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5A-12
Table 5A-3. Power Supply Troubleshooting Guide (2635A)
Symptom Fault
Line fuse blows. - Shorted A1CR2 or A1CR3.
- Shorted A1CR10.
- Shorted A1C7.
- Shorted A1C26.
Supply voltage for A1U23 and A1U22 is greater than
7V (7 to 30V).
Input-to-output short of A1U19. This fault may have
caused damage to A1Q7 and A1Q8.
VCC (5.1V) supply is at the raw supply level (7.5 to
35V dc).
Shorted switch transistor in A1U9 (A1U9-5 to 7).
Open A1C26 can cause switch transistor to short.
VCC (5.1V) supply shows excessive ripple (about
1V p-p).
A1C14 open.
VCC is below approximately 4.5V. Duty cycle of 5V
switcher supply is very low (ON time near 0.1).
Drain-to-source short of A1Q7 or A1Q8.
VCC is about 1.5V. 5V switcher supply is in current
limit.
Shorted A1CR5 or A1CR6.
VCC is below approximately 1V. 5V switcher supply
is in current limit, with very low duty cycle (ON time
near 0.1).
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. Q output of A1U22 stuck low.
VLOAD (-30V dc) Inverter Supply is OFF. Q* output of A1U22 stuck low.
VLOAD (-30V dc) Inverter Supply ripple. - Open A1CR8 (either diode).
- Open A1CR9 (either diode).
VDD (5.3V dc) supply at approximately 9.2V. Emitter-to-collector short of A1Q2.
VSS (-5.4V dc) supply at approximately -9.2V. Emitter-to-collector short of A1Q5.
VDDR (5.6V dc) supply at approximately 10V. Input-to-output short of A1U6.
VDDR supply has 4-to-5 volt spikes when the A/D
relays are switched (set or reset).
Open A1C12.
VEE (-5V dc) supply is low (near zero). - Open A1C30.
- A1CR13 open.
A1CR13, Diode 1-3 shorted or open. A1C30 may be shorted.
VEE supply is high (near -9V). Input-to-Output short of A1U18.
A1U18 input has large square wave component. Open A1C31.