Mercenary6502

Yes the plan is the to buy a PLA like the PLAnton but trying to get the EPROM to work in a REV A C64 is just an interesting challenge. That's primarily why I tired it. According to some information from Ray Carlsen's website (thanks R.Cade) the early C64's like mine have a very narrow range of acceptable timing. Not too slow, not too fast (like I pretty much discovered on my own playing with delay capacitors). I also read something about creating the CASRAM delay with some slow inverters, but that probably wouldn't make a difference though.

Update: I went a head and tried the EPROM method just because I could even though I've been considering the PLAnkton. The PLA was defiantly at fault because the computer almost always fires up to it's blue screen now which is great. The downside is that I'm having timing issues so it doesn't boot properly. At first I was getting a screen full of garbage characters, but I started playing with capacitors between ground and CASRAM as suggested by a helpful Youtube video. This has made improvements, but it still glitches and locks up. The value of the capacitor used in the video is 68pf, but that seems to be too low for my C64 (the C64 in the video is a newer revision). I've been salvaging good caps from junk boards and have had the best results so far at 78pf (achieved by combining two of the few caps I have on hand). But it still glitches and becomes unresponsive (as can be seen with the falsely reported ram size): Any ideas on how to get the timing dialed in correctly? I'm using an AT27C512R 45ns EPROM and as stated before, I believe this is an original REV A C64. Thanks

If you aren't trying to save anything but the transformer than it isn't too bad. What I ended up doing was drill a small hole through the top of the power supply box and hammered a round chisel into it. That pushed all of the contents out of the box leaving me with one big epoxy brick that I could hammer away at without the box getting in the way. The hole now serves as a place for a nice LED power indicator (right in the center of the Commodore emblem). I like to try and save transformers when I can. Depending on the application, they can be pricey and sometimes hard to find. I also love the fact that this transformer has duel outputs so a separate one isn't needed.

Alrighty, I appreciate the help everyone! Made short work of that! That one will probably go back on the shelf for awhile before I get a new PLA. I was seriously considering the EPROM method but decided to do it right by getting something professional and proven like the PLAnkton. Being cheap can cost me a lot of time and I'm starting to see that if it's not very educational, it's best not to waste my time and spend a little more. I did get the power supply reconfigured and safer, so at least I was able to get one step closer to getting that computer going again before putting it back on the shelf for now. One day! By the way, all four of my Atari computers are still running strong on the same original components from the 70's and 80's including the PSU's. Why can't Commodore's do that?? Thanks again

Alright, sounds like I should start looking into a replacement. The PLAnkton looks cool and is reasonably priced aside from shipping costs. I also just read about the method of using an EPROM (if you have one fast enough) to emulate the PLA. Anybody have takes on that? The PLAnkton does looks like the best option, but I have the resources to do an EPROM PLA and it would be free. I use Atari's more anyway.

Now that I think about it, a couple times when it was working the characters on the screen would turn into garbage after a certain amount of time and the center of the screen (not the border) would start rolling. Could a faulty PLA cause that too?

If I had another C64 that worked I would swap the PLA but I don't. Is there a procedure to test it by checking pin levels? I have a logic probe.

When the power supply failed, it was missing the 5v while the 9v was still accounted for and within tolerance. So no high voltages. The PLA does seem to run hotter than many of the other chips, but maybe it runs hot normally?

I was wondering about that, that makes total sense.

Thanks for your response. I tried entering the POKE commands but am not getting anything. I think that keyboard has a few touchy keys and needs to be rebuilt though so it's hard to justify. I do happen to have a working floppy drive which I plugged in. Once the computer is powered on, the floppy drive lights, makes some noise and stops. But I can't seem to blindly get it to read a disk directory or anything. And yes, I do get that pop in the speaker every time the computer is power on.

