Tandy 102 Service Manual page 54

12. Modem interface doesn't function
12
Check the transmit side.
Check if a modulation signal is output to connector pin 5 (in coupler mode) or
pin 7 (during direct mode) in transmission. Then check if the receiver carrier is
input to the M31 Rx Car terminal (pin 1).
(If not, check M22, M30, T4, T7, OT1 and RY2.)
Check receive side.
Check to be sure that the modulation signal is input to M31 pin 1 (Rx Car) during
data reception.
(If not, check M29, M30 , OT1, T2, T3, T5, D1, D2 and RY2. If it is input, check M22
and M31.)
Check the automatic dialer.
Check RY2, RY3, T7, T24, M36 and
M1 3.
END
13. All functions check ok?
13
Check the unit again, as described in the TROUBLESHOOTING GUIDE.