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 Forum index » DIY Hardware and Software » Klee sequencer
Testing: U5 (78L10) getting very hot
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neilbaldwin



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PostPosted: Sat Mar 08, 2014 6:16 am    Post subject: Testing: U5 (78L10) getting very hot Reply with quote  Mark this post and the followings unread

Just finished building the euro version (with the daughter board) and have been testing/calibrating.

All good so far but I've just flipped over the module to start the trimmer adjustment/calibration and noticed that U5 is very hot. I guess it's the nature of it's job but is it normal to get so warm?

Thanks,

Neil

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neilbaldwin



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PostPosted: Sat Mar 08, 2014 6:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Actually, just checked the voltage, +12V in but 0V out so I guess it's fried?
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elmegil



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PostPosted: Sat Mar 08, 2014 7:12 am    Post subject: Reply with quote  Mark this post and the followings unread

It could also be a short to ground on the 5V rail. Power off and check continuity. Possibly without the 7805 in place, in case IT is the short.
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neilbaldwin



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PostPosted: Sat Mar 08, 2014 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the reply.

Doesn't seem to be a short. I've checked the gate output and that's coming out at 10V and there's no continuity between the GND and output of any of the output sockets.

Or am I barking up the wrong tree there?

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PostPosted: Sat Mar 08, 2014 8:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Could be its not a hard short .. when the regulator gets hot it will shut down too.
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elmegil



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PostPosted: Sat Mar 08, 2014 9:06 am    Post subject: Reply with quote  Mark this post and the followings unread

neilbaldwin wrote:
Thanks for the reply.

Doesn't seem to be a short. I've checked the gate output and that's coming out at 10V and there's no continuity between the GND and output of any of the output sockets.

Or am I barking up the wrong tree there?


Jan's got a good point but I meant literally measure between the 5V rail and ground to see if it registers a short.
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neilbaldwin



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PostPosted: Sat Mar 08, 2014 10:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Hang on, there are no 7805s on the build are there?

Confused

Edit: well, there appears to be continuity between the input pin of the 78L10 and the Vcc pin of the CD4066s. That's not right is it? I thought the Vcc to the 4066 should come from the output of the 78L10?

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elmegil



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PostPosted: Sat Mar 08, 2014 2:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

neilbaldwin wrote:
Hang on, there are no 7805s on the build are there?

Confused

Edit: well, there appears to be continuity between the input pin of the 78L10 and the Vcc pin of the CD4066s. That's not right is it? I thought the Vcc to the 4066 should come from the output of the 78L10?


Sorry: brain saw U5 next to 78L10 and decided to read it as 7805. :/

What I meant still stands though: is there no, or very low resistance between the output of the regulator and ground?
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neilbaldwin



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PostPosted: Sun Mar 09, 2014 4:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Got it!

Oh man, there was a microscopic bridge between the output and ground pads of U5 but on the component side of the board so I had to remove it to find it!

Thanks all for the input and help.

Onwards with the calibration! Very Happy

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