C64/SID Problems?

MIDIbox SID
1

Hello all,

In my quest to work my way up to building an MB6582, I have been sourcing SID chips and an old C64 to yank some parts from. I just got one of the two SID 6581s that I bought off eBay in the mail, along with an old C64 that also has a 6581 inside.

I was hoping to use the C64 to test any SID chips that I buy. However, the C64 doesn’t seem to make any sound. I hooked it up to my Mac with an Elgato EyeTV adapter, and I get video, but no sound. I know that sound is coming through the EyeTV since if I pull out the cable I get static noise with the fuzzy TV signal, and when the cable is connected I can touch the screw terminals on the RF adapter for the C64 and hear static hum as well while the video picture slightly distorts. I tried to make the C64 make some noise by typing in the BASIC sound program in the C64 manual, but it doesn’t make any noise at all. I cracked open the case and there is definitely a SID chip in there alright, it just seems to be quiet. The motherboard was covered in dust, so this thing has obviously been around a while.

So, here are my questions for you guys.

  1. Is it likely that the SID chip is just dead? I looked around a bit on the web and it seems like 6581s are more susceptible to untimely death than 6582s. Is there any way to test the SID chip while the C64 is powered on besides handing BASIC programs to it? I have a logic probe and a multimeter, although I’m a relative beginner with electronics so please be gentle with any suggestions. Any other suggestions for checking the chip in situ?

I have another SID chip that is supposed to work that I could plug in to the socket in the C64, but two things are preventing me from wanting to do so.

  1. The first that worries me is that the power supply I received with the C64 describes itself as “5VDC 7.5VA” and “9VAC 9.0VA”, but I’ve read on the forums that the 6581 is supposed to take 12VDC. I’m not really sure how to interpret the label on the power supply - is it the correct one?

  2. The second thing that worries me about testing my other SIDs in this C64 is that if the one in the case is dead, I’m scared that maybe a malfunction in the C64 itself killed it. FWIW, everything else seems to be working. Should I be worried at all about putting my other SID chips in on this board?

If the answer is to yank the existing SID from the C64 and try the other one, any tips on the best way to yank the old chip out and put the new one in without damaging anything would be appreciated. It looks like you just pull it out gently with pliers, but I figured I’d ask the experts first. Many thanks in advance for any help you guys can offer me!

Cheers,

  • max
2
  1. It could be dead. Some people have successfully salvaged a 6581 from a C64. I am not one of them.

Can you observe a spike in the audio output when you turn on the C64? i.e. level meter jumps up to max then returns to nothing?

Also, do you hear anything on the audio, like noise, to suggest it’s outputting something (i.e. prove your audio input is really working)?

  1. C64s that need 12V (for 6581 SIDs) generate 12V internally. AFAIK they add 5V DC to 9V DC and then regulate this 14V through a 12V regulator.

  2. It’s hard to say what might have killed the 6581 in the C64, if it is dead. You could test the voltages on the SID socket, with or without the SID in it, to check it’s getting 12V DC on pin 28, etc.

Don’t use pliers to remove an IC. The cheapest extraction tool is better than that.

http://www.altronics.com.au/index.asp?area=item&id=T2550

I can’t really recommend what’s best… it’s probably unlikely that the C64 will “kill” your other 6581s if you try them, but then again, I also read somewhere that connecting C64s to an amp can sometimes kill the SID, which is why the MIDIbox SID module has an audio buffer to “protect” the SID.
T2550.gif

3

A perpetual question it seems.

Some answers are given here:

http://chipmusic.org…n-i-test-a-sid/

Your instincts serve you well, DO NOT TRY ANOTHER SID IN THE FAULTY ONES SOCKET (see last post on that link)

I’ve read of a fair few mystery stories on apparent non-working SID’s. Don’t give up hope yet. :slight_smile:

I’ve extracted a couple of SID’s before, i just used a flathead screw driver and slowly levered it out bit by bit end by end, took a while but the legs snap/bend if you go too rough/quickly.

