From: dnichols@ceilidh.beartrack.com (Don Nichols (DoN.))
Subject: Re: Memory upgrade questions (was: Dram chipss)
Keywords: ram, memory
Organization: D and D Data, Vienna Virginia
Date: Mon, 13 Apr 1992 03:07:31 GMT

In article <1992Apr12.035225.10048@Princeton.EDU> nmil@phoenix.Princeton.EDU (Nikola Miljkovic') writes:

	[ ... ]

>After opening the case I realized that I won't be able to finish the job
>that fast. The first thing is that holes for the memory were filled up
>and so I need to desolder them first. 

	Yes, they wave solder the machine (as any production machine would
be done, and that fills any otherwise unoccupied hole, along with those
which have objects to be soldered into them.

>One also needs  15 Cx's and 12 Cw's. That is how they are denoted on the
>board. Cx is obviously a capacitor and it has 104 written on it what
>should be 100nF, although they are really small. (Is this right?)

	Sounds reasonable.  After all, they don't need to be able to stand
more than 5VDC plus minor spikes, and they're distrubuted all around the
board, so no one capacitor needs to be very large in either sense.

>Now Cw's should also be some kind of capacitors since they are there in
>the same way as Cx's and they are "C". But they don't look as if they
>are capacitors (at last to me). I could only read 103M on them. Their
>shell is transparent and they look more like  diodes. Can anyone who
>have done the upgrade share the insight with net.

	I don't have a system dissassembled at present, so I can't verify
what you describe.  If the package has a color stripe at one end, it is
probably a diode, but the markings show it to be a capacitor.  Possibly a
glass-mica capacitor, and since it is only 10nF, and the voltage is low,
there is no need for great size.  The schematics don't exactly make it clear
what capacitors are located where physically.  Looking at the first page of
the schematics, the power bussing is scrunched together, and sumarized.

	Cw is .01 uF
	Cx is .1 uF

	And, notes say:
	1) Cw caps are used near I.C.s with 10MHz

which I take to mean that they need lower inductance and ESR than those near
lower frequence ICs.  This makes a glass-mica capacitor a possibility,
though there may be even better ones around.  There isn't much detail in the
schematics about the selection of capacitor types.

>There are also 4 resistor packs missing. What is the resistance?
>I couldn't see the label.

	RP 1, 2, 7,& 8 are shown on the schematics for the 2MB version but
not the 1MB version, and are four 33 ohm resitors, between pins 1&2, 3&4,
5&6, and 7&8.  They are in series with write data lines from IC's 11B, 11C,
11D, and 12A, all of which should be 74F258 chips.  I don't know whether
these are already  present on your system or not.

>I hope that there is someone who did this and can tell us how to finish
>the job. Thanks.

	I haven't done the conversion yet, since I can't do without that
machine long enough.  (It *is* my news and email gateway to the world, after
all. :-) There may be some other chips missing, but it is late, and I don't
have enough time to dig through all the schematics looking for differences.
(There *are* twenty-five pages for each version of the machine, after all.)
I would suggest that you get a copy of the Technical Reference Manual, if
you are going to be attempting such a conversion without a guide from
someone who has done it before.

	Good Luck
		DoN.

-- 
Donald Nichols (DoN.)     | Voice (Days): (703) 704-2020 (Eves): (703) 938-4564
D&D Data                  |  Email: <dnichols@ceilidh.beartrack.com>
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