[Coco] Help with Nitros9 on SDC?

[David Ladd]

On Sat, Jan 15, 2022 at 3:34 PM 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.
>

One of the other things is to check to see if a real floppy controller
works ok on that CoCo?

I had gotten a CoCo2B that the CoCoSDC wasn't working in and found out the
HALT line part of the 6809 was damaged.  I replaced the 6809 with a 6309
and then it worked fine.

So it is always possible that the 6809 isn't working properly.




>
> 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
> >
> > On 1/14/22 9:28 AM, Rocky Hill via Coco wrote:
> >>   Hi Don,
> >> Maybe I missed it, but did you try the SDC on  another CoCo?I read
> >> through the posts but I didn't see any mention of that.
> >> Assuming you didn't try it on another CoCo, here is my story.....
> >>
> >> I had a very similar issue with my SDC randomly locking up my CoCo
> >> 3and occasionally displaying random characters. It was frustratingand
> >> it made me yell obscenities at my CoCo 3.
> >> Most of the lockups I experienced where while launching the SDC
> >> explorer,Launching Nitros 9 EOU, or trying to run one of sockmasters
> >> demos.Occasionally my CoCo3 would crash when playing a game loaded
> >> from the SDC butRegular carts seemed to work just fine.
> >>
> >> I wasn't totally surprised this was happening to me because I
> >> expected things to act funny as this was while I was testing a
> >> recreation of the CoCo 3 board.
> >> Relative to my new CoCo3 board, most of the evidence pointed to a
> >> faulty SDC butI knew the SDC was fine or at least fine enough because
> >> it didn't crash when usingit on an original CoCo 2 or CoCo 3.
> >> Through trial and error I did eventually figure it out andthe SDC no
> >> longer crashes when using it on the new CoCo 3 board. The culprit
> >> turned out to be a slight difference in the replacement PIAI was
> >> using for IC5. The number on the chip for IC5 is "LSC81001P"but it's
> >> "6821" compatible with some extra magic to make it safer when
> >> readingkeyboard presses.
> >> WDC makes a drop in replacement for the 6821 and it is what I decided
> >> to useinstead of sourcing older PIA's. The part number is
> >> W65C21N6TPG-14.
> >> I know that this is a bit of a stretch in your case but it might be
> >> worth a thinkso here are the two things that fixed the SDC's behavior
> >> on my new board.
> >> 1- I replaced the modern PIA with an older 6821. This of coarse was
> >> the easiestthing to do but it meant I had to use an older PIA.
> >> 2- I added a 4.7k pull-up resistor to the SELA line of the SC77526
> >> DAC/ADCchip. This can be added to either pin 11 of IC7 or pin 39 of
> >> IC5.I didn't deduce this fix, I simply remembered that the CoCo 2 has
> >> a pull upresistor on the SELA line and since I had already zeroed in
> >> on thePIA as the culprit, I figured someone had a similar issue when
> >> designingthe CoCo 2 so I copied it and it worked.
> >> I added option two to the latest board revision because it's a much
> >> better fixthat allows the board to work with older PIA's and the new
> >> replacement one.
> >> Again, I know our situations are different and I'm not saying you
> >> should add a pull-up resistor but consider that the PIA might be
> >> misbehaving and at thevery least I think it might be worth a look
> >> around the PIA to make surethere isn't anything out of the ordinary.
> >> That said, adding a pull up resistor with two clips is a really easy
> >> test thatwill not hurt anything. 4.7k, 10k, 47k any of those values
> >> should work.
> >>
> >> I hope you get it figured out soon.
> >>
> >> Pedro
> >>
>
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