My summer project: A colour Stacy

[derkom]

I finally found some time today to diagnose the problem, and long story short, the Stacy is fixed.

I decided that rather than start reflowing or checking all the connections between the major chips, I would just capture data off every pin on the Glue, MMU, and Shifter. I can do that pretty rapidly and then compare data between like pins. As anticipated, the Glue was producing 15 kHz sync, despite the system being booted in mono. Didn't take me too long there to notice that RW on the Glue was stuck high, where it was quite active on MMU. This led to the discovery that RW on Glue was connected to the new 2.2k pullup, but not to RW on MMU, Shifter, or 68K. After looking at the board to figure out what had happened, I eventually realised that there was (past tense here) a tiny little trace between pin 9 on the 68K and the pullup resistor right next to it. Looks like I managed to break that when removing the old pullup.

So, a quick replacement for said trace on the underside...

IMG_20200728_195250.jpg

Boot it up...

IMG_20200728_195754.jpg

And back in business with a correct mono display. :dualthumbup:

[exxos]

:bravo: :goodpost:

[atari030]

Threads like this are gold, nice work.

[derkom]

Threads like this are gold, nice work.

:thanksblue:

IMG_20200729_075314.jpg

Looks like bus loading was indeed the issue with the relocator card last week, as GEMBench has now made it all night with the relocator installed (with just 68HC000 in one socket for now).

[derkom]

And here's the relocator board with both the R1C TOS206/IDE board and the 68HC000 installed...

IMG_20200729_085954.jpg

This is not how I plan to provide TOS 2.06 in the end, but this board is easier to install than the Cloudy.

One GEMBench run (not expecting any performance boost at this point of course)...

IMG_20200729_091758.jpg

[derkom]

While I was composing the last post, with the Stacy just sitting at the GEMBench main screen, it spontaneously rebooted. Insufficient power on the bus? Maybe my relocator needs decoupling caps?

[PhilC]

While I was composing the last post, with the Stacy just sitting at the GEMBench main screen, it spontaneously rebooted. Insufficient power on the bus? Maybe my relocator needs decoupling caps?

That relocator looks good. Pop a 100uf cap on the board and hopefully that'll help. Of course other problems can be the dreaded socket and pin combo.

[derkom]

That relocator looks good. Pop a 100uf cap on the board and hopefully that'll help. Of course other problems can be the dreaded socket and pin combo.

Yeah I'll do that at least for good measure, once it crashes again. Actually it's been solid ever since that reboot (knock on something), but regardless, a cap won't hurt. I didn't bother incorporating that into the board design because I knew it wouldn't be the final design, and it's trivial to add externally for testing.

The sockets are good quality turned pin sockets. The pins I'm using are just something from eBay, but they've performed well in the past, and seem fairly good, so hopefully they play well together. Due to vertical space limitations, the final build here is expected to eliminate the sockets on the top of the relocator (direct soldering the boards), but the socket and pin combo will still exist for the motherboard connection.

Edit: Is there such a thing as too many decoupling caps? The eventual build here will have boards in both sides that have their own decoupling caps. Is it a bad thing to have them both on my relocator and on the board connected to it?

[exxos]

More caps the better ;)

[JezC]

Only issue I've seen with more and more caps can be the inrush current when all are fully discharged; that might increase the loading on the PSU start-up.

Shouldn't be a big issue with a refurbished PSU though.