minnie |
Posted: Mon Dec 10, 2007 8:11 pm Post subject: |
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Troubleshooting Tips (ref. Figure 3-3) NOTE: Follow previously discussed “IC6501 Startup Sequence”. The five steps are in order of occurrence. NOTE: Use HOT GRND when making measurements on primary side of T6502. This includes all measurements on IC6501. Symptom: Unit goes into protection mode, LED flashes four times. Check: This indicates either a Vertical deflection or power supply problem. 1) Check power supply secondary outputs. · If voltages are present and at proper the level, then the problem is in the Vertical deflection drive circuit. · If the secondary voltages are low or missing, then the problem is in the power supply. 2) The power supply can be safely tested by unloading the +135v line. Unsolder R5013. This will unload the +135V line of the power supply, but still send necessary feedback to IC6501 for proper power supply operation. 3) If the power supply outputs proper secondary voltages after unsoldering R5013, suspect a shorted +135V line 4) If the unit still goes into protection mode after unsoldering R5013, check the following items: · D6538 (5V Zener) for shorted condition. · Check IC6505 (B+ OVP) for proper operation. · IC6501/pin 15 (this is midpoint for output MOSFETS Q6507 and Q6506). A 275Vpp, 85KHz square-wave should be present. If the waveform pulses four times and stops, check the next Item. · IC6501 Feedback circuit. The amount of current feedback can be determined by monitoring the voltage drop across R6525. The minimum current feedback is 80uA, which is a minimum voltage drop of 37.6mV. In normal operation, this voltage drop is approximately 223mV. If the voltage drop is below 37.6mV, suspect components in the feedback path e.g. PH6502 and IC6503. Reference Figure 3-3 for proper voltages at these components. · If no waveform is present when the unit is turned ON, then check IC6501/pins 1 and 18 for proper voltages (reference “IC6501 Startup Sequence” above). If these voltages check OK, check IC6501/pin 8 for proper voltage of 24V. This is the voltage used to power IC6501 after initial startup. If 18V is present at IC6501/pin8, check IC6501/pin 10 for 10.2V. This voltage is developed using the 18Vs and a voltage regulator circuit inside IC6501. If 10.2V is missing, suspect a defective IC6501. Also check voltage at IC6501/pin 14 (Use battery powered DVM for this measurement and use IC6501/pin 15 (VS) as ground ref.). The voltage at IC6501/pin 14 should be 10V. If the voltage measured at IC6501/pin 14 is incorrect, check D618. · If all the above measurements check OK, suspect a defective IC6501. |
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