Specifications

Chapter 4: Troubleshooting

Power Supply Troubleshooting

If the FP SUPPLY FAIL LED is Lit

If the FP SUPPLY FAIL LED is the only one lit, there might be a problem with one of

the supplies that goes to the front panel assembly, or a problem on the front panel

assembly. Unplug the front panel power connector (see cable connector circled in Figure

4- 9) and turn the oscilloscope on again. If no other under- voltage indicator LEDs on

the backplane assembly turn on, the fault is on the front panel assembly and it should

be replaced. If either the BP POL FAIL or NEG SUPPLY FAIL LEDs turn on, then

replace the backplane assembly and confirm that the fault goes away with the front

panel power reconnected to the backplane assembly.

Figure 4-9 Front Panel Power Cable Connector

If the oscilloscope turns off again and no under- voltage fault indicator LEDs are lit,

the bulk +12V supply may be defective and may need to be replaced.

Be sure to verify the operation of the AC OK and DC OK signals first. The AC OK

signal indicates that the applied AC signal is within the specified input range (TTL high

logic level indicates that AC input is good). It is possible for this signal to indicate that

the AC input is not within the requested range even though it is correct. The DC OK

signal indicates whether the main output from the supply (+12.6V) is good (TTL high

logic level indicates the DC output is good). It is possible for this output to be false

even though the supply output is correct.

It is also possible that there is a short circuit on the bulk +12V supply trace somewhere

in the system, which would also cause the unit not to power on. If so, you need to

isolate the assembly that is shorted. You do not need to remove the acquisition or

backplane assemblies to perform the following steps.

1 With the power turned off, disconnect the bulk +12V supply (see Figure 4- 10), but do

not remove the supply from the oscilloscope.

2 On the backplane assembly, measure the resistance across the FET (Q1409, located in

the upper right corner of the backplane) between +12V and ground as shown in Figure

4- 13, or measure the resistance across the bulk supply input pins on the backplane

assembly. Make sure the red lead is plugged into the HI output and the black lead is