Page 193 - Troubleshooting Analog Circuits

I 80 14. Real Circuits and Real Problems

Table 14.5 Troubleshooting LM723-type Regulators
Indication of Trouble Possible Cause Solution
Output voltage has Resistors incorrect? Check R1, R2.
small error Oscillation? Check for oscillation.
Reference bad? Read V at pin 6.
Amplifier bad? Check V at pins 4,5.
Output voltage much Resistors incorrect? Check R1, R2. Check
too low V at pins 6,5.4,3
Reference bad? Check V at pin 6
Comp cap shorted? Check V, ohms at pin 13.
Q1 dead? Check V at pins 12, 11.
Pull out Q1, replace.
R4 broken? Measure R4 ohms.
Load too heavy? Measure V across R4.
Remove load.
Input much too low? Check Vh with scope.
PC foil shorted? Review all data above.
PC foil open? Review all data above.
LM723 busted? Review all data above.
Test, replace IC.
Output voltage much Same as above. Same as above.
too high. Q1 shorted out? Check voltage from pin
11 to 12. If that’s OFF,
transistor should be OFF.
Input V too high? Check Vi, with scope.
Output cannot drive R4 wrong value? Measure R4.
rated load. Q 1 broken? Check, replace Q 1.
Something bad? Review all data above.
Short-circuit current Current limiter busted? Check voltages at pins
too big. 2,3. Check R4.
Replace 723.
Poor load regulation. Oscillation? Check for oscillation.
Bad gain of Ql? Check and replace Q1.
Oscillation. General: Note the frequency.
C1 bad? Add .OO 1 across C 1.
C2 needed? Add various capacitors
across C2, 10 to 500 pF.
C3 needed? Try various caps at C3,O. 1
or 100 pF or both.
Try C2 AND C3 and also
increase C1.
Q1 has bad response? Try a different type of
transistor.
Output noisy. Input noisy? Check input with scope.
Reference noisy? Check pin 6 with scope,
add 0.1 or 1 pF mylar
to pin 5.
Q1 dies at full load. Inadequate heat sink? Try bigger heat sink.
Heat sink bolts too Check bolts.
loose or too tight?
Oscillation? Check for oscillations.
Power excessive? Compute power, E x
Win-VoJ.
etc., etc., etc., etc.