Diagnostic Testing and Troubleshooting (2620A/2625A)

5

Analog Troubleshooting

Table 5-3. Power Supply Troubleshooting Guide

Symptom

Line fuse blows.

Fault

-Shorted A1CR2 or A1CR3.

-Shorted A1CR10.

-Shorted A1C7.

-Shorted A1C26.

Supply voltage for A1U23 and A1U22 is greater than 7V (7 to 30V).

VCC (5.1V) supply is at the raw supply level (7.5 to 35V dc).

VCC (5.1V) supply shows excessive ripple (about 1V p-p).

VCC is below approximately 4.5V. Duty cycle of 5V switcher supply is very low (ON time near 0.1).

VCC is about 1.5V. 5V switcher supply is in current limit.

VCC is below approximately 1V. 5V switcher supply is in current limit, with very low duty cycle (ON time near 0.1).

Input-to-output short of A1U19. This fault may have caused damage to A1Q7 and A1Q8.

Shorted switch transistor in A1U9 (A1U9-5 to 7). Open A1C26 can cause switch transistor to short.

A1C14 open.

Drain-to-source short of A1Q7 or A1Q8.

Shorted A1CR5 or A1CR6.

Shorted A1C14.

VCC is below approximately 4.5V. 5V switcher supply is in current limit, with very low duty cycle (ON time near 0.1).

-Q or Q* output of A1U22 stuck high.

-A1U23 pin 8 output stuck high or low.

-Shorted A1CR7

-Shorted A1CR9 (either diode), pins 1-3 or 2-3.

-Shorted A1C30. A1CR13 may also be damaged.

-Shorted A1C31. A1CR13 may also be damaged.

-Shorted A1C12.

-Shorted A1C13.

-Shorted A1CR8 (either diode), pins 1-3 or 2-3.

VLOAD (-30V dc) Inverter Supply is at -36V.

VLOAD (-30V dc) Inverter Supply is OFF.

VLOAD (-30V dc) Inverter Supply ripple.

VDD (5.3V dc) supply at approximately 9.2V.

VSS (-5.4V dc) supply at approximately -9.2V.

VDDR (5.6V dc) supply at approximately 10V.

VDDR supply has 4-to-5 volt spikes when the A/D relays are switched (set or reset).

VEE (-5V dc) supply is low (near zero).

A1CR13, Diode 1-3 shorted or open.

VEE supply is high (near -9V).

A1U18 input has large square wave component.

Q output of A1U22 stuck low.

Q* output of A1U22 stuck low.

-Open A1CR8 (either diode).

-Open A1CR9 (either diode).

Emitter-to-collector short of A1Q2.

Emitter-to-collector short of A1Q5.

Input-to-output short of A1U6.

Open A1C12.

-Open A1C30.

-A1CR13 open.

A1C30 may be shorted.

Input-to-Output short of A1U18.

Open A1C31.

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Fluke 2625A, 2635A service manual Power Supply Troubleshooting Guide Symptom, Fault

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