Paging Jim Wilkins

Interesting gizmo for probing circuit boards. Looks a bit clunky for what I used to do but would be nice it you did a lot of the same board repairs :)

=== Troubleshooting a circuit is easy, right? All you need is a couple of hands to hold the probes, another hand to twiddle the knobs, a pair of eyes to look at the schematic, another pair to look at the circuit board, and, for fancy work, X-ray vision to see through the board so you know what pads to probe. It’s child’s play!

In the real world, most of us don’t have all the extra parts needed to do the job right, which is where something like CircuitScout would come in mighty handy. [Fangzheng Liu] and [Thomas Juldo]’s design is a little like a small pick-and-place machine, except that instead of placing components, the dual gantries place probes on whatever test points you need to look at. The stepper-controlled gantries move independently over a fixture to hold the PCB in a known position so that the servo-controlled Z-axes can drive the probes down to the right place on the board...

Leon Fisk Grand Rapids MI

------------------------ That's an interesting idea that might help a less experienced tech troubleshoot a fault, but I think it would be too slow for most production line testing compared to other alternatives. For surface mount a fairly common fault was a failed or intermittent solder connection and the pressure of the probe might temporarily cure the problem, masking rather than revealing it, while a more experienced tech might recognize the visual or tactile clues to a bad joint while probing it. Since about half of all field returns test OK (operator error or dirty contact) it could be sent back with a hidden fault waiting to reoccur. Much of the time I found problems by visual inspection or dragging a needle probe over IC pins and listening for a change in the twang pitch when the needle struck an unsoldered pin. Another hint is the way a ceiling light reflects off the solder as you move the board or your head. A good joint should show a continuous reflection from the curved fillet, a bad joint may have a break in it.

When I was a tech at Unitrode they had wafer probers to do that on bare ICs before they were cut from the silicon wafer, or if packaged without a lid. Several probes were needed, at least two for powering the chip and others for applying control levels to inputs, injecting a signal and observing the output. Usually the probe went on the bonding wire pads but the silicon nitride protective coating could be burned through with a laser to reach the metallization underneath.

Automated test equipment goes a step further with a probe card having a probe pin for each bonding pad on the device. The pins are small enough to probe all of the adjacent pins on a data or address bus, and can test a memory chip while it is still on the wafer. Bad ones are marked with a dot of ink. Wafers with too many ink dots went into the scrap bin and many subsequently became wall art. For assembled boards there are several approaches that trade initial fixture cost for testing speed, depending on the production volume. An example is a "bed-of-nails" fixture with spring-loaded Pogo pins under or above test point pads placed by the board designer. They also can check the bare board for shorts or opens before assembly. When possible a circuit can be designed for "Boundary Scan" testing using only a simple added connector.

I could hold one or two scope probes steady on a tiny part. Usually for a prototype that the design engineer would test I extended the component pads a little to give room to solder on a fine wire to clip the probe to, plus a nearby ground to avoid distortion of high speed signals.

A potential problem with it is requiring the schematic and circuit board database to be in or convertible to a format it can use. The "PADS" layout system I used outputted Gerber photoplotter files, or a DXF file that nothing else could read. Although PADS included schematic capture I've seen and used only the more sophisticated Viewlogic for schematic design and simulation. The two were not completely compatible and sometimes needed manual file tweaking that was beyond the skill set of the usual board layout person. For example although it had been contracted out I had to do part of the board design for the geometrically complex Segway Balance Sensor Assembly.

I'm sorry you have the wrong number.

<snip>

Used to do similar. We replaced the scope probe tip with a short piece of sharpened antenna rod. Big help for keeping it from slipping off. Also did the same soldering bits of wire here and there to clip onto. Circuit speed wasn't a big issue when I was doing CRT Terminal repair. Like ADDS, TeleVideo, Wyse and even a few Heathkits back in the early

1980's. We didn't really have a jigs or prober type stuff. Needed whole units to power up assemblies/boards.

I had a couple loupes, hand magnifiers, hand-help "microscope" and different light sources. I'm really near sighted which was helpful for inspecting boards for suspicious solder joints and such.

