current-carrying noodles

As I await my order from Digi-Key for my turbopump power supply re-cap project, I decided to address the other known issue related to that subsystem of my vacuum chamber: The power supply to pump interface cable. Fortunately, included in the vacuum chamber lot were both cables for the power supply, which are rarely included if you buy a used pump or power supply. Both cables are proprietary, and thus are expensive if you could even find them.

Unfortunately, one of the cables did sustain some damage. There was a cut through some of the outer insulation, as well as the insulation and a few copper stands of some of the wires. It wasn't too bad, and the cut wires were unlikely to cause any shorts, though I couldn't help but to think it would be stupid to take any chances that could just maybe result in expensive pump damage.

The two ends of the cable. I already unthreaded and slid back the cannon plug backshell 

Outer gray insulation jacket already cut back. Nicks in individual wires visible. 

Since the damage was closest to the circular connector, that's the side I'd have to fix. I deal with this style of connector quite a bit at work, and before I removed the backshell, I was somewhat worried that the individual sockets in the connector housing would be crimped to the wires, thus requiring replacement. Not a big deal if it has a US military part number, but this thing was made in France.... It ended up being soldered, and once I knew better, I wished they actually were crimped.

I ended up having a few issues, partly because I'm currently so ill-equipped at home. No vise. No solder sucker/vac. Those would have come in handy. I tried wicking some of the solder from the cups using wire. It sort of worked, but not ideal. The wire gauge is pretty close to the limit of what the cups can accept, which make it more annoying to work with. Secondly, I didn't have much wire length to work with after cutting them down and stripping them because I wanted the backshell strain relief to clamp down on the outer insulation. Once I had a few wires soldered in place, it pre-loaded  the other wires making it somewhat of a pain to work with. The only saving grace is that I only had to deal with the sockets around the perimeter of the connector, as the inside ones are unused. I definitely wasn't ecstatic over the results, but they were acceptable.

Finally got it all soldered up. Wait a second.... When the hell did I remove the backshell? 

NOOOOOOOOOOOOOOOOOOOOOO!!!!!!!!!!!!!!!!!!!

I decided it would be easier to de/re-solder the connector on the other end so that I could slide the backshell on.

Alas! All done. The wires ring out good with low resistance, and no inter-wire shorts. Now if only I could remember what the hell I did with the little cap that goes on the backshell.

power supply to the people

As mentioned before, one of the critical bits missing from my vacuum chamber purchase was a power supply/controller for the TPU 110 turbomolecular pump. Having looked through the pump's manual, I found that it called for a Pfeiffer TCP 270. Once again, eBay was my first and last stop. Perhaps somewhat surprising, there were quite a few available. I know this particular model covered more than one model of pump, so maybe that explains the selection available. The strange thing I've noticed as of late is just how wide of a spread in pricing exists when searching for specific items. One seller might be asking $30, while another is asking $1000. Sometimes the more expensive items are unused or rebuilt, but typically that's not the case. Nor is it necessarily the case that the more expensive items are in better condition. Often even those are listed as untested and sold as-is. Perhaps those sellers "know what they got"; in other words, something likely priced too high to sell.

Once again I opted to go the frugal route, and found a power supply that appeared to be in decent condition, with a "or best offer" option. Keeping with my purchase price modus operandi, I offered an amount that would place it slightly below $100 after shipping. My offer was accepted and I soon received it at my doorstep in a well packaged state.

Huh. The corner was bent, the gauge needle sat almost midway up the scale, and the "pumping unit" button was stuck pushed in. Who knows when the damage was sustained, but given the way it was packaged, it wasn't during shipping. At any rate, I didn't care about the corner or the gauge, but obviously something would have to be done about the switch. I popped it open to take a look (actually, I did that before I even noticed the switch)

Pretty good cable management, and nice old-school wire lacing 

Yep.. The switch took enough of a beating to crack the plastic nut. Removing the nut revealed access to a pair of retaining clips for the switch face. This is how custom switch faces are installed, as well as how the indicator lamp is replaced. I found that the switch operated just fine without the face installed, but there was nothing visibly wrong with the face either. After reinstalling it and toggling the switch numerous times, it seemed to work ok, but every once in a while it would bind slightly, or it wouldn't latch when trying to engage (it's a push-on push-off style). It was usable, but I decided to swap the two switched, especially considering my pump didn't have the heating jacket option anyways, so that switch would go unused.

This was a great opportunity to try out my new soldering iron...

