
18
3. Power Supply (DA-4 & DA-4X Chassis)
Over Voltage Protection (OVP) and Under Voltage Protection (UVP): The voltage at IC6501/pin 8 (VC1) is
monitored by circuitry inside IC6501 for Under-voltage and Over-voltage conditions. The two conditions are
as follows:
OVP – greater than 33V
UVP – less than 8V
If either of these two conditions occurs at IC6501/pin 8, the unit will go into protection mode. The self-
diagnostic indicator will flash four times, pause and then repeat.
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) Ifthe power supplyoutputsproper secondary voltagesafterunsoldering R5013, suspectashorted +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. AlsocheckvoltageatIC6501/pin14(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.