[Coco] Help with Nitros9 on SDC?

[gene heskett]

On Wednesday, January 26, 2022 6:01:20 PM EST Don Barber wrote:
> Hi folks, wanted to send an update. I narrowed it down!
> 
> Basically, I got another coco3, and bought a 512k sram update and 6309
> for it.
> 
> When I put the 512k sram into my existing coco, EOU6 boots up great!
> When I put the old 512k card into my new coco, I get the same behavior!
> 
> So clearly the old 512k card is faulty. This is despite passing every
> single ram test I throw at it.
> 
Historically its been possible to plug the half meg card in too deep, try 
lifting it back up 20 thou.

> The old ram upgrade is a Tandy AXX-7117. I can't find any reference to
> it online, but its identical to the picture in
> https://colorcomputerarchive.com/repo/Documents/Manuals/Hardware/512K%2
> 0Expansion%20RAM%20Card%20%28Tandy%29.pdf which is part no 26-3334.
> 
> As the 6809 EOU boots fine on the old RAM upgrade, I suspect its
> something specific that EOU is doing when using 6309
> instructions...perhaps the TFM instruction? Maybe the old RAM just
> doesn't switch fast enough? No idea, just thinking out loud.
> 
> So...curious if anyone has any advice on testing the old ram card and
> determining whats going on there? The chips on it are MT 1259-15. There
> are also several capacitors and one resistor. Nothing looks blown or
> anything. The card does get warm. Not a big deal to simply buy a new
> 512k upgrade but willing to try to a few things to get this one
> working too.
> 
> Thanks,
> 
> Don
> 
> On 1/15/22 19:29, Rocky Hill via Coco wrote:
> >   Hi Don,
> > 
> > Darn, I was hoping for at least some improvement..... Well, our
> > situations are a bit different but at least you are ruling stuff
> > out. There are several important signals that come from the
> > cartridge connector but there is one called ~CART which is an
> > interrupt for cartridge detection. Have you noticed odd behavior
> > when using a game cartridge?    If so, I wouldn't rule out a bad PIA
> > since the ~CART signal goes from the cartridge port to IC4 which is
> > the other PIA. The ~CART line is active low and it has a 4.7K
> > pull-up resistorwhich is R7. You might want to check that one just
> > in case.  R7 is located to the bottom leftof IC4 which is near the
> > bottom left hand side of the board which is the edge of the board
> > that    faces the front of the CoCo. Good luck!
> > -Pedro
> > 
> >      On Saturday, January 15, 2022, 04:34:13 PM EST, Don Barber 
<don at dgb3.net> wrote:
> >   Quick update: adding a pull-up resister to the SELA line didn't
> >   change
> > 
> > anything. Didn't notice anything unusual 'around' the PIA either. Ug.
> > Will report back when I upgrade my new-to-me coco to 512k.
> > 
> > Don
> > 
> > On 1/15/22 12:11 PM, Don Barber wrote:
> >> Rocky, this is *amazingly* helpful, thank you so much. I have not
> >> tested on another CoCo as I didn't have access to one before today.
> >> 
> >> For you and everyone else on the list: this morning I bought another
> >> batch of Coco gear, which included another SDC.
> >> 
> >> I get identical behavior with the new SDC. So its likely not the
> >> SDC!
> >> 
> >> Also included in this morning's batch is a stock coco3, so now I
> >> have
> >> a second one. Once I get a 512k upgrade then I'll be able to test on
> >> that to confirm its something funky with my coco3.
> >> 
> >> But I have high hopes for using a pull-up resister on IC5/IC7. I'll
> >> try it later today or this weekend. Thanks so much!
> >> 
> >> Don


Cheers, Gene Heskett.
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