[Coco] Help with Nitros9 on SDC?

[Rick Ulland]

Left out of my previous. The Tandy Ax260-3336 upgrade (with same Fujitsu 
chips) is in my front room CoCo and works fine. Can't afford to blow 
that one up right now, but out of my pile I am pretty sure this was 
sorted to the OS9 machine for a reason.

-rick


On 1/26/22 5:01 PM, 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.
>
> 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
>>>
>>>
>