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V3 Assembly Notes
If you decide to assemble a V3 board, there are a few things you should be aware of, and a few choices you will have to make.
- Wherever you should use a 74LSxxx IC, you can replace it with a 74HCTxxx. This is actually recommended as it will save some power. Other variants might be compatible, but they haven't been tested. Do NOT use 74HCxxx.
- While Commodore used common-mode filters for the EMx components and ferrite beads for the FBx components, we built our prototypes using DSS1NB32A101Q91A everywhere: these filters give a better protection from EMI and RF noise than the ferrites but they used to be more expensive, so Commodore only used them where essential, falling back to ferrites wherever possible. These days there doesn't seem to be any reasonable ferrite that is significantly cheaper, so using filters everywhere is probably the best option.
- The board is designed to fit into a C64C-style case, which you can buy new in a number of different colors: I'd recommend Retro Black, of course! Note: no endorsement from/for iComp, this is just a practical matter.
- D12 MUST be installed backwards (i.e.: cathode towards the round pad).
- R96 MUST NOT be installed.
- The silkscreen indications for U5/6 and U13 contain errors, see below.
The CPU at U2 can either be an original 7501/8501 or even a 6510, thanks to Andrew Challis's adapter being integrated on the board:
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Use the bottom socket with an original MOS 7501/8501 and do not install D93 nor R93.
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Use the top socket with a MOS 6510 and solder a 1n4148 diode at D93 and a 10k resistor at R93. Note that this solution comes with a few compromises:
- You will need to use a KERNAL image modified by Andy.
- Disk fastloaders will not work.
- The Datassette motor will spin whenever one of its keys is pressed, the computer will no longer be able to control it.
I think these drawbacks are acceptable, as most fastloaders won't work anyway when using an SD2IEC which is what most people do these days, I guess, while the loss of tape control isn't much of an issue in itself. Make sure to send a small donation to Andy if you go this way.
Here's another interesting alternative, which would fit in the bottom socket, as it bears an 8501-compatible pinout.
Your machine can either have 16 or 64 kB of internal RAM. For the former use 4416 chips at U5/6, for the latter use 4464 chips (note that the silkscreen is incorrect!). In both cases, set jumpers JP3/4 accordingly. These jumpers can also force only 16 kB to be seen when you have installed 4464 chips, thus I'd really recommend going for these.
You can also go with 16 kB of internal RAM and then use an external 64 kB expansion: if pin Z on the Expansion connector is grounded, the internal RAM will be disabled. If for any reason you don't want this, cut jumper JP8 open on the back of the board.
- If you plan to install two separate KERNAL (U3) and BASIC (U4) ROMs, do not install U90 (C41 can be skipped, too) and put a blob of solder on the left and center pads of each of JP5/6/7. Note that the ROM pinout is directly compatible with W27C512 EEPROMs, just replicate the image as much as necessary to fill the ROM.
- Alternatively, you can put all ROM images into a single W27C512 EEPROM, which will save a bit of power and allow you to have the Plus/4 Function ROMs in your machine. In this case install a 74LS08 at U90, a 100nF ceramic capacitor at C41 and put a blob of solder on the right and center pads of each of JP5/6/7 and only install a single EEPROM at U4 with the images in the following order:
| # | Range | Content |
|---|---|---|
| 1 | $0000-$3FFF | Kernal |
| 2 | $4000-$7FFF | Basic |
| 3 | $8000-$BFFF | Function Low |
| 4 | $C000-$FFFF | Function High |
An original MOS 251641 PLA can be used in the outer socket at U16. In this case, leave R80 and D80-85 empty (but don't bother if you have already soldered them, they shouldn't hurt).
Alternatively, it can be replaced with a GAL16V8 programmed with the equations from Daniël Mantione's PLA16V8 project installed in the inner socket. In this case, solder 1n4148 diodes at D80-85 and a 5.6k resistor at R80 (I'm pretty sure 4.7k, which is a more common value, will work just as well).
The DB-9/DE-9 joystick ports have a standard Atari pinout, which is the same one used on the C64 and Amiga. They also have a "fixed" ground, allowing for the use of "advanced" joysticks with autofire functionalities for instance, which require power from the machine.
