Tait T830 Series, Service Manual

Page: 72 / 284

31/01/96 Copyright TEL
5.3 DC Checks
5.3.1 Power Rails
Refer to the test points & options diagrams for test point locations, and to the regulator
fault finding chart (Section 5.5.1) for fault diagnosis.
Check the 9V (TP2) and 13.8V (TP1) power supply test points in the audio com-
partment with a DMM.
Check the 20V regulator output at the test point (TP3) in the regulator compart-
ment.
Check the 5V regulator output at the test point (TP4) in the regulator compart-
ment and on pin 4 of IC303.
5.3.2 VCO Locking
Using a DMM, monitor the VCO control voltage at PL4-1 or the junction of L1 &
R1 (located adjacent to the electrolytic capacitor on the VCO PCB).
If the synthesiser is locked and the VCO aligned, the voltage at this point should
be between 5 and 13V.
If the VCO is not locked, refer to the synthesiser fault finding chart (Section 5.5.2).
5.3.3 Mute Operation
The front panel LED will show the status of the mute circuitry. It will be lit when a sig-
nal is received above the threshold level. It should always be possible to open the mute
gate by rotating the mute potentiometer fully clockwise, or by enabling the monitor
with the front panel switch.
If the mute fails to operate correctly, refer to the mute fault finding chart (Section 5.5.3).