HI, I've been in the process of optimizing and de-junking my collection, and that includes repairing my faulty computers. I just got an IBM 5150 revived by rebuilding it's PSU and now it's time to do the same with an original (Rev A) Commodore 64. Background on this computer: It was given to me for free with one of those original epoxy filled PSU's that are prone to fail due to heat. Being inexperienced and unaware that those commonly fail, I went ahead and fired it up. It worked, but only for a couple seconds and the video was very faded. I of course then discovered that the PSU was at fault. Shortly after, I opened and chiseled out the components of the PSU and looked into my options of rebuilding it, but otherwise the computer has been sitting for years without much touching until now. For starters, I needed a new PSU. I happened to still have the original transformer lying around (everything else was damaged from chiseling) and finally got brave enough to test it by wiring a power cord to it. Both outputs looked good (around 9.5VAC) so I went ahead and built a new one around the original transformer with an old-school 7805 regulator (just for the time being at least): Needs more optimizing and heat shrink so it looks scary, but I now have the 9VAC and 5VDC voltages I need! Next was the Commodore 64 itself. I fired it up and nothing happened, just an initiation pop of the SID in the TV speaker with no video. Checking voltages I found that it's on board 7805 was garbage so I replaced that and got a step further. I could now get a gray screen by adjusting the pots in the video section of the board. After about an hour of poking around and powering off and on, it suddenly fired up, and after adjusting the pots the video was much brighter and fresher than it's ever looked before! But of course, that didn't last. It'll go back to black screen (with a single dim vertical color line on the far left of the screen) after being shut off for more than a couple minutes. Poking around some more, I discovered that touching the crystal clock and/or the capacitor near it has a drastic effect on the video when it has the black screen (components marked below): It seems like a combination of touching those parts, adjusting the pots, and restarting the computer will eventually get it power up with video like above. I've done it more than once. I've resoldered those components to ensure that there aren't cold joints and also checked the capacitor to find it within tolerance. So this is where I'm at. Does anyone have any clues as to why it's acting like this? I don't have a whole lot of experience with video circuits so I don't really know where to proceed. I understand that the same crystal clock is divided and served to the entire computer, so if there was trouble there it wouldn't even boot. But it does obviously work sometimes. If I had an oscilloscope, I would check for all of those clock frequencies at time of failure but I don't. Thanks for your time! (Didn't feel like joining a Commodore community )

Those are some good pointers that I'll try to keep in mind, thanks! I used to program primarily in Basic, but I updated to the CC65 C cross compiler last year and love it. Not only is it a night and day difference in speed, it's so much easier to manage your code. Lot's of flexibility too, there's many ways to accomplish the same task. I think it's a great option if you don't feel up to assembly but want to program somewhat professionally. I do however find Basic to be very handy even when programming with CC65 when I need to quickly test code segments or check memory calculations. Not to mention that when I need to reference code in books, it's usually in Basic then I covert it over to C. So sometimes I'll quickly type in and run the program in Basic first to get a nice overview of it's behavior.

Yeah that's not cool at all. I noticed that in the book "Atari Graphics & Arcade Game Design" that some of the articles copy De Re Atari almost word for word, or pretty close anyway! But maybe permission was received, I don't have a clue. Well this is what's happening for me if anyone was curious. Been attempting some hard core programming all week and am currently working to bring the years of studying (that's been on and off) into one program in the hopes to eventually go on to make something worth while. Jack-o'-lantern shootout??? No idea. That might explain some my questionable reasoning in this tread, it's hard not to loose your mind trying to keep everything in check! It's fun though, programming Atari's in the 21st century! (Please don't question the code, it's all for experiment so it's dirty )

Right, I just meant that I put the screen data "Hello!" after the display list in memory (in the same page). It's spaced a byte or so above the end of the display list program. I apologize, I find that describing programming topics in writing correctly can be a little complicated!

Thank you, that makes sense. I was initially thinking decimal but confused the heck out of myself like I like to do. "Words" are new to me so that was a really good lesson using low and high bytes. I should have my username changed to avoid false perceptions that I'm an advanced programmer.