Re: CBM720 heads up

From: Christian Dirks <>
Date: Wed, 29 Oct 2014 23:48:35 +0100
Message-ID: <>
Hi Andre,
256 bytes shows a problem with adress line VIDRAMA8.
A8 is not affected, otherwise the machine won't be able to boot and run
the monitor.
I think this may just be a faulty video RAM ( 2k x 8 SRAM at U29) or the
74LS157 at U15.


Am 26.10.2014 21:38, schrieb A. Fachat:
> Hi,
> On Sunday 19 October 2014 21:21:22 you wrote:
>> Hi Andre,
>> on your pictures it looks like you built something to generate the 50 Hz
>> square signal, so the signal is there ?
> Yes, I built a small 555-based circuit for that.
>> 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.
> Thanks, that was a good tip. Now I can boot into the monitor and even enter 
> commands. 
> However, there seem to be some display addressing problems. Parts of the 
> screen are displayed twice (each 256 bytes). You can, however, enter commands 
> into the screen when in the "overwritten" area, and execute them. So to me it 
> looks like it's a screen addressing problem.
> André
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Christian Dirks

       Message was sent through the cbm-hackers mailing list
Received on 2014-10-29 23:00:02

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