518 Troubleshooting

5-19. LOW-VOLT AGE POWER SUPPLIES.

5-20. TRANSISTORS. The series regulator transistors are located on the fan assembly. Each is easily replaced by removing the two screws and

Table 5-3. Condensed Adjustment Procedure

Test

External Equipment Required

Procedure

Adjust

1. Low Voltage Supplies

DC Voltmeter

Measure: -lOOv (Violet) -12.6v (White/Violet) +100v (White/Red)

R200B R200C R200A

2. High Voltage Supply

DC VTVM; 100:1 Divider; Voltmeter Calibrator

a. Calibrate Divider - Voltmeter combination.

b. Measure -2350v

R319 for -2350 volts

3. Intensity Limit

b. Set INTENSITY to 10 o'clock.

R312 until spot is just extinguished.

4. Astigmatism

None

Center a low-intensity spot.

FOCUS and ASTIGMATISM for sharp spot.

5. Geometry

Audio Oscillator

a. TRIGGER LEVEL: AUTO SWEEP TIME: . . 0.2 MSEC/CM

b. Connect 400 kc sine wave to vertical INPUT.

c. Obtain pattern 8 cm high.

R343 for straightest edges.

6. Calibrator

Voltmeter Calibrator

b. Apply lOv p-p from Voltmeter Calibrator to vertical INPUT.

c. Adjust vertical VERNIER for 10 cm deflection.

d. Connect 10V CALIBRATOR to vertical INPUT.

Cal Adj. R205 for 10 cm deflection.

pulling the transistor from its socket. All other low voltage power supply transistors are located on the low-voltage circuit board.

5-21. Nominal voltages at significant points in the supply are given in the low-voltage power supply schematic. Plug-ins must be installed when checking these voltages. Correct voltages for points not marked for voltage are generally obvious by being connected (directly or indirectly) to a supply output. Transistor base voltage in most cases should not measurably differ from emitter voltages when measured with respect to ground. Voltage drops across breakdown diodes are indicated on the schematic.

5-22. EXCESSIVE RIPPLE. The cause of excessive 120-cycle ripple on any of the supplies can be isolated to input filter or regulator circuits by comparing ripple voltages at the rectifier outputs with the values given on the schematic. If ripple at these points is excessive, check capacitors C121, C122, C141, C161, or CI81. If ripple is high and is 60 cps, one of the rectifiers is probably open. If normal, the cause is most likely low gain in the amplifier transistors. In the -100 volt supply, slave amplifiers Q161 and/or Q163 could be open, and the only indication might be poor regulation and ripple at low line voltage.

5-23. FUSES. If the -100, +100, or +250 volt supply should be accidentally shorted to ground, the fuse for that particular supply will blow. This cuts off current in the supply and protects the transistors.

5-24. The -12.6 volt supply is not fused, but employs a surge protector, Q184, for protection against brief shortings of the output to ground. The supply should immediately function normally upon removal of the short.

5-25. LOSS OF REGULATION. If loss of regulation occurs in a supply, refer to Table 5-4. The procedure outlined in this table may not always pin down the exact trouble, especially if a component other than a transistor or breakdown diode has failed, but it will usually indicate the general location of the failure. In using the procedure, follow the steps listed under a particular symptom in the given order. In some cases, more than one fault may exist.

5-26. HIGH-VOLTAGE SUPPLY.

5-27. If one high-voltage supply output is zero but other outputs are normal, look for the unlit filament of a bad rectifier (V302 thru V305). Normal DC voltages are given on the high voltage schematic.

Table 5-4. Troubleshooting the Low Voltage Supply

Supply

Symptom

Procedure

Indication

Conclusion

-100V

High Output Voltage

1. Measure voltage across CR165

2. Disconnect the WHT-GRN-V10 wire from the edge of the circuit board.

3. Reconnect the WHT-GRN-V10 lead. Short emitter of

Q164 to base

4. Measure voltage across R173

Approximately 6.5 volts or less

More than approx 6.5v

Output drops

Output remains high

Output drops Output remains high

Same as output

Less than measured high output

CR165 OK

CR165 open

Q162 OK Q162 shorted

Q164 OK

Q164 shorted, and also possibly Q163 and Q161 (check emitter-collector resistance with ohmmeter.)

