Here are some pictures of the VIC area of my c64.





How do I perform this mod?

you have to swap the vic against a pal vic, and change the crystal against the crystal that is used on pal. and close the pal/ntsc "jumper".

i'd suggest you try buying a complete pal c64 from ebay (or whatever)...it shouldnt be (a lot) more expensive than a single vic, and will save you the hazzle with soldering.
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Groepaz, he wants to mod from PAL to NTSC, and he has the NTSC video chip. I know that

Unfortunately, this is the very old board revision with the discrete clock circuit. The later ones (1984 and up) use the 8701 clocking chip, which has the PAL/NTSC jumper and no other timing-critical parts. Your discrete clock circuit must be modded with a few more parts.

First of all, you can unplug the PAL VIC and put in the NTSC VIC. The computer will still start up and already show a black&white screen on your PAL monitor. Most NTSC software will run, but NTSC fastloaders will not.

For NTSC fastloaders, you have to run the clock circuit from a 14,31818MHz crystal. Remove the 17,7344MHz crystal from your PAL machine, solder in the new crystal.

The schematics show that C107 is not there on NTSC machines, but you can leave it in your machine, it doesn't hurt (and it doesn't do anything after the mod).

R26 must be changed from 100 ohms to 0 ohms - just solder a wire over that thing, shorting it out.

R52 must be changed from 330 ohms to 300 ohms. This can also be accomplished without removing the part, just by soldering a 3.3KOhms resistor in parallel.

R53 must be changed from 100 ohms to 390 ohms, which can only be done by unsoldering the old resistor.

C70 must be changed from 15pF to 16pF. Both are fairly uncommon values and they must be very precise (5% types). Since the values are very close to each other, the oscillator might work without touching this part, but just by fiddling with R27 (the trimmer next to the VIC chip) in order to get the oscillator working at the right frequency. An oscilloscope would help.

Last, there's a jumper wire, covered by C101 in both of your pictures (just bend that away). Unsolder the wire from it's current position and solder it into the position with the dashed line.

Reading this whole block of mods, it might be easier to get a mainboard rev. that uses a 8701 clock chip. This makes the mod is as easy as Groepaz described it.

Jens

Easier idea: Buy a canned oscillator with 14,31818MHz, remove FB16, feed the output of the oscillator into pin 5 of the 74LS193 (U30). You will only need to change the jumper wire - no fiddling with trimmers, precision capacitors and stuff.

14,31818 MHz is a standard frequency, found on many PC mainboards. Back when 286 and 386 computers were cool, some mainboards also used canned oscillators. This might be a good source, which might make it possible for you to find one on a weekend

good night,
Jens

well, he decided to buy an NTSC VIC chip from me, because that's a lot cheaper than shipping an NTSC machine over the big pond. I included the 14,31818 MHz crystal, so he has all the hard-to-find parts in one package.

I didn't expect him to *only* own 1983 models of the C64. Anyway, the canned oscillator will most probably the easiest thing, but there's a number of choices we have today with cheap and ever-faster logic chips. Back in the days, a 14 MHz oscillator was something that had to be tuned, today it's even working off the input capacitance of a 74HCU04 with a stability far beyond the performance if the 1983 circuit.

Jens

I think I'm going to look for an '84 model
That's better than looking for the right resistors/capacitors etc.

If you just ship the motherboard, the shipping shouldn't be too bad. Really, it will be faster and much more reliable than trying to mod one. Just put it into into a case with keyboard.

Success
Found a 1984 model, very easy mod.