Phantom power cutting volume of mixer drastically

F

fredphoesh

New member
Hello all.

I have an old Mackie 1402 vlz3 mixer and was just plugging in a Rode Nt-1 mic. When I switched on the phantom power, the output volume of the mixer to my speakers cut about 90%.
Turn the power off, volume goes up again.
I was not expecting this as I want to be able to hear what I am recording against at a decent volume.
Any ideas?
Thanks,
Mark.
 
Have You tried another phantom powered mic, to rule out a defective NT?

I suspect the Mackie’s power supply is dying...
 
cyrano said:
Have You tried another phantom powered mic, to rule out a defective NT?

I suspect the Mackie’s power supply is dying...
Click to expand...

Hi
Actually the problem exists even if I unplug the microphone... ie when I turn on the phantom power switch on the macke, the volume dips 90%... so it's not mic related!
I can't find any mention of this being normal on Mackie's site... so I am assuming there IS a fault with the mixer right?
tx
Mark
 
Yes, Mark, that’s definitely not normal. I can’t even “see” immediately what kind of fault would produce that. After all, the master out isn’t even connected to phantom power.
 
Maybe some contact cleaner sprayed in there? I'm not good or smart with electronics but it sounds like maybe an evil dust bunny/underpants Knome... :)

Where is Ecc Dave right now?
 
Probably a short circuit in the 48v supply, it´s a internal problem, this desk seems to not have a external power supply, my advice is to send to an tecnician.
 
I had this mixer and it crapped out after a gig, turns out they have ribbon cables inside that degrade over time they are similar to the wide cables we used to use to connect hard drives, If you are handy or know someone who is its a quick and cheap place to start looking.....
 
I would *not* plug another condenser into that mixer and turn on phantom power until it’s been diagnosed. And I’d go check my RØDE out somewhere known to work just to feel better ...
 
bruiser1964 said:
I had this mixer and it crapped out after a gig, turns out they have ribbon cables inside that degrade over time they are similar to the wide cables we used to use to connect hard drives, If you are handy or know someone who is its a quick and cheap place to start looking.....
Click to expand...

Yep. Mackie has history (do/did other brands too or...? Hmm..)
Another temporary fix' you can try with these is exercise the heck out every switch -and probably 1/4 jack on the unit.
My last was to do a 'drop-fixed' cut-outs on the phones Mix-B on my 24-8 bus during it's last -and final.. tracking session. :rolleyes:
 
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jimmys69 said:
Where is Ecc Dave right now?
Click to expand...

I can guess what he's going to say...

Measure the volts on the mic socket with a meter - you should see 48V between pins 2 and 1 of the XLR and also between pins 3 and 1 when phantom power is on. If it is more than a volt or so different you have a problem.
 
jamesperrett said:
I can guess what he's going to say...

Measure the volts on the mic socket with a meter - you should see 48V between pins 2 and 1 of the XLR and also between pins 3 and 1 when phantom power is on. If it is more than a volt or so different you have a problem.
Click to expand...

I understood it on the first read through; You guessed wrong! :P
 
My guess......

Faulty component (shorted?) in the phantom supply circuit. The service manual doesn't show the power transformer, but from what I can assume, the phantom power has its own secondary winding. The AC from the secondary is switched and not the DC supply part of the phantom. A shorted component may load the transformer down so the other half that supplies the rest of the mixer loses voltage and cuts volume to the output. At a guess the phantom indicator light may not be illuminating or maybe dim(?). There is a fuse in the primary, but the faulty component if shorted, doesn't cause enough current on the primary side of the transformer to pop it. There might be an audible hum from the transformer when the phantom switch is on.

I would not run the mixer too long, if at all with the phantom switch on, as it likely could heat up the transformer and eventually toast it $$$$$.
 

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arcaxis said:
My guess......

Faulty component (shorted?) in the phantom supply circuit. The service manual doesn't show the power transformer, but from what I can assume, the phantom power has its own secondary winding. The AC from the secondary is switched and not the DC supply part of the phantom. A shorted component may load the transformer down so the other half that supplies the rest of the mixer loses voltage and cuts volume to the output. At a guess the phantom indicator light may not be illuminating or maybe dim(?). There is a fuse in the primary, but the faulty component if shorted, doesn't cause enough current on the primary side of the transformer to pop it. There might be an audible hum from the transformer when the phantom switch is on.

I would not run the mixer too long, if at all with the phantom switch on, as it likely could heat up the transformer and eventually toast it $$$$$.
Click to expand...

+1 Mark, any of those components could be the fault. I would also suspect D20 gone O/C and putting the full rectified voltage on the 48V line
The TIP 29C is not particualrly suited either, only just a high enough voltage rating.

TBH if the fault is anything in that supply (which BTW has NO short or overtemp' protection) is found faulty I would rip it all out save perhaps the bridge (if of generous rating they rarely fail) and replace the whole section with the TL783C high voltage regulator IC. D.Self rates them very highly.

Dave.
 
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