52 E8257D/67D, E8663D PSG Signal Generators Service Guide
Troubleshooting
Troubleshooting Assembly–Level Problems
Power Switch On/Off Line
If the control line (ON/OFF) from the A3 Power Switch located in the front panel
assembly goes to a TTL low state, or if the line impedance is less than
500 ohms, the power supply shuts down. This signal can be measured on the
A31 Motherboard at pin 79 of P241.
To troubleshoot:
1. Turn the front panel switch on and ensure that the +15 Standby is good.
2. Verify that the ON/OFF control line is > 3.5 Vdc.
The Power Switch/Flat–Panel Interface Board in the front panel assembly
controls this signal.
Symptom: Green front panel LED and power supply LEDs
on motherboard blinking
Overvoltage or Overcurrent
The individual supplies in the instrument are not fused, but an overvoltage or
overcurrent condition can shut them down. With either of these conditions, the
front panel green LED and the power supply LEDs blink at approximately 2 Hz.
The power supply tries to revive, but if the condition does not clear, the
instrument stays in this mode. In some cases, cycling power fixes the problem.
To troubleshoot, use the following steps to isolate the defective assembly:
1. Turn off the instrument and remove one of the assemblies biased by the
faulty supply.
2. Turn the instrument on and check whether the overvoltage or overcurrent
condition still exists. If it does not, replace the assembly removed in Step
1. If it does, continue with Step 3.
3. Turn the instrument off and reinstall the assembly removed in Step 1.
Remove the next assembly and see if that fixes the problem. Continue this
process until the supply functions properly.
4. Replace the last assembly that you removed.
Remove a minimum number of assemblies at one time. If the power supply does
not have a minimum load on it, the supply voltage increases to an overvoltage
condition.
Refer to the
Power Supply vs. Assembly Matrix tables, starting on page 37, for
help in determining which assembly uses which power supplies.
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