I got a broken MiniDV camera pretty much free for the asking and took a look inside. Well, I’m glad I didn’t go in expecting a successful repair because oh no
Probably 50% of the weight of this thing is tiny screws.
I was intrigued and horrified all at once that a tiny cog belt was visible! See it peeking out there to the left of the rubber pinch roller?
The iris was stuck closed. I’ve seen this failure on a few JVC mini DV cams and had never opened one up to investigate. Upon seeing the mechanism I’m not surprised this happens. It’s a combined aperture and ND filter with two weird thin plastic blades that have stuck together, actuated by a very tiny rotary solenoid.
So there’s the tape transport, it has only two motors aside from the head scanner. A very small pancake capstan motor is under the side where the pinch roller is; the one standing in the corner controls the load/unload action.
And finally, that tiny cog belt runs between the capstan motor and a pulley that drives the gear idler. The tension is regulated by a spring loaded brake (felt?) under the take-up reel and that’s pretty much it. This isn’t exactly a very sophisticated transport.
I can’t really imagine actually repairing one of these. Everything had to come out to get to the back of the transport and it’s a total mess in there. Wow.
The hardest part of having false hope is when it all falls apart. Here, I’d been told that the PowerCD transmitter that I lovingly call the Space Station Toilet was going to be replaced starting in April or so.
Oops. Turns out nobody has any of the required supplies for that project in stock anywhere and production isn’t expected until July at least with an estimate on replacement being maaaaaybe September… and every tiny setback adds another fortnight of business days to the backlog. Time to start making this thing as happy as possible to prolong its final year (or decade?) of service…
Another adventure at the Space Station Restroom standing tall in a field by the river… This is cabinet #1 of 3. Cabinet 3 was the one that gave me such elegant fits before when I did a grid scrub. Cab 1 wasn’t causing as much drama but it just wasn’t making enough power prior to the scrub and was occasionally arcing out, roughly once a day. Let’s gooooooo to the wash!
Yes, of course it keeps trying to flip back to BG Heat every few minutes so you just have to stand there in front of it and pwap the standby button each time. Annoying. I thought about just raising the filament voltage in BG Heat but realized that’d be a terrible idea as the cooling system shuts down when you’re in BG Heat! I can’t remember if the air blower eventually goes down, but the water pump definitely does.
As I prepared to do the grid scrub (which requires hooking up an external power supply to the ESCIOT tube grid and cathode), I went into the high voltage cabinet with some isopropanol and blue shop towels and did a, well, scrub.
What’s that now? Oily sticky gook…. just like I found in the other cabinet? Hmm. I’m beginning to wonder if this is ethylene glycol that’s been electrostatically precipitated out of the air, since this rig is known to absolutely REEK of Dowtherm SR-1. The recirculating pump/reservoir unit is far from airtight so it just outgasses.
And now, Deja Moo: the feeling I’ve seen this BS before—
Look at the upper left: this robot has seen some shit, man
Amazingly I did not find it necessary to readjust the grid voltage after the scrub, it just… Worked. I was not expecting this. Not out of this turdly transmitter.
Then came the surprise. I was walking past checking the coolant system pressure on the pumps for the other transmitter in the room (a rather boring solid state ULXT-80) when I saw one of its variable frequency drives blinking “OCL”. Interesting. I first foolishly decided to take the cooling fan cover on the TEFC pump motor off, thinking I was going to find a seized pump. I spun the fan and found no unusual resistance. Upon opening the cover over the drives I was greeted by….. toast.
Not sure what went first, the screw terminal or the crimp forked terminal that was stuck in it, but something got hot until it cratered the poor drive. Ow! And to make matters more fun, as is always the case nowadays…. nobody seems to have these drives in stock anymore. Luckily, GatesAir has them, for about the same price as a better quality Fuji Electric drive from Grainger. Hmm. Do I…? I’ll have to make sure the Fuji has the right I/O first before doing anything that daring. On a side note, if GatesAir is going to charge that much for a drive they marked up like 100% they could at least take it out of the box and program it for you. They do not do this.
Then again this is the same manufacturer that charged us about $500 for four small rubber washers that I strongly suspect were just pieces of EPDM rubber hose cut carefully to length.
It’s my personal opinion that these Toshiba drives are built like damn toilet paper. They were only common in everything because they’re cheap and have tons of I/O options. Bad power will murder them in no time. It didn’t even get a chance on this one as thermal runway at the terminals Popped It.
