Assembly procedure for Simple LFO 1.5b

Here is the recommended order to assemble the Simple LFO module Version 1.5b. Please read the entire procedure before starting the soldering job. Feel free to adapt these steps to your needs and personal workflow.

This is the front side of the board we are populating.
This is the back side of the board we are populating.

Resistors

Start by soldering the smaller components. Resistors are not polarized.

R2, R12, and R13 are 470 Ohms (Yellow, Violet, Brown, Gold).
R3, R5, and R6 are 100 kilo Ohms (Brown, Black, Yellow, Gold).
R8, R10 and R11 are 10 kilo Ohms (Brown, Black, Orange, Gold).
R7 is 4.7 kilo Ohms (Yellow, Violet, Red, Gold).

IC Socket
U1 (TL074) requires a 14-pin DIP socket. Be careful, the socket is polarized. Align the notch to the silkscreen indication on the PCB. Do not insert the IC itself yet.

Small capacitors

Small, ceramic or plastic capacitors are not polarized.

C3 and C4 are 100 nano Farads.
C1 is 10 nano Farads. This is the timing capacitor for short range (higher frequencies).

Eurorack power interface
K2 is the 10-pin power connector. This connector is polarized. Align the notch to the silkscreen indication on the PCB.
D2 and D3 are 1N4007 (or equivalent) diodes. They are mounted vertically with the Cathode facing up. The Cathode side is identified by a white (or dark) band on the diode body. The Cathode pad is identified on the PCB by a white band and by the square shaped pad. Please, see pictures for more details.

PCB connectors

In case you use pin header connectors for the two switches and the output jack connector, this is a convenient time to install them. If instead you wire them directly to the PCB, you can connect them at a later time during the assembly. Follow the "wiring diagram" to find out how to orient correctly the connectors or wires.

S1 and S2 are 3-pin, 2.54 mm spacing pin headers ("KK" style). These connectors are polarized. Align the notch to the silkscreen indication on the PCB.
K1 is 2-pin, 2.54 mm spacing pin header ("KK" style). This connector is polarized. Align the notch to the silkscreen indication on the PCB.

Bigger capacitors
C1 is 1 micro Farads. This is the timing capacitor for long range (lower frequencies).

Electrolytic capacitors are polarized. Be careful! Incorrectly positioned capacitor can explode.

C4 and C5 are 1 or 10 micro Farads, 25 Volts minimum. Align the negative side, indicated by a white band on the side of the capacitor body to the white silkscreen indication on the PCB. Also, the positive side of the capacitors is the longer leg (opposite to the white band), and is to be placed in the square shaped pad. Please see pictures for more details.

Components mounted or aligned to the front panel

I highly recommend to not solder immediately the components that are attached to (or to be aligned with) the front panel:

Instead, I suggest to first position the potentiometers on the PCB, without soldering them. Second, present the front panel over the components, then secure them in place by tightening the nuts. Example here: J1 and J5 and the potentiometers.

Once everything is in place, solder only one pin per component. Check the alignement. Reflow the soldered pad for any component that would require an adjustment.

When you're satisfied, finish by soldering all the remaining pads.

This manipulation can be tedious, but the goal is to get both a perfect alignment of the controls and avoid any tension on the solder joints. If you start by soldering the pins before, and tighten the nuts afterward, you might risk to damage the pads on the PCB, bend the front panel and get poorly aligned components. Of course, the difficulty here is to keep everything in place without soldering. If needed, you can solder just one pin before positioning the front panel, but remember to reflow that pin once the nuts are tightened, in order to release the tension on the pad.

D1 is either a regular or dual color, 3mm, LED. LEDs are polarized. Note that in case of a dual color LED, if you invert the polarity, the colors will be also inverted. In case of a regular LED, it will be lit on on negative excursions of the output waveform. Install D1 after having gently bent the legs 90° at roughly 5 or 6mm from the LED case.
R1 is 9 or 16mm "Alpha" style linear potentiometer. R2 is 9mm only. If they come with a protruding tab on their front (below the shaft) remove them with pliers before assembling them.
Place the front panel, secure it with the nuts. Then solder one pin of each component, as discussed above.

Last steps
Test the module without U1 inserted. Check voltage polarities at test points T3, 4 and 5.
Finally, insert the TL074 chip in its socket. Be careful to not damage the pins. Please be careful: U1 is polarized. Align the notch on the chip to the PCB indication.
Check waveforms at TP1 (square) and TP2 (triangle). D1 should blink at the same rate.