You were on a whole nother level than me with just a couple years electronic tech school training...

Oh, it was a group page.

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I was handed a problem the Ph.Ds in another department couldn't solve, involving data corruption in 74AS logic. I requested the inner plane artworks and immediately saw that it had low speed single point grounding in the center, like a squashed starfish. The data bus that was failing crossed between arms of the ground plane about 3" from the junction. On a hunch I put a probe tip on the ground on one side and probe ground on the ground plane on the other, and triggered on the data. Sure enough, the scope captured a 3V ground bounce spike between the sending and receiving devices during the nanosecond data transition. Hey guys, you don't have to take a lab tech's word, the scope demo shows your problem.

Episodes like that probably made resentful enemies but I was given more and more design responsibility comparable to the degreed engineers.

At another company I had learned to consider the power and ground paths as a transmission line that becomes an integral part of the signal path instead of as infinite sources and sinks. At the time 50MHz was high speed, the lessons were still valid later above 1GHz. That company applied single point grounding correctly, with separate grounds for analog, digital and precision measurement, and designers had to account for and minimize the signal return current through the common junction, to a few milliAmps for the measurement circuits, in a machine with perhaps 100A of 5V TTL logic power. Even the

+/-15V op amp supplies were over 20A, yet it could accurately measure microVolts and picoAmps. I mention this to share it.

The Army school was supposed to teach how to undetectably repair a board coated with Humiseal, but the instructor couldn't teach what he didn't know, so I actually had less than an hour of hands-on soldering training and learned most of it on the job by trial and error, as components and traces became smaller and smaller. Pulling the solder through folded paper to wipe it clean of oxide is a considerable help.

That was in the hands-on repair class where they would disable a machine by installing an open dummy fuse, to teach us to check them with a meter. They had heated and removed fuse end caps to insert a label "good fuse" or blue (blew) paper or heavy but too short bus wire. I caught on quickly, then stood with the instructor watching others remove, examine and reinstall the fuses and continue troubleshooting. The overall graduation rate for that 40 week course was under 5%. Those who failed could try other MOS schools.

jsw

Oh, it was a group page. Bob La Londe

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It might possibly be a group interest. Everyone breaks stuff.

I just fixed an electrical fault in an immobile mobility scooter I bought for $100 at a flea market. Hopefully having one means I won't need it, cheap insurance. If my knee goes out again I have it on hand. At my age I may loan it to friends or family while they wait for Medicare.

My wife has been making noise about wanting an electric mobility scooter for large events she still goes to. BlizzCon, Cochella Music Festival, etc. The problem is she wants something that folds up to fit in the back of her Veloster Turbo and can be lifted in and out with some sort of crane.

I once questioned her ability to load a weeks worth of camping gear and supplies in a Miata, so I'm not saying its impossible. Just not easy.

If I went to these events it might be easier. I could muscle the the thing around a little bit as needed, but that is no longer medically allowed for her. She may have the strength, but it could aggravate or damage surgical repairs.

The problem with me going is that I actively dislike video games that suck huge portions out of a person's life, and I am ambivalent about most modern music. I am quite happy to not play mega massive multi player online games ever or have them waste any of my life, and I'm more than happy to catch a modern band or performer's one or two truly inspired songs on the radio where I don't have to sit through the 20 pieces of garbage they wrote so they could fill an album. I certainly don't want to waste a week on either of those things.

<snip>

Maybe look into getting a hitch for it. Seems they make some. Not sure if it would be heavy duty enough...

Then you might be able to add a hitch hauler that just tips or has a ramp to load it...

My wife has been making noise about wanting an electric mobility scooter for large events she still goes to. BlizzCon, Cochella Music Festival, etc. The problem is she wants something that folds up to fit in the back of her Veloster Turbo and can be lifted in and out with some sort of crane.

I once questioned her ability to load a weeks worth of camping gear and supplies in a Miata, so I'm not saying its impossible. Just not easy.