4

If the 9V rail in the C64 does not work, the C64 will not make sound - it will power up alright, and look just fine. I saw this problem a few times - one time it was a first hand experience… the fuse was blown!! No sound, still it worked just fine.. i changed the fuse, and everything worked just fine :smiley:

If you have a datasette (the cassettedrive for the C64) you can quickly determine if the 9V rail works; if the datasette does not run, then the 9V rail in the C64 is broken!

A quote from Wikipeida: “The 9 volt AC is used to supply power via a charge pump to the SID sound generator chip, provide 6.8V via a rectifier to the cassette motor, a “0” pulse for every positive half wave to the time-of-day (TOD) input on the CIA chips, and 9 volts AC directly to the user-port. Thus, as a minimum, a 12 V square wave is required. But a 9 V sine wave is preferred[31][32].”

http://en.wikipedia.org/wiki/Commodore_64

… some say that this fact does not apply to C64 with 6581, actually. I wouldn’t know - but try to check the fuse and measure the 9V just to be sure

edit: If you are curious about this, you can find quite a few threads on the Prophet64/MSSIAH-forums that discusses this matter in detail

5

Wow, you guys are awesome. Let me work my way through the responses one by one.

Can you observe a spike in the audio output when you turn on the C64? i.e. level meter jumps up to max then returns to nothing?

Also, do you hear anything on the audio, like noise, to suggest it’s outputting something (i.e. prove your audio input is really working)?

I can get static noise from the EyeTV when I disconnect the RF adapter, and get noise when it is plugged in and I touch the exposed screw terminals with my finger. When hearing this static, if I turn down the volume on the EyeTV, the static is muted. Would you say that’s a good enough test?

  1. C64s that need 12V (for 6581 SIDs) generate 12V internally. AFAIK they add 5V DC to 9V DC and then regulate this 14V through a 12V regulator.

Duly noted. It sounds like this power supply and associated innards from the C64 will be usable for the MB6582 then, even if the SID chip in the case is dead.

  1. It’s hard to say what might have killed the 6581 in the C64, if it is dead. You could test the voltages on the SID socket, with or without the SID in it, to check it’s getting 12V DC on pin 28, etc.

This I would love to do, seems like a logical next step. I’m not sure exactly how to do this though. From the diagram on http://en.wikipedia.org/wiki/MOS_Technology_SID, my guess is that GND and VDD are the pins I want to use for positive and negative with my multimeter respectively? How many VDC should I expect to see running through the chip (12VDC, I’m guessing)? Will the power be flowing regardless of whether or not the chip is making noise? Also, I see that there is an audio out pin. Is there a way I can run a sample sound program while holding the multimeter to the chip to see if audio is exiting the chip but perhaps not making it to the outside world?

Don’t use pliers to remove an IC. The cheapest extraction tool is better than that.

Thanks - also noted. I’ll go get an IC puller from Radio Shack or Skycraft here in Orlando, FL.

If the 9V rail in the C64 does not work, the C64 will not make sound - it will power up alright, and look just fine. I saw this problem a few times - one time it was a first hand experience… the fuse was blown!! No sound, still it worked just fine.. i changed the fuse, and everything worked just fine.

I think I saw your post on this elsewhere (or somebody else with the same idea). I looked at the fuse yesterday. It has a twisted wire within and appears to be intact. To test this fuse, I’m guessing I just need to turn on the C64 with the case open and hold my multimeter against both ends, expecting to see 9VDC? Sadly, I have no Datasette.

If you have a datasette (the cassettedrive for the C64) you can quickly determine if the 9V rail works; if the datasette does not run, then the 9V rail in the C64 is broken!

Sadly, I have no Datasette to test this theory. Is it possible to put my multimeter against some of the pins of the socket the Datasette uses to see if any current is flowing?

Something else I noticed is that every C64 I have seen dismantled online has a metal casing over the motherboard. This one did not have the metal casing over the motherboard - I popped open the case and the motherboard was exposed to me bare. Any concerns with this anomaly?

Lastly, the motherboard is still really dusty. I can’t see any harm in giving it a gentle blast with compressed air to clean it off. Any words of warning here?

Again, thanks so much for all the tips! I’m looking forward to getting to the bottom of this and will post my results once I know how to test the chip.

