Multicart on no-buzz models

[flip]

Hi,

I'm new around here, having bought a Vectrex a few weeks ago. Mine is one of the newer no-buzz models (serial 31xxxxx with the 7ADB rom), that have problems with some multi-carts. I found out the hard way, after ordering one of them.

Since I needed to open up my system anyway for some cleaning, I decided to poke around to get to know the insides, but also to see whether I could figure out what caused the problem. I tried to change the rom - which wasn't straightforward, since on the newer boards this is a 24pin chip compared to the 28pin ones on the older board. I replaced it with a rom adapter from a C64, which allows me to switch between rom images (B796 and 7ADB). But this made no difference for the multi cart.

After a few exchanges with the supplier of the cart, I began comparing the circuit as drawn in the service manual to what was happening on my board, especially in what IC202 (74LS00) and IC203 (74LS32) did. These trigger various chip enable and clock signals internally and on the cartridge port. And it turns out that they changed this circuit: on the newer models, the *CART signal is no longer generated and pin 32 on the cartridge port is simply not connected to anything (see detail of the schematic attached - the bit marked in yellow is no longer there). The OR gate on IC203 that creates this signal on the older boards is now connected to the OE pin of the ROM...

So i created an OR gate using two diodes (1N4148) and a pull up resistor (10k). The anodes should connect to pins 12 (E inverted) and 16 (Address line 15) on the cartridge port. The cathodes and the resistor should go to pin 32. And the other end of the resistor to GND. See the attached drawing. This 'recreates' the *CART signal, and more importantly, brought the 72-in-1 cart to life on my machine!

You can of course add this circuit to the cartridge as well, though to avoid problems on older models, you'd have to make sure to cut the *CART signal from the console.

Hope this helps others, though no guarantee. If you have any questions, let me know...

flip

Attachments:

[Mayhem]

Nice work

Hopefully this will help a few other folks...

[andygarton]

Thanks for this, I have a no buzz console as well, but not the knowledge (or balls) to mess with it to that extent unfortunately! My main reason for posting is to say that Mateos's rewriteable cartridge system does work (my 72-in-1 multi-cart doesn't as expected). I'm not sure why this is but I'm glad as it means I can do my code development testing in a no-buzz environment

[flip]

Jan 29, 2015 7:03:12 GMT -5 andygarton said:

Thanks for this, I have a no buzz console as well, but not the knowledge (or balls) to mess with it to that extent unfortunately! My main reason for posting is to say that Mateos's rewriteable cartridge system does work (my 72-in-1 multi-cart doesn't as expected). I'm not sure why this is but I'm glad as it means I can do my code development testing in a no-buzz environment

Hi,

opening up and modifying the Vectrex itself can be tricky. I'd be happy to modify the cartridge itself so that it works... Parts needed cost next to nothing. PM me if you're interested.

flip

[kokovec]

Very well done!
This is why none of my designs include the CART signal line as a chip enable function.
I do use the CART signal line for designs that require more tightly controlled timing of memory events though so this is good info indeed.

[Cybrot]

Hello. I'm in the same situation here. I actually bought the 72in1 multicart before I got my Vectrex, and I didnt know about this problem. I picked up my Vectrex last week in Sweden and it did have a serial number starting with 4. I read in some other thread here, that the menu where you select games show up, but thows you back to the menu when attempt to start a game.

But my problem i a little bit different, because when i turn on the unit, after inserting the 72in1 cart, the built in MineStorm starts up As if no cart was inserted. I've tried several times to ensure that the cart is inserted correctly, but the same result every time. And I do not have any other cart or game yet, so I actually don't know if it's the cart that is broken, if my Vectrex is broken or if this is caused by this issue Flip is describing?

So Flip, can you describe the details on how this problem appeared on you system, before you fixed it?

Any other thoughts?

Thanks in advance
Cybrot

[flip]

Hi,

Mine went straight into the minestorm game as if no cartridge was installed. Never saw the menu until I added the *CART* signal.

If you're comfortable with a soldering iron, modifying the cartridge isn't hard.


under the hotglue is a BAV74 smd diode. There's two points there that happen to be pins 12 & 16. At the top is a 10k pull up resistor. And pin 34 from the cartridge port is cut.

If you need more help, feel free to PM me...

FliP

[Cybrot]

Thanks. Now I know that my Vectrex is behaving as expected. As for the cart, I will probably have someone to help me out one day. I'm not in a hurry, I have so much to learn and enjoy with this wonderful machine.

[madtronix]

My multicarts also work fine with the non-buzz Vectrex. I use the PB6 line for switching then banks.
Cybrot: If you're interested, I'll swap your cart for one of mine. Games are more or less the same.

[Cybrot]

madtronix: Thanks, I'll pm you.