Well then, all that resolved, it was time for the last silly task of the day: go see why the surveillance camera up top was giving us no usable image….
It’s done. It’s working. It’s……. perplexing as hell……
And I think it was just merely DIRTY!!!
So I was working on the Space Station Toilet again today. Over the past few days I had been gradually baby stepping it back up to normal output power from zero, and today after several crowbar dumps I almost entirely gave up on it before deciding…. hey, maybe that isn’t the tube, but something else. Something externally… arcy sparky? Anyway..
The first thing I decided to look at was the grid voltage setting. This is described in very short in the manual – you want to hook up a spectrum analyzer and adjust the grid voltage first so that you have less than 800mA cathode current with no drive, but then so you have the best possible shoulder attenuation without excessive cathode current once you have applied drive. In theory, it sounds like you should basically have a sweet spot in between the two. In practice…. I found that varying the grid voltage one step at a time allowed me to find a narrow peak. On one side I had excessively tall shoulders like some kinda wild vintage dress from the 80s, on the other side, the shoulders would abruptly pop back up accompanied by the amp faulting out on high collector current on collector #3 or #4, but without the cathode current being all that high compared to that on the other amps. Weird but, uh, ok.
So once I had the grid peaked up nicely, I decided to try running more power. I got to 100% of normal output and it was stable! Then I walked away and walked past the cabinet again and *BANG* *thump* *gronk* *screech* everything crapped out. It crowbarred and took down the whole UPS and caused the other two cabinets to stop and restart. A real fucko boingo, as they say UwU.
I tried bringing it back with the drive off. It thumped twice at the end of the quiescent verify stage and oopsie poopsied everything again dumping out its beamy weamy.
After about three cycles of not even being able to get into beam on with drive inhibited, I got very frustrated thinking the tube might have been damaged and kicked the cabinet. Now I was able to get into beam on again. Hmmmm…. Time to look around a bit. I shut off and grounded the rig for a look around. Now, this isn’t a picture of the same exact cabinet so you won’t see what I found but I’ll describe it…
The big silver suitcase looking thing is the “ISO Power Supply”. It is mounted on big insulating rails that look like they’re made of FR4 material or something similar. I was inspecting the high voltage leads above that go to the tube when my coworker and I noticed big oily sticky patches on both sides of the ISO supply case.
There was no apparent source for any oily substance to have dripped down onto the supply, so I pulled it out and opened it just in case I was missing something weird like a leaky oil filled cap that managed to get junk everywhere. The black plastic latch releases and it opens like a briefcase… Here’s what it looks like on a spare unit we have.
Left side — Top left: grid bias supply (up to about -300vdc, up to 50mA or so). Top right: filament supply (variable to at least 6.5v, uh– 20 amps?). Right side — left: ion pump power supply (-3.5kv, few microamps). Right: microcontroller with optical canbus I/O.
Well, on this one, something jumped out at me right away, and with that, the light came on.
The arc tracked layer of filth came off with a little careful cleaning. Where it was located, it would have been arcing right near the logic side of the grid voltage supply, perhaps glitching it out. Now, one of the things that varying the grid voltage does is to cause the cathode current to change.
The way the transmitter detects a damaging arc inside the eev ESCIOT inductive output tube is by looking for sudden noisy jumps in the cathode current. The supply wire runs through this big toroidal transformer on the “Spark Gap Interface” card.
The white object that looks like a big bottle stopper is a triggered spark gap tube. There are no power or signal connections to this card. All it does is if the current on the wire looped through the transformer at left, it rectifies the resulting ac current to DC, and uses the transistor hidden partially under the wire here to pulse the primary winding of the black trigger coil. This causes the spark gap unit to arc over, abruptly forcing the beam supply to ground and causing an ugly high current fault…. but protecting the tube from damage.
And what else could have been making the beam current dance and fire the spark gap? Yeah— a glitchy grid supply which would make the transconductance of the tube do the fandango.
And now the ridiculous beast is tame, running full power, big wattage, no whammies.
Yeah so now I know why nobody ever does the grid scrub / ESCIOT outgassing procedure on this thing– it makes it nigh fucking impossible
Yeah sure just leave it in standby while ramping up the grid voltage aaaaaand I’m just going to keep repeatedly kicking out into BG Heat and reducing the filament voltage to make your life interesting.