6

I finally got some time to run the tests you guys suggested. Here’s the results.

  1. I bought a cheap chip extractor and pulled out the SID chip from the C64’s board, then powered on the board with the SID out and put a multimeter to pins 14 and 28 of the empty socket. I got a reading of 11.82V, so it seems to have the right voltage going through (12V being the expected amount).

  2. I tried checking the 9V rail. With the C64 powered on, I put my multimeter across the fuse with the meter set to VAC. I got a reading of 0.022. When I pulled the fuse out, it passed the “beep” test on the multimeter, and the wire inside the fuse is intact.

Does the reading on the 9V rail seem low to you guys? Shouldn’t I be getting 9VAC there? Does this indicate a possible problem with the 9V rail?

Thanks,

  • max
7

I finally got some time to run the tests you guys suggested. Here’s the results.

  1. I bought a cheap chip extractor and pulled out the SID chip from the C64’s board, then powered on the board with the SID out and put a multimeter to pins 14 and 28 of the empty socket. I got a reading of 11.82V, so it seems to have the right voltage going through (12V being the expected amount).

  2. I tried checking the 9V rail. With the C64 powered on, I put my multimeter across the fuse with the meter set to VAC. I got a reading of 0.022. When I pulled the fuse out, it passed the “beep” test on the multimeter, and the wire inside the fuse is intact.

Does the reading on the 9V rail seem low to you guys? Shouldn’t I be getting 9VAC there? Does this indicate a possible problem with the 9V rail?

Thanks,

  • max

max,

dont you think it would have been easier assembling a midibox sid modul on veroboard in the 4 weeks since your last post for testing the sids instead of trying to do so with an old C64 that is likely to be unreliable?

:smiley:

8

I put my multimeter across the fuse with the meter set to VAC.

The only thing you could possibly be measuring *across* a fuse would be erm, I guess the voltage drop across the fuse. Definitely not the voltage of the rail though.

9

Hmm, a potential new development following the earlier testing. I plugged my headphones in to my Mac (running the C64 through an Elgato EyeTV as before), and when I run sound programs on the C64 I am hearing a difference in tone, but not a musical tone akin to what I am expecting.

I’m using the sound program that is on page 80 of the C64 user guide. When the sound program is not running, the C64 makes a humming noise, almost like a chorus. When I run the sound program, the humming goes away and I get a constant, faint, high-pitched noise. When I stop the program, the humming chorus noise returns.

Here’s an MP3 of what I am describing. Right around the 2 second mark I start running the program, and then at the 7 second mark I stop it.

Any ideas what this means? I’m guessing that the SID chip is broken in some way. Would you guys think it’s safe to try one of the other SID chips that I have in my possession?

10

max,

dont you think it would have been easier assembling a midibox sid modul on veroboard in the 4 weeks since your last post for testing the sids instead of trying to do so with an old C64 that is likely to be unreliable?

:smiley:

Yeah, I was looking at the SID kits tonight thinking the same… :slight_smile: I’d have to build a core module, a midi input module, and a SID module though wouldn’t I?

11

The only thing you could possibly be measuring *across* a fuse would be erm, I guess the voltage drop across the fuse. Definitely not the voltage of the rail though.

Thanks for pointing that out, nILS. As stated earlier, I’m a total electronics n00b so I could use a little help here. How should I be measuring the 9V rail? To be clear, the fuse is in the C64, it’s powered on, and I’m measuring across the fuse.

12

Thanks for pointing that out, nILS. As stated earlier, I’m a total electronics n00b so I could use a little help here. How should I be measuring the 9V rail? To be clear, the fuse is in the C64, it’s powered on, and I’m measuring across the fuse.

Here :

http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/250469-rev.A-right.gif

you can find the 9VAC input : 9VAC1 and 9VAC2 pins.

The 9VAC you can measure between 9VAC1 and a fuse F1 connection points.

From your earlier posts, looks your 9VAC supply is OK ( you got a right reading of 11.82V on a Sid socket pin 28) .

Regards,

Janis

13

I would just take the C64 out of the equation and just build a core and sid board which are all you technically need to test SIDs