Service Model
8901B
Power
Supply
Check
1.
Check
test
points AlOTP2 through TP7 with a dc voltmeter. The voltages should be within the
limits shown on Block Diagram
5.
If
a short on the supply
is
suspected, continue with step 2. If
a regulator
is
suspected, see Service Sheets 31 and 32.
NOTE
The supplies are interdependent. Often a short on one supply will shut down
another.
All
supplies are dependent on the
+15V
Supply.
The switched
+15V
Supply line
is
normally grounded when the instrument
is
in
standby. The
+15V
Supply (unswitched)
LED
should remain lighted
when the
POWER
is
set to
STBY.
2.
Remove the plugs connected to A26J6
(RF
SECTION), A26J3 (DIGITAL SECTION),
and
A26J2
(AUDIO SECTION) one at a time and observe the five power supply
LEDs.
(The plugs are located
on the circuit side
of
the A26 Power Supply Motherboard.) An extinguished LED will light when
the short
is
removed from the supply. The assemblies
in
the faulty section can then be removed
one at a time until the one with the short
is
discovered.
3.
Remove the plug connected to A26J1 (KEYBOARD). (This plug
is
on the component side.)
Jumper pins
2
and
6
of
A26J1 (where the green and black wires
of
W13 normally connect)
to
turn
the instrument on.
If
the short
is
on the
A1
Keyboard and Display Assembly, the extinguished
LED will light. If the short still persists, see Service Sheets 31 and 32 and check the faulty
regulator.
~~-60
Service Sheet BD5
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