[Coco] CoCo 2 with Random Characters on Screen at Power Up

[Arthur Flexser]

On Thu, Jan 16, 2014 at 2:42 PM, Brian Blake <random.rodder at gmail.com> wrote:
>
> Once when I swapped out a 6809 for a 6309 I had a similar problem, which had
> two causes. I accidentally cut a trace under the socket when I was removing
> the 6809. I didn't find it until I started investigating why the CoCo's
> screen looked like an ASCII jigsaw puzzle. Once I fixed that, I still had
> the problem - which turned out to be a bad CPU. Either caused by the cut
> trace or it was just a bad CPU - it happens.

For which reason, Danny, I'd recommend not just seeing that the same
thing happens when you swap in the 6809 from the working machine to
the nonworking CoCo, but also checking to make sure the 6809 from the
nonworking CoCo works okay when swapped into the working one.  With
these symptoms, the 6809 is a prime suspect.

An always good possibility to check is that there's a bent-under pin
somewhere.  Easy to miss if you're not very careful.  Though the fact
that the machine worked okay for a few days would indicate that's not
what the original problem was.

Art

>
> On 1/16/2014 2:31 PM, Danny Amborn wrote:
>>
>> I have a CoCo 2 model 26-3027 that shows random characters on the
>> screen at power up.  I bought this computer knowing it had issues but
>> when I received it initially it was working fine for a few days before
>> acting up.
>>
>> I replaced the RAM and the CPU so far.  I thought for sure it was the
>> CPU because it looked like it had a burn mark in the center but it
>> must have just been some sort of blemish but it does the same thing.
>> Since this is a 26-3027 so most of the chips are socketed, lucky me. I
>> also have a 26-3026 which is the same model just without the extended
>> basic.  I am willing to swap all the socketed chips but was wondering
>> if anyone knows which chips to start swapping first?
>>
>> --
>>
>> Dan Amborn
>> slackware64 at embarqmail.com
>>
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>
>
>
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