Q165 shorted Q166 open

Low Output Voltage

1. Measure voltage across CR165

2. Short WHT-GRN-VIO wire to anode end of CR165 (away from plug-in compartment).

3. Short base of Q164 to the anode end of CR165 (away from plug-in compartment).

4. Short emitter to base on Q166.

0 volts

Approx 6 volts

Output remains low

Output rises (more negative)

Output rises

Output remains low

Output rises Output remains same

CR165 shorted CR165 OK Q162 open Q162 OK

Q164 OK

Q164 or possible Q163 open

Q165 open

Q166 shorted

-12.6V

High or Low Output Voltage

1. Check the -100 volt supply

Normal Abnormal

Trouble in -12.6V supply Trouble in -100V supply

High Output Voltage

1. Remove the WHT-GRN-BLU wire from the edge of the board.

2. Replace WHT-GRN-BLU wire. Short emitter of Q182 to base.

3. Short emitter of Q185 to collector.

Output drops Output remains high

Output drops Output remains high

Output drops Output remains high

Q181 OK Q181 shorted

Q182 OK Q182 shorted

Q185 open Q183 open

Output Low

1. Lift collector of Q184 (leave disconnected for remainder of -12.6V supply tests.)

2. Short emitter of Q182 to collector

3. Lift collector of Q183

Output remains low

Output returns to normal

Output goes higher than normal

Output rises

Output remains low

Output rises

Output remains low

Q184 OK Q184 shorted

CR184 open

Q181 OK Q181 open Q182 OK Q182 open

Table 5-4. Trouble shotting the Low Voltage Supply (Cont'd)

Supply

Symptom

Procedure

Indication

Conclusion

-12.6V

Output Low (cont'd)

4. Replace collector of Q183 and short emitter of Q183 to base

5. Short emitter of Q185 to base

Output rises Output remains low

Output remains low Output rises

Q183 OK Q183 shorted

Q185 shorted CR184 shorted

+100V

High or Low Output Voltage

1. Check -100V and -12.6V supplies

Normal Abnormal

Trouble in +100 volt supply

Trouble in -100 or -12.6 volt supply

High Output Voltage

1. Remove the WHT-GRN wire from the edge of the printed circuit board

2. Replace WHT-GRN wire. Short emitter of Q142 to base.

Output drops Output remains high

Output drops Output remains high

Q141 OK Q141 shorted

Q143 shorted Q142 shorted

Low Output Voltage

1. Short emitter of Q142 to collector

2. Short emitter of Q143 to collector

Output rises Output remains low Output rises Output remains low

Q141 OK Q141 open Q143 open Q142 open

+250V

High or Low Output Voltage

1. Check -100, -12.6, and +100 supplies

Trouble in -100, -12.6, or +100

High Output Voltage

1. Measure voltage across CR146

2. Remove green wire from edge of board

3. Replace green wire. Short emitter of Q122 to base.

Greater than approx 6.5v

Approx 6.5v or less Output drops Output remains high Output drops Output remains high

CR146 open

CR146 OK Q121 OK Q121 shorted Q123 shorted Q122 shorted

Low Output Voltage

1. Measure voltage across CR146

2. Short emitter of Q122 to collector

3. Short emitter of Q123 to collector

0 volts

Approx 6 volts Output rises Output remains low Output rises Output remains low

CR142 shorted CR146 OK Q121 OK Q121 open Q123 open Q122 open

5-28. If there is no high voltage output and none of the filaments are lit, observe the waveform at the collector of Q302 (blue wire). If an approximately 30 kc 20-volt peak-to-peak sine wave appears for short intervals, the trouble is probably a defective component in the rectifier filter/divider networks. If no waveform appears, use Table 5-5.

5-29. If the high voltage output is incorrect and cannot be adjusted to the correct value, use Table 5-6.

5-30. If the -2350 volt supply seems to be operating properly, the +5 kv post-accelerator potential may be checked by removing the left side instrument cover and measuring the 5-kv voltage at the board termination of the thick red lead.

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