The Silliest Voltmeter Ever…

The year…. something like 2004.

The transmitter…. Harris Broadcast PowerCD, a funky Inductive Output Tube based system with modular architecture supporting multiple cabinets.

The silliness: much. Much, much silliness. So here’s a hilarious one: this board is right at the power input to each cabinet and watches for power supply phase loss and provides voltage metering outputs. Power in this case is 480v 3 phase delta and the metering circuits on this card measure the voltage between A and B, B and C, and C and A. The measurement circuit is uhhhh the CACA type. 😉

This Got Hot. The resistors’ markings bleached out from the heat!

So, here’s what you’re looking at. The three resistors are 15K ohm 3 watt and are wired in series with R27 (a PTC 0.15 amp polyfuse device) and the sensor coil inside that LEM current sensor.

The LEM LV25-P sensor is a Hall effect current sensor with galvanic isolation. It accepts 0-10mA and puts out a sense voltage proportional to the current input.

The resistors are dissipating 3.84 watts total on each phase, well within their rating. However, this rating was not assuming they’d be piled up like this and crammed on a board stuffed in an unventilated space in the cabinet!

The end result of this was that one of the voltage readings constantly jumped around and caused false alarms to fill the alarm log…. while we were trying to diagnose another issue.

Note the power reading at the top– that was the Other Issue. Ow. Signal go down the hoooooooole.

I’m entirely confused as to why such a roundabout approach was taken to this when a set of isolation amplifiers with one side being powered off a voltage divider or even a small transformer on each phase would have worked with less bill of materials cost and less heat, but uh

we’re still at the bleeding edge of this technology

Don’t be upsetti, print some spaghetti

It’s…. pretty well acceptable that the sock falling off was the cause of this silliness. It’s so ridiculous I can’t even be mad.

Have a good laugh at this stupid thing.

And I never could even figure out where that leakage came from

Behold, my poor hacked on Ender-3. I had bought a clone of the Micro Swiss hotend (I believe off Amazon) so I could print PETG and other high temp materials without PFTE tubing damage issues. I’d also had issues back then with getting the PTFE tubing to seal against the nozzle so I figured this setup would be great!

Unfortunately, I bought… the lowest caliber of dumpshit.

In what I thought was just desperately throwing parts at my printing issues, which led to “missing layer” kind of faults everywhere, I bought this titanium heat break from TH3D. It works with all the other stock hotend parts, which I’d saved in a box of bits. Turns out that’s exactly what I needed… So here’s what I replaced.

Strange, unlike the stock setup, that heat break doesn’t go in there very far…
’bout five millimeters
Uh. That looks awfully rough. In fact… I ran filament down by hand and could feel it snagging.
This is how far it actually goes together

I’m not actually sure what kind of metal this was made of to be honest or if it was even advertised as titanium, stainless, —???

All I can say though is I suspect it’s way too thermally conductive. I had to print hotter than I expected on this machine and the PID tuning values were WILDLY different after changing the heat break. Previously, with the same filament, this temp tower was just starting to print acceptably at the lowest floor which is 230C; now the lower floor is string city, which makes a lot more sense for PLA. Oh, and no missed layers either.

Before I start yelling about 3d printers and capacitors


See how I had that big area of my natural color showing in back? That was a heck of a missed opportunity, and the green just wasn’t liking the base color.

Fixed that right up.

Related image:

But who wore it better?

May I just take a microsecond here

Hey, it’s me, I want to give you some good frequencies. (The part I’m referring to is the very end, and the bandpass filtered beat you hear in the background is the beat to Eple, which follows it on the album. Eple will sound familiar to anyone who’s ever fired up a fresh install of Mac OS 10.3…)

But all that aside, this is about metrology and frequency standards and things my cat likes to loaf herself on top of because they’re warm.

We’re preparing for the installation of a new GatesAir Maxiva DTV transmitter at work. I was gonna say it’s an ATSC transmitter, but… I’d at least like to hope… it’s ATSC3 ready, whenever that rolls out. Sitting in the space it was going to reside in was a weird old Axcera transmitter that never worked right and was yanked out in pieces to be e-waste’d. Sitting on one of the pallets of refuse left over was the reference oscillator for the exciter, which, interestingly, was just a standalone thing without GPS synchronization. The tub in the middle is an insulated chamber containing an oven controlled crystal oscillator. Basically, this is an oscillator in a thermostatically controlled heated chamber that keeps it stable. It MUST be allowed to warm up to full operating temperature before use, or, well… it just ain’t gonna be in spec!

