Commodore 64 PLA Replacement PLA20V8
$12.99 – $14.99
The PLA chip in the Commodore 64 is a common failing point today. The PLA or Programmable Logic Array is a computer chip that handles the memory map and the bank switching of the Commodore 64.
Along comes Daniël Mantione who designed this handy device to replace the original PLA chip compatible in most Commodore 64 computers.
Some frequently asked questions1,
Does Epyx Fastload work?
Yes, it works fine. The Epyx Fastload cartridge is a rather questionable design that performs analog tricks on digital lines. In order for the Epyx Fastload to work, a PLA needs to have similar analog properties and be stable at the border voltage between 0 and 1. This is the case for the GAL20V8B.
Does it work in all C64 mainboards?
Yes, except for the shortboard assy 250469 of course, because it uses a completely different type of chip. Assy 326298, 250407, 250425, 250466, 251103 (SX64), and C64 Reloaded MK1 have been tested. Assy 250441 and KU-14194HB have not been tested yet, but from what I know about these boards, I am confident about compatibility. Both PAL and NTSC tests have been done.
Can I use an alternate KERNAL?
Yes! An alternate KERNAL cartridge is a real PLA torture because a KERNAL cartridge changes the C64 mode two times within a half cycle and thus likes a responsive PLA. This has been tested both with the 1541 Ultimate II and with the Easyflash 3 and works perfectly.
Does Super-Zaxxon work?
Yes, it does work perfectly! Super-Zaxxon switches banks by means of accesses to the address lines of the C64 and as such, noise on the C64 address lines can cause undesired bank switches. This is a particular concern for EPROMs, which are known to cause switching noises on address changes. The way the GAL20V8 works, with an AND array and an OR array just like the original PLA, this kind of noise is not expected and indeed, the cartridge works perfectly.
More information about the PLA20V8 can be found here.
More information about the PLA can be found here.
1 - copied from Daniël Mantione's website.
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What others are saying
A couple of questions, is this the same soldering kit that is available on Daniël Mantione’s website? Also, are the two gal chips pre-programmed? I’m looking to replace a bad PLA but I do not have the tools to program the chips myself.
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Admin 8-Bit Classics –
It is the same kit but it comes fully assembled and GAL chips come fully programmed.
fkokay (verified owner) –
Shout out to the folks at 8 Bit keep up the good work! This PLA worked well no issues! Love that you guys are helping to keep these old machines running like new!
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Joshua Dolan (verified owner) –
Arrived well packaged. Square pins did not fit properly in socket of PLA on my SX-64. This should be corrected and thinner legs should be used. I stupidly forced it and it got in but now the socket is noticeably more loose with a regular chip. I can put a new socket in sometime so it isn’t the end of the world since I already added sockets for the ram.
My main issue is that it simply didn’t work. I suspected the original PLA is marginal, as the system will boot with new ram which corrected the graphic issues which pointed to at least two bad chips. Still, with the stock PLA will show odd ram sizes until a reboot and then everything is fine… almost like it needs to warm up. I figured for $15 trying a replacement wasn’t a huge deal as I wasn’t having luck online with diagnosing further without a test harness and test cartridge. This replacement gave “Out of memory in error in 0” every time it was in. I looked over GALS and noticed the legs were corroded and some looked like it was going up into the chips. With the poor fit in the socket I thought maybe there was somehow a bad connection. I tried fitting the chip to another socket I had with round legs and ended up soldering it to it to test further after checking continuity with a meter. Same result. As I don’t have another C64 at the moment to test with I had to assume it was just dead and tossed it since I didn’t want to bother with a return over $15. You win some you lose some. I will probably get another PLA replacement rather than one of these that uses GALs sometime in the future.
8-Bit Classics reached out to me after my review. My initial review was 2 stars due to the issues. However, I am updating to say they went out of their way to look up different pins for future PLA replacements and also offered to replace mine even though I had already dumped it since I had made modifications to the pins. This is great customer service and I will definitely order here again. Changed to 4 stars on that alone. (I have also bought a C64 video cable which has been working perfectly.)
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Admin 8-Bit Classics –
Thank you for the input. We will change our header pins to something smaller to fit better for future orders. If customers ever have an issue, please reach out.