Diagnostic Testing and Troubleshooting
Digital Troubleshooting
5
5-15
Table 5-4. AC Volts Troubleshooting
Checkpoint Description Possible Fault
A1Z2-1
A1U1-2 (ACBO)
A1U1-68 (RMSI)
A6U1-14
A1Z4-2
A1U1-61 (RMSF)
Input signal
Amplified input (input x 2.5)
Amplified input
Amplified input
DC equivalent of amplified input
DC equivalent of original input
A1R5, A1R5, A1C1, A1K3
A1U1, A1R11-A1R14, A1Q2-A1Q8, A1Z2,
A1AR1, A1C7, A1R16, A1R17
A1U1
A6U1
A6U1
A1Z4, A1R19, A1C10
5-14. Digital Troubleshooting
At power-up, if the display does not light or lights up and fails to report errors or begin
operation, use the following troubleshooting procedures.
First check the state of SWR1 (A1U6-21). If this status line is less than 0.8 V, basic
processor operation is intact. Examining SWR2 through SWR5 (A1U6-22 through -25,
respectively) should indicate how far the software progressed before finding an error. If
the state of SWR1 is not less than 0.8 V, the problem may be in the 6303Y Main
Processor (A1U6), the ROM or RAM decode circuitry (A1U9), the ROM (A1U8) or
RAM (A1U10), or the address/data lines among these parts.
Note
The functions of SWR1 through SWR5 as power-up status lines only
persist for 2 to 3 seconds. These functions end when the keyboard scanner
begins operation (if it can). Extremely difficult cases may require the use of
an oscilloscope triggered on the falling edge of SWR1 to examine the states
of SWR2 through SWR5.
To determine the relative health of the 6303Y Main Processor (A1U6), first check for a
valid E clock at pin 68. The default for the E clock after reset is a rectangular wave with
a period of 1.628 us and a duty cycle of about 67%.
If the processor is able to fetch instructions from the ROM, the software initializes the
processor, and the E clock becomes a square wave with a period of 1.085 us. Since this
initialization occurs almost immediately with a working meter, the resulting square wave
on the E clock line is a good indication that the software has begun to execute.
If the E clock remains a 1.628 us rectangular wave, the SWR2 (A1U6-22) keyboard scan
line may be shorted to ground. This condition would cause the Main Processor to HALT
after reset. Check whether the 6303Y Main Processor is attempting to access ROM;
LIR* (pin 64) should transition for a short period of time after reset. If it does, the
6303Y Main Processor is probably operational, and the problem is external to the
processor.
The processor can execute an instruction that stops both itself and the E clock.
Therefore, the absence of any activity on pin 68 does not necessarily mean that A1U6 or
A1Y2 is bad. If some other failure prevents proper ROM access, the processor may have
just "gone to sleep". This can be verified by checking for a rectangular wave occurring at
pin 68 for a short time after RESET* transitions high on pin 7. A1U6 and A1Y2 are
probably operational if this rectangular wave is present.
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