I have spent the past two days closely focused on the replacement for a highly configurable widget that doesn't work. The replacement doesn't work, either, in the very same way.
It is literally configured by the book and confirmed by factory technicians, looking at photographs and talking me through it. The manufacturer's installation crew, hired contractors who have worked for them before and who I found clueful, did the initial setup and testing, and pronounced themselves stumped. But they were confident the factory techs would sort it out.
This has not happened.
One complication: I admit that I have been lazy. This particular company -- we've bought major items from them for years -- has some of the worst habits I have ever encountered when it comes to drawing schematic diagrams. They rarely manage to get all of one function on one page, and their continued-on-page-n jumps are hard to follow and often fragmentary; most of something happens on one page, the circuit goes to another page and wends through a series of connectors and jumpers, splits, does minor things on two other pages, and dead-ends. You backtrack and find a tiny note that directs you elsewhere, and so on. And on and on.
RCA was plagued by this, back when RCA was a big company that made every single item in the path from, say, the camera and microphone on a TV reporter in the studio to the TV set in your living room, and they (eventually!) came up with two answers: absolutely enormous blueprints for complex subsystems (one showing the "control ladder" for a 1970s TV transmitter was a yard high and over fifteen feet long!) and summaries or "one-line diagrams" that identified and followed critical functions. Between the two, you could get from Point A to Point Z and have a good understanding of every intermediate step. But the giant drawings relied on long-gone technology (not to mention workspace with a lot of open floor area!) and the one-lines took the careful attention of engineers who knew the whole system, inside and out. Degreed-engineer time is too expensive for that these days, and by the time the product is in the hands of low-level people like me, they're six projects further on, and probably working for a different company.
All of my older drawing-package books for this company's products have a Bobbi-added extensive array of color-coded tabs with drawing numbers and titles, careful highlighting and plenty of on-page notations (they're inconsistent about telling you where to look for continuations). I haven't done that with these yet, and I need to. I'm going to have to grit my teeth and trace this thing out fully, and try to understand why one of the most common configurations of this gadget is not working for us. It's probably something simple, some detail that may be known to a few field techs by word-of-mouth but hasn't been written down.
It's happened before. The cause of an ugly and expensive fire at my work almost exactly thirty years ago came down to not relocating three large components that run very hot from an enclosed cabinet to an open-air mounting. I'd seen it done at a different installation of a similar device, and no one there ever said why; they might not have known.* The factory field-installation techs started doing it after the product had been on the market a few years, but they apparently never told the factory engineers. No factory change notice was ever issued, no memo or bulletin, and the factory support engineers don't appear to have known it was being done. But it was -- only it wasn't done in ours, and one Fall evening, at least one of them caught fire and cost my employer a small fortune. Or small for them; I could have retired on what it cost, and lived in luxury. The equipment was over twenty years old at the time.
I don't think this is quite as bad an oversight but there's a piece missing from this puzzle, and someone knows what it is. But so far, I don't know, and neither does the factory tech trying to help me troubleshoot it from hundreds of miles away.
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* Sola constant-voltage transformers, for readers who know what those things are. They run hot and often loud; this gadget had three of them, each slightly smaller than a footlocker. The place where I saw them mounted on a wall even had fans blowing air across them.
Update
10 months ago
14 comments:
Roberta: I do not envy you. Reading your description of the prints made me ill and gave me flashbacks to working on gear with documentation-by-committee-on-drugs.
Good luck on your adventure of discovery.
I wondered if your profession doesn’t have an organization or magazine that has a website where issues like this could be posted and discussed. Like you said, someone out there knows the answer and it would give you a wider reach. It’d also be a repository of institutional knowledge in a way.
By the late 1980's the Quincy Tin Works stopped using Sola CVT's in their radio transmitters; I saw them on the filament power supply on earlier boxes. It's been a few months, and our new VAXTE has performed flawlessly (I'm rapping my skull with my knuckles as I write this, especially because it's the weekend and I'm taking a week's PTO).
