Date   : Sun, 06 Apr 2008 14:06:37 +0100
From   : acorn@... (Andy Ford)
Subject: Help with 'B' video output (only mode7 working)

Afternoon :)

I have here a nice (tape only) issue 4. However, only mode7 appears to work.

I tested with RGB (using the same lead / monitor as I use for my M128) 
and there is no picture at all in any other mode. I quickly wrote this 
to check...

10 FOR A=0 TO 7
20 MODE A
30 FOR N=0 TO 100
40 PRINT "This is mode";A;
50 NEXT N
60 NEXT A
70 GOTO 10

... Just to be sure it was not me


When tested with the composite video (either with or without the colour 
jumper enabled) , I do get a very vague picture (it is offset to the 
left and almost inverse)

Testing with the UHF output gives the same (although the picture is very 
badly ghosted with UHF even in mode7) , but that could simply be the lead.

I do not know the history of this machine really. In fact it was just 
the board when I got it so I put it into a case etc. It does not have 
any of the disc upgrade chips fitted.

I added my new Go-MMC to it today actually but it was like this before, 
so that is going into the M128. I have some spares to check with (I have 
a complete but almost dead issue7 if needed)


Can someone give me a pointer or two where I should check (I do not have 
a 'scope but have a decent meter and know how to use it properly) ... I 
am hoping it is something silly like a jumper is in the wrong place or 
something.

Any pointers would be appreciated please (even if it is "try swapping IC 
x for another one etc")

Thanks in advance :D


Andy.