Posts by frno

Jens, would you recommend using the MAX1771 as a basis of a regulator design? It also sells as part of an evaluation kit, that perhaps can be modified and installed inside an C64C.

Here is another design that seems small and convenient, based on an MP2307:

https://www.electrokit.com/pro…lator-step-down-1-8v-17v/

It is also very cheap, at less than EUR 3.

What are your thoughts?

Thanks, Jens, that was helpful to learn. I suppose one could try to cut down the power cable from 1.6 m to 0.2 m or so, but if the original Commodore PSU is preconditioned for a certain length (and thereby a certain voltage drop), then I suppose the voltage may become too high. Nevermind having to put a large power brick with such a short cable on the desk. The switch and fuse could be replaced, of course, and the connector could be cleaned and resoldered.

Your regulator concept seems like a promising idea, especially if it could be built in. Would you know if anyone else has successfully attempted to do this?

Quote from Jens

The one thing I'd avoid is MeanWell chassis - all "commercial" solutions for Amiga and C64 use them, and they cause trouble all along.

Would you be able to elaborate on the kind of problems? Modern PSUs, such as Mean Well, seem to comply with significantly higher standards than the original PSUs from the 1980’s, when measuring ripple, and so on. For 9 V AC it seems transformers from Breve Tufvassons are somewhat popular in home-built PSUs, and for 5 V DC just about any modern components.

I understand that the cheapest stuff likely is crap, but surely there must exist plenty of modern and reasonably priced PSU components that by a wide margin exceeds the power requirements of a C64?

Hmm... In fact I’m currently using an original cuboid PSU looking exactly like that, and buying another one for EUR 30 or so seems like a bit of a lottery.

I recently replaced the PSU for an external SF314 floppy unit for the Atari ST with this Mean Well RPD-60A dual 5 V and 12 V PSU, and it fit nicely inside its original PSU case with minimal soldering:

https://www.meanwell-web.com/e…ame-power-supply-rpd--60a

Is it possible to find something similar to replace the C64C PSU? Admittedly, dual 5 V DC and 9 V AC could be a rare combination.

Both PSUs have approximately 5.27 V, and unfortunately pressing the reset button doesn’t help.

One peculiar observation is that the red power LED on the C64C is at about half the intensity when booting fails, as compared to a successful boot when the LED is at full intensity.

I have now also verified that the Ultimate II+ has similar issues with the PSU that the Chameleon fails with.

What are the best PSU replacement options? It would be nice to replace the PSU internals and reuse its external casing, if possible.

It turned out that the Chameleon is somehow incompatible with this C64C PSU. We tried another PSU, and then the Chameleon started without apparent issues. Now things get mysterious:

• The oscilloscope confirms that the video clock is nice and stable under all circumstances, with either PSU, and with or without the Chameleon inserted in the expansion port. The clock runs nicely despite a crashed Chameleon. We did a minor adjustment to CT1 to have it in the middle of the acceptable clock interval, rather than at the edge near grayscale problems. This didn’t help the Chameleon to boot, though.
• VCC is 5.27 V with either PSU, so the voltage appears to be good.

In short, with the oscilloscope we were unable to measure any meaningful difference between the PSUs. Still, the Chameleon refuses to boot with one of them.

One idea is that there is a difference in the PSU power-up sequence, and that the Chameleon starts executing too early, before power is stable enough, leading to an immediate crash. The oscilloscope measured the power-up from 0 to 5 V to 1.4 ms in both cases, and they appeared to behave about same.

Any idea what the problem could be?

Yes, the clock generation chip is marked K6 8701 2186 S. What is the best approach to determine whether the 8701, possibly only the CT1, needs to be replaced? A logic analyser?

Cleaning the contacts with IPA (chemically pure isopropanol) did not help, unfortunately. The cartridge fits rather snugly in the expansion port. I suppose that one possibility is that the soldering between the connector and the mainboard is loose, but I don't have any evidence of that.

Is the Chameleon supposed to blink anything with its LEDs when it boots? They remain off when the C64C is powered on.

When the Chameleon v2 is inserted into the expansion slot of my C64C, it (almost always) refuses to boot. After about 50 power-cycles, and many reinstertions of the cartridge, the C64C booted successfully with the Chameleon inserted only once. No other accessories are connected. The power LED of the C64C turns on, but the screen remains black, or sometimes displays a white screen. The LEDs on the Chameleon remain off. The power supply is a T40/E with 1.7 A on 5 V and 1 A on 9 V.

Both the C64C and the Chameleon always boot successfully when disconnected. I have noticed that the C64C on a few occasions displays a grayscale image, suggesting that its CT1 trimmer capacitor near the VIC may need to be replaced. Is the Chameleon sensitive to CT1 deviations?

Finally, it would be useful to forward keyboard commands via the IEC connector (from a C64 keyboard) or the ChaCo USB connector (from a PC keyboard), as an option, and not only the PS/2 connector. The amount of electronic waste can be reduced by not requiring a PS/2 keyboard, just for the Chameleon.

The TC64 v2 I received this week came with a Torx screw, T8 possibly T9. Thankfully it isn't the Tamper-Resistant Security Torx with a post in the middle that prevents standard Torx drivers.

I do own a PZ1 driver, as mentioned in the manual, but it is incompatible with this variant of the Chameleon. I also have Torx T4-T7 and T10, but not T8 or T9, so I'm also considering replacing the screw.