Ensoniq EPS Classic L/Headphone output Louder

Synth Repair
,
1

[Ensoniq] [EPS] – [L/Headphone output Louder]

Ensoniq EPS Classic L/Headphone output Louder

Hey. I have a Ensoniq EPS Classic.

The problem I have is when in stereo output the left output is slightly louder.

When right output plug is disconnected and using headphones in the L/Headphones the output it is the same. Left side slightly louder.

Any help with where to start is greatly appreciated.

Thanks!

2

Welcome to the forum!

If you have an oscilloscope it can help track down where the problem begins. Check out the Main Board (Analog Section) page in the schematic. In the bottom right you’ll see the left and right output filters. There’s a pretty good chance the problem is somewhere in the left output filter but it would take an oscilloscope to confirm that (unless the faulty component is visibly damaged, such as a bulging capacitor or signs of excessive heat around a component). I’d use an oscilloscope to compare the L and R output filters’ input signal and see if they are the same amplitude. In other words, compare pins 2 and 6 of U60. They should look pretty similar in amplitude when a sound is being played.

If the signals look the same, then the issue is definitely in the left output filter. From experience, probably a bad electrolytic capacitor (C125) but it could also be U60 or U61.

If the signal going into the left output filter is low then the problem is most likely further upstream or possibly U60.

A few helpful tips:

  • Inverting and non-inverting inputs of an opamp (such as between pins 9 and 10 of U61) should measure within a few millivolts of each other. If it’s greater than a few mV then the opamp is damaged. Test this with a voltmeter with one probe on the inverting input and other probe on the non-inverting. Reading should be near 0 V
  • With an ohmmeter, measuring across an electrolytic capacitor should start at 0 ohms and rise towards infinite or at least to the megaohm range.
3

Travis,

Thanks for the welcome and even more for the information and how much detail you supplied!

I really appreciate it.

I do have an oscilloscope and will check the places you stated.

Thanks again Travis! -Dan

4

Travis-Hey, hope you had a great weekend!

So the issue was indeed C125! L/R issue now resoled. Thank you so much for the information.

Seems to be fully functioning except one final issue.

Would love you thoughts:

When I enter sample mode and the screen is on the VU input meter there is no movement on the screen (when I play the sound I want to sample the VU input meter does not register anything)

However, when I hit enter and go to the REC screen it samples as it should.

Hoping it’s another easy fix.

Appreciate any insight but if to much I totally understand.