A completely functioning DI input, but dead mic input, is a common build issue in both the Lola and Elements series pres.
First, start by confirming it's not a phantom power issue. Try using a dynamic mic. Still not working? Then you probably have an issue with your relay circuit.
Relay circuits have a "normal" mode. Think of it as their default, with no power mode. With no power, current flowing through the relay coil, they sit switched in this default mode. For the Lola and Elements this default or normal mode, has the DI as the input source. So if your relay circuit is not getting power, you're stuck with the DI as your input.
If the circuit is functioning normally, there is a transistor (Lola-Q1 and Elements Q200) that functions as a switch. When this transistor is switched on the input is set to mic and when switched off it's set to DI. The switching is done by sleeve on the DI jack. When the sleeve is connected to ground, current is allowed to flow through the transistor and coil, flipping the input to mic. When you insert a 1/4" DI jack, the path to ground is broken, no current flows and the relay switches to its default non-powered DI position. Considering all of this, you can see why if there is not power to the relay, you're stuck in DI.
So what's going wrong?
- You don't have all of your DI pads soldered. The Elements, in particular, have the two power pads separated from the 6 switching pads. Make sure all 8 pads are soldered.
- Transistor that switches the relay is damaged. With the unit powered on, you should see a drop of about 0.7 V DC across the base-emitter junction. Google the transistor datasheet if you need clarification on identifying the leads.
- Relay is damaged. If everything else tests out of, you might just have a damaged relay.
- You've got a mixed up resistor and or capacitor in that part of the circuit.
- Your DI jack is damaged in the sleeve making contact to ground with no DI jack installed.