Behold the power of bacon! Er, Bakon. Bakon 950D to be exact. Several years ago I donated my soldering station to the local makerspace, which was fine because I did all my soldering there anyways. Having decided to build up my home lab again, I was in search of an iron. I fell in love with the pencil design of the Pace ADS200. I came so close to pulling the trigger on buying one, but ultimately I decided against it. Realistically, at this point in time, $300 could buy me a decent iron and a bunch of other things. So then I started gravitate towards the TS100 or TS80, but despite the favorable reviews, I really didn't like that grounding the iron was kind of inconvenient. Next up was one of the many variants of the KSGER with a T12 type tip. But there were a bunch of different ones, made by who knows how many different manufacturers, with different power supplies, using different microcontrollers for temp control, and none inspiring too much confidence. Then somehow I came across the Bakon 950D (listed as Feita 950D on Amazon). While I'd probably prefer a unit that uses T12 tips, this one uses T13. Reviews were good, power supply design was proper with name brand active components (the caps not so great), and actual tip grounding. Per this thread, the unit drives the tip with a power of ~42 watts. The original poster of that thread also modified his, bumping up the output power to roughly 66 watts. Ultimately, it was his opinions of the iron that made me choose it. I might eventually replace the included pencil with something that uses T12 tips, and perhaps an almost ADS200-like finger to iron tip distance. 

So the unit might not look very impressive, with it's simple 7-segment displays, two push buttons, and it's wannabe laptop charger enclosure, but I was immediately pleased it during my first go. I've never used an iron with a directly heated tip, so that was game changing for me. Not only does it heat up significantly faster than anything I've ever used before, but it transfers heat to solder joints incredibly quick too. So here's the kicker: I bought the iron, which included 6 different tips, for a penny under $35. Incredible. I'd definitely recommend it to anyone in need of an iron, but doesn't have the budget for a Pace, JBC, or a higher-end Hakko.

Back to the pump power supply. Scrolling through the pump's manual, I came across this little bit:

Uhhhhhh.....

Ummmmm

Ehhhhh

Well two can play that game!

Problem solved.

Maybe not that easy, but close! This looks like a job for........

The ol' universal hacking device chip.

Dropped right into place. No soldering required. 

But all that solderless work was for nothing, because.....

Well that was easy! I was actually aware of this before ordering the power supply, because most of the ones for sale were set for 1000Hz, with the few 716Hz units tending to be more expensive. Even before learning about that resistor, I figured the difference between the two would be minor. Luckily it was much simpler than I originally assumed. 

TODO: change the electrolytics -- Just in case. Clean the dip sockets and IC legs. They look slightly corroded. 

getting pumped

I knew it would be prudent to take a better look at the Pfeiffer TPU 110 turbomolecular pump that came as part of my vacuum chamber purchase, especially given the issues sustained during shipping. Presumably for the sake of providing clearance to the rack mounted electronics, there was a sort of Z-shaped duct to push the pump further towards the rear of the cabinet as can be seen here:

That meant I simply couldn't look down at it from the inside of the chamber, so I had to remove it. After removing it, I found that there was a conflat copper gasket still attached to the flange on the pump, and another on the chamber side flange. I'm not aware of stacked gaskets being acceptable practice. There was also a groove cut on the upper side of the pump's gasket, indicating that it had been reused.

After removing it, I found that there was a splinter shield at the pump inlet, in conjunction with the coarse shield at the base of the chamber. The knife edge on the flange appears good.

Happily, the splinter shield was clean of any kind of crud or debris, and in excellent condition. Though more importantly, I wanted to verify that nothing too obvious was wrong with the pump itself. Thus, I removed the shield and gave the pump rotor a twist. It spun with buttery smoothness with not a hint of grinding. Granted, things that are imperceptible at an insignificant RPM, might manifest themselves in a more dramatic manner when this thing is running at full tilt under load conditions, maybe somewhere in the neighborhood of 40,000 RPM.

I did have a slight concern about the bit of oil found at the outlet port. The oiling system consists of two bearing chambers on either side of the motor, which have some sort of wicking material to provide the bearings with lubrication. Based on the internal profile drawing found in the manual, there only appeared to be a sort of splash shield separating the bearing chamber and the rotor/stator section of the pump, which seemed slightly bizarre to me considering that it is acceptable to mount the pump on it's side. I don't think anything is actually wrong, but I can't say for sure.

