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Is my SID defect?

brostenen

Experienced Member
Joined
Jul 4, 2017
Messages
61
Location
Denmark, Northern Jutland.
As people here are extremely helpful to NOOB's like me, with a rather technical question, then I have one regarding a SID chip in one of my 64's...

The symptoms are bad sound. As an example, then the title melody in the intro of winter games played back with glitches.
Other titles like Golden Axe, will have glitches here and there in the intro music track.
If I run a C64 diagnostic tool (the one that goes through all the chips and so on), then the everything is good except SID test.
If I copy PRG from my SD2IEC to tape, using a copy tool and save as "Turbo tape" then everything is good.
The voltage levels on the SID are 11.97 Volt between Pin28 (Vdd) and Pin14 (GND) and 4.75 Volt between Pin25 (Vcc) and Pin14 (GND).
Voltage levels does not go up and down, they are perfect stable with the values they have.

So it is not the 5volt line or anything like that that are unstable or something, nor the Ram or something like that.
Well... At least that is what I can logically conclude from these tests.

And if I run a ready coded set of lines that I found, called "SID Bench" were it goes through the chips registers and so on,
then the SID will not behave like it should. It is one of those that uses POKE commands and so on, and I am not a programmer by any shot.
So I am really not sure what the lines of code actually does, yet the SID craps out, and for what I know, the code writes the SID directly.

So is my amateur way of diagnosing correct, that it is the SID that are defect?


Thanks in advance
Brostenen
 
Last edited:

iz8dwf

Veteran Member
Joined
Mar 20, 2017
Messages
810
Location
Italy
As people here are extremely helpful to NOOB's like me, with a rather technical question, then I have one regarding a SID chip in one of my 64's...

The symptoms are bad sound. As an example, then the title melody in the intro of winter games played back with glitches.
Other titles like Golden Axe, will have glitches here and there in the intro music track.
If I run a C64 diagnostic tool (the one that goes through all the chips and so on), then the everything is good except SID test.
If I copy PRG from my SD2IEC to tape, using a copy tool and save as "Turbo tape" then everything is good.
The voltage levels on the SID are 11.97 Volt between Pin28 (Vdd) and Pin14 (GND) and 4.75 Volt between Pin25 (Vcc) and Pin14 (GND).
Voltage levels does not go up and down, they are perfect stable with the values they have.

So it is not the 5volt line or anything like that that are unstable or something, nor the Ram or something like that.
Well... At least that is what I can logically conclude from these tests.

And if I run a ready coded set of lines that I found, called "SID Bench" were it goes through the chips registers and so on,
then the SID will not behave like it should. It is one of those that uses POKE commands and so on, and I am not a programmer by any shot.
So I am really not sure what the lines of code actually does, yet the SID craps out, and for what I know, the code writes the SID directly.

So is my amateur way of diagnosing correct, that it is the SID that are defect?


Thanks in advance
Brostenen

You are not telling us what particular C64 PCB revision you have.Since the SID it's getting 12V analog supply, I assume it's a 6581 on an older "breadbin" era PCB.
From your description it's likely a bad SID, and if you have another 6581 you could verify the assumption by simply swapping them. However there're chances that either the emitter follower (usually Q2, 2SC1815) transistor that buffers the audio output is bad and/or its output DC-blocking capacitor (usually C12, 10 uF) is bad (leaked, high ESR and so on).

Frank IZ8DWF
 

brostenen

Experienced Member
Joined
Jul 4, 2017
Messages
61
Location
Denmark, Northern Jutland.
Ahhh... Sorry. It is a 250407 PAL board. The bad part about this board, is that the chips are not socketed. I might have a look at that transistor, yet the board have been recently recapped, because it had this sound issue.
 

WimWalther

Experienced Member
Joined
Jan 12, 2019
Messages
388
Location
St. Paul, MN
It's not the external output circuit (transistor & cap). If it were, the symptoms would be consistent and common to every voice. SID bench is a good test tool, and its not lying to you.

Sorry, the chip is defective. It's just not that uncommon to have one voice go bad while the rest run fine.

I've had two chips with bad voices plus one with a bad output amp (internal), out of eight breadbin models.
 

brostenen

Experienced Member
Joined
Jul 4, 2017
Messages
61
Location
Denmark, Northern Jutland.
It's not the external output circuit (transistor & cap). If it were, the symptoms would be consistent and common to every voice. SID bench is a good test tool, and its not lying to you.

Sorry, the chip is defective. It's just not that uncommon to have one voice go bad while the rest run fine.

I've had two chips with bad voices plus one with a bad output amp (internal), out of eight breadbin models.

Hmmm.... Good thing I found a cheap breadbin SID on eBay. Aprox 32/33 US Dollars plus shipping.
And I have ordered 10 x Socket's as a pack. Makes more sence than a single socket (if I screw up stuff).

I have actually no idea on what is called noises. Yet that hissing noise SID Bench makes and other sounds are played back wrong.
Some are almost unaudiable and some are lower noises. Yet it is not random, as the "errors" in sound are at the same times during testing.
I would say that aprox 33% of all test-sounds coming from the speaker, are eighter non audiable, low in volume or distorted.
Plus the sound will also skip during playback in some games. (depends on what type of sound is played)

One final symptom that I have experienced today, was that when the sound all craps out in WinterGames-Intro, then the machine will
freeze up. Once I skip the intro after one second, then bobsled will play as if nothing is wrong. Even the score chart background music
will playback all fine.

So.... Is my initial diagnosis of the SID being around 25 to 33% dead, still correct?
 

WimWalther

Experienced Member
Joined
Jan 12, 2019
Messages
388
Location
St. Paul, MN
IIRC, SID bench plays a series of sounds from all three voices in sequence, one voice at a time. Does each group of three sound alike? Or does one or more voice sound different from the others?

Some of the test tones are almost inaudible on certain chips, but this is normal. What is important is that each series of three sound the same. Is this, or is this not the case?
 

brostenen

Experienced Member
Joined
Jul 4, 2017
Messages
61
Location
Denmark, Northern Jutland.
IIRC, SID bench plays a series of sounds from all three voices in sequence, one voice at a time. Does each group of three sound alike? Or does one or more voice sound different from the others?

Some of the test tones are almost inaudible on certain chips, but this is normal. What is important is that each series of three sound the same. Is this, or is this not the case?

Well.
The series of sounds are sounding like the chip is turning on and off... I will try and make a recording of it.
 

brostenen

Experienced Member
Joined
Jul 4, 2017
Messages
61
Location
Denmark, Northern Jutland.
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