Step 38) 1.5 volts on R8 & R9?

[mltamisin]

Just installed and trimmed it up to +/- 18 and went to check the common mode servo and I'm getting 1.5 volts. Any ideas on what to check?

[mltamisin]

Man, I just double checked my work and I can't find a thing wrong. I also double checked every component twice during installation. Could it be the PSU? It was already put together. What components comprise the common mode servo? I can triple check this area if anyone know's what components make it up. I have an extra 20K0 resistor so I checked and the 4 listed in the component list are already installed on the board......so I hope it's an extra.

[tpryan]

Carefully check R8, R9, R29, R30, R33, R34, C12, C13, and U3. Also, make absolutely sure that you've installed Q1 and Q2 correctly. If you can adjust the rails to +/-18v, the power supply isn't the problem. You've probably got a resistor in the wrong place or bad solder joints. It's very unlikely it's something else.

[mltamisin]

Well, just checked the components you mentioned and there's nothing wrong with the solder joints and they are the correct components. Is there any way to check each component to see which is bad. Maybe one was heated too long or something. Also, when I check the jumpers I'm getting between .002-.007. I've recapped my Amek console and built Eisen kits to give you some idea of my experience level. Q1 and Q2 have both stubs facing inward towards each other and they're as tall as the other components (pretty tall). All the colors on the resistors match the legend. The capacitors look cool to me. I'm at a loss. I'm using a Xytronic soldering & desoldering station and the temp on the solder iron is set at 550 F. I try not to apply heat longer than a few seconds. Maybe U3 is bad. Hey, thanks so much for getting back with me so soon. That's really cool of you. Happy Holidays!

[mltamisin]

More info. Just measured the resistance:
R8 & R9 = 98.2k
R29 & R30 = 5.53k
R33 & R34 = 1M

[tpryan]

What voltage do you measure at the junction of R29 and R30? Measure with respect to AGND (J3, pin 4)

[mltamisin]

I finished building a second kit and got really similar readings. It took at least 2 extra hours because I measured each resistor prior to soldering, after soldering, and compared results with the previously built C84. My anxiety got the best of me and I took a chance and plugged in a microphone and to my surprise the units sounded fine. Don't know what's going on.