Re: CBM720 heads up

Hi Andre,
on your pictures it looks like you built something to generate the 50 Hz
square signal, so the signal is there ?

My CBM 700 sometimes shows the cursor and does not start up.
Wiggling a bit at the eprom adapters helps.
The rom sockets are bad, I have to replace them.
Maybe your roms have contact problems too.
Try removing the basic roms, the machine schould then start into the TIM
monitor.


Christian

Am 19.10.2014 21:08, schrieb A. Fachat:
> Hi there,
>
> just a status on my CBM 720 repair - and maybe you can help as well :-)
>
> After replacing some capacitors in the original power supply, I checked the 
> first logic signals and found /RES continuously low. Traced it back to a 556 
> timer chip with a broken output. Replaced it, and found from scope traces that 
> the CPU was working.
>
> Unfortunately after a few minutes the old power supply went south with a small 
> "plop"... I decided to not get further with it, and instead replace it with a 
> PC power supply.
>
> That worked well, and got some video output after adjusting the screen 
> brightness with the small knob on the back (I found video signals with the 
> scope, and then decided to check that knob, which in fact ... :-) 
>
> Unfortunately it's not yet fully working, but much further. The CRTC gets 
> initialized, so that means the video output is working, the CPU as well (at 
> least to a considerable extent), but other stuff is still broken.
>
> Anyone knows the video pattern shown here?
> https://www.flickr.com/photos/afachat/sets/72157647798386959/
>
> Thanks
> André
>
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-- 
Christian Dirks
Toast_r@Idealine.info




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