Turning on STacy only 2 times out of 10 does it start.

[DoG]

There is no PAL/GAL on a MegaST.

Do you perhaps mix MegaSTe and MegaST with each other?

[Darklord]

Truly a Darklord pro job! I would never be able to do such a thing... too complicated for me! :roll:

What you are seeing there was most certainly not an overnight job, nor was it "all at once". It was
the culmination of literally weeks and months of work, trying this, trying that, seeing what would
work, what would work together and not...

I had tons of help from the Atari community. I could not have done it without them. Period.

I do not have a great analytical mind. I'm more of the "beat on it 'til it works, if not, then go get
a bigger hammer" kind of guy. :)

Ever seen the movie, "The Martian"? There's a scene towards the end where the main character is
talking to a classroom full of students. He's telling them that you solve -1- problem at a time, then
move on to the next problem. Solve enough problems, and you're done, or in his case, he got to
come home. I always think of that when I'm working on my Atari's.

So when I tell you that if *I* can do it, anyone can, I'm not kidding. Just ask the guys around here,
they'll back me up on this one. :lol:

[rubber_jonnie]

Ok, so the RTC GAL/PAL at U25 looks like it is used to send CS (Chip Select), RD (Read) and WR (Write) signals to the RP5C15 clock chip. U25 is connected to the address bus and a number of other lines.

Based on what I can see on the schematic and datasheet for U15 (RP5C15), pin 16 & 17 should both be connected to the 32.768Khz oscillator circuit and I believe what you're reading is correct for those pins. TP1 is connected to 5v for pull up by the looks of the schematic, and also to pin 3 of U15. I believe this is normal based on what the schematic shows for pin 3 of U15.

The clock circuit on the Mega schematics I have is identical to the STacy, but the output at TP1, which is connected to pin 3 of the RP5C15 on both machines is dependent on the clock output select register setting, and it could output 16Khz if the register is set specifically to do so. Nevertheless, pin 3 isn't really relevant as it goes nowhere and is simply pulled up to 5v.

I honestly don't believe a faulty RTC could be the cause of your problems. I might be wrong, but my Spidey senses say no.

If you don't have the schematics for the STacy, you need to download them and print them out, then you can scribble notes on them as you go. Get datasheets and print them too, it's far easier than referring to PDFs on a computer.

[czietz]

There is no PAL/GAL on a MegaST.

of-course-there-is.jpg

[DoG]

Cool. Totally missed that. I should clearly stop answering threads.

[Roberto]

....
If you don't have the schematics for the STacy, you need to download them and print them out, then you can scribble notes on them as you go. Get datasheets and print them too, it's far easier than referring to PDFs on a computer.

Thanks for this analytical scheme of the RTC functioning, it will help me to understand something more hoping to arrive at the solution. In the meantime I bought a new RTC (RP5C15) and a new GAL (PAL16L8ANC) that I'm going to program; by the way, the latter I think is the same as that of the Mega ST, right? Do you know if there is any site where I can download the software to program this GAL?

PS: I printed all the STacy schematics on paper when I had to change CPU. I think at this point that the problem I had at the beginning on the short circuit of the CPU has also taken the RTC circuit.

[Roberto]

i think i found the problem. I remember that my STacy does not turn on if the voltage is not at least 5.2 Volts, and as I connect other peripherals (such as diagnostic cartridge, HD controller, etc.) it always needs more initial voltage, once the ignition is over I can set the canonical 5 Volts with the DC/DC module trimmer. I removed the IC RTC PAL (the one in the photo to be clear, or U25), easy to remove since it is housed in a socket; and now the STacy always turns on at 5 volts (even less!) even with all the peripherals connected! I had opened another post on the Atari Forum because it seemed I was also having problems with the Real Time Clock (in fact it doesn't currently work), and I now find out that that problem was causing me this too! now, before I solder off (since it has no socket) also the RP5C15 IC (labeled U15), does anyone know how I can program that PAL RTC? I think it's a PAL16L8ANC but I can't find it in the list of my TL866 Plus... I would first like to change the PAL RTC before risking doing damage by changing RP5C15 since the latter is soldered to the motherboard.

07506620-3917-430F-A7E7-6A226E8C6B54.jpeg

[rubber_jonnie]

If you're running with the PAL RTC removed, then I wouldn't change the actual RTC IC until you've replaced the PAL IC.

I know the TL866 Pro does support GAL16 ICs as I just checked on the list of supported ICs for the programmer. I've burned PAL chips no problem on mine, 16V8 types.

My suggestion would be to get the datasheet for the PAL RTC and compare specs for the GAL16, IIRC the specs are much the same so you should be able to use the TL866 to program the PAL using the GAL option.

Double check the specs first against the datasheets though.

Here is the full list of ICs supported by the TL866 Pro from the manufacturers website: TL866 Pro supported ICs

[Roberto]

If you're running with the PAL RTC removed, then I wouldn't change the actual RTC IC until you've replaced the PAL IC.

I hope you tell me! Ok I'll focus on that now. It's good to know that I'm getting (I hope) closer to the solution.
As soon as I have new news I will post them here, thanks in the meantime.

[stephen_usher]

The Atmel (OK, now a different company, Microchip, but same part number) ATF16V8B-15PU GAL chips are pin and program compatible with the 16V8 PAL chips and are easily programmed by the TL866Pro, I do this often as the 16V8 GALs are very useful for address decode tasks.

The only issue would be getting the logic description (PLD file) or compiled code (JED file) if no-one else has reverse engineered it.

If you have the .PLD file then you will need the WinCPLD program to compile it to a .JED file before it can be written to the GAL device.

Unfortunately RS and Farnell no-longer stock them so you'll have to get them from Mouser: https://www.mouser.co.uk/ProductDetail/ ... v3gA%3D%3D