HP 8153A - Troubleshooting the al Processor Board; Before You Start; Running in Free Run Mode

Troubleshooting the A1 Processor Board
Before You Start Before starting to troubleshoot the processor board, first check the
supply voltages. These come from the A3 power supply board via the
mother board A2. They can be checked on the Test Connector J302
on the circuit side of the Al processor board.
J302 pin No.
Test Voltage
lb +30V
3b +5V
5b +15V
7b -15V
Running in Free Run Mode
Note
If the instrument is set to Free Run Mode, the display stays dark.
Set ali switches of Al Sl02 to the OFF position (towards rear frame).
Set SlOlA(l) and SlOlB(2) to ON position (towards front panel).
To check that the PAL (Ul06) and the processor are working
properly in Free Run Mode, trigger the oscilloscope channel A (on
the low going slope) from signal LAS at UlOl, pin 28. With channeI
B check the the timing between LAS and DETACK (UlOl pin 31).
The timing should be as shown below.
l
o approx.310ns "c= ~
~~~
L. ---' approx.190ns
- TriggerA
------,I~o---approx. 260ns ---'I
U101l31
50ns/DIV
Figure 4-3. Pulses from LAS and DETACK
Note
Due to the timing sequence, determined by the PAL, these will be
repeated every secondo
If the timing is completely different to that shown above, PAL Ul06
or the processor, UlOl, may be defective.
li the Free Run Mode cannot be initiated, check the following control
signals at the processor, UlOl.
4-4 Troubleshooting
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