If I went to these events it might be easier. I could muscle the the thing around a little bit as needed, but that is no longer medically allowed for her. She may have the strength, but it could aggravate or damage surgical repairs.

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need solid frame members to attach the base to, that will support the cantilevered load. Like everything that may be chargeable to Medicare they ain't cheap. I originally bought the CRV to carry mobility equipment plus vacation luggage for the folks. It could never be mistaken for a sports car. Maybe a delivery van.

The ~20 year old scooter I bought weighs 98# assembled but breaks down into ~30# or less pieces, the heaviest being the AGM battery pack and the rear drive assembly which both have good top handles. You have to be able to bend low or squat or kneel to disassemble or reassemble it. I couldn't find a lighter Lithium battery in the 12V, 12Ah form factor it takes that would supply more than a third of its amperage rating.

When I worked for the medical supplier I had to unload them from trucks without so much as a ramp to slide them down and some weighted 125#, enough to cripple me so I'd need one myself.

<snip>

I don't try to show up the young whipper-snappers anymore and let them have at it if they offer to help nowadays😉

For the compact foldable ones I had an idea for a frame that sets inside the car. Lift straight up. Pin to trolley on rail. Slide out on extendable rail. Minimal pulling effort on cart or extend with gas spring. Lower straight down. Unfold. Can be operated with an electric cable winch. Could possibly be locked in place with vertical jack members, bolted through cargo area bed, or tied into cargo loops depending on specific application. Light weight foldable carts only, but that is what she wants.

I had a buddy who sold and serviced electric mobility carts for a while. I've still got a couple fairly powerful DC motor around here he gave me from scrap carts. He did all his sales and service out of a mid size van.

He had one cart that was really an adult size electric bicycle/trike he used with a bicycle trailer for hauling stuff at swap meets and fairs. I think it was way to fast to be "legally" an electric mobility device, but he got away with it.

<snip>

I don't try to show up the young whipper-snappers anymore and let them have at it if they offer to help nowadays😉

Leon Fisk Grand Rapids MI

--------------------------- As the new guy I was specifically assigned the task. I talked Segway into buying me a platform stacker for similar heavy lifts, which had injured the tech I was substituting for. I had convinced the medical supply company to buy a hydraulic scissors table instead of crawling on the floor to work on scooters but it didn't lift near enough to loading dock height and was a tipping hazard itself if something fell on it near the edge.

For the compact foldable ones I had an idea for a frame that sets inside the car. Lift straight up. Pin to trolley on rail. Slide out on extendable rail. Minimal pulling effort on cart or extend with gas spring. Lower straight down. Unfold. Can be operated with an electric cable winch. Could possibly be locked in place with vertical jack members, bolted through cargo area bed, or tied into cargo loops depending on specific application. Light weight foldable carts only, but that is what she wants.

I had a buddy who sold and serviced electric mobility carts for a while. I've still got a couple fairly powerful DC motor around here he gave me from scrap carts. He did all his sales and service out of a mid size van.

He had one cart that was really an adult size electric bicycle/trike he used with a bicycle trailer for hauling stuff at swap meets and fairs. I think it was way to fast to be "legally" an electric mobility device, but he got away with it. Bob La Londe

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Good idea, I've considered something similar on wheels to hoist new shingles up to the roof. The problem may be finding stock for the extensible trolley rail, and a trolley with wheels that fit it. On one storage shed I bolt the temporary outdoor extension to a fixed inside track and place an adjustable support under the outer end. I had to modify a trolley to use back-to-back C channel for the rail and made a trolley from scratch to bolt to an HF

1300# electric winch. The HF trolley's wheels are too large for 3" C channel unless turned down. You don't want the trolley or extension moving on its own when the vehicle's rear sags as the load moves outward.

An advantage of two C channels over a solid track is that it can be suspended or spliced with a plate or rectangular tube between the halves, without blocking the trolley.

I've built a number of hoists and my favorite for loading into a vehicle is a pickup bed crane.

've used it to winch logs to the trail and lift them onto a sawbuck to cut to firewood length.

