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be at least 5,000 ohms, if less, check C1, CR1, or
CR2 for short.
(4) Connect ohmmeter across power transformer
(ACC terminal and test point F). Reading should be
at least 10 Megohms. If it is less, check T1 for shorts
or leakage.
{5} If the previous steps prove satisfactory, or
if a trouble was found and corrected, replace line fuse
and reconnect input power.
5-45 Current Limit Troubleshooting
5-46 Improper activation of the current limit protec¬
tion circuit can be caused by one of two conditions:
(1) a failure within the supply; or (2) activation of the
optional crowbar SCR (option 011 or 104). Table 5-5
shows the recommended method of isolating the
trouble to either the supply itself or the crowbar.
Failures within the main supply are covered in Table
5-5 while crowbar problems are referenced to a separ¬
ate table.
5-47 Excessive Ripple Troubleshooting
5-48 If excessive ripple or noise is encountered, the
frequency of the ripple should be determined as the
first step in isolating the trouble. Ripple or spikes
occuring at the line or twice the line frequency, are
usually caused by problems in the reference supply or
the main rectifier area of the supply. Refer to the next
paragraph if this problem occurs. Higher frequency
noise ("hash") occurring at a fixed frequency are
Table 5-2. initial Troubleshooting
SYMPTOM
/
CHECK
RESPONSE - PROBABLE CAUSE
Low output voltage
(less than 1.5V)
Check fuse FI
a. Fuse blown, Internal short — proceed to Paragraph 5-43.
b. Fuse good. Series regulator loop or reference supply
defective — proceed to Table 5-3.
High output voltage
(above maximum rating)
—
a. Series regulator loop defective — proceed to Table 5-4.
High ripple
Check operating
setup for ground
loops
a. Refer to paragraph 5-24 for ground loop information.
b. If setup is free of ground loops, reference supply or
main rectifier may be defective — proceed to Paragraph 5-47.
c. Supply may be operating too close to current limit cross¬
over point — read Paragraph 5-10, then Paragraph 5-45.
Will not current
limit
—
a. OR-gate diode CR14 open or current limit amplifier U3
defective.
Poor, load or line
regulation
Check reference
voltages (12.4V,
6.2V, and 7.5V)
a. Voltages incorrect (beyond ±10% tolerance). Check
reference supply as indicated in Table 5-3, Steps 2 and 3.
b. Voltages correct (within ±10%). Supply may be current
limiting — read Paragraph 5-10.
Oscillation and/or
poor load transient
recovery time
a. Higher frequency oscillations (above 50kHz) can be
caused by an open C13, C14, or CIS.
b. A defective output capacitor (Cl 1) or feedback capacitor
(C19) can cause oscillations in one of many frequency ranges.
c. Oscillations occuring only in the current limiting mode,
can be caused by an open C15 or CIS. Oscillation near the
current limiting crossover point are caused by an open CR15.
5-7
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