6 output
power >35W?
Q7 output
power >35W?
PA output
power >60W?
Check wireline L19.
Check diplexer &
low pass filter
(*L45, *L46, *L47,
*L42, *C66, *C70).
Check R90/R91
and matching.