Uh, oh... Defect SID chip. :-(

This is just bad… Well… At least I found a rather cheap one on eBay (not that they are cheap at all and anymore)

4 Videos of the issue…

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Is this a case of a previously working chip now not working?

Could be possible a problem in other electronics, like a filter or something like that? I can be wrong, but the SID doesn’t sound really bad in the benchmark.

Apparently it’s missing out on the higher frequencies?

Here are two links related to common C64 chip faults, maybe there’s some clue on this:

@EdS – Some MOS chips are known to be subject to age and degradation, amongst them the SID and the PLA. It’s related to the manufacturing process. (I believe, it’s one of the final layers, which is eventually degrading.) That the SID is commonly running hot doesn’t help especially.

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That is the thing. The chip is not socketed, so I have ordered a different one and a 10-pack of sockets.

If you listen carefully to the sound in the videoes, then you will hear that it is the same tone that are played wrong. If it was the filther caps, then the errors will not be the same.

Well… As the SID heats up the sound issues will become worse and worse. I have measured 5volt and 12volt lines, and they are pwefectly stable. Then I have tested with writing a game from SD2IEC to tape. Actually 12 to 13 games, and they work perfectly on my other 64. Then I have run games with different sounds. Golden axe intro makes small glitches, still the same glitches in sound at the same spots in the intro. 1942 runs issue less and the same with Bobsled in winter games. Even a C64 diagnostic program shows only issues in the sound.

So I am certain that it is the SID that are on its bleeding knees.

What you are describing may be well related to a defect in an interal counter. (Assuming this was related to some specific periods, involving waiting for a particular pattern of bits set, while this might not be an issue otherwise. Or, it’s just some harmonic issue totally unrelated to this?) But I’m not an expert by any means and just guessing.

I have ordered a replacement SID and a few sockets. That way I will find out if the chip is bad or not. I have a SwinSID-Nano in my box of parts as well. Yet first I have to install a socket. Then I will know if I have to look at other things

I recieved the sockets the other day, and so I desoldered the SID today and soldered in a socket. Mounted the SID that I got for cheap and now everything is working perfectly again. Yay!! My 250407 board is finally in fighting condition again.

As I have recapped the board recently, then I think that I need to eighter get a non-gold-lid VIC-II or create a new low profile 12-to-5-volt VIC-II socket adaptor for one of them high contrast 5volt VIC-II chip, and use it with a LumaFIX in order to get a crisp and clear picture.

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