I bought the low profile one and made an extension mast for taller bulky items like my TIG welder. The base isn't seriously in the way when not in use. They are heavy but simple enough to fabricate for smaller loads from lighter stock, or aluminum if you can weld or even bolt it together.

The boat winch pins to the boom and can be moved to my truck's front ladder rack to winch small vehicles like a riding mower up ramps. A scooter would be easy to disassemble at the top of ramps, a minimalist solution that requires only folding ramps and a small winch with added mount or eye bolt. Swinging a crane load in risks damaging the car, especially if it isn't parked dead level.

I would suggest this temporarily while you are finding and installing a small electric winch, though the brake on mine has become sticky and jams, possibly from overloading it.

The one incomplete discarded Bruno hoist I have uses a web strap instead of a cable.

Today at the flea market I bought a folding box collapsible hand truck for $5 and was towing it around with the scooter like a trailer. One of the locking clips was missing, I think I can bend a replacement from stiff wire.

A hoist geometry that's worked well for me is an A frame on pivots or ball joints at the bottom. It picks up the load on one side, swings and lifts it over the center and lowers it on the other. If the load isn't too heavy a strut stop inside and restraining rope for the outside might be enough. For a scooter the frame might be rectangular for clearance, an A works fine for logs. The lever chain hoist hanging from the top simply lifts straight up and lowers straight down.

I was thinking something that looks like a roll cage. Maybe two upper cross members and 4 support posts (made from two pieces of bent tube), and the rail/trolley being mounted on something "like" a full extension drawer slide. I did a quick sketch, but the only person who would understand it is me.

------------------ That's how I read your description. If I was doing it I might bend a sample frame from EMT to test the idea and find necessary clearances. When I tested

10' lengths for column strength 3/4" EMT bowed at 120#, 1# at 360#. Shorter lengths are stiffer, the 1" diagonals for my ladder rack held 750#, the stake pocket eye limit. I don't make orders to metal suppliers that I could add to so I use what's available locally, after testing its limits.

The gantry hoist on my shorter beam storage shed is similar, the indoor section is permanently attached to the shed beams at both ends. I quickly found that the track needed to be continuous for the full length of the permanent inside and temporary outside extensions instead of rolling or sliding out, to better control the load by hanging it from both sides (log ends) instead of only the center. The trolley wheels have unavoidable static friction and starting the load in motion sets it swinging, and twisting if it can. I couldn't fill the shed with logs if I had to crawl in to disconnect a central sling, plus that's dangerous.

On my scooter the battery pack locks the front and rear sections together, it has to be lifted with a centered sling either intact or fully disassembled, though lifting by the ends without the battery pack is OK. It can be compressed vertically while otherwise intact by removing the seat and its post and folding down the tiller, whose shaft becomes the front lifting handle.

A difficulty with moving the track while loaded is you may have to lower the load at mid travel to do it, perhaps damaging the trunk rim or losing balance. I have a similar problem with the 16' gantry, the central A frame is in the way, but resting a log on the ground to step the legs over it is not unsafe or damaging.

Your frame can be simpler and lighter if it only has to support the weight of the load, instead of 2 to 3 times its weight for a cantilevered track that moves out and isn't supported at the outer end. The drawer slide rollers would be particularly stressed as they moved close together. The scooter has to move not only its own width, but the distance from the trunk rim to the bumper edge. If assembling an extended track proves too much you have most of what you need in place to change it to a telescoping one.

I have that problem with my truck crane. The crane and bed load rating is

1000# but 700# on the hook beyond the open tailgate compresses the suspension against the bump stops, and broke the crane side one.

For light loads the outside extension could be pivoted at the joint which would make attaching and supporting the outer track very simple, an A frame should be enough. Mine is more complicated to handle 3/4 ton logs. If there were inner and outer pivot holes on the end of the fixed track the extension could be pinned to the outer one, raised and attached to the A frame, then moved to the inner one to close the track gap. This avoids balancing it level with one hand while trying to align and pin it with the other. A small gap might be needed so the track joint could pivot as the car suspension moves, instead of becoming a high stress concentration.