So yeah after I managed to get the dumb thing through the grid scrub and tried to put it back on air I experienced a very loud and through “oops I’m crowbarring and taking the whole plant down with me as I go” incident due to an arc in the tube at just 8 kilowatts output, it really isn’t ready to go back to work and is being a spicy little electron box.
Hmm, weird….. There are three different sets of CPUs and RAM in there!
what. WHAT. It left the factory like that. It passed “QUALITY” CONTROL. What.
You know what? I never want to see this again and maybe they were doing us a favor by using those crappy screws on the top cover where you have to drill out one or two because they’re galled and the head is made of pure nacho cheeze.
With the assistance of Jack Davis (Jackpot Engineering), we got in there and changed out the tube body cooler ring, and the whole thing lived to tell about it…
I didn’t get pictures of the process because my hands were two of the six hoisting parts on and off of the thing, but here was the process:
Remove tube cart, place under chain hoist.
Pluck out tube.
Unbolt input cavity/socket assembly from below, drop it down and remove.
Remove bolts holding secondary cavity to cart legs and remove screws from underneath that hold those four round black vertical standoffs to the top plate of the cart. Hoist the top of the cart up a few inches.
Unbolt and remove grid ring cooler.
Admire the corroded mess.
This looks as if water may have been slowly getting out INSIDE the ring in addition to the externally visible leaks down on the lines feeding it, it was DONE. Please note the heavy coating of black silver oxide. This continued to make itself known throughout the procedure.
This was leak #1 down…….
“Does anyone know the last time the ceramics of the tube were cleaned?”
So, good cleaning of the tube is vital as there’s a BIG voltage gradient across the large white ceramic cylinder, as well as between the filament (innermost two rings) and the next ring up, assuming that’s the ion pump (3.5 KV!)….
I didn’t even realize the very bottom there had a ridged porcelain bushing around it – it looked to me like some kind of dull finish aluminum alloy piece from all the mess stuck on it.
Note the spot where I wiped it with my finger which came away black. I guess this also illustrates where all the air gets sucked out at time of manufacturing – it’s got a center exhaust like a light bulb!
The unglazed part of the bushing appears to just be permanently stained. I even tried Scotch-Brite pads on it. The glazed outside cleaned up perfectly.
And now, time for some massive, ugly cleaning.
Ever had a faux leather case on something or a piece of clothing where the outermost texturized layer of the material started shedding, forming an evil sticky glitter-like flaky substance that sticks to everything and spreads everywhere like the DISEASE of craft supplies itself?! Yeah— imagine that, but made of silver oxide, CONDUCTIVE, and coating most surfaces of the output cavities. Gee, no wonder I was getting cavity arcs in the log every day or so. YAAACK.
Brush, vacuum, brush, vacuum, bleeech.
Finally it was time to put it all back together, at which time I experienced leak number 2 — one of the Hansen couplers blew its o-ring and started spraying water down the back of the tube cart. These things work just like pneumatic line couplers you may be familiar with from air tools, just, big and angry and stuff. You can’t see it well at this angle but there’s a hard nylon ring up inside there followed by a rubber gasket. The rubber gasket had ceased to be, just like any of the Barnstead filter gaskets every time you look at them wrong.
So I left the amplifier running into the combiner load overnight, came back the next day and found a nice puddle of red splooey on the floor below the external glycol piping behind the cabinets. LEAK #3!!!
The source was the mid-body seal of a ball valve that literally would never have been touched since the day the transmitter cooling system was filled up and made ready for the rig to go on air. It’s a valve that’d let you bypass the outdoor heat exchangers and just circulate the Dowtherm glycol solution through the pump/tank unit and the amplifier cabinets. I’ve never seen a ball valve fail this way before. have you? Probably not. IT’S JUST POWERFULLY CURSED OK
COVER WITH J-B WELD, FULL SEND, BYE
Finally, Leak #4 happened on some of the blue hoses at the Barnstead filters, I was so done with this thing I didn’t take a picture, just cut the hose a little shorter and smashed it back onto the fittings, BYESIES
So that’s the tale of FOUR LEAKS on the Harris PisserCD.
Stay tuned for when I attempt a grid scrub / outgassing procedure on this stupid thing which has been last performed probably about when the tube ceramics were last cleaned, which is to say, oh, half a decade ago. -29mA grid current? Ok yeah sure thanks for that. What else is even left on this thing to leak??