C64 fault

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Boydie
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C64 fault

Post by Boydie » Mon Apr 09, 2018 12:59 pm

I recently obtained a breadbin C64. Initially, it did nothing. Opening it up showed that the large glass fuse had blown. One replacement later, it gives the BASIC header and number of bytes free. However, there’s no cursor and the keyboard’s dead.
Swapping the two 6526 CIA chips changed the problem - the startup text on the screen became weird blank areas where the text should be, and the keyboard still didn’t work.

Any suggestions where to try?

markdryan
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Re: C64 fault

Post by markdryan » Mon Apr 09, 2018 2:12 pm

Have you checked out the pictorial c64 fault guide?

http://derbian.webs.com/c64diag/index.htm

Perhaps something there corresponds to the issues you’re seeing.

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richardtoohey
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Re: C64 fault

Post by richardtoohey » Mon Apr 09, 2018 8:55 pm

That's a great-looking resource! Need an Acorn version of it ... :D

Got a couple of C64s under my bed ... or somewhere ... need to dust them off and remind myself which issue(s) they have!

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Lardo Boffin
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Re: C64 fault

Post by Lardo Boffin » Mon Apr 09, 2018 9:55 pm

That is impressive. I had a dodgy breadbin which turned out to be RAM - the start up screen matched the appropriate screen shot almost perfectly!
BBC model B 32k issue 4, 16k sideways RAM, Watford 12 ROM board, Viglen twin 40/80 5.25" discs, Acorn 6502 coproc
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crj
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Re: C64 fault

Post by crj » Tue Apr 10, 2018 1:10 am

richardtoohey wrote:That's a great-looking resource! Need an Acorn version of it ... :D
Unfortunately, ten times as many C64s were sold as Beebs. That means (a) they have a bigger pool of failed machines to draw from in getting screenshots and (b) they have more people in the community who want the resource, which probably motivates them better.

And maybe the Beeb is just more reliable. (-8

(Plus, blown PSU capacitors don't have a characteristic effect on the video display.)

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1024MAK
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Re: C64 fault

Post by 1024MAK » Tue Apr 10, 2018 6:26 am

The trouble with most Beeb faults, is that a hell of a lot of them look very similar. But have different causes.

One class of fault, and the reason, is that there are lots of faults that prevent the CPU running the OS. So the sound chip never gets told to 'shut up' and the display shows nothing useful, as the 6845 CRTC is never loaded with valid values to generate a proper output.

Mark

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richardtoohey
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Re: C64 fault

Post by richardtoohey » Tue Apr 10, 2018 6:43 am

So the first 20 screenshots will be blank? :P [-X :-#

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Re: C64 fault

Post by SteveBagley » Wed Apr 11, 2018 10:02 am

crj wrote:(Plus, blown PSU capacitors don't have a characteristic effect on the video display.)
Maybe we need an olfactory Beeb repair guide? :)

Steve

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