Nearly there..

A place to eternalise your Gigatron build photos. From box to BASIC.
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Z00l
Posts: 3
Joined: 24 May 2019, 22:05

Nearly there..

Post by Z00l » 24 May 2019, 23:19

I assembled my Gigatron and powered it up.

The flashing LEDs are running and the Menu appears on my monitor. :)

If I select anything from the Menu which requires graphics, I get problems:

Snake - brief flash of random pixels, then screen blanks, displays "no VGA signal" and stays blank. LEDs keep flashing. Press "start" to reset.
Racer - screen fills with random pixels, blanks, fills with random pixels. LEDs keep flashing. Press "start" causes LEDs to freeze and system lock-up.
Mandelbrot - screen fills with random pixels, blanks, "no VGA signal" and stays blank. LEDs keep flashing. Press "start" to reset.
Pictures - the screen blanks, displays "no VGA signal" and stays blank. LEDs freeze and system locks-up. Pressing "start" has no effect.
Credits - appears to work fine: credits text displayed in different colours. Press "start" to reset.
Loader - displays "Ready to load" and a red stripe + a line of random pixels. Press "start" to reset.
Tetronis - brief flash of random pixels, then screen blanks, displays "no VGA signal" and stays blank. LEDs keep flashing. Press "start" to reset.
Bricks - brief flash of random pixels, then screen blanks, displays "Bricks" on a blue background. LEDs keep flashing. Press "start" to reset.
TicTacToe - screen fills with random pixels, blanks, fills with random pixels. LEDs keep flashing. Press "start" to reset.
BASIC - screen fills with random pixels, blanks, fills with random pixels. LEDs keep flashing. Press "start" to reset.
WozMon - - screen part filled with random pixels, plus fragments of previous display. LEDs keep flashing. Press "start" to reset.

The Gigatron is plugged in to an Asus VE249H LCD monitor. Have I found the first incompatible monitor?

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marcelk
Posts: 304
Joined: 13 May 2018, 08:26

Re: Nearly there..

Post by marcelk » 25 May 2019, 18:17

It sounds like an "advanced" variation of "system doesn't start, but does show garbled pixels" as described on the Troubleshooting page. We haven't seen it in this form before, but this behaviour is not far off from just showing random pixel data. If the VGA shows something (even garbage) and the lights are running, there is some software running on the Gigatron.

Screenshot 2019-05-25 at 20.07.10.png
Screenshot 2019-05-25 at 20.07.10.png (358.81 KiB) Viewed 240 times

What all your items have in common is that the main menu has to load the selected application from EPROM into RAM first. If we get bad data, I can imagine we see such things. The part that's responsible for booting the main menu itself seems to work (might be luck). So I suspect the connections in the EPROM, PC high and Y-register area. But in reality it can also be in other parts. Loader looks to behave normal (you can check in the online emulator). But that's a crazy small program.

[Edit: I'm pretty sure I have a very similar ASUS monitor at home, and it works fine.]

Z00l
Posts: 3
Joined: 24 May 2019, 22:05

Re: Nearly there..

Post by Z00l » 27 May 2019, 19:15

Thanks.
My garbled pixels have much more structure than yours!

I notice something interesting: if I keep pressing the Start button, on the 2nd restart, the A sine-wave of Pac-Man ghosts appears! I can control the speed with the joy-pad and it can run for some time before the screen blanks and the Gigatron halts.
I'm guessing I have an open address line or so, but my eyesight isn't what it was and I'll need to get a magnifying lamp to investigate further..

Cheers.

Z00l
Posts: 3
Joined: 24 May 2019, 22:05

Re: Nearly there..

Post by Z00l » 04 Jun 2019, 10:32

I found the problem: PC13 and PC15 were open due to dry joints and socket U7 not seated evenly.
Re-soldering with iron set to high solved the problem.
My Gigatron now works nicely. Thanks.
:-)

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