Z-Ampli Fier - Philips PM3055 Service Manual

3-12
Time-ba se un i t
3 .2 .5
Th i s uni t incorporates the main t ime-b a se ( MTB ) , the de l ayed t ime -base
( DTB ) , t he hor i zont al ampl i fier and the Z amp l i fier c ir cui t . Al l
func t ions are contro l l ed by t he CXl and CX2 s i gnal s , gene rat ed by the
HORIZON TAL CONTROL CIRCUIT b l ocks .
* Main t ime-b a se ( MTB ) :
The MTB t rigge r s ignal c an b e e i ther d i r e c t l y
CONTROL CIRCUIT or firs t routed via the TV TRIGGER SELECTION for the
TV tr igge r c oupl ing. When in t he AUTO mode , in the ab s ence o f t r i gger
s igna l s , the MTB wi l l be free running.
The MTB CURRENT SOURCE appl i e s the sawto o th charging current to the
MTB sweep c ircui t . Thi s b l o ck generates the MTB s awtooth s i gnal , wh ich
i s rou t ed to the HORIZONTAL DISPLAY MODE SWITCH.
The HOLD OFF and the ALT CLOCK PULS E b l o cks are a l so under contro l o f
the T IME BASE CONTROL C IRCUIT. Hol d o f f t ime i s var ied b y the front­
pane l HOLD OFF control. The output o f the HOLD OFF b l o ck i s rout ed t o
the T IME-BASE CONTROL CIRCUIT aga in.
The ALTCLN-pulse i s appl i ed to the PRE-AMPL IFIER UN IT.
3 .2 .6 XYZ un i t
Th i s un i t compr i s e s the final ampl i fiers fo r the ver tical ( Y ) and
hor i zont al ( X ) d e f l e c t ion and for the b l anking ( Z ) c ircui t . In add i t ion
to thi s , the CRT c ontrol c ircui t s are al so incorporated in the uni t .
* Final ver t i c al ampl i fier :
The out put s i gnal from the pre-amp l i fier un i t 1 s firs t routed vi a the
DELAY LINE to give suffic ient d e l ay to ens ure that the s t e ep l e ad ing
edge s of fa s t s i gnal s are d i s p l ayed and then fed to the DELAY L INE
COMPENSATION. Thi s b l o ck c ompensates the s i gnal for d i s tort ion
o r iginat ing in the DELAY LINE b e fo re it is app l ied to the FINAL
VERTICAL AMPL IFIER. The output of the FINAL VERTICAL AMPL IFIER fe eds
the ver t ic al defl e c t ion p l a t e s of the CRT.
* Final hor i zont al ampl i fier :
The hor izontal de fl e c t ion s ignal i s routed to the FINAL HORIZONTAL
AMPL IFIER , the output of wh i ch fe eds the hor i zont al d e f l e c t ion plates
o f the CRT.
* B l anking c ircui t :
The out put s ignal from the Z PRE-AMPLIFIER o f the t ime-base un i t , that
determines trace b lanking or unb l anking and modulat ion i s routed to the
F INAL Z-AMPLIFIER. Aft e r ampl i fic at ion the b lanking s ignal i s s p l i t
in to t � paths :
- the h.f. s i gnal s are fed via a high vo l tage c apac i t o r to gr id Gl o f
t h e CRT.
- the l .f. s igna l s are used to modu l a t e the ampl i t ud e of an osc i l lator
wave- form , wh i ch then pas s e s via another h i gh vo l t age c apac i tor and
i s demodul a t ed in the DEMODULATOR b l ock to retr ieve t he o r iginal
s ignal.
No te that the o r iginal h.f. and l .f. s igna l s are a gain rec omb ined on
t he gr id Gl.
rout ed to the T IME-BASE