Re: 7854 RAM card upgrade only - any interest?


 

On 14 Mar 2016 10:05:59 -0700, you wrote:

Agreed on adding resistors, but you would have to make sure the longer turn on time of KBID does not cause a problem.
The resistors have no effect on KBID. All they do is limit the
current when the open collector outputs driving K0 from the external
keyboard and K7 from the memory backup switch conflict with the output
of U310 when U310 is enabled before the open collector outputs are
disabled.

Having to put a resistor inside the keyboard could be an issue for some. I finally got the stuck screw out of mine. I replaced all 4 screws with Robertson (square drive) 6-32 x 3/4" flat head. Of course I did not tighten them the way Tek's 300 pound gorilla did.
The external keyboard can probably be left alone since there is no
history of a failure of U310 or the open collector driver.

What a great idea to put the diagnostic ROM on the card. There is apparently a whole library of manuals for diagnostics, listed on page 1-1 and 1-2 of the 7854 Service Manual. We would need to start a search.

A 7854 was sold by Solanotraders on Ebay on Feb. 28, which included the 067-0961-00 diagnostic card (Version 4 if the label on the back of the scope itself is any guide) and the front keyboard diagnostic overlay. I wonder if Solanotraders would be willing to pass a message on to the buyer on our behalf, asking if he would be willing to communicate with us? The 7854 he bought is a candidate for the new memory card. Maybe he's already reading Tekscopes...

Cliff
I do not remember running across any ROM images from the diagnostic
card. The 7854 mainframes have a sticker on the back which says which
version of the diagnostic board is needed for that particular
mainframe.

It looks like there is more to using the diagnostic memory board than
I knew. The instructions for using it with the late 7854 include
changing both jumpers on the combined memory board which disables the
ROM and the RAM. Maybe the diagnostic memory board includes its own
RAM or its ROM is large enough to overlap the RAM address space.

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