Troubleshooting Bias Supplies
+5V on A2 Control Board. The PWM A2U6 includes a clock generator (45KHz set by A2R53 and A2C26), and a current limit (2Adc set by 0.15Vdc across A2R50). It turns off each output pulse using the difference between the voltage at voltage divider
Circuit Included. + 5Vdc bias supply circuitry from connector pin
Setup. The Main Troubleshooting Setup, page 29. Apply the ac mains voltage to the bias transformer, and set the external supply to 0Vdc.
Input: |
|
|
NODE + | MEASUREMENT | SOURCE |
≈ 20Vdc | A1CR6,A1CR7 | |
Outputs |
|
|
NODE | MEASUREMENT |
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≈ 2 to 4Vdc sawtooth, 45KHz |
| |
≈ 19Vpk, 15∝s pulses, 45KHz |
| |
A2Q3 (emit) | ≈ 20Vpk, 5∝s pulses, 45KHz |
|
A2U5 (OUT) | 2.5 Vdc |
|
A2R50, A2CR11 (anode) | ≈ 0 > V > |
|
A2R161, A2R163 | 2.5 Vdc |
|
To check if load on + 5 V is shorted, remove jumper A2W3
Table
SYMPTOMS | DEFECTIVE CIRCUIT | CHECK COMPONENTS |
Error when pressing DISPLAY SETTINGS | Limits display. | A3U1, A3U9 |
Error in VOLTS or AMPS | Input ranging or DVMS. | A3U1,A3U2,A3U4,A3U5,A3U7 |
* one or more display digits out | Display LEDs. | A3DS1 through A3DS7 |
Unable to adjust VOLTAGE or CURRENT | Potentiometers. | A3R4, A3R5 |
or always max |
|
|
VOLTS decimal point error | Decimal drivers. | A3U6 |
*Note that the Volts and Amps tests (Table
Table 3 5. Performance Failure Symptoms
SYMPTOMS | DEFECTIVE | CHECK FUNCTIONAL CIRCUITS |
| BOARD |
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Unexplained OVP shutdowns | A2 | OVP Circuit, CV Circuit |
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|
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No current limit | A2 | CC Circuit |
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|
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Max current < 30Adc | A2 | CC Clamp, CC Circuit |
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|
|
Max power < specified | A2, A1 | Power Limit, 20KHz clock, transformer A1T1 |
|
|
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Max voltage < 20Vdc | A2, A1 | CV Circuit, diodes |
|
|
|
Cycles on & off randomly | A2, A1 | |
|
| Select switch A1S2 |
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