Date   : Fri, 05 Jun 2009 15:51:02 +0100
From   : acorn@... (Andy Ford)
Subject: Issue 4 will not accept a 1770

Hello.

Just a bit of advice really :)

I have here an Issue 4 'B. As far as I am "aware" , this has always been 
a tape only machine. However, I am unable to get a 1770 based DFS to 
work in it. It's simply completely ignored.

To confirm a few things first.

The parts I am using (I have tried two different sets, one by WE and one 
by RetroClinic) , both kits function and are 100% ok in another machine. 
It's just this particular Issue 4 that does not seem to like it for some 
reason. As I say, all the kit parts do work in another machine.

IC86 = Fitted a link
IC87 = Fitted a link (as an extra note I did have a spare 74LS123 that I 
tried as part of my "testing" too)
IC79 + IC80 = Fitted 7438's (tried the ones from the WE machine too)

The other links are set as follows (have not touched them)

S18-North
S19-East
S20-North
S21-2 x East/West
S22-North
S32-West
S33-West

I do not have enough spares lying around to try a 8271 based interface 
at the moment (yet) although I really only want the 1770 kit to work. 
Yes, I did fit the ROM and the module (as I say, I have two kits and 
have tried each component in another machine and it all works fine) , I 
traced a few of the pins of IC78 and they seemed ok.

It was suggested to me to replace the 7438 on the far left side ( thanks 
Mark :) ), this I did yesterday evening (after cursing Acorn for not 
fitting a socket here, I have done) , although it's no better (I made 
sure the socket I fitted was fine regarding continuity etc)

Just wondered what the next sensible thing to test / replace would be 
really. I have a multimeter but I do not have an oscilloscope so can 
check a few things if directed. I do have a machine on its way here via 
Ebay to put this kit into but I'd rather not have this machine in this 
kind of "limbo" state if possible.


Thanks :)