[Coco] Help with Nitros9 on SDC?

[Don Barber]

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.

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%20Expansion%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
>>
>>