Eurorack SMD Synth DIY Uncategorized

MI Tides build

MI Tides Ramp generator

This board is of similar complexity to MI Clouds and Rings (the biggest challenge being the STM and the DAC in terms of fine pitch soldering), and I wasn’t expecting any major issues building it, but this is the only module out of 3 cases worth that I’ve given up on and started from scratch.

Having finished the first attempt, I noticed I had a short from the VEE rail to ground. OK, here we go. Open Eagle, check schematics, open the board, check the VEE net. A handful of components – the regulator that produces the -10v A_REF, the two TL072s, a power protection diode and a few passives – decoupling caps, etc.

Having seen no obvious cause, and after more head scratching, I resorted to removing components off the -12v line, one by one, rechecking for the short after each.

No joy. With no components on the VEE net, and with their pads cleaned off with flux and braid, I’m still getting a short to ground. Normally, I think it’s far more likely that I’ve screwed up something I’ve not spotted, rather than there being an underlying fundamental problem, but on this one I think there might be a board fault.

I’ve got a third board coming and I’m going to port all the components across, then check the depopulated board for the short. This will give me a spare to run the sheep firmware on.

In the meantime, I build another Tides from another PCB. And screwed up AGAIN. Not being familiar with the module, I flashed it with an ST-Link and put the pots etc in without soldering them to test it out. First test – great, everything working. Panel on, solder everything in, power it up, and…

No response from the Frequency or Fine Tune knobs. OK, back to Eagle. Both are just voltage dividers. Both check out their respective voltages. They feed an op amp which goes to pin 14 of the STM. All that checks out too, voltages change where they should and end up where they should.

It then occurs to me to check the manual. Sure enough, there’s a Clocked/PLL mode that disables the Frequency Controls that is accessed by pushing the two buttons together, which I must have done by mistake. Taking it out of that mode, it works perfectly.

So, all built and working but not my finest hour.