SID Problems

Melted48k · Newbie Joined: 03 Jun 2012 Posts: 3

So, I've recently got hold of a breadbin C64 (SN:501688).
The unit itself looked like it hadn't had any love for a fair few years.
It was caked in dust. The keyboard was unresponsive. The PSU was intermittent but it did work.
I stripped it down and cleaned the keyboard and contacts, give the PSU input a bit of attention and hey presto, it works and looks lovely.
Or so I thought.....

Games load up (from cassette) no problem. keyboard, joystick etc. work fine. Theres just absolutely no audio at all Crying or Very sad

Up to now I've checked:
5VDC and 9VAC supplies - OK
Internal fuse - OK
12V at the SID chip. Across pins 28 and 14 iirc with the chip removed (its socketed) - OK
Cassette works OK which, as I understand, is another indication that the 9V supply is fine
I've tried a few test POKE commands but as I'm not too savvy with the C64 operation I can't be 100% sure that theres no sound because of a fault or input errors on my behalf.

Any thoughts on this? Or does it look like another SID KIA!!!

Cheers

boulderdash · Posted: Mon Jun 04, 2012 1:48 pm Post subject:

next step would make sure the tv/monitor `s speaker works and make sure the a/v cable you are using is working
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Melted48k · Newbie Joined: 03 Jun 2012 Posts: 3

boulderdash wrote:

next step would make sure the tv/monitor `s speaker works and make sure the a/v cable you are using is working

Ha, yeah! Can you imagine... Laughing

They are.
I use the same TV for all my other consoles.
The actual RF lead I use with my Atari Jaguar

Having said that, I guess it could perhaps be the RF modulator?? Hmmm.

boulderdash · Posted: Mon Jun 04, 2012 2:26 pm Post subject:

well anything is possible with the c= ,,,we love the thing despite its quirks Wink

you can also try pulling the sid out and seeing if any of the legs are dirty or bent over
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e5frog · Posted: Mon Jun 04, 2012 4:28 pm Post subject:

Try getting the sound directly from the A/V connector, if it's still dead I'd check the capacitor and the amplifier circuit between SID and A/V socket.

Easiest would be to plug it into a working C64 and see if it worked there. Wink

Melted48k · Newbie Joined: 03 Jun 2012 Posts: 3

e5frog wrote:

Try getting the sound directly from the A/V connector, if it's still dead I'd check the capacitor and the amplifier circuit between SID and A/V socket.

OK, thats something I haven't checked. I've got a maintenance book so hopefully it will cover that...

and wrote:

Easiest would be to plug it into a working C64 and see if it worked there. Wink

This is the million dollar statement right here Laughing

Rybags · Groupie in Training Joined: 17 Mar 2006 Posts: 103

You can check operation of SID by playing a note on Voice 3 and seeing if the waveform output is reflected at the Random number generator register.

Code:

POKE 54296,15
POKE 54287,50
POKE 54289,8
POKE 54291,0 : POKE 54292,240
POKE 54290,33

Then ? PEEK(54299) repeatedly, you should get the sawtooth output (very rapid ramp from 0-255)

Then verify pulse output. POKE 54290,65 and keep repeating that Peek line, it should give values of 0 or 255.