Tascam M-320B Hum - no Signal

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stream210

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Hello and Good Day!

The Problem:

Tascam M-320B Console will turn on, but only admits a "loud 60Mkz hum" (or some freq. in that area) in the headphone set connected to console, but no sound is admitted to amp from the console other than "AM/FM" interference. And when I say there is a loud hum in the headphones, that also means there is no control over that hum, even with all connected equipment turned off or disconnected. I think that there must be two power supplies: One that turns the board on and the other that powers the signal to the amp, which would explain why the board turns on and meters indicate signal when audio signal is present, but no signal is getting to the amp. I haven't opened the unit up yet and I don't have a service manual, so I'm just guessing.

This is the second time this has happened in two days. The first time, I turned the unit off for an hour or so, fired it up again and it was fine for the rest of the session. I thought it was a "city power surge" or something, no other equipment seemed to be affected. When it happened the second time the next day, the "hum" remained and no signal is getting to the amp. I've owned this Tascam M-320B Audio Console for some 15+ plus years without incident. Some would say money well spent and I would agree. It may very well be time to look for another mixing board. However if this unit can be fixed, doing the work myself, all things considered, this would probably be the best option right now.


Taei
 
Ouch! I have teh same board. That would make me cry:(

It sounds from your description that perhaps some caps (coupling) went in your power supply. I haven't been inside of mine in a while, but I believe this is a very doable DIY fix.
I will try to find them in my schematic when I get back home tonight....
 
Excellent! I'm starting to feel better already, .... really, Thanks!:) And perhaps there is a "Quick Access" to its "innards" (meaning not wasting time on unnecessary screws) that you may be aware of.
 
IIRC- there are large metal plates on the bottom, about 4 screws each. Then every channel is on a card. You have to take off the nuts for the pots of the cards you'd want to remove....
 
Here's what a friend of my at Sweetwater shared:

• Sounds like some of the caps (capacitors-his reference) are starting to go in it.* Have you contacted Tascam about it to get their take on it? The other
possibility is that the transformer is coming apart in its winds. Without cracking it open, tough to tell.

• The DC blocking caps (capacitors-his reference) on the input channels that all share the same ground.* If DC noise is getting dumped down the ground/ chassis it may be seeping into the input channels if the caps are not there to block it. Big bangs and crunches are not good in my opinion....... Not sure how to recmd troubleshooting this without being there to actually look at it.

You both sound like your on the same page, I would say. What about the possibilities of a transformer shredding winds?

And again, I haven't open up the unit just yet, because it will be like operating, "Heart Surgery" on a patient, connected to a "Gazillion External Blood Vessels".
As you can tell, I'm getting the jitters, having to operate on a patient that has no Medicaid or Health Insurance, however knowing that I'll have to "flip" the
patient over, disconnect all the blood vessels and remove its underside (panel(s)) is quite helpful, I must say.

As you can see, I really like, whenever possible, to have a good "Mental Visual Representation" in my mind so as not to leave the patient unattended for to long a
period. It could take a few hours, a few days or weeks or years, if my hands should slip, or even if body parts are available on the "black market"! And to think that
you'll be "Operating Remotely" is quite a feat in itself, I must say! Thanks in advance, Doctor Guido!

Now once the patient has been opened will I be able to see any visual signs of damage, either caps or transformer or will I be in the dark, so to speak? Or perhaps
my nose will lead me to the problem? I'm being serious now! Again many thanks for your patience, time and assistance and I hope you don't mind my silliness, it
keeps me from crying my eyes out, as you have already pointed out. You wouldn't want me to operate under that condition ..........would you?

So feel free to comment, as much as you would like, about what to expect once I begin. Besides leaving the tools inside of the patient, is there anything else I
should be mindful of.

stream210
 
I doubt it's the tranny. Caps are notorious for expiring in old gear. It's what they do.

Bad caps will actually have exploded, leaking white stuff, or sometimes they just become distorted in shape (bulge). Google it for a better idea/description.

The reason I think it's the power supply is that it's across the entire board.

You are right, this could take a while, but you can probably do this yerself. Get a packing/movers blanket to put the mixer on to protect it when you flip it over.

Do you have the manual?
 
Do I have the manual? Not presently!

When you say:

The reason I think it's the power supply is that it's across the entire board.


Are you referring to the fact that there is a loud obnoxious hum coming from the board, with all channels off, all buttons in raised
position and all input to the board off?

And these caps you speak of, I assume are readily available, perhaps?

stream210
 
Last edited:
1. Bummer
2. Yes
3. Yes

You might be able to find the manual on Ebay.

The caps (capacitors) should be readily available at Parts Express or Mouser
 
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