Date   : Sun, 06 Apr 2008 16:26:26 +0100
From   : acorn@... (Andy Ford)
Subject: Help with 'B' video output (only mode7 working)

Additional info...

I have just this moment tried swapping IC5 and IC6 with ones from a 
issue3. This "spares" issue3 machine does work (it has some faults but 
the video is ok)

But there was no improvement. I don't mind desoldering if needed but I'd 
like to be (as much as possible) that I would be doing the right 
component if someone thinks it is item X etc.

:)




Andy Ford wrote:
> 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.
>
>
>
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