Phantom Power Troubleshooting

[rjraffa]

Just finished testing 4 newly built preamps (C84, N72, J99, A12), and they sound great. Unfortunately, the phantom power is not working on any of them. I went through the assembly guides and double checked everything with the jumpers. I even tried new cables as well as tested the mic with other mic pre's that have phantom power that work.

The first time I turned on phantom power on the C84, I heard a slight hum but no juice to the mic. I turned the phantom power off, and then back on again. No hum and no phantom power. I flipped the 48v swith on all of them and used a DMM to check voltages. All 0v.

Is there something I could check in the preamps as well as the power supply to troubleshoot this? I checked the forum for previous posts but didn't see anything, Thanks in advance for your help.

[rjraffa]

I did some additional testing. I turned on the Phantom Power for each preamp, and I'm getting readings of 62.5 volts (not 45v) for each one. Also, the red indicator light is not lit.

I created a quick short on one of the preamps (dangerous but I gave it a shot). All of the preamp Phantom Powers then worked (44.7v or right around there on the DMM reading for pins 1 & 3 in the XLR), and the red indicator light was lit.

I shut the power off. Waited a few seconds, and then powered back on. The issue returned. I'm getting 62.5 volts on the XLR pins, and the red indicator light is off again.

Any suggestions?

[rjraffa]

I unhooked all of the power connectors from the pre-amps, and I've narrowed it down to the Power Supply. Even when not connected to anything, the red light (phantom power identifier) is not lit on the power supply. I saw this post (viewtopic.php?f=9&t=1773&p=8007&hilit=LED#p8007) and this post (viewtopic.php?f=9&t=783&p=3691&hilit=phantom#p3691). I purchased this chassis from SCA with the power supply already installed, so should I remove the power supply and check for any issues with it? Any suggestions on trouble shooting the power supply to see where the issue may be?

I know the phantom power can work (see previous post), so it must be a short or a bad solder joint in the power supply. Any suggestions would be a help. Thanks!

[rjraffa]

Just wanted to include some closure on this one. After reviewing the board, I found one of the resistors had not been completely soldered. Even though the resistor had nothing to do with phantom power, this unit came preassembled, so I asked Tim for some assistance.

Tim got back to me, and I ran through a few tests he provided. I was still getting 60v, so I sent the unit back to Tim. He checked it out, and all readings came up fine (in the range of 45v). Tim mailed the power supply back (along with the B16s I ordered YES!), and power supply is fully functional. Excited to be recording again.

Tim, thanks for the help and your quick feedback!