All that said, first impressions are overall quite positive. I have reasonable confidence that the pump is in good, operatable condition. However, I will at least give it an oil change.

department of trustworthy marketing

I've been wondering if package delivery people have been getting tired of delivering to my address as of late. Maybe I should leave some milk and cookies out on a table next to the fireplace as a sacrificial offering. Perhaps next time. For now they'll just have to be satisfied with my autograph. That's actually a lie; they're not requiring acceptance signatures due to COVID-19.

Obviously I mention this because I must have received yet another thing in the mail. Another eBay buy, naturally. Nothing too fancy, but rather just fancy enough.

What we have here is a GW Instek GDS-1022, a basic, somewhat dated and low-end 25MHz Digital Storage Oscilloscope. For just shy of $100 shipped (not including $15 worth of probes), I'd argue it's a decent deal, and ticks pretty much all the boxes to suit my needs. As it turns out, these $100 purchases are somewhat of a reoccurring theme with me. You can get an impressive amount of hardware for that money. One thing I forgot to mention in that whole vacuum chamber debacle is that I received a partial refund from the seller due to the damage caused by lousy shipping prep. How much did I get back from the $260 winning bid? $100, of course.

Back to the scope. It's about as basic of a DSO as they come. It's a 2 channel, with a 25MHz bandwidth, and a claimed 250MHz sampling rate, with an abysmal 4k points recording length. The display is 5.6" with a fairly crap 320x234 resolution, which isn't surprising given that this thing is probably from the late 2000s. I didn't merely choose this device only because it was among the cheapest DSOs I could find (it was), but also because GW Instek from Taiwan is arguably a bit more reputable of a brand than some of the cheapies hailing from mainland China and sold new via eBay or Amazon which have pretty much non-existing warranties. Better to be out $100, than closer to $300.

Like far too many other software-heavy devices, the GDS-1022 shares most of it's technical specs with it's "higher-end" brethren. Meaning that this, and every other model below the top range 100MHz unit may have it's bandwidth limit set artificially via software. I can't say for certain that this is the case, but I think there's a very good chance that it is.

Things that I like:
Overall the menus are simple and intuitive. Separate volts per division and vertical offset knobs for each channel is appreciated. The unit isn't some heavy beast, but I think that thanks to it's physical depth, its quite stable when pushing buttons. The same can't be said for some other modern scopes. No frills. It does basic oscilloscope stuff but with the digital niceties such as various signal measurement capabilities and transient capture+store not found in analog units.

Now that I know it actually works, it's time for a quick teardown.

Here's the back cover removed. All it did was add some rubber feet, stickers, and a consistent look to match the front plastic. Seemed a bit unnecessary, but a nice touch that maybe adds a little bump protection. The top, bottom, and sides are all exposed chassis sheet metal.

The top/sides of the chassis is held in with 3 screws and, with a little effort, slides right off. I like the sheetmetal design and quality, and find the overall mechanical construction of the scope to be pretty good. As for the electronics, the rear side unsurprisingly contains the power supply (including LCD backlight inverter) save for a USB and calibration coax breakout board, with the rest of the electronics mounted to the front.

I'm not an expert, but the power supply seems like a pretty standard fare, with nothing too egregious going on. Sure, there might be a TO-220 or two "flapping in the breeze", but Dave Jones doesn't need to know about it. All the wires are terminated with a connector, which tends to be appreciated. The electrolytics appear to be Chemi-Con brand. Sadly, the same can't be said for the main board.

And here's the big money bits. On the digital side is an Altera Cyclone II FPGA and a Max II CPLD, plus some flash and ram. No idea what the CPLD is for. Interestingly, there is no CPU IC anywhere as far as I can tell (unless it's hiding on the other side - doubtful), so it likely has a soft core implemented in the FPGA. The analog input section is probably a partially discrete design? Most of the ICs are pretty standard op-amps save for a 4:1 buffered "video" mux. Immediately to the right of the shielding and doing some hocus-pocus to the input section are 8-channel analog mux/demux's.

