White screen with STacy

[Roberto]

Hi everyone, I started with a post with this problem with my Atari STacy in the Atari forum, but unfortunately it has not been working for a few days. As I have just received the diagnostic cartridge from exxos, I am eager to proceed with the identification of the problem (and of course its solution).

Here I summarize what has happened to my STacy and what I have done so far to identify the problem.
After I cleaned the motherboard (it was really dirty but working), I plugged it into a power supply and I heard tick-tick-tick coming from the power supply; it looked like it had shorted out. On the second attempt I heard a small "stac" from the motherboard, so from there it no longer worked properly, and more specifically, connecting the motherboard to a color monitor gives me a completely white screen, while on a monochrome monitor (external) , it gives me out of range while in the original display, of the STacy, it remains black.

I did a test by powering the motherboard from an external power supply, directly into the floppy drive cables, with + 5V (as suggested by a fantastic user who helped me on the Atari forum and unfortunately I don't remember his nickname).
In this case I see a white screen on a yellow frame.

In any case, no characters on the screen.

I assume that the original DC / DC power board of my STacy is working and I state that all the cards (DC / DC and EPROM), have been inserted correctly in the motherboard sockets.

I received the long awaited diagnostic cartridge from exxos just the day before yesterday. I then tested my Atari ST, either directly from the menu displayed on the monitor, or via serial, by connecting my Atari ST to a high PC via serial cable, and also in this case I see the menu to perform the various tests. My Atari ST is working fine.

So, I did the same thing with my STacy (the dip-switches remain in the same position as an ST), but unfortunately no menu via serial.

So, just yesterday, I read a post here on this forum, by rubber_jonnie at this link: https://exxosforum.co.uk/forum/viewtopi ... =91&t=3143

where at some point it says:

"It should be noted that there are situations whereby neither the on screen menu nor the serial terminal mode do not work. If there is a problem with ROM space on an ST, generally speaking you will see a plain white screen when booting to low / med res.

Because the diagnostic cart maps into ROM space, a problem with the onboard ROM space will prevent this from happening. On a positive note, it means you can focus on fixing what's wrong with the on-board ROMS, so at least this sitll points you in the right direction.

If you plan to repair STs, then the diagnostic cartridge is an essential tool. "

I forgot to mention that I have already tried to replace the GLUE chip and another one of similar shape, whose name I can't remember, putting these two components from the STacy to my Atari ST and they work.

I think at this point that they could be the two EPROMs of the STacy.
I haven't had the chance to change them because I can't find them and as always they are different from those of a normal TS; they are from Toshiba and have different pinouts and my EPROM programmer does not support that EPROM model.

Of course, any idea is welcome! Thank you.

This is proof that the cartridge configuration works:

image0.jpeg (160.45 KiB) Viewed 1904 times

This is the white screen that my STacy offers:

IMG_6422.jpg (160.72 KiB) Viewed 1904 times

[derkom]

a fantastic user who helped me on the Atari forum

Awww.

Glad to hear from you again!

Okay, since we now know that you're getting no serial output from the diag cartridge, we can move on. I'm glad you've come over to exxos forum, because we've got a few hardware guys here who know far more than I do, so hopefully together we can track this down.

In order to help with your process of elimination, I am happy to send you a fresh set of ROMs, if you PM me an address to send them to, and tell me which TOS language you want.

[Roberto]

In order to help with your process of elimination, I am happy to send you a fresh set of ROMs, if you PM me an address to send them to, and tell me which TOS language you want.

Oh my God! I think I'm happier hearing from you than solving my problem!

So do you also think that at this point it is the EPROMs? I am now trying to contact you to send you my address, Thanks derkom!

[derkom]

So do you also think that at this point it is the EPROMs?

I suspect it's something else, but this is easy enough to test, and having a spare set of ROMs never hurts. If ROMs are eliminated, diagnosis starts to get a lot harder.

[stephen_usher]

Indeed.

The diag ROM requires that the machine can at least run the first few instructions in the ROM so that it can check for the existence of a cartridge and transfer execution to the code in the cartridge.

What equipment do you have available to you?

If you just have a multimeter this is going to be difficult, but you can check a few things, e.g. is the /HALT line on the CPU low? Are the voltages on the address and data lines sort of in the region of 3V - 4V? (If so then they're probably active. If they're 5V or 0V then they're not.)

With an oscilloscope then they are in a far better place to diagnose things.

[derkom]

I am happy to send you a fresh set of ROMs

Well hrmph. I seem to be unable to program EPROMs for @Roberto.

I've got some Toshiba TC571001D EPROMs I picked up a long time ago, back when I was starting on my colour Stacy project, and I've got a GQ-4X4 programmer. It reads these chips just fine, but every attempt to write fails. Following some advice from an arcade forum, I gave them a good 60 minute UV erase session, even though they already test blank successfully, but that's made no difference.

The programmer's supported device list includes the TC571000D, but not the TC571001D. Can someone who understands these things better than I do have a look at the datasheet and confirm for me that writing the TC571001D is the same as writing the TC571000D, and therefore my programmer should work?

[DoG]

...
The programmer's supported device list includes the TC571000D, but not the TC571001D. Can someone who understands these things better than I do have a look at the datasheet and confirm for me that writing the TC571001D is the same as writing the TC571000D, and therefore my programmer should work?

What happens if you make an adapter and switch OE and A16 (pin 2 and pin 24)?

[derkom]

What happens if you make an adapter and switch OE and A16 (pin 2 and pin 24)?

I've pondered that. Figured I'd fish for some advice first. The datasheet specifies that for programming, /OE can be either high or low, so my assumption has been that it won't have any effect. But I do plan to give that a shot if nobody knows for sure.

Edit: Well what do you know, that actually works. Thanks! Based on what I'd seen on the datasheet, I really didn't think that would work. Unfortunately, the way I quickly bodged it together to test it has destroyed one EPROM (leg is about to fall off now), but I've got more. I'll figure out a nondestructive way to do another one.

[derkom]

What happens if you make an adapter and switch OE and A16 (pin 2 and pin 24)?

stacyrom1.jpeg (66.53 KiB) Viewed 1774 times

Heh heh. Couple of stacked sockets gave me enough space that I didn't need to bend the legs much. Clip on a couple of leads and jam them down into the programmer's ZIF socket and we're good to go!

stacyrom2.jpeg (26.28 KiB) Viewed 1774 times

Okay, ROMs successfully written and verified working in a Stacy, with the diag cart to boot.

Will drop these in the mail to @Roberto tomorrow.

[stephen_usher]

Yay!!!