Possible OT-2 issue

Love Rhino · 614

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Offline Love Rhino

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on: March 14, 2021, 01:41:50 PM
An issue has come up with a 3.0 kit that was sent to me.  There was damage during shipping, including the screws holding the OT-2 coming loose (and in one case coming off entirely) and the wood frame breaking.

I reviewed and repaired what I found on the amp and it passed resistance checks very well, with the only potential flag being #22 reading exactly 1.0.  Every other check was pretty much spot on.

Deciding to move forward with voltage checks.  After about 10 seconds of power the right side LED on the board flicker and go out.  What I believe is the the right OT-2 is making a ticking sound, like the second hand on a clock moving at triple speed.  The first group of voltages measure fine, but when I move from 16 on things get bad.  At terminate 17 I am getting some electrical arcing when the voltometer is about 1-2 milimeters away from the terminal and the sound from the OT-2 stops.  At this point I stopped measurements.

2: 66.3
3: 17.4
4-5: 0
6: 384
7: 397
10: 375

16: 370
17: hard stop!




Offline Paul Birkeland

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Reply #1 on: March 14, 2021, 01:46:34 PM
16 is just telling you that there's an issue with the first stage of amplification on that side.

The OT-2 could be dead shorted or dead open and the amp will otherwise function just fine.  If something is ticking, I would be looking for loose connections or broken wires.  If that Alps pot doesn't have a PC board attached to it but rather has the wires soldered to the pins, I would pull it out and throw it away, then put the stock pot back in.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man