7800 RAM Cart with Pokey anyone?

[CannibalCat]

Hey, I tried building a RAM cart w/Pokey chip recently from online plans with little success. Tried several different RAM chips as well per the recommendations. Does anyone have a pre-built one (or maybe could build one) that can offer up?

 

I've already modded my 7800 with DevOS 0.2 (works fine) and build the parallel port cable (from PC to joystick port) and was able to dump a cart successfully, so I know that part works, just need the RAM cart!

 

Thanks!

[+GroovyBee]

Can you post a link to the circuit you are using and the part number of the PCB?

[Eckhard Stolberg]

Can you post a link to the circuit you are using and the part number of the PCB?

It's the Ballblazer board which can be configured by jumpers to use ROM, EPROM or EEPROM chips and is therefore quite easy to modify into a RAM cart. Graham Percy posted the plans for this on his Geocities site which unfortunately is down now. But there is a mirror here.

 

The the OP:

It's difficult to diagnose the problem with your cart with so little information. Maybe you could post pictures of your board, so we could check the wiring? And what command do you use to upload a program to the RAM cart, and what kind of error do you get?

[CannibalCat]

Yes, it was the 32K Pokey Dev cart from the doc you mention:

http://www.oocities.org/gjp57/devcarts.pdf

 

Image of my attempt:

http://imageshack.us/photo/my-images/507/27289910150255715674496.jpg/

[kenfused]

If you haven't already, check the continuity of all the traces that pass through or under the ROM (now RAM). I found it very easy to nick or trace or two on ballblazer boards when removing the ROM. A simple multimeter than beeps is good for this.

[Eckhard Stolberg]

Image of my attempt:

http://imageshack.us...5715674496.jpg/

I had a quick look at my Ballblazer RAM board, and I noticed, that it has a capacitor bridging the middle and the right hole of C2. This seems to be missing from you board. It's been a long time, but IIRC Graham told me to add it, because I had problems getting my POKEY RAM cart to work at first too. Maybe that's you problem as well.

[CannibalCat]

Eckhard,

 

Could be... what is the value of the cap you used?

[Eckhard Stolberg]

The capacitor is the same as the other two near the RAM and the POKEY. It's a "104" or 0.1 uF.

[CannibalCat]

The capacitor is the same as the other two near the RAM and the POKEY. It's a "104" or 0.1 uF.

 

Ok, tried it, same thing (nothing)... but I do notice that the RAM chip is getting really hot really fast... sound like a short?

[Eckhard Stolberg]

Yes, if the chip gets that hot, you probably have a short somewhere. If you can't find it by checking your connections again, it might be a good idea to solder a low-profile chip socket to the board and plug the RAM chip in there. That way you don't have to go as artistic with your soldering as you do now. My POKEY board has a chip socket, and I can easily fit in a RAM chip similar to yours, if I bend up the fat part of all the pins and then bend down the thin ends in the right distance to match the holes of the socket.

[CannibalCat]

Eckhard, thanks for the advice! And thanks for a wonderful development system!

[CannibalCat]

Ok, found the short... seems to be working until I try to SEND a binary to it, stops at 256 bytes (of 2048) every time and says "Timeout". Same thing with a 16K binary (stops at 1792 of 16384 bytes)... any ideas?

[+GroovyBee]

Double check that the address and data lines are wired correctly (no opens and no shorts). Do you have any test equipment better than a multimeter? If you have a logic probe check that you see address/data bus activity on the RAM .

[CannibalCat]

I don't have anything else equipment wise... I kind of bailed on the whole setup / idea for now since I got a Harmony cart for 2600 work. But thanks for all your help!