Then there's the (single) ADC... It's an Analog Devices AD9288-100; a 2 channel 100MSPS part. But wait, GW Instek claims the scope has a 250MSPS sampling rate. What's going on here? They're either overclocking the chip by 250% (doubtful), or they're overclocking by 125% (a little less doubtful), then, by the magic of marketing, adding the sampling rate of the two channels together and claiming 250MSPS. The manual, unsurprisingly, does not specify. Also, from just my quick glance at the PCB, it looks like the output of each analog front-end connected directly to one of the two inputs of the ADC, so unless there was something else going on in there, I don't think they fed any channel to both inputs, and then sampled each ADC 180^o out of phase from each other. It's possible, but the manual doesn't specify different sampling rates depending on how many channels are operating, unlike some other manufacturers. But lets give them the undeserved benefit of the doubt. Still, 250MSPS is pretty much only good enough for 25MHz bandwidth. The 100MHz unit with the same sampling rate would do what to a complex 100MHz signal?

Prior to purchasing this scope, I did some due diligence and tried to find whatever info I could. There was so little info it almost seemed as if they didn't exist. There was a post (I believe on the EEVblog forum) by someone who noticed this:

A 0Ω resistor next to a number presumably representing the unit's model number. In the image above, you can see it next to 1022, my scope being a GDS-1022, while the 100MHz unit is the GDS-1102. As I recall, the poster had a 1042 and attempted to solder the resistor into the 1102 slot. No change was observed, as the scope still indicated it was a -1042. Someone else mentioned that the firmware might need to have been reprogrammed to have the changes take effect. I kept this in mind when buying the unit as that would have been a cheap upgrade. But knowing what I know now, it's doubtful the "100MHz" version would be worth a shit. Still, I'm satisfied with what I have, and I think it'll serve me just fine. Time will tell.

transformers vs iron dude

This post will be about the remaining two rack units, and a quick look at what's inside them. As I mentioned before, this vacuum chamber appeared to be used for the purpose of outgassing some kind of filaments (for mass spectrometers, maybe?). Once again, here's what inside the chamber looks like:

The image isn't blurry... You're just drunk!

You can see 3 banks of filament holders here, with each bank running to one of three cathode heating current power supply sections:

No, I didn't take a crappy pic.. You're just drunk.. Still.

A look inside will reveal what's going on:

Pretty simple. Without having actually delved into it, line voltage comes in and is routed to the switches on the front panel, which then runs through the beefy wire wound pots (which all look to be in good condition. Nice!), setting the current through the primary side of the transformers. The secondary side goes through the panel meters and then to the filament banks. This is entirely AC. The interesting bit is the pink wire that's seen coming in through the rear of the enclosure to the right. Where does that go?

You can see the pink wire on the upper left side. The upper grey box with the twisted wires coming out of it is the power supply we just looked at. The lower box that it's plugging in to is what appears to be for setting the filament emission current, and so the pink wire carried that return current. This must have been a timed process, hence the timer. This was purpose built, and maybe one off equipment.

Center top of the last image shows a brown wire soldered to what looks like some kind of coax connector. This is connected to a plate mounted to the top of the chamber lid, partially visible in the first image of the post. That completes the emission current circuit.

I will need a filament power supply for my experiments, but I'll want it to be regulated DC. I'll probably reuse some of the above components for that purpose.

let ions be bygones

As seen in my previous post, the rack mounted electronics were some of the things that didn't fare so well during shipping of my vacuum chamber. The one that I really had any concern with was the Granville-Phillips GP 270 hot cathode ionization gauge controller. This type of gauge is used in the higher vacuum range of 10^-3 to 10^-10 Torr, for which most other vacuum gauge types are unsuitable. Of course, I wouldn't know the extent of the damage until I opened it up, so I did. Here's a peek:

As it turns out, the damage was limited to 5 of the 6 front panel toggle switches (top side of image), and bent LED legs, with a few of them breaking away from their solder joints. There are no cracks or lifted traces on either of the two PCBs. There's no apparent reason that would make this unit unsalvageable. The choice to be made is whether it is worth fixing. 5 switches really isn't a big deal, as well as a handful of red LEDs. The manual for this unit had a complete parts list, and it called out various C&K switches. These are relatively high quality parts, at least when the toggly ends don't go smashing into the ground with the force of a linebacker behind them. Therefore they aren't exactly the cheapest thing, and since most of them are different types from one another means I can't just easily buy a bag of cheap equivalents. Obviously I don't have a stash of switches, otherwise I wouldn't even be mentioning this. Ok, still, this is fairly specialized piece of hardware, so replacing several $5 switches must be the cheapest route, right? Right??? Sort of. Now, I could have potentially made the repair even cheaper since two of the switches are for toggling between manual and auto ranging. I could have just jumpered it to always be in auto mode and gone on my merry way, but as it turns out, it's necessary to go into manual mode for calibration purposes, so the switches would need to be there. Back to the point I was trying to make, yes, replacing the switches is likely the cheapest route if I wanted to replace this with the exact same model, but as it turns out, there are equivalents on eBay sitting in the $50 to $100 range. Some of these even support additional vacuum sensors such as the thermocouple types. These are useful for measuring a range of vacuum before the ionization types can function. If I repair the device that I have, I still need something that'll work with sensors for lower vacuum levels. As it turns out, for me, the total cost appears to be lower if I just replace this unit. If I buy a similar model with additional features, I can use what I have for spares should I need them. I haven't pulled the trigger yet, but I think this is the route I'll take.

