Finally! No mouser package, but I was able to find all the needed ceramic caps in my junk boxes, and the last missing item, the sliding switch, arrived today from China, so my all-socketed C64 is finally up and running with a new RF modulator replacement. I'll have to submit to the same treatment one of my shortboards next year.
As soon as they're available again, I'll also buy a lumacode encoder for this C64, and will probably go for a sidkick pico too. The SID in here doesn't sound terribly good.
I also built a few KungFu Flash carts, so it's time to play around a bit... Any pointers to nice C64 games on itch.io, people?
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Also, why not replacing the DRAM with SRAM?
I used this for the carrier: https://github.com/go4retro/DRAMCarrier (there is an error on this board: pin 1, which is /OE, of one of the ICs is left floating, I had to jumper it to GND, like it is in a C64C) and https://github.com/jamarju/c64-sram (here the BOM lists an HCT32 to handle /RAS and /CAS but I had timing issues with that, the issues went away with an F32).
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Further work on the experimental C64, to attempt lowering the temperature inside the case: removal of VR2 and replacement with a switching module from Murata (I have an abundance of these). I also added some additional filtering with ceramic caps on the bottom, and, while I was there, replaced the 10uF caps across the board with newer, higher rated ones.
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Oh I ran into a small issue with the SRAM replacement board from the previous post!
See those two tiny pixels under the cloud? At the main screen of ZetaWing II there is a segment of flickering pixels just under that cloud. The issue disappears when using the original 4164, or even when replacing them with two 4464, so I'll go with the second option.
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I checked a few photos of other SRAM adapters for the C64, and they all share the same basic circuit, latching the address lines on /RAS and enabling the SRAM when both /RAS and /CAS are low, so, I guess the problem with the one I found on github are timings. Either the SRAM is too fast or the glue logic is.
So I designed an experimental board for my C64, supporting both DIP ICs and a few SMD variants that I already have in stock. We'll see if I find a glitchless combination!
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Ok, SRAM replacement for the #C64 250407 built in two versions and under test!
Good news is it works!
Bad news, the damn glitch on the title screen of ZetaWing 2 persists! Doesn't matter the timing of the SRAM or the family of the ICs I use.
At this point I need to ask, does anyone here has a PAL C64 with a SRAM mod installed AND ZetaWing 2? I guess it'll be heavily dependant on the motherboard model.
I'd like to know how it behaves for you. My glitch is a flickering lines of pixels under a cloud in the title screen of the game.
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Found out that using an HCT to OR the /CAS and /RAS lines for the SRAM module leads to instability on this C64. They are gone with an ALS/LS or F gate.
The same was happening with the other SRAM module I used, found on GitHub, designed for the C64 shortboards. In that one I replaced it with an F gate.
Looking at the schematics (https://github.com/bwack/C64-250407-Replica-KiCad/blob/main/250407_.pdf) and saw C203 in my board is not fitted, I tried with a random 330pF cap directly soldered on the adapter between /CAS and GND. It is now rock solid. I'll do another revision with a proper place for the cap.
Also, seems I am not the first with the issue: https://www.lemon64.com/forum/viewtopic.php?t=80031
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Ah interesting! I modified this C64 motherboard to accept 8565 VICs, and with this, the graphical glitches when using a SRAM adapter disappeared! The previous VIC was a 6569r3.
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