don't get cocky with old gear (don't turn it on, always take it apart) - Page 1
Forum section: electronics / testgear

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2021, 04:15:45 pm
content: So I got a keithley unit in the mail and the BNC connectors were tarnished and the main switch was dicky. I decided instead of turning it on to take it apart so I can clean up the connectors in the ultrasonic and replace the switch. I ordered the switch and last night decided to take apart the front and back panels to desolder the BNC and clean em up. When I was done I had a look at the mains input, and it looked all good, thin wires, turrets, nicely soldered up..However, upon closer inspection, there was a random piece (maybe 1 inch) of heavy gauge wire (the unit is like 20AWG, the random piece of wire was like a 14 or 12 gauge) soldered to the live portion of the circuit, torn and exposed on the non soldered end, and bent /wrapped around the mains inlet, about 0.5mm from making a short circuit to the chassis (or maybe it was shorted and I nudged it out of the way, not sure), bypassing the fuse. Unit did not look serviced, apart from 1 missing screw. It was not obvious from a quick glance. I think it would fuse to the chassis and blow the breaker (best case) if I decided to turn it on before taking it apartSo be sure to carefully inspect your input wiring from all angles when you get old shit from estate salesThis was a type of instrument that you would not think needs any service (keithley is normally really good compared to Hp etc, in terms of long term reliability, because they run puny currents through their stuff).. I have a bunch of their stuff and it almost feels like a stupid OCD thing to take their stuff apart because its usually really good (and expensive for old gear).

author: bob91343
author_rank: Super Contributor
timestamp: May 07, 2021, 05:11:48 pm
content: Sabotage?

author: Algoma
author_rank: Frequent Contributor
timestamp: May 07, 2021, 05:15:03 pm
content: "Estate Sale" ....

author: Black Phoenix
author_rank: Super Contributor
timestamp: May 07, 2021, 05:22:33 pm
content: Quote from: bob91343 on May 07, 2021, 05:11:48 pmWhy would anyone do that? If the objective is to have the unit not being sold into the 2nd Hand Market because of some regulation of a Government body who use it then they can simply destroy it in small little pieces together with some fire. Not sabotage it.If it was a seller then it is even more low standards if he sold it knowing that it had that problem, or made that on purpose for some reason I can't really point out other than being a "low life dumb fuck"!!!/rant OFF

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2021, 06:01:37 pm
content: Well, I think maybe someone had something weird in there, maybe a light bulb was soldered in there or something, to keep it warm maybe, or something weird like that. No clue why the hell you would put a high gauge wire there, because the unit has a 200mA fuse on the main, and there is no solder joints that would accept such a large wire even (its small signal stuff)I don't think they replaced the connector because the screws were tightened identically, like X X, and its all ny-lock and stuff that normally would not be used, + it has a old HP style 3 prong connector (non IEC), that looks original (same tarnish levels), + it came with the cable (so they had the correct cable) and all the original fuses are in there and they are weird ones that look original (keithley OEM).Also, getting the back panel off was difficult, 2 bolts were super seized, I needed to use the dremel with a cutting wheel to make a notch in the screws so I can take them out with a flat head because they were so tight they were stripping on me.I don't want to say the equipment name because I am not sure what I can do, but I see it has a inspectors tag from the factory. I thought to call keithley maybe, but I doubt they can help with 70's stuff. The only other thing I can think of is maybe someone grabbed it on the assembly line from someone else (maybe stole it off a work bench because they ran out of parts and the manager is mean, so they stole a connector from something high current and tried to yank the wires off in a hurry.. but it has a hand-initialed 'wire inspectors' initials on it (it has like 4 sets of initials on the label on the bottom).also the added wire looks like a silicone/rubber/soft PVC type insulation, its different then the rest of the insulation used in the equipment. I don't think its off the same wire rack, usually people seem neurotic about wire racks.I think they merged wire inspect and inspect (2 boxes) because one is not filled in, but anyway.. the stuff that looks like keithley is inspected or at least done correctly, they have some of the nicest BNC soldering I have seen. Someone was there with round nose pliers doing very good worksmanship...

author: nctnico
author_rank: Super Contributor
timestamp: May 07, 2021, 06:04:30 pm
content: I do a safety inspection on any piece of second hand or cheap Chinese equipment I buy.

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2021, 06:09:43 pm
content: but this is aerospace looking wire harness keithley from the golden age of electronicsthey spent ALOT of money doing this right, this was made before the bean counters started getting dirty with the gear IMO. thick gold plating, cinch card edge connectors, lots of strain relief, wafer switches, silver plated BNC, etc. the transformer is a fully shielded potted torroid. i bet it was mil spec. the potentiometer is also a special deal. I imagine it was made with highly paid assembly line workers singing and smoking pipes or whatever they did back then.I think someone was doing something with it, but what, i cannot imagine. the 'abnormality' is REALLY out of place.

author: wizard69
author_rank: Super Contributor
timestamp: May 08, 2021, 04:17:34 am
content: First off it is second hand so you have to assume it has been worked on. Further you can't really tell by simple visual inspection in many cases.As for modification to hardware I've seen big corporations do"interesting"things to off the shelf hardware. Sometimes you have to think that somebody took a stupid pill in the morning before taking on his engineering role. This includes things like taping into the AC circuit past the power switch to get AC power to drive an external device on a print engine. Usually these modifications are done without documentation and sometimes I literally believe to justify a position. A common one for the electrical engineer it to claim that a new tool brought into the organization doesn't meet NEC requirements and then demand that the electrician install a fuse block, relay or other hardware for the hell of it. If you are lucky the electrician will leave a sketch of the modification in the tool control cabinet, the engineer being too lazy to document his "work".So yeah it is hard to tell what happened here. It isn't like Keithly to engage in dodgy work so that kinda leaves the history of the machine open for inspection.

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2021, 04:21:10 am
content: usually I see something cut when there is a modification, this is just a weird addon. I still think its possible maybe they ran out of connectors in the storage box and someone grabbed some random crap and failed to clean it up. The wire is ripped, its not stripped and left into place, just like fray ripped.so someone would have to solder something in there, then decide to rip it out of the connector, its odd. then bend it over to hide itthere is like no room back there either, its a tight chassis thats completely filled with PCB cards, you have maybe 1 inch from the back to the first PCB and in that space you have a transformer in the middle on the back panel, a bunch of BNC connectors, selection switch, etc. You could maybe wedge a power resistor in there. not your typical open keithley box. I would say its85%filled in all three dimensions. There is not enough room for a film canister even, front or back, and the chassis is a fully overlapped shield.btw those fuses man i dunno if thats a job justifier, people hate including fuses into something because it increases the price, so you get fuseless wonders. thats a good modification. better then smelling up the dump for 2 weeks.. manufacturers just want to get something out the door, i don't blame anyone for wanting a fuse on something, its shady sales territory, they got mentats with 2 foot wide brains 'figuring' way too much about laquer, and its a really good way to gouge a customer, sell them non fused stuff so they can't repair it, replacing a part with solder, the manager says ok, asking for sand paper, conformal coating and a PCB trace repair kit and suddenly you are out big money because 'we dont do that kind of repair here'.