I'll hate myself for asking, but do you have a backup transmitter and a coaxial switch with their nifty little controller? (MSC-X and the Dual Switch Driver.) Nobody's been able to figure out why we don't have a working interlock output for the backup.
Let us know what you figure out, please.
Not being in the broadcast biz, Quincy Tin Works was a real head scratcher for a bit. How did people ever learn stuff before the internet?
They're justifiably proud of their metalworking lines. Any more, it's a lot of 3-D machining, as well as sheet metal work.
No in-house circuit board manufacture, though. The environmental concerns are such that it makes more sense to farm it out to a subcontactor who does nothing but, for many other companies, essentially pooling the disposal/recycling cost of the harsher chemicals and valuable metals..
We have the coax switch, dummy load, and the controller, but no backup TX. Corporate instructed us to scrap the old box, which we have done. There is an overtemp interlock line wired from the dummy load, which I presume was tested by the installer.
Robert, my understanding, possibly wrong, is that this particular manufacturer got the Quincy Tin Works nickname after another company bought them in the 1950's, then started some "value engineering" of the products.
If it's typical, the interlock goes to the Dual Switch Driver, which then routes it to the interlock logic when the transmitter is connected. There's another input for an antenna interlock (!), which nearly always gets a jumper across it. That's a "gotcha" wire, which looks unimportant but can shut the whole thing down.
The idea is sound. The execution is okay. (I'm not a fan of the connectors on that driver, and I'm uncomfortable with the tiny, soldered-in relays.) The documentation is...horrendous.
Yep. But they always have had a serious in-house sheet metal shop. It's one of the things that helped them compete with the big guys. Compared to RCA, Western Electric, GE and Collins, they were tiny. Raytheon got into and out of making broadcast equipment almost on a whim, with nearly as full a line of equipment as they offered.
There was "value engineering" all along -- but they sold it for what it was worth, and did all right.
Yes they have...the sole survivor of the broadcast lines you listed.
One of my clients has a Raytheon RA-1000 AM transmitter in the basement. A beautiful box built like a brick latrine, but at 2450 pounds, a bit awkward to move.
I have a deep and abiding love for the Raytheon RA-1000. Not only is is a textbook example of a conventional AM transmitter -- and nice-looking, to boot -- one of them saved me from going after the wrong problem, when a local 5 kW AM station (with a beautiful Bauer for their main transmitter) was having trouble. It looked like a mismatch to the antenna system, but when we switched to the Raytheon backup, which had every normal meter reading marked right on the meters, it looked perfectly normal and sounded great. So it wasn't the antennas or phasor. Eventually the guy I was working with and I tracked it down to a single blown fuse in the three-phase primary of the plate transformer. With the plate voltage unusually low, everything was messed up. The Bauer did still run that way, though. We put in a new fuse and it was back in business. Those fuses had never been touched since it was installed.
Roberta:
Do you remember the symptoms of the missing phase? Like oddball peaks 'n valleys in the RF envelope or buzz on the audio? SWR moving around?
We lost a phase coming into one of our computer rooms. Three phase, 400Hz, 1.5kv. The machines didn't like it and luckily, I was low enough in the food chain that a higher up got to stick his hand into the panel holding a Simpson 260 on steroids. No fun.
Just what one might expect: RF final amplifier plate voltage and current much lower than expected, reduced power output and the audio sounded bad.
Typically, these plate-modulated transmitters use one high voltage supply for the modulator and final amp. "Something's gone terribly wrong with the phasor" (power splitter/phase shifter for a directional AM system) wasn't an unlikely possibility; he'd called me up wanting to borrow a high-power impedance bridge, and I'd told him I'd loan it, but I had to be the one hooking it up and turning the knobs.
We never got that far. I showed up, admired the Bauer, observed it was indeed unhappy, admired the Raytheon and realized it would give us a quicker indication of the problem than the impedance bridge. It did -- but not what we were expecting. Whoever it was marked those meters, with little slivers of tape on the glass, knew what he was doing. I have made a point of having a written record of all the normal meter readings for every transmitter I have been responsible for ever since. We're not reading them every half hour any more; we're not going to know at a glance if something's not right.
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