And for your viewing pleasure:

shipping and manhandling

As I stated in my very first post, the intent of this blog is to primarily write about my experiments with electron vacuum physics. In order to do that, I need equipment capable of pulling a high vacuum - somewhere in the range of 1 × 10^-5 to 1 × 10^-6 Torr. Unfortunately, achieving this level of vacuum requires careful chamber design, material selection, and somewhat fancy equipment. Luckily for the budget-minded experimenters, eBay comes to the rescue. There are plenty of resellers of used research and industrial equipment, so it never ceases to amaze me the types of things you can find. Sometimes it's stuff I never even knew existed. Often for a tiny fraction of what it must have cost when new.

I've been keeping my eye out for equipment necessary to build a vacuum chamber, trying to get a rough estimate of what it would cost, and of course, any obviously good deals. You can find out more about what it takes to build such a setup by checking out Ben Krasnow's blog (specifically related to his incredible DIY scanning electron microscope) and Sam Zeloof's homemade ICs. As luck would seemingly have it, I found the following:

 An early R2D2 prototype, best I can tell

First off, sorry to anyone reading this who I may have outbid. I was pretty set on winning that auction, and win that auction I did. From the description, it wasn't entirely clear what it originally was for. Best I could tell, it was for degassing mass spectrometer filaments, but I couldn't really find similar examples online. Anyone out there reading this know? Leave a comment! The listing didn't say much other than it was a vacuum chamber and that it had a Pfeiffer TPU-110 turbomolecular pump. After gleaning through the available not-so-high res images, I determined it was basically a backing pump and a turbopump power supply/controller away from being a complete setup. The lowermost rack unit was the controller for the hot cathode ionization vacuum gauge, with the actual sensor visible in other images. The middle rack was obviously some sort of timer, and the top rack was a triple filament power supply for the 3 banks of filament sockets

There were some other random bits in there that I was able to verify after receiving it, such as an electromechanical valve, a thermocouple-type vacuum sensor, and some other process/safety-control related bits. 

I ended up winning the auction for $260! If the pump was in operating condition as claimed in the listing, that's a hell of a bargain. I was planning on taking a trip midway across the country in a rental van to pick it up, just to realize the seller specified no local pickups. That sucked. I would have felt much better knowing preparation and transport was in my own hands. As it turned out, my concerns weren't unwarranted. 

After the seller quoted me almost $500 to mount it on a pallet and ship it via freight, all I had left to do was to pay up and wait for it to arrive. It came in a week later, and basically the first thing the truck driver told me was that I need to look it over and decide if I want to accept it because it was damaged in transit. Ugh. We hopped in the back of the truck, and the first thing I noticed is that it most definitely wasn't on a pallet. Nope. This top heavy piece of equipment of nearly 400 pounds was shipped on it's own casters wrapped in a few layers of plastic film. I expected better from a seller with over 80k sales. Even without removing all the plastic, it was obvious that it probably did a few faceplants during loading and unloading in transit. 

I had to make a decision. Accept or refuse. Since I wasn't planning on using it for the same functions it was designed for, I didn't care about all the included equipment. My main concern was the condition of the chamber and the pump. The components of the chamber are pretty stout, and the damage looked minimal and serviceable. The pump itself was impossible to gauge. Did the bearings survive? Well, the ion-type sensor which is in a glass envelope did, so just maybe, or hopefully, the pump did too. Maybe you're wondering why I would even consider keeping it when I could just get a refund and start over. Truth is, it's very difficult to find and equivalent setup for such a price, and so I weighed the risk, and took my chances. Here is how it looked after unwrapping:

Not even good from far, and definitely far from good.

Some of the screws that held in the racks must have gotten stripped and popped right out. Each unit had damage. I'll detail the extent of those in a later post. For now, I'll give you more schadenfreude ammunition.