I changed the ROM on it for a CMOS, changed the 74LS14 and LS08 with HCT chips.
I really like this little board as it consumes very little power compared to other C64 boards and consequently produces very little heat. No heat sink is required on any of the chips including the 8562 HMOS VIC-II.
All the tests I ran on it went well except for one; running carts with my 1541 Ultimate I+
A few years ago, Lordcrass converted the .CRT images of the Zaxxon and Super Zaxxon cartridge games in a slightly different format to make them compatible with EasyFlash 3 and it turns out this format is also compatible with the cartridge emulator of the 1541 Ultimate series updated firmware. Super Zaxxon (the cart version, not the disk version) being one of my favorites I was thrilled.
When I tried using emulated carts with the 1541 Ultimate on the 64c board, most of them failed including the Super Zaxxon cart.
1541 U I+ cartridge emulation works perfectly well on my board 250466.
A few years back, I converted my 250466 to use a 8500 CPU and 8562 VIC-II to make it leaner. The change of these 2 chips to HMOS technology didn't cause any problems.
Back in 2011 I posted:
r.cade noted I have in fact used a 8562 - the 8564 is a 48 pin version of the VIC-II specifically designed for the C128.Yet again, my good old "uncle" 250466 based 64 went berzerk on me because its 6567R9 NMOS VIC-II overheated.
Over the last few years, I made sure I had a good heat sink on this chip but it seems it wasn't enough.
I was told the HMOS based 8564 used in the 64c produces almost no heat but never bothered to verify. I didn't even know if the pinout was compatible. Turns out the only difference is with pin 13 (Vdd) where the old 6567 receives 12V and the newer HMOS wants 5V. A direct swap would probably bust the new chip.
All I did was bend outward pin 13 of the new chip, solder a 0.1uF cap. between pin 13 and pin 20 to filter the voltage and attach pin 13 to pin 40 where the 5V comes in.
Well, the legend is true, the HMOS 8564 produces virtually no heat compared to the original VIC-II and has a better quality video signal.
No more lockups, crashes and screenfuls of garbage.
Note to Groepaz, the soldered 906114-01 was replaced by a good 'ole M27C512-90B6 and no bus contention ever occurred; tested with a 500MHz logic analyzer...
At this point I have strictly no idea why 1541 U cart emulation will work ok on the 250466 and crash on the 250469.