+wavemotion Posted March 3, 2003 Share Posted March 3, 2003 Hello all, OK - here's a tough one, but you guys always seem to come through so here goes... About 6 months ago I build my first carts. I bought 10 (ten) 2732 EEPROMS and some spare carts (old Pac-Man, E-T and Space Invaders) and build me some homebrews. I built 9, holding on to the 10th for the next great 4k game to come along. All 9 worked perfectly (using the 74LS04 hex inverter) in my 4-switch Atari and have continued to work flawlessly for many months now. I recently got a 6 switch Atari that apparently works great. All my stock carts work great with that new 6 switch unit. However! 7 of my 9 homebrew carts work great but the other 2 carts do not... they seem to power up (I can see the game screen briefly), but the main screen does not stay stable. It often flickers or sometimes goes out completely, as if power is not sufficient and the cart cannot stay up and running. I thought maybe it was the unit (or power supply) but I got a 3rd six-switch unit (with different power supply) and it does the same thing on those two carts. Both of those carts work great on my 4 switch unit. I opened up one of the "bad" carts - and it was using an AM2732ADC EEPROM (from ADC). I noticed the spare EE I have is a TMS 2742A (I think from TI). I think most of my EE were of the TMS 2732A type. Based only on a weak guess... I'm guessing that 2 of my EEs were the AM2732 type - and maybe those draw and/or require more power (and with the addition of the hex inverter which also draws some small power it is enough to make the whole cart go flakey in the six-switch unit). I don't want to break the new label seal on my other homebrews just to find out if the working carts are using the TMS 2732A EEPROMS. Has anyone else had some trouble with 2732 EEs? If so, does the brand name above ring a bell?! I'll try to find the spec sheets on both, but does anyone know if the A in 2732A has anything to do with lower power draw? Thanks much in advance! Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted March 3, 2003 Share Posted March 3, 2003 A couple of questions before I come up with a theory: 1.) Which EPROM board are you using ? 2.) Did you install a capacitor on the board ? Quote Link to comment Share on other sites More sharing options...
+wavemotion Posted March 3, 2003 Author Share Posted March 3, 2003 A couple of questions before I come up with a theory: 1.) Which EPROM board are you using ? No special board. These are old 4K common carts that I pulled the PROMs out of to make room for the EEPROMS. This one was either a Pac-Man, Space Invaders, Defender or ET. 2.) Did you install a capacitor on the board ? No. Any suggestions on what type and where it should be installed? Thanks! Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted March 3, 2003 Share Posted March 3, 2003 AFAIK, if you use those old boards you need to use 2532 EPROM's and a hex inverter, I am not sure if 2732's will work. A better choice for you would be to get a couple of these: Atari 2600 PCB Quote Link to comment Share on other sites More sharing options...
+wavemotion Posted March 3, 2003 Author Share Posted March 3, 2003 AFAIK, if you use those old boards you need to use 2532 EPROM's and a hex inverter, I am not sure if 2732's will work. Except that they do work... In my 4 switch unit (actually the other seven 2732's work in ALL three Atari units)! Based on a little scope work, I think the problem is timing of the CE through the inverter. I'm going to switch to an open gain collector 7406 inverter tonight to see if that makes a difference (the rise time on that should be much faster - in fact I seem to remember reading somewhere that the open gain collector 7406 was a more robust solution working with a greater variety of 2732 chips - I think that was mentioned in Randy's 2nd revision of his cart building sheet). If that works, the only reason I could think of for the 4 switch unit working and the 6 switch unit not working would be in the timing or tolerance on the CE line. Thanks for the help! Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted March 3, 2003 Share Posted March 3, 2003 It could very well be the timing, you could also try shortening the cables to the inverter. Also, what AWG wire did you use ? I mentioned the 2532 because that is what Randy used in most of his hacked-up boards back in the day. Quote Link to comment Share on other sites More sharing options...
Cassidy Nolen Posted March 3, 2003 Share Posted March 3, 2003 No, stock boards without caps work fine with carts. Half of the Polo run was set up that way. All working to the best of my knowledge (LMK if someone has one that isn't). I am more interested about your use of two things: One: The EEPROM term. That is different than an EPROM? I am not a pro, but I think they are different. How I am not sure. May be the source of trouble? Second: The 2732A programs at a different voltage than a 2732. Were all of your carts 2732A's, or maybe some were just 2732's. IIRC, 2732A's program at 21V, while 2732's program at 25. I could be wrong, but a bit of poking online should clean that up. Could the program not be "written" well enough for the older system to see it? I am really out of my league, but just wondering. I would imagine it could be a resistance issue, but only if the contacts were extremely dirty on the console, or maybe very worn out. I have had a few tempermental six switches, but a reflow of solder around the cart connector on the board solved those. Good luck, Cassidy Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted March 3, 2003 Share Posted March 3, 2003 EPROM - UV erasable EEPROM - Electrically erasable The programming voltage doesn't matter as long as the operating voltage doesn't exceed 5V, which it doesn't. And your quote on the programming voltages is spot on. Quote Link to comment Share on other sites More sharing options...
+wavemotion Posted March 5, 2003 Author Share Posted March 5, 2003 OK - here is the Solution. I tried a few other flavors of 7404 (S LS and ALS). None worked with the AMD 2732A chip with the 6 switch Atari. I switched to the 7406 open-gain collector inverter and had to do the appopriate rework (ugh!) but that worked fine for both AMD EEPROMS. So it's definitely a timing issue with the chip-enable. Maybe the AMD EEPROMS are slower in response than the TI parts that worked so well with the 7404 Hex Inverters. The 7406 inverter definitely has faster and sharper rise times so I'm pretty sure that's what solved it. In any event, I'm back up and running - and enjoying my favoriate Homebrew again - SPACE TREAT! I'll probably go with 2532's for any future cart making I do. Quote Link to comment Share on other sites More sharing options...
+wavemotion Posted March 5, 2003 Author Share Posted March 5, 2003 I am more interested about your use of two things: One: The EEPROM term. That is different than an EPROM? I am not a pro, but I think they are different. How I am not sure. May be the source of trouble? Sorry, I tend to mistype. I'm using 2732A EPROMS (not EEPROMS which are electrically erasable and programmable as opposed to EPROMS which are erasable via UV light). I have 2 manufacurers of these parts TI and AMD. It's only the AMD parts that are not working (though they work in the 4 switch unit - so the EPROM is being properly programmed at the specificed 21V). Thanks for the reply - and to CPUWIZ for additional help! See my post above - looks like I'm back and working again. Quote Link to comment Share on other sites More sharing options...
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