Jump to content
zCRP

DIY Coleco 63 in 1 multicart

Recommended Posts

Hi Guys,

 

I have built this multicart and used the two bin files to program the two eproms. I can get to the menu but the loading is very erratic. Sometimes the game loaded is not the one selected from menu and other times it crashes.

I have I think an issue with a socket where the eprom is not fitting tight but is loose. 

Can someone let me know what is the value of the pull-up resistor? I put a 10K but not sure this is the correct value to use.

 

Thanks and great project for our beloved Coleco :-)!!

Share this post


Link to post
Share on other sites

I haven't really looked at the schematic, but... 10K for the pull-up resistor should be good.

It could be a timing issue. Does the selected game work after pressing reset? If not, it still could be a timing issue, with latching of the upper addresses (sorry, would need to investigate further into the schematic, but could try putting small capacitor, maybe a couple hundred picoFarads between timing signals (such as latch, clock) and ground - try one at a time to see if anything helps).

Also, are there bypass capacitors on all or at least most of the chips? (from +5V to ground).

 

Share this post


Link to post
Share on other sites
Posted (edited)

Hi 5-11,

I have built this cart based on the gerber and schematics available for it. There are no bypass capacitors.

I have made some extra testings after finally replacing the loose socket with a good one. Basically all games stored in the second eprom are working fine when selected from the menu (the pcb is making use of two M27C801 of 1024k each). If I select a game stored on the first eprom then the Coleco will either crash or load the prompt screen asking to insert a cart and reset will just do nothing. I have checked the first eprom with the programmer and it verified good with the original bin.

Here is the schematic of this project.

image.thumb.png.28a8681d9b0a7719b84e11e75c3e1a99.png

Edited by repetto74

Share this post


Link to post
Share on other sites

You could try swapping the two ROM chips. If the problem stays with the board location, there might be an issue with the FET (or possibly circuitry leading to the FET). If the problem moves to the other board location, there might be an issue with the EPROM chip.

Share this post


Link to post
Share on other sites
Posted (edited)

If I swap the two eproms then the Coleco will load the game available on the first memory bank of the second eprom. As the menu is on the first eprom then i can only load this unique game but indeed it loads.

 

It is maybe irrelevant but worth to mention. The 74LS688DW I have installed is marked 74LS688 and the package was not the good one (smaller then the pad positions on the pcb) but I managed to solder it properly without any shorts. Question is are pinouts different from one package to another?

Edited by repetto74

Share this post


Link to post
Share on other sites

I have tried to program another 27c801 in position 1 but same issue. I have checked the CE signal on pin 22 and I do have 4.5V when not selected then dropping to 0V when a game from that eprom is selected.

Share this post


Link to post
Share on other sites

It might not be switching CE fast enough, or maybe some other timing issue? Does it work if you press reset after selecting the game? - is that the way it's supposed to work anyway?

Share this post


Link to post
Share on other sites

The Coleco will usually crash when trying to load a game stored into the first eprom. I'll get a garbled screen like this one enclosed or a freeze on the cart menu. 

Pressing the reset will either load the same game stored into a certain position on the eprom (DK something) or show up the message to insert a cart into the module.

 

 

image.thumb.png.10050ef529e6356ba30b7b816447354c.png

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...