Tait T855 - Page 190

C5.14 T856/857 Fault Finding M850-00
31/09/98 Copyright TEL
Y
N
Y
Y
Correct DC V
present on Q1 VCO?
N
Check inductors,
biasing resistors
& Q1.
Replace if faulty.
Go to B.
Loop filter &
components around
op. amp. (IC750) OK?
N
Noisy synth;
poor residual FM.
C
Isolate audio
modulation on VCO;
still noisy?
Trace audio fault.
Y
Y
N
Y
Y
Y
Change trimmer;
still noisy?
Change Q1;
still noisy?
Change TCXO;
still noisy?
Change varactors;
still noisy?
Replace VCO
assembly.
Synthesiser OK.
N
N
N
N
Y
VCO phase locked?
3-16V present on
control line?