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Can you replace your C64 PLA for under $3?

Adrian's Digital Basement

179,984 views

Bad PLA chips (MOS 906114-01) are a super common problem for the "breadbin" Commodore 64 machines. There are replacements around but they aren't that cheap. How about one you can build yourself at home for under $3?

The GAL-PLA has been tested on longboard PCB 326298, 250407, 250425 and the SX64 with no compatibility issues or modifications required. Tested with Super Zaxxon, 1541 Ultimate II and Easy Flash 3 with no issues on both NTSC and PAL machines.

0:00 - GAL-PLA Overview
10:57 - Testing the GAL-PLA with Super Zaxxon
13:45 - How to build your own PLA
25:43 - Cost breakdown of the GAL-PLA replacement

--- Video Links

** GAL-PLA Website by Daniël Mantione: (All of the information and files to build your own) **
http://www.freepascal.org/~daniel/c64...

The "PLAin" Truth About the Commodore 64 PLA (and why MOS PLA chips fail so often)
#10 'The PLAin Truth About the Commodore 6...

More information on the PLA including timing requirements:
ftp://ftp.zimmers.net/pub/cbm/c64/firmware/C64_PLA_Dissected.pdf

Super Zaxxon Cart provided by Geek With Social Skills:
geekwithsocialskills

--- Parts for this project

PCBWay to the GAL-PLA project:
https://www.pcbway.com/project/sharep...

TL866-II Mini Pro Programmer:
https://www.aliexpress.com/item/40000...

Lattice GAL20V8 (Qty 10):
https://www.aliexpress.com/item/33023...

PIN headers:
https://www.aliexpress.com/item/32692...

24 pin narrow sockets:
https://www.aliexpress.com/item/32950...

--- Tools

Deoxit D5:
https://amzn.to/2VvOKy1
http://store.caig.com/s.nl/it.A/id.16...

Jonard Tools EX-2 Chip Extractor:
https://amzn.to/2VazxDS
https://www.jonard.com/Products/EX-2-...

Wiha Chip Lifter:
https://amzn.to/3a9ftWw
https://www.wihatools.com/precision-c...

O-Ring Pick Set: (I use these to lift chips off boards)
https://amzn.to/3a9x54J

Elenco Electronics LP-560 Logic Probe:
https://amzn.to/2VrT5lW

Hakko FR301 Desoldering Iron:
https://amzn.to/2ye6xC0

Rigol DS1054Z Four Channel Oscilloscope:
https://www.rigolna.com/products/digi...

Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:
https://amzn.to/3adRbuy

TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)
https://amzn.to/2wG4tlP
https://www.aliexpress.com/item/33000...

TS100 Soldering Iron:
https://amzn.to/2K36dJ5
https://www.ebay.com/itm/TS100-65W-MI...

EEVBlog 121GW Multimeter:
https://www.eevblog.com/product/121gw/

DSLogic Basic Logic Analyzer:
https://amzn.to/2RDSDQw
https://www.ebay.com/itm/USB-Logic-DS...

Magnetic Screw Holder:
https://amzn.to/3b8LOhG
https://www.harborfreight.com/4-inch-...

Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
https://www.ebay.com/itm/14-16-18-20-...

RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)
http://www.retrotink.com/

Plato (Clone) Side Cutters: (order five)
https://www.ebay.com/itm/1-2-5-10PCS-...

Heat Sinks:
https://www.aliexpress.com/item/32537...

Little squeezy bottles: (available elsewhere too)
https://amzn.to/3b8LOOI

--- Links

My GitHub repository:
https://github.com/misterblack1?tab=r...

Commodore Computer Club / Vancouver, WA – Portland, OR – PDX Commodore Users Group
https://www.commodorecomputerclub.com/

--- C64 Stuff

JaffyDOS:
http://blog.worldofjani.com/?p=3544

C64 Test Harness I use:
Building a Commodore 64 Diagnostic Test Ha...

C64 Homebrew cartridge PCB: (used for the DeadTest / Diag Cart I use)
https://www.ebay.com/itm/Commodore-64...

EasyFlash 3 Multi-Cart:
http://store.go4retro.com/easyflash-3/

--- Instructional videos

My video on damage-free chip removal:
How to remove chips without damaging the c...

--- Music

Intro music by:
Nathan Divino
@itsnathandivino

Outro Music:
Abyss by | e s c p | https://escp-music.bandcamp.com
Music promoted by https://www.free-stock-music.com
Attribution 4.0 International (CC BY 4.0)
https://creativecommons.org/licenses/...

--- Image Credits

TI99 Image Credit:
By Rama & Musée Bolo - Own work, CC BY-SA 2.0 fr
https://commons.wikimedia.org/w/index...

