10
Baker Instrument Company
The Measure of Quality
CRT
BLANK WHEN
PTT
BUTTON
DEPRESSED
/
SURGE MODE
This particular fault is associated with the loss of one or more of the following signals:
line trigger, stack power, real test or sync trigger.
1.
Check the stack power signal at P1 pin 2 on the Power board, this signal should be a
360 volt AC sine wave with the negative portion clipped at zero (0) volts. Frequency
will be at approximately 60 Hz. If not present remove the P1 connector on the Power
board and remeasure at R2. If still not present, check T1, D1, and R2 for defects and
replace. If this signal is loaded down upon reconnecting, then check FET Q6 on the
Stack board for defects.
2.
Check the line trigger signal starting at the junction R1 and T1 pin 5 on the Power
board. This signal will be an AC sine wave with an approximate amplitude of 900
volts peak to peak with a 60 Hz frequency. At P1 pin 1 this signal changes due to
components tied to this signal line on the I/O board. At his point, this signal will be a
1.2-volt square wave with a frequency of 60 Hz. If this signal is not present or
incorrect proceed to the I/O board. Check D1, Q2, and U9 for defects and replace if
necessary. Signal at U19 pin 3 should be a 5-volt square wave with a frequency of 60
Hz.
3.
Check the real test signal at U29 pin 16 on the Controller board. This signal will be
5-volt logic and should be a positively pulsed waveform with a changing high state
duration of approximately 1 to 20ms. Frequency will be 5 Hz. Depressing the PTT
button will activate this signal. This signal is then routed to the I/O board at U19 pin
5 and also through an inverter U4 to U19 pin 4, if these signals are missing or
incorrect, then any of the three components listed above are suspected to be faulty.
4.
Sync trigger will be the output from the flip-flop U19 pin 1. This signal should be a
positively pulsed waveform with an approximately 450
µ
S high state duration with a
frequency of 6 Hz.
5.
The PTT button again needs to be depressed to activate this signal. If signal is not
present, replace U19 on the I/O board. Check the stack trigger signal at R22 on the
A/D board for a 10-volt positively pulsed waveform with a frequency of 5 Hz. If not
present, check Q1, Q2, and Q3 for faults. The Stack trigger signal is then routed to J1
pin 4 on the Stack board. Possible loading of this signal can also be attributed to
component defects in the Stack board trigger and charging circuit such as C1 or Q6.
