Hi Chaps, thanks for the interest. :smile:
I should probably have taken some photos, but I'll make more with my spares over the next few days and do a proper photo how-to.
For now, Required parts:
-USB Power adaptor (2 Amp. Don't use your PC!)
-DIN Plug (C64 power socket compatible)
-USB Cable (I went for a Type A to Micro)
-MAX660 CMOS Monolithic Voltage Converter
-Two 22uF Tantallum Capacitors (1uF to 150uF likely fine, electrolytics may be too big)
-Hot glue (probably optional)
My non-expert understanding:
The C64 has some funny old power requirements. As I understand it 5v dc and 9v ac, the latter because the clock chip needs a waveform to keep time. Other voltages too, but the computer sorts those out for itself.
So... A USB supply will give the 5v easily enough but what about the 9v ac? Well, it seems the first thing the C64 does with that 9v ac supply is to turn it in to dc -doh! So it should be fine just to use 9v dc instead as long as you don't need to use that pesky clock chip... does anybody?
Ok. 5v x2 = 10v, which is kind-of close to 9v... especially once you take the machine's internal regulators in to account and 9v ac peak-to-peak is near 10v anyway...ish!
That suggests if one uses a charge-pump circuit you have all the ingredients you need to power a C64 off a sufficiently strong USB supply.
Advantages:
Fairly easy to construct from readily available components
All the parts can fit inside the DIN plug shroud
No more potentially dodgy C64 PSU
Disadvantages:
You may consider the above plan to be dodgy in itself!
Non-functioning clock chip
As constructed the MAX660 could struggle to supply enough juice for "long board" C64
Construction:
1) Lop the MicroUSB end off your USB cable and expose about 1.5cm of the four wires within. Trim off the excess outer shielding. Be sure to buzz out which two are 5v and GND, tin the ends with solder. Of the two remaining wires leave one in tact (see later) and cut the other off right at the base - don't throw it away! Tin both ends and keep it for later.
2) Take your MAX660 IC and remove pins 1 and 7 - a little waggle should see them snap off. For the remaining pins only snap the ends off at the shoulder where the thick part comming out of the IC narrows to the bit where you'd normally fit in to a socket/PCB. Then fold the now stubby legs under the IC.
3) The next bit is hard to explain but is fairly obvious with parts in hand. Take each of your caps in turn and fashion their legs in such a way that the longer one looks a bit like a fish hook turned toward the shorter one, the shorter one with very small kink at the end pointed away from the larger...
...Why?
The plan is to solder the two caps to the the remains of IC such that their legs are laying flat on each side of the IC with the bodies just hanging over the end of the IC with the notch. (Um, think testicles! I wish I'd taken a photo)
"C1" needs it's positive leg soldered to pin 2 and negative leg soldered to pin 4
"C2" needs it's positive leg soldered to pin 8 and negative leg soldered to pins 5 and 6
(For more info Google MAX660 and see page 1 of the data sheet. The Positive Voltage Doubler diagram)
3) Take your 5v USB wire (probably red) and carefully expose the copper a few mm above where it exits the stripped-back shielding. Give it bit of a kink at that point and carefully tin that spot. Don't expose too much! Push the (non-testicle) end of the IC up to where the wires exit the cable shielding and then solder the kink to pin 3 of the IC being careful not to short anything. The MAX660 now has power and you still have a 5v wire.
4) Do the same with the GND wire (probably black), this time soldering the tinned-kink to pin 5 or 6 (these are already shorted by the negative leg of "C2")
5) Remember that wire you cut, saved, and tinned both ends? Solder that to pin 8 of the MAX660...
6) ...and the last wire? Wrap that round the length of the IC passing between said testes.
The idea is the IC should now be protruding lengthways from the end of the USB cable with a couple of little gonads closely dangling as if it's a bit of a cold day. The unconnected wire wrapped around the length of the IC to help strengthen it, and three wires (+5v, +10v, GND) kind of adding to the genitalia vibe.
7) Solder GND to pin 2 of the DIN plug, +5v to pin 5, and +10v to pin 6. No further connections are needed and our little gonads should be closely nestled to the circle of pins so keeping things tidy and stopping any shorts.
8] Did you remember to put the DIN plug's plastic shroud over the USB cable before starting?
9) Next reassemble the din plug itself. You should find the electronics fit neatly within the metal bits and the cable poking out as hoped...
...If you find (like me) the metal bit that has the cable clamp is too short to clamp said cable but instead is getting in the way of the IC see below.*
10) Disasemble, wrap the electronics with electrical tape, reassemble, crimp the cable clamp over the cable, and push the plastic shroud in to place.
:-DDone!:-D
...Now time to see if it works or you have a dead C64 on your hands! Did you carefully double-check everything?
*If you had to remove the cable clamp I'd suggest taking a leaf out of Commodore's rather dodgy PSU assembly book:
Don't wrap the electronics with tape, instead cover the whole thing in hot glue being sure no metal bits are exposed. Then before it fully sets squeeze the metal shrouds round your lump of goop and top up any gaps with more hot glue. Make sure this extends on to your cable and quickly pull the plastic shroud over the lot. If you're too slow just heat it up a bit and have another go. There, just like a C= PSU, no user servicable parts inside!
PS
As mentioned above this works fine with my C64c (short board) but probably won't provide enough juice for a long board equipped machine. A second MAX660 wired in parallel with the first (maybe some diodes!) could be the answer.
will send pm
