Tandy 102 Service Manual page 47

Checking Procedure
1. Doesn 't work at all
1
Check the power.
• Check to be sure that the batteries are in and that the AC adapter is connected.
• Is the memory back-up power switch ON?
• Is the power switch ON?
Check the DC/DC converter circuit.
• Is 3.6 - 8V applied to pin 1 of the converter transformer?
(If not, check C82, C83, battery contacts and adapter jack.)
• Check all output voltages.
a) VDD ..... +5V (if not, check D13, C84 and ZD1)
b) VEE ..... -5V (if not, check D15, C85 and ZD2)
c) VB ..... +5V (if not, check T27 and T28)
• Is T21 oscillating?
(If not, check T22, T13, C81, R126, R127, R140 and T20.)
Check the RESET signal.
• Is it high level (+2.2V - 5.3V)?
If not, check T10, T11, T25, T9 RESET signal.
• Is it low level (0.8V - 0.3V)?
If not, check T10, T11, T25, T9 RESET signal.
• Check the CPU clock frequency.
(X1 terminal = 4.9152 MHz; CLK terminal = 2.4576 MHz)
(If not, check X2 and M 19.)
• Try replacing the LCU unit.
• Check all ICs.
END