(insert commentary here on how silly it is that I’ve seen OCXOs in battery powered equipment that has a shorter battery life than the warmup time)

Most modern stuff uses GPS sync because it’s a good inexpensive way of obtaining a stable reference frequency and timecode. The usual arrangement is to have a voltage controlled oscillator that’s PLL locked to a 10khz timing signal output from a GPS receiver head. Aside from a little bit of phase noise possible in the system, it’s always spot on. This is why you’ll see funky little cone shaped GPS receiver antennas all over the place at broadcast facilities.

Here’s the Evertz system we have that takes GPS time and frequency references and generates our facility master clocks, black burst, and trilevel video sync. I’ve never really gotten that good a look at the way it operates but I think the black burst is generated inside the automatic changeover unit which also has some distribution amplifiers in the back as well. One of the outputs is a 10.000.00000 (I’m not sure how many significant figures) reference which can be used by a wide range of equipment. After having an, uh, experience, with one of these changeover units (see link above) I wisely do not even look at it hard while we’re in anything but 4:00 AM Sunday morning backwash programming. A frame of Grass Valley distribution amplifiers near it is used to distribute its black burst, LTC timecode, and 10mhz signals to where they’re needed throughout the facility.

This will come into play later.

The toroidal power transformer has two primary windings which were series wired for operation on 240vac. That’s why it says 240 on the AC terminal block shield. I swapped them to paralleled for 120.

More pictures and calibration process — onward

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this is our solution

This got pretty badly stuck in my head yesterday for…. reasons

I figured out the root cause of the issue I posted about earlier on with the crazy fan circuit…. waaaait for it:

The pin was never securely inserted and latched into the housing of the fan connector! Welp. Lacking the correct tooling for this connector series (I have yet to be able to identify it!) I broke the rounded end off one of those plastic stirrer sticks from Starbucks and used it to prod the thing into place. It snapped in and I plugged the fan in and it’s happy again. Speaking of fans and drama, this greeted me with a rhythmic pounding noise from the office roof yesterday morning. I sent the HVAC contractor a photo of it and he arrived at the door at 9 AM laughing with a replacement propeller in hand. The cause of this one appeared to be that the “belly band” mounting Trane uses for the fan allowed it to slip down.

By design, these Trane units have a behavior that I consider to be just this side of “broken by design”. When the thermostat calls for cooling, the compressor starts and pumps gas (R-410A in this case) into the condenser, where it gives up heat into the metal finned tubes, condenses into liquid, and is sent to the output lines and into the building to boil inside the evaporator coil, cool the air down there, and come back to the outdoor unit as gas… the usual vapor compression refrigeration cycle. As the condenser heats up, the gas head pressure leaving the condenser starts to rise due to thermal expansion. You can hear the sound the compressor makes change as the head pressure rises, and I’m guessing the motor current starts climbing too. Once it rises to a certain point, a pressure switch trips and starts the fan, which cycles on and off based on the head pressure.

This causes it, in practice, to cycle in about 5-10 second intervals, repeatedly flexing and stressing every part of the nasty stamped sheet metal assembly up there.

The first time I encountered a unit like this in the wild, I thought I was hearing it repeatedly overheating and tripping a safety cutout. I had to ask an HVAC contractor if that’s normal. They said that (sadly) it is. Why?! I guess it might save a LITTLE power, but I don’t think it’s worth the reliability problems.

On a side note, my parents’ house had some ancient Sears “Good Neighbor” condensing unit that was made by Whirlpool, part of a retrofit from the 1970s or so (best I can find from trying to Google the thing). It claimed to be a two-speed condenser, but in reality, was a single speed compressor paired to a two speed fan that’d switch between high and low as needed based on the compressor discharge line temperature/pressure. It never outright STOPPED if the compressor was on. Yes, this was done… better… over four decades ago. Sigh.

