Since this was written, there have been some minor changes to the PC board to improve reliability. Major changes have been made in the firmware, but this is automatically updated when you update to the latest I/O Libraries. Whenever an old E8491A is sent in for service, it is updated to the latest PC board. The change from the Adaptec PCI card to the Solectron OHCI compliant PCI IEEE-1394 card and the firmware changes are responsible for considerable performance improvements.

Sent: Thursday, May 03, 2001 4:23 PM
Subject: RE: E8491A and E8491B difference.

There have been only 4 PCO's of significance since the E8491A rev. A board was

created.  The most important of these occurred prior to the release of the E8491A

product, so any production unit should have this set of fixes - a number of kludges

to the Rev. A PC boards.

Of the three remaining PCO's, two were for power pin errors on a comparator and

an analog switch that could cause early failures of these parts - there was NO

functional change at all on these PCO's.  The last was the removal of the 4 diodes. 

These diodes were CR401/2/3/4, and are located near the

middle (top/down) of the board about 2" from the VXI connector backplanes.

They are colored black on my Rev. A2 PC board, so they probably aren't the blue

parts you mentioned (blue parts on my board are resistors).

The current PC board is revision B and it has been used on both the E8491A & B.

Revision A was only for early E8491A's and should have kludges.

A2 and earlier are prototypes and may have problems when you operate the

VXI cage and computer on separate power mains.

The only other E8491A/B changes are front panel changes to allow locking

FireWire cables, and silk screen changes for the product # change.