my diy multicart works with some eeproms but not another?

[Javaman]

Hi everyone,

 

I wired up a little 2k/4k multicart that uses a 74LS04 for a CE hex inverter.

 

It works with the AMD 29F010A-90PC and with some minor wiring changes, the smaller Atmel 28C64-15PC

However, it will NOT work with the Atmel 29C010A-12PC and I've tried several.
Sometimes I get a glimpse of the game screen before it blanks out.

An older post http://atariage.com/forums/topic/21851-2732-eeprom-and-problem-with-6-switch-atari/?do=findComment&comment=240804

describes a similar problem (though I have a 4 switcher) and he solved it by using a 7406 inverter.

Before I take a chance on that inverter does anyone know what might be causing this problem?

I'm trying to understand why it would effect the 120ns chip but not the 90 or 150?
I really would like to use these chips since I have a few lying around.

Many thanks.

[Javaman]

I fixed my problem. Sounds strange but by disconnecting the ground wire from the ground pin of the eeprom all glitches & flickering disappeared. It had nothing to do with the inverter or speed of the chips. All my Atmel and AMD eeproms work perfectly without a ground wire attached. I even tried this on my handmade 8k multicart based on the pixelspast schematic. That also works better now. Maybe someone has an explanation but I'm glad to have it working.

[electrotrains]

Javaman,

 

Are you using a decoupling (0.1uF) capacitor across the +5V/GND of the EEPROMs? I had similar issues when developing a multicart for the atari 8-bit.

On a breadboard, I also found that I sometimes also needed an additional 10uF capacitor too.

 

Robin

[Javaman]

Javaman,

 

Are you using a decoupling (0.1uF) capacitor across the +5V/GND of the EEPROMs? I had similar issues when developing a multicart for the atari 8-bit.

On a breadboard, I also found that I sometimes also needed an additional 10uF capacitor too.

 

Robin

 

Yes, I had the 0.1uf cap connected to the 5v & GND pins. Honestly, I tried it both with and without the cap & never noticed a difference.

It was only after removing the wire from eeprom GND pin to the GND on the cart that my problem was fixed.

 

I still have the decoupling cap but it's connected to 5V on the eeprom with the other leg directly to ground on the cart. Nothing connected to GND on the eeprom.

[Shawn]

pictures?

[Javaman]

pictures?

 

First one is the bank switching cart based on the PixelsPast schematic. EEPROM on top, GAL20V8B underneath.

Got a bit messy tearing it down looking for the original problem. A jungle of wires but amazingly it all fits inside the case.

 

I added extra DIP switches so I could turn on/off the address lines depending on whether there's a F8/F6/F4 GAL in the socket

or just running a chip with 2k/4k games. Game selection just uses one DIP. They hold 128k so its (32) 4k games or (16) 8k games, etc.

 

The second board is the first I made. It's a 2k/4k with inverter for chip enable plus an LED just for fun.