NEED HELP REPAIRING YAMAHA EMX860ST - diyAudio
Go Back   Home > Forums > Live Sound > PA Systems

PA Systems A forum for discussion of all parts of a sound reinforcement or DJ system: loudspeakers, mixers (desks) etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 9th May 2013, 04:29 AM   #1
diyAudio Member
 
Join Date: Apr 2011
Cool NEED HELP REPAIRING YAMAHA EMX860ST

I hope someone here can suggest what is wrong with a EMX860ST PA Head. Basically the input signal inserted in almost any front panel input jack ends up at other outputs when it should not. i.e. 1Khz sine wave through 1/4 phono or XLR input, any channel 1-6, nominal gain, panned left- produces a signal on both L&R & Monitor Led's and speaker outs, not equally, seems to favor the R side. Sweeping the channel pan knob causes some cancellation near mid point. Same thing happens raising the master gain. Raised a little further and the wave becomes non-symmetrically distorted shown on the O-scope. The only input that doesn't do this is the R ch (non-mono) inputs of ch 7&8, where it doesn't go to the L output even when panned L.

BTW: This unit had quite a few bad components starting with visually cracked power trans, both EQ chips had one leg burned off, the EFX processor chip, 15V regulator, and others. At least now it doesn't draw high current through the Variac when powering up!
  Reply With Quote
Old 9th May 2013, 04:49 AM   #2
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
Well, start at the start. Verify all the power supplies as up to voltage and free of ripple.

If you had as bunch of burnt stuff, look closely at the copper tracery for burnt open spots, usually at a narrow spot.

Apply a signal to one of those inputs and scope the power rails to see if the signal is riding them.
  Reply With Quote
Old 9th May 2013, 07:42 AM   #3
diyAudio Member
 
Join Date: Apr 2011
The power supply voltages are all good.
I fixed a burnt trace early on with a jumper wire and glued it down.
The input grounds are not common with the PS ground- 8 ohms.

Please explain a bit- "scope the power rails to see if the signal is riding them"

Thanks Enzo!
  Reply With Quote
Old 9th May 2013, 07:54 AM   #4
diyAudio Member
 
Join Date: Oct 2007
Location: Aarhus, Denmark
Hi ...

This is not my area of expertise but when reading what you write my thought was that it could be feasible to isolate matters as much as possible and then look at minor parts of the circuitry at a time. I.e. look at the input circuitry and see how it performs isolated from the other parts of the circuitry etc.

This way you might be able to find out where what doesn't work as it is supposed to. My guess is that your oscilloscope could guide you in this.

Regards,

Jesper
__________________
... Being mindful about sustainability also in my audio endeavors matters to me ... paying CO2 - and a quite fair pollution compensation helps create a good listening "energy" ...
  Reply With Quote
Old 9th May 2013, 08:45 AM   #5
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
First thing I would do is go through and check every single ground node has continuity to the main ground. A floating node can sometimes cause very strange signal routing faults.

Actually, the first thing I would check is that all ribbon and pcb interconnect cables are making good contact and are plugged in the right way around.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 9th May 2013, 10:48 AM   #6
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
I was suggesting putting a signal through the system and set up so the unwanted crosstalk is occurring. The check your power supplies with a scope to see if your signal can be seen on the power supply. In other words is your +15 (or -15) sitting there at about 15 volts, but also wiggling to the music. A lost ground could cause a loss of decoupling between stages.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
WTB: Yamaha NS-500M or Yamaha NS-1000M speakers Aerolite360 Swap Meet 0 28th February 2013 01:58 AM
Need help with Yamaha EMX860ST - blown monitor amp? flsurflover PA Systems 3 14th February 2012 02:03 PM
For Sale: Yamaha B1 and Yamaha C1 michaelnj Swap Meet 3 8th July 2010 09:48 PM
Repairing woofers Bama Slamma Multi-Way 1 6th March 2007 11:21 PM
repairing Yamaha NS-690 II speakers TimboW Multi-Way 14 1st November 2006 02:16 AM


New To Site? Need Help?

All times are GMT. The time now is 06:35 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2