Oberheim ob xa service manual

Page 2

k DBXa TEST PROCEDURE [FIELD SERVICE]

This precedure will enable the technician to calibrate the following
functions:

- l.Power Supply
2.Modu1ation Assembly
3.5ontrol/Processor board
4.Voice Cards

5.Mother board

Equipment required:
Digital Voltmeter (4 1/2 digit minimum)
Strobe tuner (optional)
Audio amplifier with speakers or headphones
7 Oscilloscope

POWER SUPPLV TEST

CMDS MEMORY CURRENT DRAIN

BEFORE APPLYING AC PDNER, the current drain of the CMDS memory (6514s) is %
measured.

g

rIt is important no power has been applied to the unit for a minimum of u
. m. .tes before making this measurement.]

Check for any ground connections to the DVH common input other than the one
ground lead used for the measurement.

Locate the 10K resistor to the right of the battery on the upper control

board.
Measure the voltage across the 10k resistor. It should be less than 50 mV.

This corresponds to a current drain of SuA.
- POWER SUPPLY CALIBRATION and VERIFICATION
Two voltages are adjustable, the -5V and +15V supplies.

Locate the trimmer next to the leftmost 723 voltage regulator: it is labled
"-5. Locate the trimmer next to the rightmost 723 voltage regulator; it is

labled "+15".

Attach the DVM ground lead to pin 4 of connector C (on the lower control
board).

+15V ADJUSTMENT

Attach the DVM positive lead to pin 6 of connector K (upper control board).
Monitor this voltage; adjust the +15V trimmer for +15.000V +/-20mV.

-5V ADJUSTMENT

Attach the DVH positive lead to pin 10 of connector C (upper mother board).
Monitor this voltage; adjust the -5V trimmer for -5.0000V +/~20mv.