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9754 pre amp troubleshooting help please
http://www.paia.com/talk/viewtopic.php?f=8&t=355
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Author:  James [ Mon Nov 07, 2011 7:44 am ]
Post subject:  9754 pre amp troubleshooting help please

just assembled a 9754 pre amp and am having a bit of a challenge getting it to work. It powers on ( meaning no magic smoke) but the LED is lit solid even with the gain turned all the way down. I put the output from a properly assembled and working 9751 noise module into the input of the 9754 and have the switch set to "unbalanced" and get no output at all from the 9754. My power supply is the new prototype 9700 +/-15vDc power supply that is working properly at all power headers I installed.

I'm going to go thru and test the following:

the + & - voltages at their test points while powered up
look for solder bridges
check that the polarized caps are installed in the right direction

anything else I should be looking for / at to help with diagnosing the trouble?

Author:  James [ Mon Nov 07, 2011 8:16 pm ]
Post subject:  Re: 9754 pre amp troubleshooting help please

I went through and checked all the test points.

TP1 = +12Vdc o.k.
TP2 = -12Vdc o.k.
TP3 = 0Vdc o.k.
TP4 = +7V DC (this is the LED Drive tap..not sure what voltage it's supposed to actually be.

no solder bridges..everything looks good and clean..the polarized caps are in correctly.

any thoughts on what else I could test?

Author:  PAiA-Scott [ Tue Nov 08, 2011 2:03 pm ]
Post subject:  Re: 9754 pre amp troubleshooting help please

Hello James.

There shoudn't be voltage at TP4. Does it go away when switched to Balanced mode? If not, does touching the input pins associated with the XLR/TRS connector cause hum in the audio output signal?

Can you email (scott@paia.com) a photo of the top and bottom sides of the board? It is probably either a solder joint that didn't flow, or, the op-amp has failed. I might be able to spot something in the photo and reply.

Author:  James [ Tue Nov 08, 2011 7:58 pm ]
Post subject:  Re: 9754 pre amp troubleshooting help please

Thank you for the follow up Scott..I'll test out the balanced switch and the TRS/XLR jack as well. I'll go through and recheck and re-heat any solder joints that look questionable. If no go, then I'll send you photos.

Author:  James [ Tue Nov 08, 2011 9:50 pm ]
Post subject:  Re: 9754 pre amp troubleshooting help please

fixed it.. :D went through and reheated all the solder joints and added a touch of solder to a few of them. The it powered up and functioned fine. I've got my 1st lesson about trouble shooting a kit under my belt. :) On to the next kit. Having loads of fun learning and building..

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