I have 80# of track to lift overhead and attach at both ends so I balance both 40# channels separately on scrap wood placed across the rungs of a W fold ladder that can be lifted off afterwards. My helpful neighbor can't lift his arms above shoulder height to assist, I tell him that's because Marines never surrender.

1" EMT telescopes into 1-3/8" chain link fence top rail to make the A frame sectional for storage in the trunk. The top rail is swaged smaller on one end so it can be cut in half to disassemble for storage too, though the swaged end fits loosely.

You could look into a discarded garage door opener for the track and rollers and maybe other parts.

Generally 1/2 and 3/4 EMT is pretty affordable tube. Rigid metal conduit is functionally about the same as schedule 40 water pipe, and its priced like it which I consider to be pretty expensive these days. There used to be a nice compromise called IMC. Intermediate metal conduit. Technically it still exists, but last time I looked I was not able to find any locally. With one "supplier" it was a bit of a chore to even find out they didn't have any, "but they could get it." A brick and mortar industrial supplier who doesn't stock things is worse than worthless. Several phone calls and emails and voice messages lead me to the point where I realized the salesperson just wanted to "establish a relationship." I didn't want to date the asshole. I just wanted a price. I guess he was hoping he'd seduce me into wanting to buy his friendship with over priced crap. Finally I gave up and called the store instead of trying to use their quoting process. The guy who answered at the front counter gave me the first honest sentence in a couple days of bullshit. "We don't stock it, but we can get it for you." I never did get a price.

Anyway, there used to be an intermediate conduit at an intermediate price that was a little stronger than EMT and not as expensive as water pipe. I used to be able to buy it from local electrical suppliers. I think at one time they even had it in Home Depot, but that was when they first opened here and were trying to see how many other businesses they could make go bankrupt. After they hit their watershed they started cutting selection and raising prices.

Generally 1/2 and 3/4 EMT is pretty affordable tube. Rigid metal conduit is functionally about the same as schedule 40 water pipe, and its priced like it which I consider to be pretty expensive these days. There used to be a nice compromise called IMC. Intermediate metal conduit. Technically it still exists, but last time I looked I was not able to find any locally. With one "supplier" it was a bit of a chore to even find out they didn't have any, "but they could get it." A brick and mortar industrial supplier who doesn't stock things is worse than worthless. Several phone calls and emails and voice messages lead me to the point where I realized the salesperson just wanted to "establish a relationship." I didn't want to date the asshole. I just wanted a price. I guess he was hoping he'd seduce me into wanting to buy his friendship with over priced crap. Finally I gave up and called the store instead of trying to use their quoting process. The guy who answered at the front counter gave me the first honest sentence in a couple days of bullshit. "We don't stock it, but we can get it for you." I never did get a price.

Anyway, there used to be an intermediate conduit at an intermediate price that was a little stronger than EMT and not as expensive as water pipe. I used to be able to buy it from local electrical suppliers. I think at one time they even had it in Home Depot, but that was when they first opened here and were trying to see how many other businesses they could make go bankrupt. After they hit their watershed they started cutting selection and raising prices. Bob La Londe

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I use conduit in the smaller sizes I can bend with the manual tool, then as loading increases change to water pipe or square tubing with joints prepped on the milling machine and stick welded. Flat sided tubing is nicer to attach to the side of, round to fit something to the end.

Rigid conduit is effectively water pipe without the interior weld flash, and possibly closer to round. I haven't seen IMC either and have been satisfied with what I can do with chain link fence post, which is available with thicker gauge walls from fence suppliers. Its OD is the same as water pipe though the nominal size may differ, being closer to the actual measurement, which isn't an exact fraction for sizes below 2". EMT has the ID of the same nominal size of water pipe, so in some sizes it can telescope with Big Box thin-walled fence post.

If I was building this for myself instead of suggesting how to accomplish it your way I'd add a post or other single point attachment at/near the front of the trunk and support the other end of the gantry hoist track with an external folding tripod. I came up with a design for a tripod in the 90's and have used it extensively since, mainly to lift firewood logs to cut them at waist height because I can't bend down for long and the ground here is all sand/gravel/rocks.

