Tandy CM-8 - Ou Bleshooting Guide

TROUBLESHOOTING GUIDE
Circuits checked:
• Power regulator circuit
• Protector circuit
• Horizontal sync circu it
Circuits Checked:
1. No raster appears.
• Power circuit
NO POWER
Does 150V appear between the
cathode of D703 and ground?
0702,0701,SCR701,D707 , D708,D706
0705, D709,C708, F702,D710,D714
T701
NO RASTER
• Horizontal sync circuit
Does 115V appear between
cathode of 0710 and ground?
• Protector circuit
2. A high voltage develops
but no raster appears.
Yes
r - - - - -:- - - - - -,
SW701 D704 I
F701 R701 I
No
D701 C701
D702
D703
I
- --------
Note: Fir st be sure th e signal cable is
plugged in securely and turn the com -
puter
power on. Now input any signal to
produce the raster on the screen.
No
Power/ hor izontal
sync/
protector
circuit
• Video output circuit
3 · A high vo I tage is not r-C_h_e_c_k_t_h_e-vo_ l _t_ag_e_ I e_vi...e_l _a_t_t_h_e _ c_o_l_I e-c -t o _ r_o_f~
developed. 0851 . If the voltage is no rmal, the voltage
•
High voltage circuit can be varied between 120 to 140 with the
brightness
control.
CRT and its
related circuits
,-- ---.....,
I CRT R872
1
I_ T~03 ~8~9 _:
Does the signal
appea r?
No
IC451/ comput er
Check the connections between the
monitor and computer .
Defective
Does 4
.8V appear
--- at the emitter of
0402?
IC451/computer
0401, 0402 and
its
related circuits
~ 0401 R413- i
I 0402 0404
I 0405
L.-----~--_J
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