Troubleshooting Information - HP 652A Operating And Service Manual

Power Supply. These same five blocks also appear on the
troubleshooting tree. To use the tree, decide if
or false, and proceed to the next step along the pertinent
branch of the tree. At each step use the additional
information given in Paragraph 5·52. Refer to the block
diagram in Figure 6·1 , and the schematics of Figures 6·2,
6·3 and 6-4, when using the troubleshooting tree.
5·51.

Troubleshooting Information.

5-52. This section provides information for each particular
step of the troubleshooting tree.
Check the output at both output connectors, and
ensure that it is undist.orted and within specifica­
tions, over the entire frequency range of the
instrument.
Check fuse Fl if there is not output and the line
indicator lamp does not light; also, ensure that the
1 1 5/230 V switch, S5, is in the correct position.
o
Check the signal at A2 pin 5 with an oscilloscope.
3.
The signal should be a sine wave of between
1 0 V and 12 V peak·to·peak; it should remain
essentIally constant regardless of the settings of
the OUTPUT AMPLITUDE control or the FRE·
QUENCY controls: if true, proceed to b ranch I I
of the troubleshooting tree.
The AMPLITUDE VERNIER control will
change the level by about 0.2 V, this is normal.
b. If the signal appears when the OUTPUT
AMPLITUDE control is fully counterclockwise,
but disappears as the control is turned clockwise,
then the Power Amplifier is shorting the oscillator
signal; proceed to branch 1 2.
c. If the signal amplitude changes significantly
with frequency or if the amplitude is twice
normal, then proceed to branch 6.
d. If there is no signal present, check that
A2C l 2 is not open, then proceed to branch 4.
False if either (or both) supply is not present.
Check the power supply connections to external
circuits.
A procedure for checking the oscillator circuit is
given in Paragraph 5·53.
Check the ac input voltages at Al pin 3 and 5 and
A l pin 6 and 7.
CD
is true
NOTE
Momentar y shorting of the + 30 V or
power supply may cause a Locked Current
Limit condition if the power supplies are still
loaded by the 652A circuitry. In the Locked
Current Limit condition the de output drops
to less than 2 V and does not return to normal
when the short is removed. This does not dam�
age the power supplies. Proper power supply
voltage can be restored by switching the instru­
ment off and then on again.
If the positive power supply cannot be adjusted to
+
30 V, proceed as follows:
a, Verify that the positive power supply is not
in a current limit or foldback current limit condi­
tion by disconnecting the power supply load Al
pin I (red).
The Normal Meter circuit is part of the Al PC
Assembl y. To completely unload and isolate the
652A power supplies, lift one end of
A IR24, A IR26, A IR28 (-).
+
b. If the 30 V power supply is restored by
disconnecting one particular load circuit (Oscilla­
tor, Output Amplifier, Expand Meter, or Normal
Meter), troubleshoot that circuit for shorts or
leaky components.
+
c. If the 30 V power supply is not restored
by disconnecting the load circuits, troubleshoot
the positive power supply. Refer to Figure 6-1 and
Figure 6·4.
If the negative power supply cannot be adjusted to
. 25 V, proceed as follows :
a. Verify that the negative power is not in a
current limit or foldback current limit condition
by disconnecting the power supply load Al pin 2
(violet).
b. If the · 25 V power supply is restored by
disconnecting one particular load circuit (Oscilla­
tor, Output Amplifier, Expand Meter, or Normal
Meter), troubleshoot that circuit for shorts or
leaky components.
c. If the · 25 V power supply is not restored by
disconnecting the load circuits, troubleshoot the
negative power supply. Refer to Figure 6-1 and
Figure 6-4.
®
Check T l and the line filter components,
LA,
through C2, C3, C4 and C7. Also, check
Al CRI through Al CR4.
NOTE
. 25 V
NOTE
A
IR I 7(+ j ana
Ll
5·1 7