M4000 Insulation Analyzer User Guide
72A-1230 Rev. F 4-15
July 22, 2005
Negative watts obtained in
UST or GST-Guard circuit
This may simply be due to surface dirt and
moisture. Clean and dry the specimen’s
surface and retest it. This condition is most
often found when testing bushing C
1
insulation, transformer Ch
1
insulation, or
rotating machinery interwinding insulation.
In the case of a bushing, the offending
surface may be that on the lower part of the
bushing inside its parent apparatus, or on the
inside surface of the shell. See the paper in
1987 Doble Minutes on negative watts, page
2-501.
Communications error
message
If any of a variety of
communications-related error messages (see
Appendix C) is displayed, take the
following steps in sequence until the cause
of the problem is identified:
1. Run the Communications Loopback
Test described in ”Communications
Loopback Test” on page 4-40.
2. Check the communications cable
(between the M4100 and M4200c) for
bent connector pins and breaks or frayed
areas in the cable jacket. Replace the
cable if necessary (see item 5 of
”Accessory Bag” on page A-2).
3. Check the M4100 power supply
voltages as described in ”Low-Voltage
Power Checkout” on page 4-51.
Replace the Low Voltage Power Supply
Board if necessary.
4. If no other cause is determined, replace
the I/O Protection Board in the M4100
(see ”Replacing the I/O Protection
Board” on page 4-83).
Table 4.4 M4100 Troubleshooting from Symptoms (Continued)
Symptom Suggested Action
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