RE: LOW VOLUME SOUND C64c

From: Bil Herd <bherd_at_mercury-cg.com>
Date: Tue, 31 Jan 2012 22:11:28 -0500
Message-ID: <5296ab3efdf8345bca0ebbc30ab79d27@mail.gmail.com>
Hi Ed, et al.

Yeah as you saw +4/264 didn't have a SID we made the raucous squawking
noises on the same chip as the video.

The order of things is pretty much:
1)Check power supply which is why it was recommended to check the fuse.  I
would also check any other voltage pins directly on the SID: +5 on pin 25
and +9/12 on Pin 28.
2)Since it is socketed, swap the part.
3)Finally if you have a scope look at the output directly on pin 27, you
should see at least ..3v-5v AC when it's working.  You should actually see
roughly the same amplitude of AC signal at the output Pin 3 on  the DIN as
the transistor is an Emitter Follower and doesn't have voltage gain.  If
you are losing the signal through the transistor stage,  it could be that
the transistor is gone or that C77 or C76 have dried out being that they
are 25 years old.

The good news is that since you hear sound (as opposed to utter silence)
it should be fixable.

I used the schematic at
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/250469-rev
.B-right.gif to pull the pin details, as you can see there is not much
except the SID chip, a couple of caps for the filter and then the
transistor buffer circuit.

Good luck, feel free to shoot over intermediate results.

Bil

-----Original Message-----
From: owner-cbm-hackers@musoftware.de
[mailto:owner-cbm-hackers@musoftware.de] On Behalf Of Ed Johnson
Sent: Tuesday, January 31, 2012 11:54 AM
To: cbm-hackers@musoftware.de
Subject: RE: LOW VOLUME SOUND C64c

It's socked.

Best regards,
Ed Johnson


-----Original Message-----
From: owner-cbm-hackers@musoftware.de
[mailto:owner-cbm-hackers@musoftware.de] On Behalf Of Gerrit Heitsch
Sent: Tuesday, January 31, 2012 11:49 AM
To: cbm-hackers@musoftware.de
Subject: Re: LOW VOLUME SOUND C64c

On 01/31/2012 04:09 AM, Ed Johnson wrote:
> I see there are different revisions of the SID chip. I have an 8580R6
> Can I use any 8580 revision SID? Or even use a 6581 ?

You sure about the 8580R6? So far I have only seen the 8580R5.

You can't use a 6581 since it needs +12V and different capacitors. Sure,
that can all be done, but you need to be handy with a soldering iron.

  Gerrit


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Received on 2012-02-01 04:00:11

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