External Input - Philips PM3055 Service Manual

4 -2
The imped ance conver ter s e r ve s a s an inve r t ing buf fe r c ircuit for
the h 1 gh 1mpedance at tenuator. For the l .f.- fe edback the output s i gna l
o f this s tage i s routed to the l .f . s ummat ion po int N 1 0 0 1 -2 .
The l ow impedanc e a t tenua tor r educ e s the gain b y x1 , x2 .5 and x5 ,
depending on wh i ch r e l ay i s ac t i va t ed .
x1
x2.5
x5
The c ont inuous c ircu i t ( OQ0 203 ) , the d i fferen t ia l input vo l t age s of
which are fed to p ins 4 and 5.
Th i s s t age c ompr i s e s the fo l lowing func t ions :
- Cont inuou s ly vari ab le control ( pin 1 1 ) .
Gain x1 ( pi n 2 and 3 ) wi th o f fset ad jus tment R1 064 ( R1 1 64 ) and gain
adjus tment R1069 ( R1 1 6 9).
Gain x1 0 ( pi n 6 and 7 ) with o ff se t ad jus t ing R 1 0 7 2 ( R1 1 7 2 ) and gain
ad jus tment R 1 0 7 6 ( R1 1 7 6).
- x1 / x 1 0 control , ( pin 1 0 ) t o sel ect the 2 , 5 and 1 0 mV/DIV s e t t ings .
The d i f fe rent i al output c urrent from p in 1 3 and p in 1 4 i s rout ed via a
c ommon-ba s e c i rcui t V 1 06 3 , V1 064 and app l ied to the pre-ampl i fier uni t .
4. 2

EXTERNAL INPUT

The ext ernal input c an b e s ub d i vided into four s t age s :
Input coupl ing , b a s ic al ly s im i l ar to the ch.A input coupl ing.
�i gh impedance a t t enua tor for the x1 a t t enuator only , whe re the l .f.
s quare-wave c an be adjus t ed with trimmer C 1 2 06. The l .f. part i s routed
to the s ummat ion po int N 1 2 0 1 - 2 . R1 2 1 7 serve s as an o f fse t compensat ion
for N 1 2 0 1 . For l .f.- feedback the output of the impedance converter i s
a l so rout ed to th i s s umma t ion po int.
Note that the output o f this s t age i s a l so a recons t i tuted ve rs ion of
the input s i gnal .
Impedance c onve r t er , 1 s b a s ic s im i l ar t o the ch.A impedance
conve rter.
The d i f fe r ent ial ampl i fier V 1 2 1 1 , V 1 2 1 2 conve r t s the vo l tage from
emi t te r- fo l l ower V 1 2 09 into the d i f ferent i al c ur rent s i gnals EXT+ and
EXT-. Th i s s ignal is appl i ed to the pre-ampl i fier uni t and serve s a s
e xternal t r i gger s i gnal or as an e xternal d e f l e c t ion s i gnal.
The cur r ent for this s t age i s app l ied from current source V1 2 1 3 .
RE LAY
K1006
K1 007
K1008
RE SISTOR DIVI DER
R 1 0 5 3 vs R 1 0 5 6 , R1 05 7 and R 1 0 5 8
R105 3 , R1 0 5 6 and R105 7 v s R1058