Sega MegaDrive controllers can be used, too. They expect to be powered from pin 5 though, which is normally unconnected. You can bring power to those pins by closing JP9 for Port 1 and JP10 for Port 2. Be careful though, as other joysticks/mice can short that pin to ground upon the press of a button. R91/92 will protect your power supply in that case but you'd better not rely on them.
The Commodore 1350 mouse is NOT supported, nor are analog joysticks or Paddles. A SID Card can help with those.
The board is designed to accept an original C16 keyboard, C64/VIC20 ones can also work to a certain extent, please see this issue.
If you need to tune the brightness of the LED, try different values at R14.
Note that while the footprint for U13 states that a 74LS245 can be used, it can't. If you don't have a MOS 6529, take a look at these alternatives:
The replacement of the joystick/power connectors forced the removal the reset button. This is still available on the JP11 pin header though, so that a switch can still be connected and placed somewhere (maybe in the former RF-connector slot), or left hanging through the cartridge slot (Please do NOT drill any holes in your case!). Maybe it could be that could be fit in the top section of a newly-designed 3D-printable side bracket replacement, where there seems to be some space available.
The RF modulator was removed and replaced with a circuit that can provide either Luma+Chroma (say S-Video) or Composite Video.
That circuit had some trim pots that can be used to adjust the luma and chroma levels. If you don't want to do so, install a 56R resistor at R84 and a 150R resistor at R87, do not install RV1 nor RV2 and short JP81 and JP82 on the back of the board.
Commodore didn't care much for ESD protection on the C16. They started retrofitting some diodes after they must have had a lot of failures, but even those do not actually do much.
- If you want to do exactly what Commodore did, install 1n4148 diodes at D94-99.
- If you want to have much better ESD protection, solder DT1042 ESD Suppressor Diodes at U91-95. Unfortunately this is a surface-mount (and pretty small!) device but I couldn't find any through-hole equivalent.
Only do one thing or the other. This is something you want to decide right at the start, as soldering the SMT components is much easier if you do it first thing.
You are strongly recommended to use a new C64 power supply, being able to provide at least +5VDC@2A and 9VAC@10VAC. Be careful with old VIC20/C64 ones, those often have higher output voltages that will destroy whatever you plug them into.
For the power switch, there are a number of parts you can use:
- Salecom T80-R (R8011L/R8012L), for sale on RetroTech and eBay; near perfect match.
- Sky KS-SP-222A, for sale on eBay (may be listed as KSSP-222A).
- C&K 7201J50V5QE2 (silver contacts) or -SE2 (silver with tin contacts); these would be a special order since nobody stocks them. Turns out, the gold contacts are not rated for the amperage used by the C64 so couldn't be used. [7201=DPDT switch, J50=the correct cap for C64, V5=the thin pin support mounts, Q for silver or S for silver with tin, E=epoxy sealed, 2=black cap. Info based on datasheets]
- C&K E201J50V5QE2 or -SE2 with the same part number coding used above. These would also be a special order as nobody stocks the switches with the thin pin support mounts. Everything anybody stocks has thicker standoff brackets on the bottom that would misalign the switch cap with the hole on the C64 or 1541-II or 1581.
- NKK M2022TXW41-FA or -DA [M20=switch series, 2=DPDT, 2=on/on, TX=narrow frame for small actuator, W=silver contacts, 41=right angle vertical mounting, F=.450" wide rocker {rocker model # AT4150} (D for .365" wide rocker, but it's .169" {4.3mm} taller and might not fit the opening on the side of the computer or disk drive case), A=black cap. Info based on datasheet.] NOTE: This switch may have the raised bracket on the bottom rather than the thin mounting pins. If it's the bracket, that would have to be cut off before mounting. If anybody has bought one of these switches, please let us know.
- There are also similar switches on AliExpress. These would be electrically compatible but they are somewhat shorter and you won't be able to toggle the switch fully.
(Reworked from this post by Lemon64 Forum user Skyfox.)