Commodore 128 Startup advice

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Commodore 128 Startup advice

AndyG
I am messing about with a 128 and would like to ask for advice..... As background, this computer has had some of it Memory chips replaced and it boots fine in 128, 40 column config. I had to replace another memory chip myself to enable it to boot into C64 mode without an Out of Memory Error.

It now appears to works fine in both modes as far as I can tell. I am used a SD2IEC device to load programs etc.

It will run GEOS fine,in C64 mode.

Now to the issue.... if I boot (128 mode) from cold I sometimes get a garbage screen (with green border). If I hit the reset button (or restart it again) it will boot to the proper startup screen and work OK. If I have a joystick plugged into Port 1 (after using GEOS and the Joystick to move the mouse pointer) then I may have to do this a couple of times to get it going then it seems to works fine after that.

This morning after being powered down overnight, it booted fine - this garbage screen issue appears a little random!

It seems to boot directly into C64 mode with no problems if I hold the C= down whilst powering on.

To address the startup issue

    Do you think I may still have a memory chip issue on the lower bank (assuming C64 mode uses the other bank and works fine) - if so I will just remove the old memory chips and replace with "newer" types ?
    Should I recap the board as the issues seem to be from cold boot ?
    Should I do both ?

Cheers
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Re: Commodore 128 Startup advice

Ruud
Hallo,


I'm a bit confused. First you say the C128 boots fine in 128, 40
column config, then you say it won't, that is, from cold.

You didn't mention the 80 columns screen at all so I can assume you
are talking only about the 40 columns mode.

My first problem: I got my experience for repairing computers by
using the try and error method. The actual problem: I hardly ran
into brooken C128s. The most common failures: RAM and CIAs, and in
one occasion a ROM.

It boots fine in C64 mode so we can rule out the first 64 KB of RAM
anyway. If possible, swap the banks and see if it boots fine in C64
again. If so, you can rule out the RAM. If not possible, the C128
uses the second bank for BASIC and IMHO won't affect the boot
process.

Recapping is not needed IMHO as bad capacitors cause problems
randomly, not just at boor up.

Once booted up in garbage, have you tried to enter commands like
DIRECTORY? If it is just a screen problem, the drive should start to
rotate. One thing you can do is to replace the CIA serving the IEC
bus and userport. If you don't have an extra CIA, swap the two on
the board. And then boot the computer.

The boot problems could be caused by a flaky ROM. Whatever you have,
replace the for sure. (easy for me to say because I have tons of
them laying around).

Just trywith what I gave and let me know what happened.


--
   
Kind regards / Met vriendelijke groet, Ruud Baltissen
www.Baltissen.org







---
Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware.
https://www.avast.com/antivirus


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Re: Commodore 128 Startup advice

AndyG
Hi Ruud,

Thanks for the reply. It has me confused also as I am now finding it not to be entirely reproducible.

Yes I am working in 40 column mode ... I do have the capability to go to 80 column but only using the luminosity channel at present.

I tried the C128 the past two mornings and it booted fine ... just tried it now and got garbage screen ... hit the reset and works fine again.

Will try swapping the CIA chips and again reseating all the other ones. Will get back to you.

I don't have any replacement parts for the unit sadly.

Andy
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Re: Commodore 128 Startup advice

AndyG
In reply to this post by Ruud
Hi Ruud,

Thanks for the reply. It has me confused also as I am now finding it not to be entirely reproducible.

Yes I am working in 40 column mode ... I do have the capability to go to 80 column but only using the luminosity channel at present.

I tried the C128 the past two mornings and it boot fine ... just tried it now and got garbage screen ... hit the reset and works fine again.

Will try swapping the CIA chips and again reseating all the other ones. Will get back to you.

I don't have any replacement parts for the unit.

Andy

> On 8 Mar 2017, at 16:26, [hidden email] wrote:
>
> Hallo,
>
>
> I'm a bit confused. First you say the C128 boots fine in 128, 40
> column config, then you say it won't, that is, from cold.
>
> You didn't mention the 80 columns screen at all so I can assume you
> are talking only about the 40 columns mode.
>
> My first problem: I got my experience for repairing computers by
> using the try and error method. The actual problem: I hardly ran
> into brooken C128s. The most common failures: RAM and CIAs, and in
> one occasion a ROM.
>
> It boots fine in C64 mode so we can rule out the first 64 KB of RAM
> anyway. If possible, swap the banks and see if it boots fine in C64
> again. If so, you can rule out the RAM. If not possible, the C128
> uses the second bank for BASIC and IMHO won't affect the boot
> process.
>
> Recapping is not needed IMHO as bad capacitors cause problems
> randomly, not just at boor up.
>
> Once booted up in garbage, have you tried to enter commands like
> DIRECTORY? If it is just a screen problem, the drive should start to
> rotate. One thing you can do is to replace the CIA serving the IEC
> bus and userport. If you don't have an extra CIA, swap the two on
> the board. And then boot the computer.
>
> The boot problems could be caused by a flaky ROM. Whatever you have,
> replace the for sure. (easy for me to say because I have tons of
> them laying around).
>
> Just trywith what I gave and let me know what happened.
>
>
> --
>
> Kind regards / Met vriendelijke groet, Ruud Baltissen
> www.Baltissen.org
>
>
>
>
>
>
>
> ---
> Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware.
> https://www.avast.com/antivirus
>
>
>       Message was sent through the cbm-hackers mailing list


       Message was sent through the cbm-hackers mailing list
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Re: Commodore 128 Startup advice

AndyG
In reply to this post by Ruud
Hi Ruud

OK - I just went through re-seating all the chips and found pin 28 on the Character Rom IC was bent in at 90degrees and may have been making intermittent contact ..... I am sure it wasn't me who bent it whilst removing the chip but will see.

The Basic IC rom is also an EPROM (with a printed sticker) -  I wonder if the previous owner has been trying to fault find the machine.

It powered up to the Boot screen fine 1st time... will try again tomorrow...with more in depth testing.

Andy