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.
Hey, let’s also try to give it variable speed fans, based on…. uhhhhhhh…
Whatever This Shit Is. Uhhhhhhhhhhhhhh—-
Now let’s put a water misted cooling pad system on the air inlets and make it look like something that was field expediently whacked together in the back of a barn OH FUCK GO BACK NO
Here’s the end result. At some point someone cleared out the electrical cabinet of everything but the main disconnect and rebuilt it with……a mountain of weird shit. This is the left side where the contactors for the compressors and fans would have normally been. I don’t know what the deal is with that thing that looks like a transformer, it’s just an 3 phase “reactor” – an inductor.
Not particularly visible at the bottom: a set of current transformers on the Turbocor’s power wires that set off the water misters when it begins to spool up, and a pair of fans rigged in the bottom to keep the VFDs cool…ish. They’re powered through the barrier strip on the far right.
In the compartment which would have formerly held the logic board that controlled the old setup, the two relays to the left of the Turbocor interface board turn on the cooling fans at the bottom, and…. well, I have no idea what the second one does. I couldn’t trace this out and there’s no documentation left with it. In short, I have already run out of fucks to give.
Um, what the fuck happened to R12? Again, lack of fucks to give, the thing still runs ok. Not sure what the LEDs are indicating but when D5 through D8 flicker periodically.
I’m fairly sure the Turbocor must actually be capable of commanding variable frequency fan drives to cool the condenser, but oops, someone put that weirdass blue pressurestat in place instead. That thing is fucking weird. It sits there and does nothing until the pressure is like 4 PSI below setpoint, then the command voltage it sends just abruptly leaps up from 0 to 10v, making the variable frequency drives… not so variable…
Anyway the reason I had to mess with this thing is one of the drives lost a 24VDC cooling fan. Our HVAC contractor looked into ordering a new fan and found out that a replacement would be at least SIX MONTHS OUT. The original, an NMB 3110KL-05W-B50 (80mm, ball bearing, 24v, 0.15A) appears to be Fuck You NLA. In fact, almost all 80mm 24VDC fans appear to be unavailable. I begrudgingly, out of desperation, dug into my own supplies and grabbed a little switching buck converter that’d take the 24VDC from the VFD and step it down to 12V to run a fan that actually IS available and extremely common.
Now the dumb thing spits out cold water again and I’m not quite as mad. I’m still going to swear at the fucking bellend thing though.
First off, here are the innards of a MRC Variable Rate Modem – it uses one to four QAM carriers to send high speed data. The I/O on the back supports some kinda T1 circuit stuff that— let’s just be glad it predates me or something— and ASI streams for video. The four identical boards are the individual modems for each channel. Thing’s hardcore, and it still works, I just had to change a memory backup battery and reload some settings and send it back up to the mountaintop to work for another 15 years.
Its input and output are a common 70 mhz IF frequency that, in this case, is passed through MRC DAR radios on 7 ghz.
Isn’t it just unusually cool?
The looks on everyone’s faces in the studio when you blast K.K. Slider songs through the overhead speakers is precious.
There are flattering angles from which you can take a photograph of someone and this is not one of them:
What happened when I tried coloring part of my hair purple. It wound up a kinda deep plum color, then maybe dark burgundy, then a dark blonde as it faded. It was a really nice strawberry blonde for, oh, a day or so.
Also a small plasma ball on which I was pondering the fact that a persistent leader of the discharge goes down that hole at the bottom and terminates in the sealing pip. Look to the left of the center column.
In 1986, Panasonic felt the desire to launch a competing format to Sony’s Betacam SP professional videocassette system.
By 1990 it was all but entirely gone, a commercial flop, guilty of trashing so much footage entrusted in it with massive tape dropouts.
It’s bizarre. It uses cartridges that look a lot like VHS, and it’s in fact possible to stick a VHS tape into the MII deck— and get it jammed there because it’s not exactly compatible with the loading ‘elevator’ and tape transport. It’s actually kinda more like S-VHS, but… terrible.
Apparently my station is lucky enough to have been one of the few that used the format for a while, and still has one working deck to access video on it.
The only thing I like about it is that this deck has a really cool display and the firmware will actually report to you in plain English when something’s wrong. It also uses the same reel speed ratio trick to tell you approximately how much tape is left, which Sony has had on pretty much…. every one of their professional formats, ever, so that’s nothing special, but it’s cool that it stays on the display all the time. In the photo below of the transport, you can see a roller to the left of the yellow cadmium plated elevator motor. It’s got a slotted encoder on its base that lets the deck sense the actual tape travel speed for this calculation. Interestingly, this one also leaves the tape threaded in fast forward and rewind, so you can see the timecode spin away, but on a fresh unused tape that’s never been “blacked” or used before, these sensors are the only way it’d be able to calculate the time remaining.
I’m suspecting that’s a 40×2 char VFD under the plastic there.
When I first got the deck powered up, it said “ERROR: LOADING MOTOR” or something along those lines, because the threading ring motor’s belt had lost its elasticity and grip. I was lucky enough to still have a couple of belts that fit it.
Yes, it’s got a VHS looking cartridge and a threading ring……. believe it or not that’s not the only time that nonsense has happened, there was actually a VHS transport that threaded up that way. Oh, you’d think with a name like “MII” it would use M-shaped threading like a VHS, DVCAM, or DVCPRO transport, but that wouldn’t have been AWFUL enough.
