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Hello all,

I'm in the UK and am new to the group, though have seen messages here when doing web searches for information on HP equipment.

I'm looking for help with a 16500A logic analysis system. I have both a 16500B and a 16500A in good working condition and am trying to make two useful machines, each with both DSO and logic analyser modules. The 16500B is no problem and supports everything. The problem comes with the 16500A. I've fitted it with 16530A/16531A DSO modules and a 16550A logic analyser module. Sadly, as reported by others in this group (back in spring of this year, I think) some examples of the 16500A only have 1MB of RAM which isn't enough to accommodate the 16550A system software. Mine is one of these, and it complains when loading the SYSTEM_.032 module.

Examining the CPU board, it has 8 44C256 1Mbit DRAM chips soldered to it. I've done a bit of reverse engineering and established that the board is in fact wired for 4Mbit parts, which is promising for an upgrade. However, 4Mbit DRAMs (44400 and so on) sadly don't seem to be available in the DIL package that the board is laid out for. I am contemplating all sorts of hackery involving wiring SIMM slots up, or adapter boards to take surface-mount RAM chips stolen from old SIMMs, but it would be time-consuming and the space available on the CPU board is limited. There's no guarantee of success, either, since the ROMs on the CPU board might not support more than 1MB of RAM.

I'd like to hear what peoples' opinions are of ways to proceed. Has anyone ever upgraded an early 16500A CPU board with more RAM? Do the ROMs support it? Might I need to change the ROMs to the later version? Or should I simply swap out the CPU board for a later one? In which case where would I find one?

I know the 16500A is pretty old, but it would still be a useful machine to me. The 16500 series don't seem to be all that plentiful in the UK so I haven't found a ready source of donor machines to pull parts from.

Thanks in advance
Chris