I've held off describing my tripod top connection because it may be unique and possibly patentable, at least I haven't found another instance of it on commercial products. The legs are free to move in all directions and visibly self-adjust to distribute the load, how evenly I don't know. I've assumed k=1 for column loading of the legs, pinned at the top and a ball for the foot, axial with no or minimal cantilevering. The angular geometry is somewhat variable and too 3-dimensional for me to calculate. It's so simple to do that there is nothing to manufacture and sell, anyone with a drill and hacksaw could copy it. Should I reveal it here for comments? jsw

In a past life I ran a fair amount of conduit. I have bent upto 1-1/2 EMT with a manual bender, but I didn't like it. 1/2, 3/4 and 1 aren't to bad, and I still have lever/foot benders for those. When I had to run 2" speced for fiber optic runs I either bought prebent elbow pieces, or used a harbor freight hydraulic pipe kinker for custom offsets.

I want as little as possible that must be manually deployed before it can be used. As is I am struggling with even the fact that for my design to work there will be a minimum of two pins or latches that must be engaged or disengage during operation.

I am aware that the extended or telescoped rail is at a significant mechanical disadvantage. Not just from bending, but also from possible twisting depending on what can go wrong. My original thought in the regard was a "brace" or frame to either side that is attached the extended rail at the center, and rides in a support track at the outside ends. It is easy to make quite strong this way, but I also do not want to permanently obstruct 100% of the cargo space above the stowed cart. Jack posts in the back (towards the front of the vehicle, or support clamp towards the rear of the vehicle can be used to anchor it from tipping. That's rather small consideration in the grand scheme.

Fortunately the carts my wife is looking at are pretty light as electric mobility carts go.

I came up with a design for

I wonder if it isn't a variation of the old cooking support tripods. My son made one in a blacksmithing class he took in college for fun. He uses is at renaissance fairs in his "camp." He also made an adjustable length pot hook to use with it that simply slides to the length you want, and locks with the weight of the cooking pot.

That's entirely up to you. I am curious of course if your mechanism is really different, but if I found it particularly clever I would be tempted to copy it.

On 8/14/2023 11:41 AM, Jim Wilkins wrote: ...

I want as little as possible that must be manually deployed before it can be used. As is I am struggling with even the fact that for my design to work there will be a minimum of two pins or latches that must be engaged or disengage during operation.

[[The operator interface spec ultimately defines the implementation, otherwise you create VCRs that permanently flash 12:00 because the owners can't figure out how to set them. I'll guess freely until you realize I need to see it, then I'll follow it. When programming I write the user interface first to define the requirements and then make it happen.

With those requirements I have to repeat a frequently used German phrase from the PBS detective program Luna & Sophie, "keine Ahnung", "I haven't a clue." ]]

I am aware that the extended or telescoped rail is at a significant mechanical disadvantage. Not just from bending, but also from possible twisting depending on what can go wrong. My original thought in the regard was a "brace" or frame to either side that is attached the extended rail at the center, and rides in a support track at the outside ends. It is easy to make quite strong this way, but I also do not want to permanently obstruct 100% of the cargo space above the stowed cart. Jack posts in the back (towards the front of the vehicle, or support clamp towards the rear of the vehicle can be used to anchor it from tipping. That's rather small consideration in the grand scheme.

Fortunately the carts my wife is looking at are pretty light as electric mobility carts go.

I wonder if it isn't a variation of the old cooking support tripods. My son made one in a blacksmithing class he took in college for fun. He uses is at renaissance fairs in his "camp." He also made an adjustable length pot hook to use with it that simply slides to the length you want, and locks with the weight of the cooking pot.

------------------------ There are no friction locks on the tripod, though I use them in preference to mechanical devices on rope.

the faster to tie tautline hitch.

It's just bolts and short chains, connected in a way that may not seem right at first but survived 3000# proof testing on a stump.