Ngingring Change Ord6r

product affected:

OB-a drawings affected:

eco no.


□ future production

□ retrofit production & inventory

□ retrofit in field. □ as needed g drawing correction only

reason for change:

add ob-8 midi interface to os-ô


inte£face pcs)


of change: add pcr assy no. (ob-8 midi per attached instructions.


2250S<xrth Barmgton ZW**, Los Angeles. Catforro90064. (2G>473-6574

Oberheim MIDI Interface Update Installation Instructions 1/31/84

The Oberheim MIDI Interface can be retrofitted to all existing 0B-8s. The installation requires removal of two I.C.s, changing one endbell, and installation of a printed curcuit board. The installation should be performed only by qualified personnel.

1. This procedure will clear the offsets stored in memory and will destroy patch data. So the data should be stored to cassette BEFORE any further actions ere taken.

2. Disconnect the power cord.

3. Remove the 2 screws located along the top edge of the endbells that secure the front panel (4 total) and raise the cover to expose the main processor board.

4. Remove the left endbell, and replace with new endbell with MIDI din connectors on it. Return old endbell to Oberheim Electronics.

5. Remove the 40-pin I.C. from socket 26 of the main processor board. Install this chip in socket 8 of the interface board, being careful to match the notches on the chip and on the socket.

6. Remove the 16 pin 74L5139 chip from socket 41 of the processor board and put into .socket 5 of the interface board, again being careful to match the notches on the socket and the chip.

7. Remove the 24-pin 2732 chips from sockets 21,22,23, and 24 of the main processor board and return to Oberheim Electronics.

8. Install the 24-pin 2732 chips as follows:

1) Insert chip labled B3-0 into socket 24 of the processor board, again being careful to line up the notch on the chip with the one on the socket.

2) Install chip B3-1 into socket 23 of processor board.

3) Install chip B3-2 into socket 22 of processor board.

4) Install chip B3-3 into socket 21 of processor board.

5) Install chip 83-4 into socket 7 of the interface board.

9. Remove the four screws from the main processor board located at:

1) the upper right hand corner of the processor board

2) middle of the top edge of the processor board-

3) middle of the right hand edge of the processor board.

4) the middle of the processor board (near U40).

■lQ. Turn the Interface board chip-side down with the ribbon cables stick out to the left. The 16-pin ribbon will be above the 40-pin ribbon. Pin . of both ribbon cables is located at the tops of the sockets. Insert the * pin ribbon header into socket 26 on the processor board, being careful to line up pin-1 of cable with notch on socket.

11. Insert the 16-pin ribbon header into socket 41 on the processor boarc When the header is properly installed, the cable will stick straight out from the right side of socket 41.

12. Position the four spacers over the four empty screw holes in the processor board. Turn the Interface board over and position the four hole in the corners over the spacers. Insert the long screws through the corner holes in the Interface board through the spacers and into the holes in the processor board.

13. The middle cable on the endbell assembly is "MIDI OUT". Connect this cable to the molex connector on the Interface board labled "MIDI OUT". The rear cable on the endbell assembly is labled "MIDI IN" and should be connected to the molex labled "MIDI IN" on the interface board. "MIDI THRU should be connected to "MIDI THRU".

14. To insure proper operation after changing the EPROMS, the RAM chips should be cleared. To do this carefully remove each RAM from it's socket a then carefully put it back in. Do this with all three RAM chips. They are I.C.1 s 18,19, and 20.

14. Close the front cover and replace the front cover screws.

15. Re-connect the AC power cord.

16. With the memory protect switch OFF (rear panel), turn the power on. Load the saved data from cassette, including the offsets. See page 43 of tl 08-8 owners manual (included).

17. Press AUTOTUNE.

18. Apply sticker to the rear of the 0B-8 above Computer Interface connector.

xm OB-8 Owner's Manual

Software Calibrations

1. Tape Storage of Calibrations

The calibrations of your particular 08-8 stared in computer memory are recorded cn tape automatically each time you save your programs. If for some reason your OB-8 gets out of calibration (due to memory drop), the calibrations on tape can be loaded back into the 08-8 in much the same manner as patch programs are loaded into the C8-8 from tape:

1) Enable the Cassette Interface with the switch on the rear panel.

2) Press PLAY on the tape recorder. You will be able to monitor the tape through the main outputs of the OB-8. The MASTER VOLUME will control the volume for monitoring the tape.

3) Hold down all six buttons in the FILTER section (OSC 1 ON, OSC 2 HALF, OSC 2 FULL, NOISE, 4 POLE, and TRACK).

4) As soon as the "leader" tone is heard, press the PLAY switch on the OB-8. At least three seconds of the "leader" tone must come between pressing PLAY and the rough sound of the memory information. The light on the PLAY switch will be lit from the time the switch is pressed until the first of the. memory information is recognized. At that point, the GROUP lights (A, B, C, D) come on in sequential order.

If the MEMORY PROTECT switch on the Rear Panel of the OB-8 is 3et to PROTECT, the PLAY light will not operate.

4) If an error is detected, the PLAY light will flash.

The PLAY function can be cancelled by pressing the HOLD button.

The calibrations should only be loaded in if the OB-8 has lost its programs, or the envelope generators do not seem to be operating properly. It is important that these calibrations are loaded in only from a tape made- from the same 08-8, otherwise the wrong calibrations will be loaded in.

Checking a data tape will also check the calibrations on that tape (See CASSETTE INTERFACE).

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