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shoestring

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About shoestring

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    Sydney
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    C64, Apple, A8 & Amiga junkie. Video game & electronic repairs, homebrew dev (arcade diagnostics software), guitar & music.

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  1. I hear ya. That's a weird issue for sure. For clean power, the VIC-II requires a separate +5v power rail via an internal 7805 which is supplied by the 9v AC. To the bottom right of that board on a heatsink. I assume Commodore were trying to eliminate the noise / jail bars you typically see on all c64s. It's also vital for the clock generation ( MC4044,LS629, LS74 and LS193 ) and a few transistors in the chroma/luma output need it too. The modulator is also fed with CAN +5v which is the secondary 5V supply. Would be interesting to know if the components tied to the secondary 5V supply are flickering as well. Good luck.
  2. I think that answers your question Just like the Atari XL/XE power supplies, the 7805 is used in most of the c64 linear power supplies so the same failure modes. I did have an old c64 supply that was getting really hot in summer, so I replaced the 5v circuit with an LM2956 DC-DC buck converter and added a 5.7v clamp circuit to it. I did the same to my XL/XE power supply.
  3. Regarding the 5v 'blinking' and assuming the power supply is working OK on the other motherboard. Have you a ruled out a dodgy power switch on the c64 ? The power switch in the 64 is known to oxidise internally. Have repaired at least one c64 that either gave me a blank screen, booted to junk or failed to a blank screen randomly during use. Each time I had a blank screen, the LED went off. So that was a hint that I was dealing with a power issue. After power supply, I'd be looking for bad capacitors and closely examining the power switch.
  4. Good choice. I think I'll be doing the same if the SID stops working in my breadbin and it's pretty close to the real thing, besides I don't have any use for paddles and mice.
  5. Looks like you're on to it. Other parts you can search for are. 6526A, 6526B or 8521 ( hard to find ). For troubleshooting, you could use some 8520s from an A500 ( if you have one ) temporarily and those will work for the most part. Not recommended though as a perm fix.
  6. It could be the non inverting buffer ( cd4050 ) after the GTIA at the output. I had something similar to what you've described.
  7. My bread bin has one from 88 ( 2488 21 ). Obviously, this was completely rebuilt with sockets at some point before I bought it in 2007. I recently added a bunch of heatsinks to all the major chips ( 6510, PLA and SID ), it should help but I'm not counting on it to save the PLA from certain doom.
  8. That was Bil Herd, the C128 designer. The TED machines had the same issues. He's done a lot of talks about the process they used to manufacturer those chips. The other issue was high power dissipation on a small die area which sped up the aging of the PLA. I believe it was the early PLAs that had this problem from 82-83. Not sure about later batches. http://skoe.de/docs/c64-dissected/pla/c64_pla_dissected_a4ds.pdf Edit: You can also use a PLS100N which run much cooler and more reliable. Commodore originally used 82S100 before going to the mass produced mask version ( 906114-01 ).
  9. Those are the /CE ( chip enables ) lines to the three roms. Guarantee the other signals to the VIC-II will be funky as well. Definitely a bad PLA.
  10. There are some additional things you could try using Ray Carlsen's page as a reference / guide. http://personalpages.tds.net/~rcarlsen/cbm/c64/c64blank.txt As you can see a lot of things can cause a black screen.. even a bad SID or shorted CIA. Good luck, but I am sure you'll get it working soon.
  11. Check the other ram chips as well. There's also two ram address multiplexers at U13 and U25 ( MOS 7708 ) which are identical to the 74LS257. Other things to check. 1. PLA 2. Kernal rom. 3. Try a cartridge if you have any 4. Signals to the 6510 ( NMI and IRQ ). 5. VIC-II
  12. You only need 3 wires. http://www.mathyvannisselroy.nl/xl600k64.htm
  13. Based on experience, you may still get noise/jail bars coming through the display even with the SCCC / UAV installed if you don't have clean power or a decent ground from the vertical block. Once I fixed up the grounding issue, I had a very nice and clean picture on my 800 that surpasses the display in any of my other 8bits.
  14. Here's a nice write up about the physics routine used in the demo. https://medium.com/@peterbudziszewski3/iocaste-physics-routine-1f86570cdc63?fbclid=IwAR1E6PFr5Sh4l1nM4JK57xwNSUTPktT4yHQdD1pid1vNTc3UoNRB65SaEZA
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