Help identifying a chip inside a Commodore 64C

[gzsfrk]

I recently picked up a Commodore 64C with a Rev. 4 mainboard inside. It's had some modifications done to it, one of which was the installation of a 28-pin JiffyDos kernel ROM. The other change, I'm not so sure of. From what I can tell, the SID has been replaced by either a third party module or some kind of custom job. (You can see what a stock 8580 in that slot looks like here.) Of course, I'm by no means up on the Commodore modding scene. Can one of you guys take a look at the below pic of the mainboard and tell me what exactly that is in the SID slot and what it does different from the standard 8580?

 

 

The "chip" in question is circled as number 2 in the above pic. I've played a few games on it, and the music and effects sound just like they do on my stock bread box, for the most part. (I did notice a very slight bit of humming a couple of times.)

 

Any ideas? I'm pretty sure it's not the SID stereo-out mod I've read about, although it would be awesome if it was and I just had to finish the wiring.

 

Also notice what I believe is the 28-pin JiffyDos kernel replacement ROM circled as number 1 in the pic above. There is some wiring on the back of the mainboard associated with that chip, as such:

 

 

I haven't seen any instructions for JiffyDos that required soldering wire bridges on the back of the board. Was that simply for the purpose of foregoing an external switch and instead hardwiring it to keep JiffyDos permanently enabled?

 

Thanks in advance for any help explaining things to a C= hacking newb.

 

- m@

Edited January 16, 2014 by gzsfrk

[Rybags]

Probably a good idea to put tape over the window of the Eprom.

 

The wiring, I would agree probably hard-selecting one of the available OSes. It looks to be a 128 Kb ROM which = 16K or enough for 2 Kernals.

 

The SID replacement looks a lot like a MicroSwinSID http://www.swinkels.tvtom.pl/swinsid/

 

Generally the hardware implementations of SID don't emulate the filters to a high accuracy and many of them don't have support for paddles.

Unsure what SwinSID offers in that department.

 

Stereo - generally a stereo install would have an extra output wired up for the right speaker, or even 2xRCA jacks.

There's various addressing methods to use the second SID (WinVICe emulator options should cover what's out there) - extra wiring would be necessary for addressing a second real or replacement SID since it is accessed by /CS and there's only sufficient address lines to cover 1 set of registers.

[TMR]

On a C64C, the BASIC and Kernal are stored in one ROM so that's just a replacement for both rather than selectable if it's 16K.

[carlsson]

Curious to find a SwinSID inside a random C64. What does it mean to pick up in this context, something you found on a flea market, eBay, swap meet with other collectors etc? I've got one of those as well, but I didn't yet install it into any computer.

[gzsfrk]

Curious to find a SwinSID inside a random C64. What does it mean to pick up in this context, something you found on a flea market, eBay, swap meet with other collectors etc? I've got one of those as well, but I didn't yet install it into any computer.

 

Grabbed it off a random eBay auction. It came with a somewhat ghetto SD2IEC adapter, so you can tell it was from a guy that liked tinkering. Any advantages to the SwinSID vs. the real thing? Or is it just a cheap replacement option for those who don't have a stack of old breadboxes to scavenge from?

[TMR]

Any advantages to the SwinSID vs. the real thing? Or is it just a cheap replacement option for those who don't have a stack of old breadboxes to scavenge from?

Pretty much the latter, it does an okay job but won't pass for anyone who really knows their SID tunes.

[carlsson]

Theoretically, the SwinSID should be reprogrammable but I don't know which practical options there are. Often you would want it to sound as much like a real SID as possible, which IIRC is the default programming but if you like, you could get it to sound more different. I think it also has additional features/registers that a real SID doesn't, but then again virtually nobody except the developer has released any programs or even music that would utilize those possible extra features.