DP 1000 and filing off IC identifiers? Why?

[steven at malikoff.com]

Terry said
> I have a third party TRS-80 Model 1 expansion unit that I used with my
> System 80 when I first got disk drives.  I’ve decided I should add some
> pics and info to the System 80 website as I know they were used here in New
> Zealand with System 80’s and, also in the U.K. for the Video Genie.  A
> modified expansion cable was needed to convert from the System 80 expansion
> bus to the TRS-80 Model 1 bus on the unit but that was straightforward.
>
> The interface is called a DP 1000 by General Northern Microcomputers Ltd.
> It has no RAM, but contains a disk controller and printer port.  It was
> designed for ‘80s Model 1s and compatibles that had 48K of RAM under the
> keyboard, rather than requiring it in the expansion unit, as was the
> standard configuration.  Many System 80s had their memory expanded under
> the keyboard so it was ideal for these.  Mine was like this, and I found my
> DP 1000 worked very well with it.
>
> Before I put some info up, I’m wondering if anyone knows any more about
> General Northern Microcomputers Ltd, the company that made the DP 1000?
> I’m pretty sure it’s a U.K. company.
>
> Also, most of the chips have their ID’s shaved off (see the circuit board
> image)??  Why would they do this?  I can only assume it was to stop reverse
> engineering?
>
> Here are some pics:
> http://www.classic-computers.org.nz/system-80/hardware_DP-1000-front-800.jpg
> http://www.classic-computers.org.nz/system-80/hardware_DP-1000-back-800.jpg
> http://www.classic-computers.org.nz/system-80/hardware_DP-1000-circuit-board-top-hi-res.jpg


I have an Apple II RGB card made in 1981 by D.M.S. Ltd, also in the UK. Its 9 chips also have the ID's
removed but they did a much smoother job than on your board with the whole top blank, presumaby being
sanded off before assembling. Maybe the smaller UK companies like were more worried about reverse
engineering, considering the retail cost of microcomputer peripherals at that time. Certainly here in
Oz things such as Apple add-ons were not at all cheap.

I don't think it would be too difficult to figure out what most of those chips are. Looking at the
printed traces I'm just guessing the two 20-pin ones to the right of the WD 1771 FDC are perhaps
74LS244 tri-state buffers.

Maybe they can be tested in-circuit with a pulser but otherwise if you didn't mind unsoldering them
(resocket afterwards) one of these gizmos could help:
  https://www.ebay.com/itm/IC-Tester-74-40-45-Series-lC-Logic-Gate-Tester-Digital-Detection-IC-Series-Mete

Steve.