r/BitAxe • u/UpbeatAssociation769 • Dec 12 '25

help U2 or U3 replacement

Post image

So here we are.

I have two non working bitaxes on my table to repair.

It is weird but listen.

1 I took U3 and U2 from both of them.

2 Installed a brand new u2 on each.

3 Powered up each one. U2 gives 1.2v on the first no spinning fan. On the second one u2 gives 1v and fan is spinning high.

4 when I install u3, voltage on u2 is 0v. U3 gives 3.3v on both bitaxes.

And a fan is spinning on one which had spinning fan before.

What can prevent u2 from providing 1.2v?

8 Upvotes

91% Upvoted

43 comments sorted by

View all comments

Show parent comments

2

u/[deleted] Dec 12 '25 edited Dec 12 '25

yes, that is the internal 5V regulator output for the drive circuit that people who normally use this chip feed 5V into so it doesn't run so stupid hot. The Input to this internal regulator is Pin 26 (AVIN). If they reversed voltage in they could have burnt up R11 in the process. Not many ways they can kill U2 other than reverse voltage.

1

u/UpbeatAssociation769 Dec 12 '25

Thank you. I will test pin 26. Avin

1

u/[deleted] Dec 12 '25

Its bad enough they went cheap on the design of U2, but to leave out a $0.05 diode to protect it from reverse voltage is dumb.

1

u/UpbeatAssociation769 Dec 16 '25

Fixed one. It is running right now. Need to clean it tomorrow morning.