See that spinning thimble to the left of the head drum in this photo? That’s the top of the capstan. That’s the only other thing I LIKE about this powerfully cursed device: you can hold an isopropyl alcohol soaked shop towel against the capstan and turn the thimble to scrub the crappy oxide off it.
It’s got two linear audio tracks (like standard VHS) and two FM multiplexed helical scan audio tracks (like Hi-Fi VHS) – channels 1 and 2 are linear, 3 and 4 are helical. It’s like someone decided to use the worst of both worlds. Fabulous.
So if you’re wondering why I love this thing enough to have put the little drawing of Popuko on it, this deck also has the nastiest weak rack slides accompanying it, which broke and turned into a horrible ski jump while I was trying to pull the deck out of the rack to clean its heads. I was sitting on the floor and all 80 pounds or so of the thing came flying out, landed on my lap, arm, and leg, and generally left me wanting to yeet it off the roof. I’ve never had a rack slide fail in the same way these did— the mounting ears just snapped off at the screw holes like some kinda Twix bar.
It will now remain on the CART OF SHAME until it’s eventually fecking e-wasted where it belonged in the first place.
I wonder just why Panasonic even bothered with this. Everything about the system feels like they had intended to be able to create a competitor to Betacam SP that would have had a higher profit margin, BUT—- then they took every step possible to make the damn thing insanely complex and difficult to produce ????
Variable frequency AC drive controllers are all sorts of amazing. They rectify AC power to DC then give you 3 phase AC at the desired frequency to let you run the motor at the desired speed, anywhere from just a few RPM up to full tilt. They can also, if misconfigured, drive you up the wall at 60 cycles per second.
I’ll save you the pain of having to watch me scream about Johnson Controls Metasys, here’s the data showing that this one air handler is not happy. This graph is showing its air output temperature. This morning I came in to find half the facility nearing meltdown and decided to see if I could do anything about it.
There’s the drive for that unit’s blower. I found it shut off on a DC bus overvolt fault. The automatic fault restart was not enabled, so it just sat there.
I restarted it and watched it ramp up to full speed…. fearsomely. After it’d let the place cool down a while I revisited the settings. This Yaskawa controller actually has pretty good documentation and a setup routine designed to aid in quick deployment (I CANNOT say that for all the controllers I’ve come across in the wild). Right away I noticed the amperage and wattage limits set in the controller did not match the motor, which did not appear to be original to the unit.
Yeah uh I’m gonna have to recommend you not do that. I filled out the proper values in there, turned on fault restart, and ran the auto tune, which sounds like angry crickets on this unit.
Aside from the drain pan looking suitably foul, I’d say it’s happy again.
I dunno, I realize that variable frequency drives are probably a bit of crazy black magic to a lot of HVAC people, but pleeeeeeeeeaasseeeee make sure you have the thing configured right for whatever motor you’ve wired to it! It does make a lot of difference!
Oh, and the Johnson Controls corporation is a bellended bagbiting cockwomble. There i said it ok
I’ve been using the Texas Instruments TPIC6595 and TPIC6B595 shift register with high current low-side driver ICs for a while for various tasks, usually driving LED lights and displays.
Someone posted a picture of an old gridless Tung-Sol VFD tube on Facebook and I thought to myself, well…. these are neat, but if you wanted to connect them up to a modern microcontroller, you’d need tons of pins unless you can easily multiplex it. TPIC6B595 wouldn’t really help you here as you’d need to drive +30V or so to the anodes.
I remember trying to figure out if there was a nice convenient high-side equivalent to the TPIC6595 series when playing with flip-dot display panels, and came up with nothing. Well, now I searched it again and came up with the MIC5891 which is exactly that, and it’s good to 35 volts! It’d be perfect for driving the VFD anodes.
The Important Fun Note: Driving a display this way with latched drivers will allow you to achieve a completely flicker-free readout, which is VERY important if you want to have your display appear on screen in film/TV applications! ESE clock displays operate like this (though I seem to vaguely recall they use something like 7490’s behind a set of D latches).
Another day, another case of being thoroughly perplexed by RF Central gear—
When the mast goes up but the signal doesn’t go out, it’s time to investigate.
The forward/reflect/12vdc return meter always seemed to show 00.0 if the PA was off… -1 if the PA was on, in any field.
TWO different bad amplifier units…. one was waiting on the shelf as a spare, one just came off the truck.
So what’s inside? I forgot to take a photo but if you remove the hex screws on the back it reveals a Stealth Microwave SM2025-44L, 25 watt linear amplifier for 2000-2500 megacycle DVB applications. Sadly. Stealth Microwave is long gone.
Interestingly the amp bricks are specified as having an internal output isolator. Nifty.
The other major part inside the amp brick is a bias tee that splits 12vdc power sent up the coax out to run the fan and the amplifier.
And now, it gets… horrifying.
I found a datasheet on the SM2025-44L and it’s specified as taking a mighty 8.5 amperes. I mean, at least it isn’t gonna arc furnace anything, but the voltage drop CANNOT be nontrivial anymore.
This has to get to it on the coax. The coax from the indoor unit in the truck to the outdoor amplifier unit is not a short sweet little run. See the big black coil up the mast in the first pic? There’s probably at least 45 feet of coax in there, plus another dozen at least to land it from the feedthrough in the roof to the IDU in the rack.
WHY DID THIS EVER WORK AT ALL? Or does it? I don’t….. I can’t even——- No——— I need to go home and collapse in bed and place the kitteh on top of me and stop trying to think for this week. DONE. I’m so done. What the hell.