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ε12 Magic Smoke

PostPosted: December 24th, 2019, 10:48 am
by Mullet
I've had a pair of these in an EHHA Rev A for years. Amp at some point went south with mains hum, ground loop, etc. I decided to rebuild amp and when hooking things up might have reversed polarity because the result was magic smoke. Flipped wires on E12 and swapped out with a 3rd known good E12. Magic smoke. :( So it looks like I'm still having a polarity issue. My guess is Q1, Q2, and maybe D1 need to be replaced on 3 units.

EHHA Rev A has two boards - one for each channel. Both are ±30v and GND. I was just applying ±30v to the E12. Is there a way to test by applying 9v battery without the amp in line?

Re: ε12 Magic Smoke

PostPosted: December 24th, 2019, 5:08 pm
by amb
A 9V battery will become ±4.5V (probably more like ±4V) for the ε12, too low to be of any use. If you have a 20V power supply then you can test the board separately using the “Initial setup” procedure as found at the ε12 website.

Re: ε12 Magic Smoke

PostPosted: December 25th, 2019, 12:16 pm
by Mullet
Thanks for the confirmation in terms of supply voltage. Looks like I'll have to test in circuit then.

I'm thinking I blew D1 in the unit that I thought was good. I had fixed that unit in the past and if I remember correctly, I just had only replaced Q1 and Q2 and not D1. If D1 is bad, my guess is Q1 / Q2 will blow.

Re: ε12 Magic Smoke

PostPosted: January 8th, 2020, 7:57 pm
by Mullet
Just to close the loop... after frying 3 E12s... 2 at once and a 3rd that I think never was fixed from a previous accident, I replaced Q1, Q2, and D1 and all 3 are back in action!

Re: ε12 Magic Smoke

PostPosted: January 8th, 2020, 9:26 pm
by amb
Great!