Installation guide

Troubleshooting
Troubleshooting Assembly Level Problems
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not on or the measured voltage is less than the acceptable value, one of the assemblies may be loading down
the power supply. To find where each power supply is being used, refer to Table 1-12, Table 1-13, Table 1-14,
and Table 1-15.
To troubleshoot and isolate a defective assembly, turn power off to the signal generator and remove one of the
assemblies being biased by the faulty power supply.
NOTE It is important to have only a minimum number of assemblies removed at one time. The power
supply expects to see a minimum load, otherwise the power supply voltage will increase until
an over-voltage condition exists.
Turn power back on to the signal generator and check the suspected faulty power supply. If the condition is
still bad, turn power off to the signal generator and re-install the first assembly that was removed. Remove
one of the other assemblies being biased by the faulty power supply and see if the problem is alleviated.
Continue this process until the power supply is functioning properly. Replace the last assembly that was
removed.
If the Front Panel Power Switch is Not Functioning
When the front-panel power switch is switched on, the control line (ON/OFF) from the A1 Keyboard is
momentarily grounded and the A6 Power Supply is enabled. The ON/OFF signal is routed from the
A1 Keyboard through J32-20 to the A23 Motherboard. Circuitry on the A23 Motherboard uses the ON/OFF
signal to generate the Pwr_On_L. This line is routed to the A6 Power Supply and the A12 CPU; the A6 Power
Supply is disabled when the Pwr_On_L line is a TTL high or open.
To troubleshoot
1. Measure J28-34 with a DVM to assure that the +15 Vdc Standby voltage (+15 STBY) is correct.
• If the +15 Vdc Standby voltage is good, use the DVM to measure J32-20 (ON/OFF).
The DVM should read approximately +5 Vdc.
a. While monitoring the DVM, depress and hold the front panel power switch.
This grounds the ON/OFF signal and the DVM should read less than a few millivolts.
b. Release the front panel power switch.
The ON/OFF control signal should again be approximately +5 Vdc.
2. With the front panel power switch off, the Pwr_On_L line at J28-32 of the A23 Motherboard should be at
approximately +5.8 Vdc; this signal is generated on the A23 Motherboard.
• If the voltage is less than +3.5 Vdc, remove the A6 Power Supply and ohm the connection from J28-32
to ground; the impedance should be ≥ 1 Megaohm.
— If the impedance is correct, replace the A6 Power Supply.
3. When the front panel power switch is turned on, the Pwr_On_L line goes to < +50 mV.
• If the A1 Keyboard is functioning properly and the Pwr_On_L line is not, replace the A23 Motherboard.
• If the Pwr_On_L line is functioning properly, replace the A6 Power Supply.