Whitechapel Computer Works MG-1

[Jules Richardson]

On 11/30/2014 11:53 PM, tony duell wrote:
>>
>> On 11/30/2014 12:51 AM, tony duell wrote:
>>> It needs a good set of NiCd cells on the power control board to start it up.
>>> If not, you have to do a 'jumpstart' involving connecting a 9V battery to a connector
>>> on that board. Some owners added an external socket wired there to make it
>>> easier to so this.
>>
>> I think I've seen four of the machines in total; every single one of them
>> had suffered significant corrosion to the main PCB beneath because of the
>> batteries.
>
> The main problem in my experience is corrosion of the (tin plated) Molex
> KK connector between the power control/battery PCB and the motherboard
> This carries the system power (!) and corrosion leads to all sorts of problems
> due to the fact that the 5V line is anything but.

Yes, I seem to recall that those were bad - but the corrosion had spread 
quite far around the connectors. :-(

>> That particular system has an ISA serial board and some flavour of ISA
>> video board (whatever the latter is, it has 8x 41264 dual-port RAM chips,
>> and there's a 20-way ribbon cable attached which runs off somewhere beneath
>> the ISA adapter board). Unfortunately the machine - like the MG-1's - had
>> also suffered significant corrosion.
>
> I wonder if that's the colour video output card. Does this CG200 have the normal
> MG1 motherboard in it? I seem to remember a connector on the motherboard
> that carried at least the video timing signals.

Unfortunately I don't seem to have any MG-1 photos here to compare it 
against, and it's been 7 years since I've seen one. In the CG-200 the 
memory boards sit along the left-hand edge of the system, and I think that 
is true of the MG-1, but four of the primary nsxxxxx ICs live on a little 
plug-in daughterboard - I have a feeling that wasn't the case with the MG-1 
(its primary ICs lived in sockets directly on the motherboard), and hence 
that it's a different animal.

The amount of RAM on the video board is 512KB, I think - which is an odd 
number; not enough for an 8bpp version of the MG-1's 1024x800 display, and 
yet rather high for a mono display (I think CRTs in the multi-megapixel 
range likely existed then for specialist applications where money was no 
object, but if someone had the cash to burn they'd probably be buying 
something other than a Whitechapel). Of course maybe it outputs 
1024x800 at 4bpp, but I thought that by the mid-80s serious colour-capable 
hardware was generally outputting 8bpp minimum (and non-palettised outputs 
were appearing on the scene).

While I can see a 6845 IC on the board in my photo, I can't make out what 
the other large (28 pin) IC is on the board near to the video connector - I 
suspect it's a DAC of some kind, but knowing exactly what might be useful.

cheers

Jules