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My C64 is toast!!!

Left it on and took the dog for a walk and when I came back (because it turned stormy with lightning) it was dead and so were both the 1541 drives. It sort or works. If you turn it on it boots to the ready prompt, but typing produces garbage and cause it to have a seizure. The two drives don't work either. Tested them on another C64. One does nothing, the other starts if you access it, but all you get is the spindle turning and it wont stop till you turn it off.

The lightning must have hit a nearby power line.

Sounds as though CIA #1 went to chip heaven and reached out through the serial bus to take a disk with it.

It'll go into the ever expanding "For Repair" cabinet until it somehow becomes a priority to have a look at it.

Our C-64 broke because the cable guy did not ground the cable coming into the house.

Trying a different (known good) power supply might help narrow down the problem.

By the way, if you don't have a known good C64 power supply, you can drive it off of just a solid non-C64 5V source and ignore the 9VAC. The latter is used by the SID and the TOD clocks, and can power external peripherals. The machine boots fine without it.

However, typing & serial bus are heavily tied to the CIAs. You could try swapping the two CIA chips with each other and see if the failure mode is different, since they're identical.

Thanks for the tips folks.

Thats true for newer C64 boards with ASSY250469. Older boards depend on 9VAC to generate 12V for the VIC-II and hence won't run with only 5V supplied.

Safest bet for a power supply replacement is to get two wall wart type power supplies, one 9V AC 1A, one 5V DC 2A. Ugly but works, and no fiddling with mains.

How 9V should the 9V AC be for a C64C? I had this twin-wart set up as bought from eBay and didn't bother checking the soldering inside the DIN 7 plug. I should have checked the previous owner's work because the soldering was awful (lots of stray strands of wire and solder that looks as if it were "painted" on) and I suspect that's why the 9V AC wart sold with it is now showing 0V and the primary winding is open. I've made a really nice job of rebuilding the DIN 7 plug but the replacement "9V" wall wart I bought is showing 10.2V AC (not plugged in of course).

Would 10.2V on the 9V AC pin be OK? I note a 7805 in the schematic that might run slightly hotter and I don't plan to use the datasette (1541 Ultimate II+ takes care of storage) or the 9V AC on the user port. Does the 2V7 zener in the circuit that drives the TOD mean that it will be OK too? What else is the unregulated 9V used for?

I gave away all our C64 stuff including the books with fold-out schematics in the back; but I expect 10.2V unloaded will come down noticeably under load and be well within tolerance.

10.2V measured on the open leads is not a problem, it will drop to ~9V when under load.
If you are in fiddling mode, replacing that 7805 with one of those pin compatible switching regulators (Recom, Traco) is a good Idea.

C64 needs the 9V AC to generate 12V for VIC and SID, generate separate 5V for the VIC, also as a clock source for the CIA tod clock, as someone already mentioned.

Newer C64s with ASSY 250469 will start with 5V only, as the 8562/5 VIC-II uses 5V only and is supplied from the same 5V rail as everything else. The 8580 SID will not work as the 9V DC id needs are generated from the 9V AC.
So newer C64 with 5V only: Works, but no sound.

It makes one want to go out an buy an Oniac transformer. The place where
I worked would require these for equipment sold in states with a lot of
lightning.
They are a constant voltage transformer.
I recall buying a pile of modems that all had lightning damage.
One could clearly see the arcing across the boards near the transformers.
I was able to swap parts and get many working again. Only one or two
part would usually fail.
I suspect the lightning damaged the regulators and over voltage did the damage
to the rest of the computer.
Dwight