[Coco] 128K CoCo 3 is DOA D:

[Juan Castro]

I would greatly appreciate some help in the mechanics of removing the
GIME. Can I do that with a small flathead screwdriver?

On Sat, Oct 6, 2012 at 10:52 AM, Retro Canada <retrocanada76 at gmail.com> wrote:
> juan its a 512 ram coco. check the ram chips first. the gime is a hard chip to remove. if you do so remember its orientation since there are no marks.
>
> i would say its a memory problem since you see the emulated vdg screen.
>
> check the voltage on TP1 and TP2 (there are 2 small test points on board labelled as) and they must be IIRC 8v and 5v
>
> good lucks
>
> Sent from my iPhone
>
> On 2012-10-06, at 9:16 AM, jdaggett at gate.net wrote:
>
>> Juan
>>
>> The black border and green screen background is default for the COCO. If that comes up
>> then at least part of the GIME chip is working.
>>
>> IF you have no prompts then you may have a DRAM or CPU problem. In the COCO3 on
>> power up there is a block of code that is copied from the ROM into RAM. If RAM is corrupt or
>> the CPU is not working then the GIME reads bad data from the low resolution text screen
>> area. Blowing the address and data ports on the CPU in the COCOs is not all that difficult to
>> do. Problably the weakest part of the 6809 design and the COCO itself is the lack of robust
>> drive capabilities and protection of the address and data buses through the expansion port.
>>
>> Try reseating the DRAM chips. I still think the DRAM chips are available through surplus
>> outlets like Jameco and others. If not then I may still have the set of DRAMs that I pulled out
>> of my COCO3 over twenty years ago. I don't remember if the 6809E wsa socketed or not. If
>> so then change CPU if you have a spare. I also have 680B09Es also even thought they are
>> still available on the net.
>>
>>
>> james
>>
>> On 6 Oct 2012 at 2:12, Juan Castro wrote:
>>
>>> On turning on, there's the familiar VDG green with black border -- but
>>> no text. Turned it off quickly and opened it. There seems to be some
>>> busted capacitors by the left. Could these be the sole cause of the
>>> problem? (Please don't tell me I have a busted GIME.)
>>>
>>> https://picasaweb.google.com/lh/photo/HPZWguZCACN3cwolSptlu29XcHdiH80reA6_ygAbi6M
>>> https://picasaweb.google.com/lh/photo/zSjUBF2jnDgYYnnQ8ZpuOG9XcHdiH80reA6_ygAbi6M
>>>
>>> Intriguing cheat sheets. What the kalamazoo is "JIMDOS3"? Custom ROM?
>>>
>>> https://picasaweb.google.com/lh/photo/mLgGG3Zumnc7GDloyQQO-29XcHdiH80reA6_ygAbi6M
>>> https://picasaweb.google.com/lh/photo/FylCx2Wh5fArnKY-mNAH429XcHdiH80reA6_ygAbi6M
>>>
>>> Juan
>>>
>>> --
>>> Coco mailing list
>>> Coco at maltedmedia.com
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>>>
>>>
>>> -----
>>> No virus found in this message.
>>> Checked by AVG - www.avg.com
>>> Version: 2012.0.2221 / Virus Database: 2441/5313 - Release Date: 10/06/12
>>>
>>
>>
>>
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>
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