Classic piece a coworker brought in today - US Navy scope - Page 1
Forum section: electronics / testgear

author: rrinker
author_rank: Super Contributor
timestamp: February 18, 2016, 08:46:25 pm
content: USM-117, from somewhere around my own birthdate of 1966. Controls are all a bit crusty, the slightest tap will throw the trace all over the place, but I was able to get a steady display of the calibration output. There seems to be no stops on the manual centers on the various switches - I mean no click stops like on other scopes I've used when you turn to the CAL position, there's a physical stop on this but never does it latch into the CAL position. But this old beastie still fires up and with some careful tweaking of the knobs I got the steady trace. It's not that big, the screen is approximately 4" diagonal.

author: cdev
author_rank: Super Contributor
timestamp: February 18, 2016, 11:05:23 pm
content: That would make a good beginner scope for somebody.Interesting that there is no manufacturer name on it. Does it say who made it anywhere?

author: retrolefty
author_rank: Super Contributor
timestamp: February 18, 2016, 11:09:04 pm
content: Quote from: cdev on February 18, 2016, 11:05:23 pmU.S. Military test equipment rarely if ever allowed any manufacture labeling/branding. Sometimes the name-plate data would state the manufacture. Some military test equipment were actually manufactured by different companies at different times on a different procurement contract.

author: rrinker
author_rank: Super Contributor
timestamp: February 19, 2016, 12:39:24 am
content: Nameplate was removed, probably by my coworkers brother who scrounged it when it was being 'scrapped' - he was still active duty in the navy at the time.Others I've seen pictured on the internet show it made by AEL Products in Colmar, PA (not far from here - and also near the Naval Air Development Center in Warminster PA). They folded a while ago.Other than the controls which probably just need a good cleaning, the power cord needs to be repaired and the BNCs, especially the seldom used ones, are quite crusty and need a good cleaning. Vertical is dead on with the calibration signal, horizontal seems reasonable, hard to get a good view of the tiny screen when any disturbance makes the trace jump around. Also needs probes. My coworker has had it for some 30 years, he's not sure when his brother acquired it.I did pop the top, there's a panel on top with 4x quarter turn fasteners to give access to the fuse holders and some calibration pots. And the whole case comes off with single quarter turn fastener dead in the middle of the back.

author: cdev
author_rank: Super Contributor
timestamp: February 19, 2016, 01:42:19 am
content: Watch out for high voltage - which can remain on capacitors for a very long time after power is removed. You may want to replace any electrolytics in there. I would.

author: cvanc
author_rank: Frequent Contributor
timestamp: February 19, 2016, 02:04:29 am
content: Nice - pictures of the inside would be fun!

author: crispy_tofu
author_rank: Super Contributor
timestamp: February 19, 2016, 02:46:35 am
content: Very cool!

author: Cubdriver
author_rank: Unknown
timestamp: February 19, 2016, 05:24:06 am
content: Quote from: cvanc on February 19, 2016, 02:04:29 amAgreed. I'd love to see the innards. Nekkid scope pics!-Pat

author: rrinker
author_rank: Super Contributor
timestamp: February 19, 2016, 02:05:10 pm
content: If he hasn't collected it yet, I'll open it up again and snap some pictures.I know all about the HV part. And despite being aware and taking care when messing around with this tuff, it still scares the hell out of me. That said, as a kid I did take apart this small portable B&W TV I had to see if what I suspected was true - that the tuner and display boards were separate and connected by a standard video signal. Sure enough - they were, so I hacked in a toggle switch and an RCA jack I screwed tot he back of it so I could switch between TV watching and the video output of my first computer. The RF modulator I bought with the computer I could never get to work, so this was my backup plan, direct video.But yeah, I steer well clear of the anode cap, the flyback, and any capacitors around there.

