Model 428B
pairs of pins is significantly higher than between the other
5-59. TROUBLESHOOTING. pairs (by about 3 times), an open probe coil is indicated.
Any open circuit indicates a broken conductor between
5-60. FRONT PANEL TROUBLESHOOTING. the plug and the bridge. The broken conductor is probably
5-61. The Front Panel Troubleshooting Tree was a broken wire in the cable. Either condition could indicate
designed for use as a means to guide the repairman to a broken wire at the Probe Terminal Section (see wiring
a block of circuitry. This procedure, in combination with diagram, Figure 6-1).
the adjustment, calibration, and performance checks 5-66. Power Supply Check.
should be adequate to repair most 428B's.
5-62. In any case where the front panel troubleshooting 5-67. To test the power supply:
does not lead to the problem, it will be necessary to a. Measure +272 ?6 Vdc between Test Point 5 and
troubleshoot the instrument in detail. ground.
b. Measure +12 ?1 Vdc between the cathode of CR10
5-63. DETAILED TROUBLESHOOTING. and ground.
5-64. Probe Check. c. Measure -7 ?1 Vdc between the anode of CR9 and
ground.
5-65. Resistance between pins 1-3, 1-4, 2-3, and 2-4 of 5-68. Where the +272 V and the +12 V have both failed,
the probe cable connector should be nearly identical
and in the area of approximately 4 1/2 to 5 ohms. Where check the +12 first. Check CR10, Q1, C66, and C69.
a resistance measurement between any of the above
19 |
ACEC
