E8257D/67D, E8663D PSG Signal Generators Service Guide
Troubleshooting
Troubleshooting Assembly–Level Problems
1-27
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:
CAUTION 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.
NOTE Refer to the Power Supply vs. Assembly matrix tables, starting on page 1- 15, for help in determining which
assembly uses which power supplies.
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.
Symptom: Amber front panel LED blinking
Thermal shutdown
With thermal shutdown, the front panel green LED and the power supply LEDs blink as long as the condition exists.
There are two temperature sensing devices in the instrument: one on the A8 Output, and one on the A19 Power
Supply.
To troubleshoot:
1. If the instrument is hot, ensure that the fan is working and let the instrument cool off.
2. If the instrument still shuts down, remove the Output assembly.
3. If the instrument still shuts down, replace the Power Supply.
or
If the instrument powers on, but the amber LED continues to blink, replace the A3 Power Switch assembly.
Symptom; +9, –6, or –5.2 V LEDs not on
These supplies are generated on the YIG Driver Assembly.
Troubleshoot using the Power Supply vs. Assembly Matrix that begins on page 1- 14.
1. At P112 of the Motherboard, ensure the YIG Driver Assembly is receiving the +32, +15, +10, –7, –15 Vdc supplies.
2. If the supplies are present at P112, note in the matrix where each supply is used.
3. Power down the instrument and remove one of the assemblies that is biased by the faulty supply.
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