From: nmil@bird.Princeton.EDU (Nikola Miljkovic')
Subject: Re: Problems upgrading 1Mb motherboard to 2Mb.
Summary: 1 to 2MB upgrade
Originator: news@ernie.Princeton.EDU
Keywords: ram upgrade
Organization: not organized
Date: Thu, 23 Jul 1992 09:45:40 GMT

In article <1992Jul17.210743.25384@olaf.wellesley.edu> lhawkins@olaf.wellesley.edu (Lee Hawkins) writes:
>Hi all:
>After my recent success in upgrading a 512k motherboard to 2Mb, I
>decided to upgrade the 1Mb motherboard in my office to 2Mb.  I installed
>the 4 additional 74F258's, their pullup resistors, the filter caps for
>the additional 1Mb of 4256-10's, and double-checked that the trace between
>E2 and E3 had been cut and E2 had been jumpered to E1.  (BTW, this is a
>factory original 1Mb board).

This is most probably the reason it does not work.

>So far, so good.  HOWEVER, when I boot up
>now, the computer still only sees 1Mb.  No parity or other memory
>errors, indeed no indication that either the OS or the Diags realizes
>that I now have 2Mb on board.

Exactly that happened to me when I did the upgrade before I set the
jumpers.

>My suspicion is that there is a factory 
>'mod' to original 1Mb motherboards that keeps them from looking for the
>extra 1Mb (more specifically, keeps them from looking for the second
>bank of memory), and that I need to change this to the way things are on
>a 'real' 2Mb or 512k board, so that the OS can 'see' the second bank.
>I've looked in detail at the schematics, and can't see what the
>difference is.  Any help would be greatly appreciated.   
>
>
>Thanks in advance,
>--Lee

Some time ago I did this upgrade (I am typing from it). At first I had
the same problem since there is no mention of 1->2Mb upgrade in the
archives. There are articles for .5->2Mb though.

Thanks to the people from net I found the right jumpers and made it
work. If you are really sloppy there could be some solder making a short
or even some burned chip, but after stressing my motherboard quite a bit
I got it to to work from the first time. Still you might want to check
that too.

Anyhow here is the part from the old article that deals with the jumpers.
If there is an interest I could post the whole stuff or better send it
to David for inclusion into the archive.

%%%%%%%%%%%%% How to set the jumpers for 1Mb -> 2Mb ram upgrade %%%%%%%

	The second type of board can be configured for either 512K, 1MB,
	or 2MB.  This is what I have.  There are two banks of jumpers/resistors
	near 12B and 11H.  If you have a 1MB system, these should be
	configured as follows.

	1 MB system:

	o--R 145--o   1K resistor		o---JR1---o   Empty
	|						  |
	o---JR5---o   Empty			o---JR7---o   Empty
							  |
	o--R 144--o   Empty			o---JR8---o   Jumper
	|					
	o---JR 6--o   Jumper			o---JR9---o   Empty
						|
						o--JR10---o   Jumper

	Converting to the 2MB system involves moving JR10 to JR9, removing
	R145, and installing a jumper JR5.

	2 MB system:

	o--R 145--o   Empty			o---JR1---o   Empty
	|						  |
	o---JR5---o   Jumper			o---JR7---o   Empty
							  |
	o--R 144--o   Empty			o---JR8---o   Jumper
	|					
	o---JR 6--o   Jumper			o---JR9---o   Jumper
						|
						o--JR10---o   Empty


IN CASE OF TROUBLE:
-------------------

	If you turn on the system, and nothing appears on the screen, look 
	at the LEDs in the corner of the system board.  If two of them are on
	it means that the built-in memory diagnostic has failed, and there
	is still hope.  If you see some other pattern, some other damage
	has occurred to the system and you are on your own as far as getting
	it repaired or replaced.

	First, put the jumpers back in the 1 MB configuration and boot
	the system.  If this does not work the problem is either with the
	original RAM or the data lines common to both banks and should narrow
	the problem down a bit.

	A data sheet for the 256K DRAMS is probably handy at this point.
	The memory on the board is divided into 4 banks of 18 chips
	each.  These banks are selected using the RAS lines on the
	DRAMS.  You can verify this with a continuity tester, noting that
	all the RAS lines in each of the four rows of two chips are connected
	together.  Banks 3 and 2 are the original DRAMS, while banks 1
	and 0 are the newly installed devices.

	The jumpers at 11H control the RAS decoding and are wired like this:
	
				-----------------
	+5 Volts o--R 145--o----| A1		|
			   |	|		|----- RAS3
	  LA2    o---JR5---o	|		|
				|		|----- RAS2
	+5 Volts o--R 144--o----| A0		|
			   |	|		|----- RAS1
	  LA1    o---JR6---o	|		|
				|		|----- RAS0
				| Decoder	|
				-----------------

	In the 2MB configuration, address lines 2 and 1 are used
	to select one of the four RAS lines.  In the 1MB configuration
	only LA1 is used, and A1 is pulled high.  This ensures that
	only RAS3 and RAS2 will ever be selected.

	By looking at the figure above, you can see how it would be 
	possible to move the jumpers to connect the 5 volt pullup to A0, 
	and LA1 to A1.	This will still be a 1MB configuration, but uses 
	RAS3 and RAS1.  In other words, it uses 18 of the original DRAMS and 
	18 of the new DRAMS.  Try booting the system in this configuration.

	You should also be able to see from the above figure how to
	connect LA1 to A1, and Ground to A0.  This will select only
	RAS2 and RAS0, in other words the other half of the original
	RAMS and the other half of the new RAMs.  Try booting the system
	in this configuration.

	If you are lucky, one of these configurations will boot, and 
	one won't.  This will narrow the problem down to one bank of
	devices.  Some careful work with a continuity tester should
	isolate the open or shorted connection.  You may also want
	to try swapping the upper and lower banks of the new DRAM to
	determine whether the problem follows the devices or the
	sockets.  (Aren't you glad you used sockets?)

	This was how I found the problem on my board.  It turns out
	that one of the address lines was shorted to ground, pin 1 of
	one chip had bent over and come in contact with pin 16 of the
	chip next to it which is ground.  Once I fixed this, the system
	worked beautifully.

Gary S. Trujillo                              gst@gnosys.svle.ma.us
Somerville, Massachusetts                     {wjh12,spdcc,ima,cdp}!gnosys!gst

%%%%%%%%%%%%%%%%%%%%%%%%%%%%% End of jumpers story %%%%%%%%%%%%%%%%%%%%%%%%

I hope this will help.

Nick