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Taito Rastan Digital Noise on Output

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Post Options Post Options   Thanks (0) Thanks(0)   Quote adsa1971 Quote  Post ReplyReply Direct Link To This Post Topic: Taito Rastan Digital Noise on Output
    Posted: 14 Feb 2020 at 3:57pm
Hi Folks
Have an issue with digital noise on the output of my JAMMA rig. Other PCBS are silent but Rastan is noisy on a digital level. When screens change the pitch and chirping changes. I have replaced a load of electrolytics with no difference and ordered some Tantalums. -5V is present but wondered what you guys would do to fix this.

Cheers
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monstermug Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 4:15pm
Could be a faulty DAC? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adsa1971 Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 4:32pm
OK cheers. Will look at whats going on with the DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote caius Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 5:18pm
It's likey due a bad (or both) TL074 OP-AMP, replaced load of them on this board.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adsa1971 Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 6:08pm
Cheers. Will order some and keep you updated.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Equites Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 7:33pm
Originally posted by caius caius wrote:

It's likey due a bad (or both) TL074 OP-AMP, replaced load of them on this board.


This, common failure point on these.

Atari PCB's (and most non-Atari), AR2's, Vector Deflection/HV boards repaired & refurbished.
Wanted: Non-working Atari PCBs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adsa1971 Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 2020 at 12:19pm
That unfortunately did not work. Have replaced both chips. When I removed the suspected faulty Op-Amps I then checked to see this wasn't the output amp with issue. Completely silent, but hummed appropriately when I put my finger on the input.

Could this be the DAC?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonhughes Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 2020 at 12:57pm
I recently repaired a Rastan sound fault. Turned out to be the Oki chip. I found the board not so easy to trouble shoot (chips relying on other chips within the circuit) as I suspect you are finding replacing many parts. You do have connector H on? I can't remember what that does once it's disconnected (mono/stereo convertor connector I think).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adsa1971 Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 2020 at 1:28pm
Connector H is on. Digging further... Thanks for all the responses.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monstermug Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 2020 at 6:25pm
Check if output signals on YM2151 @ IC63 is okay.  Then check YM3012 DAC @ IC78.  It's got to be either of those two.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote paulcan69 Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb 2020 at 2:52pm
Might well be the classic pc060ha chip going bad
Repo is coming
Search pc060ha on here
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Post Options Post Options   Thanks (0) Thanks(0)   Quote caius Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb 2020 at 3:33pm
The Taito 'PC060HA' replacement is already done and successfully tested but the few units went very quickly hence I have to restock it.Expect a new batch in a month or so.
Anyway, I don't think your sound issue can be due to it, the 'PC060HA' accomplishes digital functions except for a pin that mutes the amplifier.Perhaps if you could provide a video of the issue we can help you better.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monstermug Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb 2020 at 3:33pm
Rastan Sound section schematics here


Edit:  Yes I agree with Caius.  Unlikely to be the custom. 


Edited by Monstermug - 21 Feb 2020 at 3:38pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adsa1971 Quote  Post ReplyReply Direct Link To This Post Posted: 24 Feb 2020 at 1:52pm
I removed the YM2151 and there was still some humming and noise although far less. Took out the YM3012 and noise completely stopped. Awaiting new chips. If I still have the issue I will post a video.

Thanks for helping guys. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adsa1971 Quote  Post ReplyReply Direct Link To This Post Posted: 24 Feb 2020 at 8:47pm
Hi Folks

I have made a video and hope you can open it. Please tell me if you cant as its my first video.


Both chips have been replaced and no difference. I am wondering if its my setup being sensitive. Probably different in a cab.


Edited by adsa1971 - 24 Feb 2020 at 8:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monstermug Quote  Post ReplyReply Direct Link To This Post Posted: 24 Feb 2020 at 9:44pm
I don't hear anything that's pcb fault related.  You are getting interference elsewhere. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adsa1971 Quote  Post ReplyReply Direct Link To This Post Posted: 24 Feb 2020 at 10:30pm
Thank you. I appreciate the feedback.
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