Tascam MS-16 no passing audio

M

man-bot

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Just got this (new to me) MS-16 set up and I have 3 channels that don't pass audio in sync or repro. I have changed out the relays so they are not the culprits. These channels will show levels in input so it's nota meter issue...

Thoughts?

Mike
 
With the power off first, try swapping the channel cards out with known good channels to see what happens. If the problem follows the cards, you've got an issue with the cards. If they don't, then you'll have to look elsewhere. Head to amp unit umbilical cables as a possibility.

Cheers! :)
 
Have the bad card been checked for zero settings on the trim pots, oxidized contacts on the edge connector pin slots, any visuals of cold solder joints, parts that appear burnt, etc?
 
Okay - no pots are zeroed. Oddly off the (basically) brand new MRL I get no response at 1k and 100hz but perfect response at 10k & 16k.

Its not the heads because other cards respond fine to all tones when in that slot...

Something funky here!!
 
I don't know what that could be. Highs pass but mids and lows don't. Bias trap? Bias oscillator? Bad caps?

Sorry, that's all I can think of.

When I had my MS-16, I had 4 spare channel cards. Perhaps look into picking up a few?

Luck!

Cheers! :)
 
could be capacitors, do a visual inspection, also for potential broken parts unsoldered. These parts are old now, they may have been modified or gone through some abuse. Spare cards for that machine can be found for $50 on the net. If you have a scope, trace the signal path.
 
I do have a Fluke Scopemeter so I can trace it - however I don't have schematics (or an extender card!) so I'm in the dark a bit.

I can make an extender card - but the schematics would be a huge help!

Does anyone have the MS-16 schematics? I have downlaoded the manual but no schems were included - I assume the originals were 11 x 17 thus why they likely weren't scanned.
 
Found some Tascam 58 schematics and I understand the cards are the same so this should be a good enough road map to get started.
 
Sounds like some coupling caps have gone bad. As they lose capacitance they lose their ability to pass low frequencies.
 
I'll have to see if I can determine which are the coupling caps. No problem in a guitar amp, but may be a bit more of an exercise with me on these cards. I'll trace the signal and pay attention to caps between opamps (I assume they're doing the amplification in this circuit)

If you have any tips I'm open!
 
They are generally between any stages in the chain. Tascam loves 10uF/15v caps for this. It will probably take a scope to do it easiestly. But you could do it with a digital multimeter. set to AC, input a test tone of 60hrz, that way any handheld could be used. Thats how Id start if I didnt have access to a scope.
 
Thankfully my fluke meter has a scope on it (which has been indispensable!).

I need to pick up a few Molex KK connectors and then I can wire up an extension so I can get these cards working on the bench and then probe away....
 
The older Ms-16s had non-sealed relays on the cards.They used hermetically sealed relays later.I have also seen hinky solder,(ring voids), on the backplane- but would suspect relays first...
 
Okay - I have been poking around inhere and still cannot seem to solve what is happening. Again, the unit records at 10K and slowly declines in level as the freqeuncy is turned down. Recording is non existent at around 2k.

MS-16 issue.jpg

This shows where I have found the issue when tracing the signal. All is good up to R49/C24. I have swapped them out with the same result, same with the bias trap. Also C22 has been changed out with no effect.

So I'm a bit stumped!!! I would rather not have to ship my whole machine off to the tech to tesh it out so if anyone could provide ideas I would be very grateful.

Again it is definitely with the cards as if I swap known good ones in there is no issue. You can grab the complete card schemo here if you like: Index of /~michael.lett/

Thanks - Mike
 
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Have you tried playing back tapes you recorded from before the problem occured?
In case these are fine the problem might be in the desk or whatever you used as a preamp.

Now this might sounds overtly simple and this could very well be the first thing you tested but in case not you should try.
 
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