[Coco] 128K CoCo 3 is DOA D:

[Gene Heskett]

On Saturday 06 October 2012 09:56:31 Retro Canada did opine:

> 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.
 
But it is so marked!  Please note there is one beveled corner, both on the 
chip and the socket frame.

But all this noise about removing the chip should be coming accompanied by 
the phrase

 "using a PLCC puller"!

It is very dangerous to the socket frame to attempt to pry it out, 99% of 
the time you WILL crack the frame, and there goes the majority of the 
sockets contact pressure between the chip and the socket.  The pullers are 
about a tenner in USD & that the shack did carry them at one time.  
Otherwise people like Jameco or Digi-Key have them.

> 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/HPZWguZCACN3cwolSptlu29XcHdiH80
> >> reA6_ygAbi6M
> >> https://picasaweb.google.com/lh/photo/zSjUBF2jnDgYYnnQ8ZpuOG9XcHdiH8
> >> 0reA6_ygAbi6M
> >> 
> >> Intriguing cheat sheets. What the kalamazoo is "JIMDOS3"? Custom ROM?
> >> 
> >> https://picasaweb.google.com/lh/photo/mLgGG3Zumnc7GDloyQQO-29XcHdiH80
> >> reA6_ygAbi6M
> >> https://picasaweb.google.com/lh/photo/FylCx2Wh5fArnKY-mNAH429XcHdiH8
> >> 0reA6_ygAbi6M
> >> 
> >> Juan
> >> 
> >> --
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> >> Coco at maltedmedia.com
> >> http://five.pairlist.net/mailman/listinfo/coco
> >> 
> >> 
> >> -----
> >> 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
> > 
> > --
> > Coco mailing list
> > Coco at maltedmedia.com
> > http://five.pairlist.net/mailman/listinfo/coco
> 
> --
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Cheers, Gene
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