Tait TP9100 - Page 145

TP9100 Service Manual Interface Fault Finding 145
© Tait Electronics Limited May 2005
Tas k 7 —
Function Keys or
PTT Faulty
Use this procedure if a function key fails to activate the programmed
function, or the PTT fails to key the transmitter. Before proceeding:
■ For function keys, make sure there are functions programmed that have
obvious effects on the radio (such as backlighting and monitor), and
recheck the faulty keys.
■ For the PTT, use CCTM commands to check that the fault is not
transmitter-related. See “Check the Transmit and Transmit-Audio
Functions” on page 132.
If a function key or the PTT is faulty:
1. Remove the front panel and main-shield assembly.
2. Remove the main board and apply power using an open radio test
lead.
3. Connect a multimeter or oscilloscope to the non-3V3 end of R922
(PTT – see Figure 7.3), R923 (function key 1 – see Figure 7.2), or
R924 or R295 (function key 2 or 3 – see Figure 7.4).
4. As each key is pressed, monitor the voltage on the appropriate resistor.
The signal voltages should be as follows:
5. If the logic levels are not correct then replace the relevant key switch
and retest. If the logic levels are correct, or replacing the key switch
does not repair the fault, replace the main board.
PTT: R922 (non-3V3 end)
function key 1 (top of radio): R923 (non-3V3 end)
function key 2 (side of radio): R924 (non-3V3 end)
function key 3 (side of radio): R925 (non-3V3 end)
Not pressed: > 3.0V
Pressed: < 0.5V
Figure 7.3 PCB layout showing R922 (top side)
R922 indicating
non-3V3
end (*)
*