[Coco] Aussie 2 meg installation - results - the saga continues

[Bob Devries]

Well, well.

I changed the GIME to a 1987 version, and I now get a different set of 
results. One pair of SIMMS now actually gives me 1 MB of ram, most others 
either don't work at all, or just give me 512K.

Grrrr.

--
Regards, Bob Devries, Dalby, Queensland, Australia

Isaiah 50:4 The sovereign Lord has given me
the capacity to be his spokesman,
so that I know how to help the weary.

website: http://www.home.gil.com.au/~bdevasl
my blog: http://bdevries.invigorated.org/

----- Original Message ----- 
From: "Robert Gault" <robert.gault at worldnet.att.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Tuesday, July 11, 2006 5:02 AM
Subject: Re: [Coco] Aussie 2 meg installation - results


> Bob Devries wrote:
>> Well, I installed the 2 Meg board as per instructions (Well, almost).
>>
>> Firstly, I just connected it as I would expect it to work, that is the 
>> DAT board is in, the memory board is in with 2 1MB SIMMS. 4 wires go from 
>> the DAT to the mem board, and one from the mem board to GIME pin 2, and 
>> one from the mem board to Pin 40 of IC5.
>>
>> This did not give a workable screen, however, when the plug on the mem 
>> board was removed, BASIC came up as usual.
>>
>> I then inserted a 150 ohm resistor in series with the wire from pin 2 of 
>> the GIME (the resistor as close as I can get to the GIME), and fired up 
>> again.
>> Hey presto, it comes up right now.
>>
>> Run the supplied MEMTEST program.
>>
>> This goes through until it gets to block 47 ($2F), and quits - BAD 
>> MEMORY.
>> If I now pull the plug off the mem board, and run the test again, it does 
>> the same; i.e. gets to block 47 and quits.
>>
>> A couple of things come to mind:
>> - The Coco3 I am using may be flaky.
>> - The 2 Meg kit may be faulty. I have no way of testing this.
>> - the wires between the DAT and MEM board are too long and/or need some 
>> shielding. (the wire from GIME pin 2 needed to be run from the bottom of 
>> the motherboard. Maybe I should run that in shielded cable?
>> - The SIMMS may be faulty.
>>
>> Any comments from the hardware gurus?
>>
>> -- 
>> Regards, Bob Devries, Dalby, Queensland, Australia
>
> Assuming this memory test program is doing what I think it should, you 
> don't even have 512K active memory.
>
> What does "pulling the plug from the memory board" mean? Does that 
> disconnect the four wires going to the DAT or something else? If the 
> memory board is disconnected, does that mean there is still 512K 
> conventional memory installed in the Coco3?
>
>  If the simms are faulty, swapping them might show something of interest. 
> What happens if you try running with just one simm?
>  If the original memory is still installed, I'd remove it as that is what 
> is required with all/most add-on memory boards. Also caps 65&65 are 
> typically cut. These load the CAS/RAS lines.
>  Your choice of 150 ohms for the resistor is based on the NTSC schematics 
> but you don't have an equivalent circuit. It seems you need a high 
> impedance input to the memory board to prevent degradation of the master 
> clock signal. However, without a scope on GIME pin#2 you can't tell 
> whether 150 ohms a large enough value. Still as the Coco boots, 150 ohms 
> probably is OK.
>
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