[aka180]

Hi all. I recently assembled a CMOYBB from jds labs with no problem so i figured i would try an O2 next. I put it together and performed all the tests with a dmm recommended on Nwavguy's site and everything looked fine. I set up with for rear power and I left out bt2 because I'm planning on installing an ODAC later too. I installed the board in a case making sure nothing was grounding and powered it up with no issues. I left it on with some cheap headphones and everything was fine for about half an hour. Suddenly I caught the odour of hot electronics. After taking it apart and trying it on a bench, I can see u5 and u6 are getting burning hot with the power switch off. I can't find any bad solder joints or shorts and I tested all the components up stream and can't find a problem. I'm assuming that I'll have to replace the regulators but I want to find the problem first. I'm completely frustrated now. Any help would be appreciated.

 

[DrKC]

If your regulators are getting that hot, something's not wired right.  Have you gone through the troubleshooting guide provided in the blog?  It has some very good techniques for checking the power section.  Also, the construction section has some hints on clipping off excessive lead length with the switch and jack.  Shorts to the case bottom are also mentioned, especially for U5 & 6.  I'd start with the troubleshooting guidelines provided and the overall circuit description, especially for the power management section, can give you some insight.  If you thoroughly understand how it's supposed work, troubleshooting it will easier.
It's hard to tell you what's wrong without having in front of me.  But look at this as an opportunity rather than a problem.  When you do find the problem, you'll know more about the operation of it than you do now.  I know, not much help, but if you've gotten this far with it, you'll probably figure out where the possible short is.
 
Good luck

 

[aka180]

Thanks for the advice. I went through the circuit again and found a short across pin 1 and 2 of u5. It was on the top of the board too. It worked fine before I put it in the case so I think I may have got some metal particles in there from the install. I remove the ic, resoldered it and then did all the recommended check. Works great now. The sound is amazing

My concern now is that there is a scorch mark between the pads. I'm just wondering if this would affect the amp in the long run.

 

[DrKC]

While it's powered down, take a Qtip with some 90% alcohol and wipe the area off.  That's just to make sure there are no loose carbon particles.  Other than that, there shouldn't be any long term issues.  Glad you tracked it down - I thought you would, given all that you had put into at that point.