author: rrinker
author_rank: Super Contributor
timestamp: February 19, 2016, 04:27:19 pm
content: Ask and yea shall receive! Here are some shots I took of the insides.First one is the topRight frontLeft rear(had to split the pics up, too large for one message)Also, maybe I'm missing something, it's been over 28 years since I messed around with an analog scope, but there are two settings for internal trigger, + and -, yet when displaying a symmetrical square wave, nothing happens when switching between the two. Shouldn't the waveform shift by half a wavelength? The trigger level center knob also seems to do nothing - you can feel the pot turning, so it's not mechanically disconnected. The only other trigger options this scope has are line + and -, and then external AC or DC coupled. I don't have anything to use to apply signals unless I cobble up a quit Arduino program, I was displaying the square wave AC output of my DMMCheck Plus.Note this isn't mine, my coworker is also an EE, even further removed for the field than I am (he's a lot older, and he's an account rep with us - sales. Early in his career he did EE design work in IR instruments), and he doesn't want to part with it, at least not now. He more or less wants to play around with it, absolute accuracy isn't critical. Just that it works.

author: rrinker
author_rank: Super Contributor
timestamp: February 19, 2016, 04:28:22 pm
content: Rest of the pics.BottomRight RearLeft Front

author: Cubdriver
author_rank: Unknown
timestamp: February 19, 2016, 05:29:12 pm
content: I like the date code on the TO-3 transistors. Why bother with a two digit year? That extra number will cost $$ to stamp, ya know!-Pat

author: rrinker
author_rank: Super Contributor
timestamp: February 19, 2016, 08:07:23 pm
content: Germaniums, even!

author: chris_leyson
author_rank: Super Contributor
timestamp: February 19, 2016, 08:23:24 pm
content: All I can do is smileWhat a beautiful piece of engineering, still fully functional and repairable, more than you can say for a piece of injection molded plastic with and LCD screen that will fail, eventually, sooner than later.

author: rrinker
author_rank: Super Contributor
timestamp: February 19, 2016, 09:35:46 pm
content: Yeah, all hand wired, hand built - you can see the variance in a row of resistors where one wasn't pressed tightly to the board before soldering, etc. Some of it looks top soldered to a plated hole, but the board is single sided - with a few components soldered to the track side. All the pots, both the ones connected to knobs and the internal adjustment ones, are all metal cased, the red anodized aluminum things. Never saw a pot like that. I supposed that was in part to seal it from salt air in a shipboard environment. The variable caps - they are ceramic backed. What stands out is how fine the internal wiring is - even the wires from the AC main input to the switch and back to the power supply looks like #26 or so.

author: rrinker
author_rank: Super Contributor
timestamp: February 19, 2016, 09:48:47 pm
content: One that fell outside the camera frame is on the front right of the unit. They needed a resistor to chassis ground, so they screwed a standoff to the chassis with a lug terminal under it, connecting to one side of the resistor. The standoff then has an insulator, and a solder pin at the top, to which the other lead of the resistor and a wire connecting it to one of the boards. It might seem like a bit of a bodge, but it's also kind of elegant.The power indicator seems to be an early LED - I'll bet that cost a pretty penny.

author: tooki
author_rank: Super Contributor
timestamp: February 20, 2016, 12:15:47 pm
content: Quote from: Cubdriver on February 19, 2016, 05:29:12 pmDon't be silly. It's obvious it's the 52nd week of 1905!

author: rsjsouza
author_rank: Super Contributor
timestamp: February 20, 2016, 12:26:00 pm
content: Thanks for sharing this, rrinker. It is very nice to see the all the testpoints and voltages in the subassemblies - even an "emitter follower circuit" inscription pointing each member of the gang of devices.

author: eas
author_rank: Frequent Contributor
timestamp: February 20, 2016, 11:29:10 pm
content: Quote from: retrolefty on February 18, 2016, 11:09:04 pmAn early exception: Thisenormous US. Army Signal Corps Scope from Western Electricat theMuseum of Communications in Seattle