Mounting the LM3886
Mounting the LM3886
Now it's time to solder in the LM3886. First, drill the holes in the heatsink. Make sure that the holes have no sharp edges. Mount the IC's without having them soldered but you must have them mounted at the pcb. This is for avoiding mechanical tensions. If you use LM3886TF which is insulated, you only need thermal grease, compound. Don't mess with it! Use a thin layer equally distributed. Bolt the IC's and than solder them also. If you use the LM3886T which is NOT insulated (but have higher power dissipation) you must use a washer of mica, Kapton (orange thin plastic film) plus a bushing insulating the screw. Apply a thin and smooth layer of thermal grease on both sides of the washer and tighten the screw. You can also use silicone rubber with or without the grease.
Last a warning: The grease is messy. Don't use more than you need and you need very little! The grease will also creep away from the LM3886 and the result is dust collecting.
Change fuses to 500 mA fast, or 1 A fast, just as a precaution.
Check once more that the LM3886 has got both it's inputs connected somewhere, if not the fuses will go. Check especially J2.
Apply voltage and check the current consumption which should be max 150 mA (guessing right now). Measure the voltage at the output. Should be less than 1 V (guessing). Disconnect the supply voltage.
If you have chosen to have DC servo, solder in the IC's for the DC-servo, IC4 or IC5.
Apply supply voltage, check the output DC voltage. It should very low. With AD8620 max 2 mV, probably much less, like 70-100 µV! With OPA2134 I'll expect a slightly higher value, maybe less than 5 mV.