20 Comments

@danielmantione 6 years ago Pinned

The reason why the PLAtinum fails is clearly that they have their CAS to CASRAM delay wrong. Later C64 boards uses a resistor+capacitor to delay CASRAM a little bit, and the modifications advised are intented to increase the delay on the mainboard side. Another solution is to replace the multiplexers on the mainboard with faster ones, if you replace the 74LS257 with 74ALS257 or 74F257, PLA compatibility problems are solved. I actually did this on a board with a broken multiplexer, not for compatibility (original PLA was working fine), but just because there wasn't a lot of reason to use the older, slower LS part.

As the creators did use a CPLD, they should have been able to route the signals through different macrocells to add delay, just like I was able to do, but they didn't. You need to dig a bit into the low-level details in order to achieve this, perhaps they didn't do this. For me it was't that hard at all to get the CASRAM delays right and I believe most PLA replacements do get it right.

The RAM in the C64 has to respond in something in the order of 250ns to the CPU. The entire chain of logic (PLA, multiplexers, RAM itself) has to happen within this 250ns. With 150ns RAM, there is about 100ns left for PLA/multiplexers. The lower bound is approximately 20 ns and this means there is quite a bit of range, the PLA isn't quickly too slow, even above 50ns you would still be on the safe side. However, modern chips are fast, so quickly get in trouble with the lower bound.

@kiningroseburg9288 6 years ago

22:59 "Boom! Blue screen! Looking good!!" Said no system administrator EVER!

@branchonequal 6 years ago

BTW, the exact reason why the PLAs fail is because the glass separating the layers of the die contains too much boron which destroys the aluminum interconnections.

@ddummer 6 years ago

"Boom! Blue screen... looking good!" ... those were the days long before windows... ;)

@quirin1727 6 years ago

Blue Screen!
C64 User: Yeah, it works! 👍
Windows User:😞

@dan_loup 6 years ago

"oh yes, my computer bluescreened, which means it worked!"

@StevenIngram 6 years ago

I remember the old Pr1me mainframes. When 2 devices tried to communicate on the bus at the same time it generated an error code called, "Fatal Embrace." LOL

@jamesbennettmusic 6 years ago

Cheap breadboards are brilliant for holding pin headers for soldering!

@ThereIsOnly1ArcNinja 6 years ago

Damn, it really took me over 30 years to realise, that we C64-afficianados prefer to get a blue screen - in contrast to Windows

@osgrov 6 years ago

This is awesome! Daniël deserves a medal, for sure. :)

@copperdog01-i2o 6 years ago (edited)

You might be able to talk to The 8-Bit Guy about testing the Epyx Fastload cartridge.

@iamdarkyoshi 6 years ago

Lovely solution, kudos to him for giving source code and gerbers instead of just selling them closed source

@matthewday7565 6 years ago

Windows user - reacts with horror at blue screen
C64 user - blue screen is my friend

@IntegerOfDoom 6 years ago

As awesome as powerful as modern computers are I find this classic hardware infinitely more interesting.

@Vermilicious 6 years ago

I've never used a C64 in my life, but I think it's awesome that people find fixes like these to prolong their use. Kudos!

@marky26uk 6 years ago

Hi Adrian, just letting you know i now have all the parts, TL866II PRO Programmer, Gal's, ic sockets, i got the pcb's made at JLCPCB, soldered all sockets/pins to pcb, programmed the gal's which all went through first time with no problems, plugged the gal's into the pcb then plugged the pcb into the pla socket of my c64 and.........wow worked first time with no problems, tried it with fastload cartridge, ultimate ii+ cartridge, loads of games and all worked fantastic.
I would just like to thank you for showing us the procedure and parts required Adrian, and a big thank you to Daniël Mantione for his work on this new c64 pla replacement, AWESOME !!!!!!!
Thanks guys, love your channel Adrian keep up the good work :)

@tpcdude 6 years ago

Pals and gals were great technology, my company used a pal to replace a part on DEC Unibus interface that they would not sell us since we were a competitor. Also, in the telephone industry when two sides of an interface were enabled at the same time we called that "glare" since both sides would just look at each other and do nothing.

@kaitlyn__L 6 years ago

Appreciate the cost analysis. Not a lot of people will admit that there's a higher upfront cost from buying in bulk, many will focus only on the final per-unit cost. You put it plainly in the spreadsheet.

@jeffweber8244 6 years ago

Wow. This jogged my memory of designing circuits using new GAL chips at Raytheon in the late 80s.

@MrWaalkman 6 years ago

So it took awhile to get all of the pieces and parts in, but I built one yesterday and the most challenging thing about it was locating my TL866 to program the GALs. Thanks for the excellent video!