1980s Echoplex EP-4

[FenderGuy]

Decided to tackle my old Echoplex after it has been sitting gathering dust for the last 7 years. It's a late release Teller-Harris EP-4 that has developed the old erasure problem. Cleaned everything well and installed a new Dunlop tape I had stored. Bleed thru isn't bad at low recording volumes but still evident after a full loop. Tape starts to saturate if recording levels are in the normal range. The problem I'm having is identifying two trim pots located on the bias oscillator board. The Maestro schematic only shows one to the record side of the head and the erase side has fixed bias?

I bought this unit from the original owner two decades ago and he has long passed but was a professional tech. Perhaps he modified the board? IDK. Was wondering if anyone had the skinny on the late boards.
This is the first tape unit I've attempted to tackle and really could use some input. Have oscilloscope ready to test the signal to the head. I guess my question is where to start with the trim pots w/o causing more problem?.

Thanks

[FenderGuy]

Scratch the pots. I found the problem; wobbly slider in the carriage causing clearance on erase side of head. Works okay if slider is tilted to the left, lifting the right side of the head.

Now to figure out how to fix a worn carriage.

Perhaps bend the tabs that run the carriage rail to tighten the slider......