DIY Mic Pre Kits, Lunchbox Mic Preamp Kits, Power Supply Kits

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PostPosted: Fri Jul 04, 2008 11:22 pm 
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Joined: Mon Jun 25, 2007 6:09 pm
Posts: 1261
Location: Music City
guitarguy12387 wrote:
Well, i spent some time fiddling today. Replaced the fuse. Took some readings at the secondary of the trafo:

AC1 and CT: 106mv

AC2 and CT: 162mv

AC1 and AC2: 182mv

For some reason, when i touch just one of the leads from the multimeter to the board, it jumps up to like 200mv and i don't know why. I get the feeling i am doing something wrong with the multimeter.

When i measure across the outputs and ground, i get no reading, DC and i get around 30mV AC. LED 1 lights up but two does not. I have no idea whats going on. Thanks.

Oh, by the way. I have spent some time inspecting the board too. Its... well its not my best work by any stretch haha. But it isn't that bad... i would think it should still work. Nothing appears to be bridged or broken. Theres a few minor scratches and burns on the back of the board, but again, nothing major... the pads are still intact and everything. Bottom line is i don't see anything that would be causing a short or open circuit.


millivolts is nothing. That's almost zero volts.

You probably have your PSU wired incorrectly to the transformer/fuse/switch.

Did you follow the instruction guide? Do you have a photo of the project with all the wires laid clearly showing where it goes?

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Oh, by the way. I have spent some time inspecting the board too. Its... well its not my best work by any stretch haha. But it isn't that bad... i would think it should still work. Nothing appears to be bridged or broken. Theres a few minor scratches and burns on the back of the board, but again, nothing major... the pads are still intact and everything. Bottom line is i don't see anything that would be causing a short or open circuit.


Post a pic so I can see. You probably have cold solder or incomplete solder. You need to work your way and find out where the voltage disappears.

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PostPosted: Sat Jul 05, 2008 4:08 pm 
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Joined: Tue Jun 17, 2008 8:33 pm
Posts: 96
Hey thanks owel. Well i decided to get out some older analog multimeters i have. And much to my delight, i'm reading power at the outputs. About 48v, 15v, and -10v DC. I got these readings on two separate analog meters. Stupid radioshack DMM. So i contacted tech support to see whats up, because i'd like to dial the output voltages as close as possible to the right voltages.

Anyway, only problem now is LED 2 isn't lighting up still. I switched the leads, just in case, but still nothing. Any ideas?


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PostPosted: Sat Jul 05, 2008 4:34 pm 
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Joined: Mon Jun 25, 2007 6:09 pm
Posts: 1261
Location: Music City
Adjust the onboard trimmers to get +/-18V.

For the LED, it's either inserted backwards or burned out.

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PostPosted: Sun Jul 06, 2008 12:53 pm 
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Joined: Tue Jun 17, 2008 8:33 pm
Posts: 96
Success! Output voltage dialed in. Both LEDs now work. You were right... it was backwards hah. Thanks again for all the help and patience, Owel!


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