Yamaha Powered Mixer Emx 860st

[e_c_mccollum]

Anyone have a schematic for a Yamaha Emx 860st?

[Zero Cool]

Still need a schematic for this? I purchased the service manual from Yamaha. I also have one for parts if needed.


Zc

[e_c_mccollum]

Found it. Yamaha sent one to me.

Both L+R level leds max out when turned on. Replaced bad capactiors in main (L+R) preamps. Replaced open resistor for DSP chip power. Still No Luck. Guess I have to start replacing preamp IC's.

[e_c_mccollum]

Zero Cool, what works and does'nt work on that amp you have for parts.

How much?

[pkrieter]

I am using a yamaha emx 860st powered mixer and I am checking into a problem. I have the proper speakers connected to the amp, however,about the time the lowest L.E.D on the main amp starts to light, the limiter light comes on and starts clipping the output. The volume level is O.K. but it certainly don't sound loud enough to be hitting the limiter. according to the manual, it says to try to keep it at or below the 0 Db. level if possible. In the book there is also a conflict of terms. At the beginning of the book,it says "if the input is overloaded then the limiter is activated.Later on in the book it says that if the output is overloaded,that it will activate the limiter. If someone has an idea of what might cause it or if someone has a schematic for it, it would be much appreciated.

[Zero Cool]

I am chest deep in the rebuild of this thing and i am NOT impressed with the design so far.

I have had 4 of these. 3 of which got hit by lightning. I was able to use the amp from one and the preamp section from another and got one running and out the door. the one i am working on now was pretty much toast.

But i was able to get the amp repaired and then moved on to the pre-amps and reverb boards. There were so many problems I couldnt even start trouble shooting the thing. I ended up having to breadboard up an opamp test board and remove ALL and i mean EACH AND EVERY opamp in the thing and test each one.

I learned some interesting things. 1- opamps when hit by lightning fail in lots of different ways. the most confusing was some opamps when you would inject a signal into section one, nothing would come out of the section one output, BUT, you would get output from section 2~! Section 2 would work just fine on its own. So that caused some very major confusion when trying to trouble shoot the dang thing.


Over half the opamps had failed (imagine that). I had several other boards from various Yamaha PA heads and was able to scrounge up enough opamps to rebuild the boards.

BUT, the BA6137 LED driver IC's were dead on ALL of the boards i have. I have a half dozen of these ics all dead and i am having a hell of a time locating them. I found one seller Cicon electronics out of NY also known as Global Electronic Solutions Corp. that had the IC's. I placed an order and have never heard from them. Had to file a paypal claim. supposedly they are sending out the chips this week. beware, be cautious when dealing with them. lots of info on the net about these guys and there lack of communication.

At the moment i have the preamp section running. but there are still some problems. lots of DC stability issues. when you adjust the master volumes, there is a large DC swing from the power amp that takes a second to settle.

I am betting there are lots of dead or bad caps and thats a major task...

I have several spare parts boards if anyone needs something i may have it. lots of pots, sliders, controls etc. Some IC's. but no LED drivers. and i have 2 of the EQ chips that have been tested ok. those seem to be a weak item as well.

[Nigel Goodwin]

I don't really see how you can criticise the design when it's been struck by lightning?, it's hardly 'fair wear and tear'

I see a lot of lightning damaged equipment, generally it's not worth repairing, even if you get it working other parts may well fail later.

I have repaired a number of TV's over the years though, and on quite a few of them the CRT was damaged as well, small well defined purity errors, like the shadow mask has been deformed by the lightning.

Are these for your own use?, or are you trying to repair them for a customer?.

[pkrieter]

Still am new and can't email directly so I am still looking for the schematic for the Yamaha emx 860st powered mixer

[pkrieter]

Someone was installing carpet and they put a staple into the speaker wire! It wasn't completely shorted out but we were installing a new mixer with more channels and I decided the check the resistance of the left and right speakers. One was normal (around 6 ohm give or take ) and the other was 1.8 ohms. I unplugged the speaker wire and checked it at the back of the speaker and it was identicle to the other speaker. I checked the wire (unplugged at both ends) and it showed around 2 ohms. After a short hunt, I found the offender !

[keymaster98683]

Hi Zero Cool... I see where you have spare parts for the EMX860st Mixer. I'm trying to find some replacement Pots. I actually need 8 but If I can find 2 to replace the Volume pots for the Main and Monitor Volumes I would be Happy.

Any chance you can help me out?

Thanks,

Dave
keymaster98683@yahoo.copm