An Engineering Change Order has been issued recently for Obsession Processor Units (ETC P/N 4052A1003) as used in tower systems only. Please make arrangements to complete this ECO on any unit manufactured prior to 9/7/94.
ECO 1637 - Obsession Processor Unit:
Add a load resistor to the 12 volt rail. This provides the minimum load required for proper regulation of the 12v rail. We are providing a load resistor kit (4052A 1026) which consists of the load resistor mounted on a plate with appropriate pigtails to connect to the terminal strip. The plate mounts next to the fans. See the ECO document (5 pgs.) for instructions.
Although there are no specific symptoms associated with this change, it is possible for the 12v rail to exceed 13.2v without the load resistor I which is the upper design limit for the DC-DC convertor on the SERF board. We have run extended tests with the 12v rail set to 14 volts without any problems, but we feel that design limits should not be exceeded.
We recommend that all CPUs be upgraded as soon as possible, but that special or urgent action is not required.
New NFS-50 Power Supply Alignment procedures:
One of the documents appended to ECO 1637 calls out new procedures for adjusting the power supply used in the Obsession Remote Processor. This procedure should be used following the load resistor upgrade and any other time the power supplies are adjusted, and replaces the procedure circulated with Technical Update #001.
Please call me at 800/688-4116 if you have any questions
Todd L. Johnson
Technical Services Manager