It may be worth noting this was a pretty small R-12 system, couldn’t really fight the Florida heat well, but lasted a LOOOONG time. The condensing coil was much smaller than it is on modern high efficiency systems and I remember the temperature of the air coming out of that condenser being fearsome. You couldn’t comfortably touch the top of the unit after it’d been running.


2014 Subaru Forester Fan Relay Diagram For The Rest Of Us

I hate cars. They’re just giant expensive pieces of cost-engineered crap that cause horrible anxiety. Apparently, the service manuals for them pile confusion on top of that as well.

I don’t know WHO this diagram was designed for, but it was clearly not to be seen by human eyes and minds. OUCH.

From the factory service manual:

Ow. My brain. I mean— this IS a schematic, but… ow.

I redrew it to make it easier to understand and follow. The scanner in my office doesn’t understand the orange I highlighted the wires that should be energized off +12V ignition switched and turned it kinda beige-ish. Whatever.

I omitted the “Through Joint Connector” points shown here. I have no idea what those physically are – my best guess, being that I didn’t see a bunch of connectors in the circuit, is that they mean those are internally connected on the ECM harness plugs or in the fuse/relay holders.

Fuse F22 is a horrible mystery. Check it for yourself – the factory schematic suggests that the ONLY thing it powers is the “Sub Fan” relay coil, not the actual fans themselves. Why? Actually WHY ANY OF THIS???

In general I have a love/hate relationship with any cooling fan control system that incorporates a low fan speed for pretty much no good reason, and by that, I mean, I love to hate every single one of them. I’d rather hear a single loud fan cycling on and off than knowing that the whole control system is a ball of spaghetti wrapped around a meatball of ticking time bomb complexity. I also love that when I was trying to figure out how this works (the manual doesn’t really explain it) I found that there’s a reasonably useless possible state for the system of running one of the two fans.

I’m having an issue with one of the relays causing one of the fans not to spin. Specifically, it’s the “main” fan on the driver side, suggesting an issue with Main Fan Relay 2, which I was able to get the cover off of and look around inside… it looks like it’s gotten hot and both contacts looked pretty raunchy. It is not the logic state that you’d get to if the ECM were to ground pin B12 and not B11, which would cause the main fan to run only, at high speed.

So here’s the adventure so far—-

I’ve been through one radiator fan which might not have even been bad in the first place, though it spins kinda rough and probably needed to be changed even if it WAS functioning (that being the case, it may have been drawing too much current and pitting the relays).

Pictures from this silly adventure ahead (let’s keep this post from making the main page a kilometer long!)
Read more “2014 Subaru Forester Fan Relay Diagram For The Rest Of Us”

Have You Driven A F[n]ord Lately?

I swear, every Ford Econoline is just powerfully cursed. This one sharted out its coolant somewhere on the passenger side. Good times waiting for the tow truck, at least it’s a nice cool day so far with no heavy smoke.

What the fuse??

Fuses are wonderful electrical protective devices. They work till they don’t, and in the case of glass cartridge fuses, looking at the remains when they blow can give you some insight into what happened at the moment of fault (prolonged overload, dead short, slow overheating, etc).

Or in this case, uh, what

Today’s contestant: a 1.25 amp with some delay characteristic out of a switching power supply in a bookshelf stereo.

One look at this told me there was no need to fear a big nasty fault with the power supply. It went out very, very gently, in fact, STRANGELY so.

If you see the element slumped, that indicates it was running hot a while.

The element blowing up and becoming silvered to the glass indicates a high current fault. Often that’s a shorted rectifier bridge or caps when it happens on a switching supply.

What follows is an attempt to get a photo of this under the microscope.

VERY unusual. Note that the fuse wire itself looks perfectly fine and the fault looks like it occurred without any serious heat.

I really just don’t get it. My best guess is the fuse wire actually cracked instead of melting, possibly due to long term thermal cycling or vibration.

The alloy bead is a heat sinking feature to give the fuse element a time delay curve. As heat builds up on the fine wire it will be absorbed through the connections to the end caps and to this blob. Once it gets the blob hot, the delay time ends and a sustained overload will melt the element. Of course, a high current fault can always blow the element to slag in a very quick instant.

See, this all makes sense, right? Here’s something that doesn’t… a CrapTrex Freedom SW unloading undocumented fault codes like a bag of soda cans at the recycling center.