Sharp MZ-80B Service Manual page 66

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i.
•
• Adjustment
Adjust and check the following when exchanging IC7, 20, 26 (74LS123N), TR 1 and their peripherals.
When adjusting, add power voltage 5V to TP7 (+5V) and TP9 (DV) and apply 4MHz clock (duty ratio 50%,
TTl level) to TP2.
VR 1 Adjustment
As shown in Fig. 1, apply a negative pulse with a period of more than 30/1s-50/1s to TP3 (READ DATA).
At this time, adjust VR1 so that the width of the negative pulse appearing at TP5 i. 5/1',
~ 10.2-0.4#S
TP3
-{;""s .
'U
U .
3D.us ...... 50",s
TP5
#
------------------------,~
Fig. 1
VR2 Adju.tment
Apply a negative pulse with a period of 5/1' to TP3 (READ DATA). At this time, adjust VR2 So that the
width of the negative pulse appearing at TP4 is IllS.
0.2.-..... 0.4
j..lS
TP3 - -
---.Ml-t====;:::::======:::t
--0
4IJ.s
TP4
- ---j~1:".=':r------------_t
Fig. 2
VR3 Adjustment
Apply a negative pulse with a period of 4/1s to TP3. At this time, adjust VR3 so that the voltage of TP8 is
2.65V. After adjusting, change the period of the negative pulse added to TP3 and check that the VCO
output is within a periodic range of 4ps ±l,us.
Adjustment range
The following shows the adjustment range for each adjustment.
• VRt adjustment
• V R2 adjustment
• VR3 adjustment
5/15 ±O.2J15
1J1s ±O.D4/15
2.65V ±O.05V
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