OJ’s projects…usually breaking stuff.

[olivier.jan]

Finally found the issue causing the pixel garbage, it’s the ET4000 card itself.
Plugged it in a 486 like the other day and it was fine but after a few minutes it started acting up and displaying some garbled text.

I guess I didn’t test long enough last time or it got damaged during all the tests done this past few days.

Anyway, I tried to clean up all sockets, pushed all the chips deep in the socket but it doesn’t fix the problem. I guess I need to find a new ET4000 now

[frank.lukas]

Take a closer look at the soldering of the ET4000AX chip and may be resolder it with a lot of good flux. I also had a defective card where the bus driver chips were defective. For the data bus 74LS245 chips and for the address bus faster 74F244 chips may be swap these out?

[olivier.jan]

I actually reflowed most of the chips and it seems to be working fine now. I just launched a gem bench in a loop to see if it stays ok.
If it’s OK, next step will be to get it to work with the ST536.

[olivier.jan]

Just reached the point where the Atari is going to stay in storage fo a few days and I am going to do something else for a while.

Just received fresh EPROMs from Ecco’s store yesterday, flashed the modified TOS 206, installed the ST536 (without STGA for now) and… blank screen at boot. Reverted back to the known working vanilla TOS 2.06 and… blank screen.
Put back original CPU and ROM with the ST536, it works.
I thought, OK, it might be these F#%$}#£¥ PLCC sockets, cleaned the contacts, pulled them a bit to help… blank screen.
Tried a second ST536 without even changing the EPROM (it has a small RAM issue but otherwise works fine)… blank screen
The ST536 was working perfectly fine last week, I guess I will let it rest and forget the Mega ST until after Christmas before doing further troubleshooting.

[olivier.jan]

I waited after Christmas, and even a bit longer as I only took the Mega ST out of storage today, one year later.
This actually led nowhere, I tested both ST536 and both gave me blank screen, I switched to a good old 520ST and same blank screen, so the the Mega ST has nothing to do with the issue.
I reflashed the CPLD with the latest version, flashed the latest ROM, but no progress.
I finally reflowed both boards completely and managed to damage some pads on that f@#€%ng PLCC socket (really why not use through hole sockets for PLCC) on one the board.
The other might have a short as now the ST doesn’t boot at all when it’s plugged in….

I guess I will have another look tomorrow for the short and maybe try to repair the pad and associated trace.
Anyway, now that the ST536 is out of stock and that Exxos is not shipping to EU anymore anyway, there are not too many option but to fix this.

[olivier.jan]

Finally didn’t take the time to work on the ST536, I preferred to spend some time on a C128 I had for a while and never really used. I’ve never had Commodores before, it looks nice but I’m a bit lost.
Anyway, new topic : I just received an ST first generation from Germany this afternoon and I can’t get it to display a picture.
I checked voltages, all good. Removed all socketed chips and used contact cleaner, but no change.

I tried my usual setup, ST to Scart and an OSSC but the OSSC can’t lock on the sync, it keeps jumping all around and the screen stays black. When I press reset, I finally get the standard white screen, but it goes away as soon as I release the reset button.

When I use an UBESwitch or Exxos basic VGA adapter, I get a proper sync at 15khz or 31khz depending on the resolution, but just a black screen.
A good thing though, the signal is PAL, so the CPU and ROMs are working to some extent.
is there anything special about the video circuit of these early STs?

In the coming days I will try a direct connection to a VGA monitor and then I’ll trace the signals coming from the shifter using the scope…

[stephen_usher]

I'd use the 'scope to see if there's any activity at the processor... the usual "before doing anything else" stuff of power, clock, reset. Once those are out of the way check for the /CS on the ROMs, as if they're not being selected then there's no chance.

Once these are out of the way it's time to just 'scope the address and data lines to see if the CPU is even trying to run code.

Testing the video output is way down the check list.

[olivier.jan]

Agreed, and I will clearly look at these signals.
My assumption was that the CPU and ROMs were Ok as the sync signal I get is switching from 60hz to 50hz just after boot, which is normally done by some ROM code very early in the boot process. Getting a proper sync signal means also that the GLUE is doing at least parts of its job, and that the clock is OK.

[olivier.jan]

Some progress this morning on the short ST:

- Checked Clock(32,16,8) , Reset, Halt - All Ok.
- Checked Data lines: Activity for a short while, then it stops
- Plugged diag cart, connected a serial adapter to the MFP and : I3 RAM Address check, seems to be a problem with D9 stuck high.
- Swapped MMU with a more modern IMP one: different message, I2 Disturbance
- Back to original MMU, now the diag cart menu appears on the serial interface.
- Turned off computer, plugged display, turned on: black screen again.
- Now diag cart message is I6 error No(I6) ….

So:
- we know assumptions are bad, thanks Stephen for reminding me to check the basics and not jump to hasty conclusion.
- we know the CPU, ROM, MFP and GLUE works to some extent as some code get executed, including the diag cart, there’s a sync signal from the glue and the serial interface of the MFP is working.

Next step will be to try with a bench power supply as I don’t fully trust the current PSU, voltage are ok but there’s a LOT of ripples.

I will review the solder joints of the MMU after that along with the socket’s contacts.

[olivier.jan]

Small progress, but still no picture.
I can now get the diag cart menu to display, RAM and Timing tests pass all the time and no more i6 error.
How to do that: use the scart cable or Exxos VGA switch. If I use ubeswitch, keeps sending i6 errors and never display the diag cart menu

From the diag cart, I can switch 50/60hz and I can see on the OSSC that the sync is properly changing, if I boot in high res I can also get the 71khz refresh rate, etc… but still totally black screen.

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