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Post subject: EVH 5150 iii head problem
Posted: Wed Mar 21, 2018 11:19 am
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Joined: Wed Mar 21, 2018 11:05 am
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I am a proud owner of the EVH 5150iii 100W head for a couple years already.
The head worked like a charm up until recently when the following problem occured:

On Channel 1 when I play, sometimes the volume suddenly increases significantly in split second (by significantly I mean to such extend that you immediately stop playing and need to reduce the volume knob)

I have identified that the issue is something with the GAIN potentiometer - when I move the meter sometimes the above-mentioned sudden volume spike occurs. The issue never happens when moving the volume knob.

I was wondering that this could be either faulty potentiometer or condenser.

Anyone with similar experience and ideas on how to solve the issue?

(I have been looking on EVH web page but no spare parts available there, therefore such change as mentioned above may be kind of an issue.)


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Post subject: Re: EVH 5150 iii head problem
Posted: Sat Mar 24, 2018 3:51 am
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Joined: Fri Feb 05, 2010 4:31 am
Posts: 14047
Location: Province de Québec, Canada
Zasran wrote:

I have identified that the issue is something with the GAIN potentiometer - when I move the meter sometimes the above-mentioned sudden volume spike occurs. The issue never happens when moving the volume knob.


)

Pots ;
Try a good contact cleaner like Deoxit , not some radio Shack , too cheap , they won't do the job


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Post subject: Re: EVH 5150 iii head problem
Posted: Tue Mar 27, 2018 7:41 am
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Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
It ustabe a crackly pot would cut out. The new amps go to a higher volume when they go bad. Instead of the old voltage divider circuit, the new ones use a pot in the nfb circuit of the op amp.
A common issue with these pots is the rotor comes loose from the shaft. It can occur simply by pulling off the knob.
Look at the spot where the shaft goes into the body of the pot. Now tug gently to see how much of a gap there is. A good pot only comes out a few thousandth. A bad pot will have a wider gap than the rest. The spring tension you feel is the wiper contacts against the resistance ring. So less tension means a bad contact.
Use 2 small screwdrivers to alternately pry the undersides of the knob to gently lift them.
You can pull the pot and remove the cover. Then push the rotor down to increase the tension on the wiper. Glue the rotor the shaft.


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