replacing eprom on old cart atari xl

[prysm1]

Hi all

 

this has probably been asked before, but my search did not turn up a relatively recent info...

 

I am thinking of posting a want to buy in the forums for old unwanted atari xl carts. I am planning to try a few of the cart/bin online by replacing eproms.

I am assuming this is all doable and basically just dropping in a new eprom. I am also assuming that the eproms are still available from digikey or jameco.

 

I just wanted to see if there are any issues I might be over looking.  I am thinking this is cheaper than having to get fancy multi carts stuff, that will probably not use often.

 

regards

prysm1

[myriadcs]

old EPROMs are not that cheap, it might be cheaper/easier to get brand new PCBs and more modern EEPROMs

[TGB1718]

I had 10 new cart PCB's made and used standard 16K EPROMS to make a few cartridges.

the ones I had made use 27128 EPROMS and a 74HCT00 chip on board.

 

I think the PCB will also use 8K EPROMs too

 

http://www.grandideastudio.com/pixels-past/

Edited October 21, 2021 by TGB1718

[manterola]

Let me add that those PCBs are compatible with the brown label/metallic back cartridge cases. I have used those for several cartridges of standard 8KB and 16KB games and apps. You can get Eproms (2764 and 27128) from not "standard" sources: Aliexpress, ebay, etc.

You need to be aware that the particular EPROM you get uses a Programming Voltage that your Eprom programmer can reach. I learned the hard way: I got several 2764 with Vp=25V. So check the maximum programming voltage your programmer can achieve and then when buying, look for the datasheet to the particular manufacturer and variation to find the Vp.

Many AMD eproms shows the Vp in the eprom itself... that is convenient... for example in the sample picture you can see that it says 12.5V PGM (programming)

[prysm1]

cool thanks for the inputs.

 

but wouldnt it be cheaper for me to get some old atari xl cart. unsolder the eproms put in a socket, buy a new eproms from digikey? this way i get the a case also.

 

[manterola]

53 minutes ago, prysm1 said:

I am assuming this is all doable and basically just dropping in a new eprom

I assumed the same and I was wrong. The ready available 27xxx eproms are not pin compatible with the ROMs Atari used. It is possible to modify the Atari internal cartridge PCB to accept 27xxx eproms but I thing it is too much work considering you can get several new PCBs for few bucks if you are patient and get them from China. I can send you one PCB I have available if you want so you can take a look. I can put it in a envelop with a stamp if you are in located in USA.

 

 

 

Edited October 21, 2021 by manterola

[prysm1]

2 minutes ago, manterola said:

I assumed the same and I was wrong. The ready available 27xxx eproms are not pin compatible with the ROMs Atari used. It is possible to modify the Atari internal cartridge PCB to accept 27xxx eproms but I thing it is too much work considering you can get several new PCBs for few bucks if you are patient and get them from China. I can send you one PCB I have available if you want. I can put it in a envelop with a stamp if you are in located in USA.

 

 

 

ah. thats info i needed. thank you. i am in canada . i will look into those new pcbs.

[cwilbar]

There is one EPROM (8 kilobytes) in size that will go in either socket of an Atari 16K cart.  It is not a common EPROM, and you'll probably pay more for one than a PCB and EPROM that you can then use more 'modern' parts on.  I have a few of these when I found a source and picked them up for a decent price.  I use them to fix 8K carts.  I could use them to fix a 16K cart too, but I'd need an inverter chip on the PCB as well, as what Atari did with the 16K carts was use one masked rom that was selected with a low pulse, and one selected with a high pulse (you could order your masked roms when made to be selected on a low or high signal).  This would allow them to eliminate the need for logic to drive the chip selects to pick the right 8K masked PROM in a 16K cart. 

 

Interesting side effect of this, is if you do acquire one of these rarer EPROMs, when used in an 8K cart, you can put it in either socket ?

 

I used one a while back on a basic cart with a bad PROM, and created a Rev C basic cart from it.