Week 15: Approved
The big news this week is that we have been approved for a mortgage at last. After five weeks in which it felt like I was being asked one pointless question per week, I sent a sternly worded email asking why it was taking so long, and whether the fact that I kept being asked so many questions that were irrelevant to our situation indicated some deeper misunderstanding.
A few hours later, the broker replied to apologise, to say that they had spoken to the mortgage underwriters, that they had everything they needed, and that the mortgage would be approved later that day. And it was!
The squeaky wheel gets the grease, I suppose.
I built a few Eurorack modules this week. I’m quite obsessive in my assembly process, always cleaning off flux after soldering, and visually inspecting all the joints under magnification, so it’s rare that I have any problems. But this week, I did. On testing the TELEXo module that I built, I discovered that the topmost trigger output wasn’t triggering anything, although its accompanying LED was flashing as expected.
Even though hardware and software are completely different, the process of finding faults is similar: systematically measure and eliminate possibilities until you find out what is wrong. It’s just that there’s a lot more effort when you’re doing it in the physical world.
I referred to the circuit diagram, which told me that each trigger output was pretty simple: the 3.3V digital output of the microcontroller is boosted to 5V by a buffer, fed through a 1kΩ resistor for protection (in case two outputs are accidentally connected together, or it’s briefly shorted when a plug is inserted) and then wired to the tip of the patch socket.
By probing, I could see that the microcontroller pin was going high as expected. The output of the buffer was also going high, although (foreshadowing) at 4.85V it was lower than I expected. But the output side of the resistor was at 0V.
Must be a defective resistor, I thought. That’s quick and cheap to replace, so I replaced it. Still no good.
I measured and found continuity between the tip and ring of the output socket. The tip was connected directly to earth. This explained the 4.85V I found earlier: the missing 0.15V was the voltage drop of the resistor between the buffer output and ground. The protection resistor was doing its job, at least.
I removed the socket and checked the board. No continuity! Great. So it wasn’t the board. Perhaps it was just a blob of solder on the component side.
I replaced the socket. Continuity. Boo. I removed it again.
I connected another socket on trailing wires. This time, there was no continuity, and I could even use that trigger output. It was something that was happening when the socket was on the board. And then I saw it: there’s a small pin header mounted under one of the sockets to join the ground planes of the stacked circuit boards together, and the lead of this must have been be touching the tip terminal inside the socket.
I nipped the leads down as far as possible, applied a layer of kapton tape over the top for insulation, and soldered the socket onto the board. And this time it worked.
I won’t say it was fun, because desoldering components is much harder than soldering them in the first place, but it was satisfying. Total cost: two sockets and one resistor, and a bit of time.
The letting agents sent an electrician to inspect the wiring in our current flat, as they’re obliged to do from time to time. I took advantage of it to mine the electrician for information about what they actually do when they’re inspecting. There’s less to it than I thought. You’re basically paying for someone with a certification to use a multimeter.
I had a pint al fresco (and it was pretty damn fresco when the sun went behind a cloud) at the Dog and Bell in Deptford. How modest my horizons now are.
My cheek is much better. There’s still a lump, but no discomfort. I really must have done some damage when I bit it.