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grommeteer 31st December 2012 01:11 PM

In search of schematics for Phonic MR2643X
I would like to repair this mixer for a friend who is a music teacher.

Is there somebody in the community who has a schematic of that unit and who is willing to share it with me?

Btw, fault is: no sound on any outputs. Power LED and -20dB LED on the inputs work. Checked +/- 15V on random OPs and they were all ok.

Thx and a happy new year to all of you.

turk 182 28th January 2013 06:27 PM

don't take this the wrong way but did you double check that 1: the input is properly selected between mic/line and that the channel is "on" and 2: it's routed either through the sub groups or direct to the left right masters?
the other possibility with no sound at the masters might be bad/defective insert jacks.
as there's direct out's on the independant channels i'd check for signal there first

grommeteer 28th January 2013 07:18 PM

You may be perfectly right. I got the mixer described as "totally mute". I pushed buttons, tried to figure out what goes where, no signal on main, no signal on the headphone jack, no reading on the LED bar. I bought the manual, undid a few dozen screws and started to follow the signal all the way through quite a number of OPs, switches and pots. And guess what, everything works, main out, headphones, LEDs. Either I moved something in disassembly or I missed that one button on the first day....
I need to talk to the owner once again.
I had my probe on every point you mentioned.
So, thank you for your help.
Greatly appreciated, it's just that I cannot fix it as long as it is working.

turk 182 28th January 2013 07:50 PM

if you still have it opened up on the bench grab a magnifying glass and look over the solder joints on the xlr's and 1/4" jacks at both the in's and out's you may find cracked solder joints.
it's not uncommon to find cracked solder joints on the patch points they go through alot of mechanical stress.Phonic,Mackie,Peavey and many more mixer's of this caliber generally have this kind of problem which is due to the construction.the frame/mount is not rigid transferring the stress from inserting a connector which also flexes the pcb it's soldered to.
as a quick test does the signal crap out if you tap or move the unit?

grommeteer 28th January 2013 08:06 PM

Thx, will do! I have moved it around a bit, which is quite annoying with two chassis and lots of ribbon cables between them. No dropuots.
I feel it started to work when I removed a plastic/alu shielding. I need to double check if it was shorting something.

turk 182 28th January 2013 10:59 PM

let me know how you fare from here!
if the insulator (plastic) isn't punctured or showing severe wear it could still be intermittant / cracked solder joints
i guess i'm mentioning it again because all too many times it's caught me... just get done re-assembling a gabillion screws and jack nuts and plastic strips & clips to find out the gee dam thing went south again dagnabit!!

Enzo 28th January 2013 11:00 PM

I don't know that mixer, but if it is like most, it has patch jacks. Jacks marker preamp out and power amp in, or graphic out and graphic in, etc. One VERY common mixer problem is the cutout contacts on such jacks failing. Find the power amp in jack, and poke a plug gently in and out a few times to open the cutout contacts within. That should interrupt signal going to the power amp. When the plug comes out, does the sound come right back instantly? Or does it ever hesitate or get iffy?

I'd spray cleaner into each patch jack and plug in and out to move things around.

And this sort of problem is also the sort of thing that can temporarily correct itself by your working inside the unit, from flexing and vibrations.

And if nothig else, use the jacks as test points. PLug a signal into the power amp jack, and does that come out the speaker? Plug a signal into a channel, and see if it comes out the main mix out jack. etc.

turk 182 28th January 2013 11:24 PM

tell me about it.
i once had a mixer go down just before showtime because of bad inserts on a Pm 1000.
diagnosing that while the road manager and promoter are yelling at you to start the show is an interesting learning experience for sure!

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