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Now let's get rid of the nasty stuff first. No liability is assumed with respect to the use of the following information. In other words if you screw-up trying to install this modification, then it's your responsability.
If you do not feel up to it PLEASE take it to a Commodore repair center or a repair service that can work on computers and let them do the installation. I will warn you that most Commodore Repair Centers will not or do not like to do this modification. When they do, it can be expensive. If you belong to a Users Group, tell them about the project and ask if there is anyone there that could perform the operation. This modification will NOT hurt the computer in any way, unless it is installed WRONG.
You can make your own piggy back board or you can do what I am going to describe (since it is a little hard to put a schematic in a text file).
You should ground yourself with a static guard wristband (such as what Radio Shack sells). Even though the chip is quite durable, just the right static discharge can ruin all or part of the SID chip.
For those of you that are not familier with the way pins are numbered on an IC chip here is a short explanation. On one end of the IC you should find a little notch, looking at the chip with the notch at the top the numbering goes this way. The upper left corner of the chip is pin 1 and they are numbered consecutively, counter-clockwise around the chip. Some chips do not have a notch in one end, but instead dot is placed in one of the chip corners to designate that pin 1 starts in that location.
notch
----,,----
1-!. !-8
2-! dot !-7
3-! !-6
4-! !-5
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I have included the information that is needed to install this modification on the Commodore 64, 64C and 128. I haven't been able to look inside the 128D, so I cannot provide the information with any accuracy.
There are TWO different 64C circuit boards and both use DIFFERENT SID chips. You can tell the difference by opening the 64C. If you see a 64-pin chip on the board and the board is only 5.5-6 inches wide then you have the narrow board 64C and must use the 9 volt 6582 SID chip. The number of the chip in the 64C narrow is an 8520 and is the same as the 6582.
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Parts Commodore 64, 64C (wide) & 128
1 - 6581 SID chip from Jamco or Kassara Microsystems
1 - 2N2222 transistor Radio Shack 276-1617
2 - 220pf capacitors Radio Shack 272-124
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Parts Commodore 64C Narrow Board
1 - 6582 SID Chip From Jamco or Kassara Microsystems
1 - 2222A transistor Radio Shack 276-2009
2 - .022uf capacitors Radio Shack 272-1066
2 - 1k ohm 1/4 watt resistors Radio Shack 271-1321
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Parts 64, 64C (all) & 128
2 - 1k ohm 1/4 watt resistors Radio Shack 271-1321
1 - 1000 pf capacitor Radio Shack 272-126 listed as .001 mf this is
the same as 1000pf
1 - 10k ohm 1/4 watt resistor Radio Shack 271-1335
1 - 10 uf electrolitic capacitor Radio Shack 272-1025
1 - 5 inch length of wire
1 - 5 inch length of shielded cable
1 - surface mount female RCA plug (this is what you normally find on the back
of your stereo.
On the C-64 and 64C (wide) the SID is IC U18 (the IC number will be marked in white on the circuit board). It is usually located in the middle of the circuit board, next to the metal video chip case or up between and just below the serial and monitor jacks.
On the C-64C (narrow board) the SID chip is IC U9. It is located in the middle of the board, just a little to the right of center) and called 520.
On the C-128 the SID is IC U5. It is located at the back of the circuit board just to the right of the metal housing for the 40 and 80 column video chips.
First bend out pins 23, 24 and 26 and cut them off of the 6581/6582 SID chip. These are for the two analog and one audio input lines. They will cause problems if connected and since they will not be used it is best to remove them.
Now bend out pins 1, 2, 3, 4, 8, and 27.
Solder one of the 220pf capacitors (64C narrow uses 0.022 uf) to pins 1 and 2 then solder the other 220pf (64C narrow - 0.022uf) capacitor to pins 3 and 4. The capacitors control the upper and lower frequency range and filters of the SID chip.
The reason I am using 220pf capacitors is because of problems with the filters in the SID chip. The C-64 first came out with 2200pf capacitors, but they were changed to 470pf. The reason for this was because the filters of the SID vary from chip to chip and using 2200pf caused a lot of them to sound muffeled when the filters were on. I have found that by lowering the capacitor value to 220 pf helps even more. If you wish, you can use 470s if you feel it would be better, but DO NOT use 2200pf.
The 6582 SID chip for the 64C narrow must use the 0.022uf capacitors, as the filter range is much different.
Solder one end of your wire to pin 8 of the SID chip. This is for the chip select line. We will connect this to the cartridge port. This tells the computer where in memory the chip resides (described later).
Now solder the remaining pins (excluding the ones we have bent out and/or removed 1, 2, 3, 4, 8, 23, 24, 26 and 27) to the sid chip currently in your computer. You may have to bend those pins inward just a little for them to get a good grip on the SID chip. Be very careful not leave the soldering iron on the chip TOO long as you could ruin BOTH SID chips. I would put some heat sink (silicon grease) between the two chips before soldering them together. This will provide better heat dispersal on the bottom chip.
Now that you have the chips soldered together (place the SID chips back in the socket if you removed them), solder the wire from pin 8 (on the SID chip) to pin 7 of the cartridge port on the back of the computer.
Set the computer infront of you like to are getting ready to type, with the back of the computer away from you. Look at the cartridge port (located in the upper right corner of the circuit board). You will see two rows of pins connecting the cartridge port to the circuit board. You want the row of pins closest to the front of the computer. Now, count the pins starting at the LEFT side and counting to the right.
You want to solder the wire from pin 8 of the extra SID chip to pin number 7 of the cartridge port. This is the same place on all of the models C-64, 64C and 128.
This will tell the computer that the extra SID chip is at address $DE00 hex or 56832 decimal. You will access it just like you would the regular sid chip but starting at this address.
I am no longer describing how to connect for address $DF00. This address causes problems with the RAM Expansion Units and numerous other cartridges. From now on address $DE00 is the ONLY address for the SID chip.
Now partially reassemble your computer (be careful that nothing shorts out the pins still sticking out). Turn the computer on and load the player program provided and tell it to load in 'TEST'. If you get sound then so far so good. Turn off the computer and disassemble the case.
Drill a hole in the back end of the computer just large enough to anchor the RCA plug. Then solder the center wire of the shielded cable to the center post of the RCA plug. Insert the wire through the hole you have just drilled and anchor the plug to the case. Now solder the ground wire to the ground tab on the RCA plug.
Here comes the difficult part to explain. This is the coupling circuit for the audio output. Here is a rough schematic.
Pin 27 on 12volts dc,
9volts 64C (narrow)
SID chip resistor
!--. 10k ohm !collector
27!----.--/!/!/--.-----O 2n2222 or 2222A
--' ! ! !emitter
! ! !
1k ! ! +
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