TINY-2/MICRO-2 Technical Ref., 2. Ed 1989
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ing an Analog Loopback. If the loopback works properly, then reset the output level taking care to
set the drive level lower than previously. Note that direct connection to typical microphone inputs
requires the drive trimpot to be turned to near the minimum signal position for proper signal lev-
els. If the Analog Loopback falls to operate properly, perform a digital loopback. If this test oper-
ates correctly, the CPU, Software, and SIO are operating correctly and the modem circuit is sus-
pect.
Uncopyable received packets
If some but not all packets are copied, set the command MCOM ON. Many packet transmissions
are control frames and contain no printable information. MCOM will cause these frames to be dis-
played. Confirm proper wiring of the radio cable by opening the radio squelch and raising the vol-
ume level with some type of signal tuned in. If the DCD LED flickers or solidly illuminates then re-
ceiver audio is reaching the packet controller modem. Test the modem by performing an audio
loopback. If the test falls, perform a digital loopback to be sure the problem is really in the modem
section. Listen to the audio signal from the radio applied to the packet controller or examine the
signal with a scope for hum or other noise which might make the packet signals uncopyable. Con-
firm the proper level of the audio signal is applied to the packet controller with a digital meter or
scope.
DCD LED flickers excessively or stays on
If the DCD LED flickers on and off excessively or remains constantly on only with the signal cable
connected, be sure the radio is operating with squelch closed, that shielded signal cable is being
used, and that the audio drive level from the radio is not excessive. If audio is being obtained from
a speaker output or other low impedance output, place a jumper on JPR located near R12. If high
impedance audio is being used, JPR should be off. If these areas all check out, consider changing
the value of resistor R10 to a lower value between 10 and 100 Ohms.
Transmitter locks in transmit condition
The TINY-2/MICRO-2 is protected against PTT malfunction by a watchdog timer on the keying line.
However, if unshielded, improperly grounded cabling is used to feed the transmitter key line, and
other signal cables, RF energy can get back into the packet controller and lock up the keying tran-
sistor. Precautions are especially necessary if a high power amplifier is being used and there is a
strong RF field in the area of the packet controller.
