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Turn-On Checkout 55
Series 668xA Supplies
The line fuses are located on the rear panel (see Figure 2-4). Proceed as follows:
l. Turn off the front panel power switch and remove the input power (unplug the power cord or open the safety
disconnect).
2. Remove the ac input safety cover from the rear panel.
3. Unscrew the fuse caps and remove the fuses.
4. If one or two fuses are defective, replace all three with fuses of the same type (see Table 1-5 in Chapter l).
Note: If all three fuses are blown, the Check Fuses LED will not blink and the power supply probably has a
defect that requires service.
5. Turn on the power supply and check the operation. If it is normal, replace the ac input safety cover.
Maintenance Note It is recommended that new line fuses be installed every four years.
Condensation Fault (Series 668xA Only)
If the front panel Dew LED is on, then there is excessive (near 100%) humidity inside the power supply. (This could occur
if the supply is rapidly moved from a cold to a warm environment.) The power supply will not turn on when this LED is lit.
If the LED remains on under conditions of normal humidity, the power supply has a defect and requires service. If
condensation occurs after the supply is successfully turned-on, the Dew detector circuit will not turn off the supply.
Error Messages (All Models)
Power supply failure may occur during power-on selftest or during operation. In either case, the display may show an error
message that indicates the reason for the failure.
Selftest Errors
When a selftest error occurs, it prevents all front panel operation. The display may show either a power-on error message or
a checksum error message.
Power-On Error Messages
Power-on messages appear as:
En- - - - - -
Where "n" is a number listed in Table 3-3. If this occurs, turn the power off and then back on to see if the error persists. It is
possible to recover from the EE CHKSUM error (see "Checksum Errors"). If any other message persists, the power supply
requires service.
Table 3-3. Power-On Selftest Errors
Error
No.
Display Failed Test Error
No.
Display Failed Test
El
FP RAM
Front Panel RAM E8
SEC RAM
Secondary RAM
E2
FP ROM
Front Panel ROM checksum E9
SEC ROM
Secondary ROM checksum
E3
EE
CHKSUM
EEPROM E10
SEC 5V
Secondary 5 V ADC
reading
E4
PRI XRAM
Primary external RAM Ell
TEMP
Secondary ambient
E5
PRI IRAM
Primary internal RAM
thermistor reading
E6
PRI ROM
Primary ROM checksum E12
DACS
Secondary VDAC/IDAC
E7
GPIB
GPIB R/W to serial poll
readback