Tascam MS-16 amp card became microphonic, outputs continuous wind noise

A

AnalogApples

Member
Here's an odd one. One of my Tascam MS-16 rec/amp cards intermittently began outputting a loud roaring noise, and it's microphonic. It's been working fine for years. I wiggled the card to see if it needed re-seating and noticed the card itself is now microphonic. I can hear my finger tapping the card in the mixer output. Weird. The roaring sound makes me think one of the caps has failed. explore it more one of these days but I figured someone might've experienced this and can give me a hint. Sorry for the limited info!

Also, It still passes audio and records audio, it just records it at maximum volume, distorting the tape, and along with a roaring sound. Maybe the record volume calibration pot is shorted.

Thanks, if anyone has any input.
 
In my experience when audio either is not present except for on loud peaks, and is crunchy at that, OR just goes full tilt all the time, and it’s an IC opamp-based signal path, usually a failed opamp. But just to confirm you’re saying it does the same thing when you’re just monitoring the input and not even involving tape? The MS16 signal path is hybrid…combination of discrete and opamp amplifier stages. So let me know on my question and that might narrow down what to look at.
 
sweetbeats said:
In my experience when audio either is not present except for on loud peaks, and is crunchy at that, OR just goes full tilt all the time, and it’s an IC opamp-based signal path, usually a failed opamp. But just to confirm you’re saying it does the same thing when you’re just monitoring the input and not even involving tape? The MS16 signal path is hybrid…combination of discrete and opamp amplifier stages. So let me know on my question and that might narrow down what to look at.
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I might be incorrect about this but when I monitored the input things seemed ok but I could still hear a quieter roaring sound that I didn't notice until I switched to RERPO mode. In Repro mode the roaring redlines the VU meter on the tape machine and board. It still passes audio, but the audio is at max volume and very distorted. I have some extra opamps that I think were correct for this card so I'll look into that! Thank you for the hint!
 
So my suspicion is it’s not on the input side even though you can hear it some. I’m guessing that’s just bleed from whatever is going on, which I think is on the playback side. U3 is the input opamp. That’s not my first suspect. The first stage of the playback side is discrete…Q1 & Q3~8, servo integration happens at U1 2/2, and then U1 1/2 and U2 2/2 handle playback EQ filter input stage and output booster, and then U2 1/2 is the overall output booster. You could shotgun U1 & U2, but before that you could take your audio frequency level meter, make sure it is set to AC voltage and clip it to test point 1 and test point 5 and see what you have there. If you have substantial signal without any input or playback happening we know there is a problem with the playback circuit.
 
sweetbeats said:
So my suspicion is it’s not on the input side even though you can hear it some. I’m guessing that’s just bleed from whatever is going on, which I think is on the playback side. U3 is the input opamp. That’s not my first suspect. The first stage of the playback side is discrete…Q1 & Q3~8, servo integration happens at U1 2/2, and then U1 1/2 and U2 2/2 handle playback EQ filter input stage and output booster, and then U2 1/2 is the overall output booster. You could shotgun U1 & U2, but before that you could take your audio frequency level meter, make sure it is set to AC voltage and clip it to test point 1 and test point 5 and see what you have there. If you have substantial signal without any input or playback happening we know there is a problem with the playback circuit.
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This is great! I can tell you've got the manual in front of you. Thank you! I will check if I'm getting a signal at those test points.
 
I turned on the tape machine and the problem was gone. While in repro mode, I tapped the amp/rec card with my finger and the problem came back in full force. Tapping again did not stop the problem. So I will first check for cold solders and try it again.

In sync mode it happens if I disengage the track, so basically putting it back into repro mode. And I was wrong, the problem isn’t present at all in input or sync/input mode. I’m going to check for cold solders near the opamps, and then shotgun the opamps SweetBeats suggested and report back here. Might take me a couple weeks if I don’t have any of those opamps here.

I would never have guessed opamps because I’m an amateur so I can’t thank you guys enough!
 
I’m having a little bit of a hard time following what conditions elicit the faulty behavior, but if it is not present on power up, and then starts with tapping, that’s really odd. It could still be a failed opamp that is stable until there is any kind of signal or fluctuation at all, which could be spurred by the tapping, and then it goes into full broadband oscillation or something. But if it is not present when monitoring the input, U3 is not involved. It is something from Q1 downstream.
 
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