US MIL Spec Scope  / Based on HP1707B - Page 1
Forum section: electronics / general

author: kallisti5
author_rank: Contributor
timestamp: November 03, 2012, 01:29:41 am
content: I was recently was looking for a project and decided to get a US military spec oscilloscope (This is the first analog scope for my collection)The thing is a wildebeest (AN/USM-338) and seems to be based on the HP1707Bhttp://www.ebay.com/itm/380485571993I plan on cleaning up, replacing any caps that need replacing, replacing the MIL power cord, etc.Anyone have an experience on these and could provide some tips on what i'm getting myself into?Here are a few internal pics online from someone else who had one. (Yeehaw! There's gold in them-thar hills!)http://mark.rehorst.com/AN_USM_338/index.htmlEveryone online seems to want $175+ for the them.. so the $74 USD didn't seem *that* steep.Thanks!-- Alex

author: kallisti5
author_rank: Contributor
timestamp: November 10, 2012, 09:14:17 pm
content: Got the scope in, working great! Did a bunch of cleaning this morning, changed the power cable, etc.Anyone have any idea what happened to these caps? (At least I *think* they were caps)http://twitpic.com/bc41um/fullGood thing they are on the DC input and not the AC input.

author: SeanB
author_rank: Super Contributor
timestamp: November 11, 2012, 06:09:01 am
content: Overvoltage most likely. They might have only have had a 25V rating originally.they also may have dies when somebody was running it off a DC supply and it was floating to a high voltage WRT the scope, or they disconnected the earth lead to use it on mains.

author: amyk
author_rank: Super Contributor
timestamp: November 11, 2012, 10:07:29 am
content: They look like globs of toffee... were they cylindrical like the ones below when intact?

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 11, 2012, 10:56:43 am
content: I've seen coils like that dipped in 'chocolate', so if they conduct just leave it like it is, it's probably original.

author: tekfan
author_rank: Frequent Contributor
timestamp: November 11, 2012, 11:42:13 am
content: Those are not caps but are RF chokes inline with the DC input. Looks like they used some strange potting compound. The coils are wound with a quite thick enamel coated wire so in case of overcurrent, the coils would be the last component to overheat. I would expect burned wires rather than the chokes. Measure their resistance with a multimeter. You should get close to 0 ohms.This is HP's advertisement picture for the scope.Suppoesdly it can also survive repeated drops from 3 feet onto concrete. (try it at your own risk unless you have some spare CRTs)

author: free_electron
author_rank: Super Contributor
timestamp: November 11, 2012, 07:12:46 pm
content: damn. i gotta get me one of those. the first scope that can be used underwater while scubadiving... so i can finally combine my two hobbies.suck on that tektronix ...

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 11, 2012, 07:54:12 pm
content: Quote from: free_electron on November 11, 2012, 07:12:46 pmYeah, I can see a nice combination too!** hint, it's not the scope

author: SeanB
author_rank: Super Contributor
timestamp: November 11, 2012, 08:01:26 pm
content: I think she might be an OAP now...............

author: kallisti5
author_rank: Contributor
timestamp: November 12, 2012, 05:17:20 pm
content: Quote from: tekfan on November 11, 2012, 11:42:13 amYeah... I looked at them a little closer and saw a small bit of red peeking through the brown chocolate.. probably a choke. They just didn't pass my initial 'what could be horribly wrong' check of unknown equipment. I'll check and confirm their resistance.Quote from: tekfan on November 11, 2012, 11:42:13 amWow! I never saw that image, thanks for the link!I don't think i'd trust it that far anymore...* The pressure equalizer valve on the top was missing... stuck a bolt in it to cover it.* Several rubber domes and seals on the face are cracked from age.Plus a 37 year old scope holding 20k+ volts dunked into water doesn't sound like a great ideaEDIT: just noticed, no power cable on the front of the scope in that picture... must be using the optional internal battery (which I don't have)The caps all look ok for the moment. Definitely needs some calibration love though.. seems a little short vertically and horizontally.Finished changing some 70's era fuses over the weekend and cleaning switch contacts. Gently using denatured alcohol on the yellow painted case seems to be taking away most of the "military surplus funk" and grime. I'd definitely recommend picking one up if you spot em'. Seem pretty solid and should last quite a while longer. One issue though is the lack of stock replacement parts. The knobs have the 70's bad plastic in them causing several to crack to various degrees. Trying to source a location of replacement knobs now. (The delay knob plastic is broken off but functional)

author: kallisti5
author_rank: Contributor
timestamp: November 12, 2012, 06:21:51 pm
content: Ah:http://www.hpmemory.org/wb_pages/wall_b_page_02.htm"AN/USM-339" different model then the one I have (338)... but seems to be the same general scope (minus feature differences)QuoteNeat! That definitely answers some historical questions.

author: kallisti5
author_rank: Contributor
timestamp: December 01, 2012, 04:29:26 am
content: A follow up *BIG* word of warning on this scope for any other buyers...I started lightly sanding the chipping yellow enamel off of this scope to repaint it with new enamel. While sanding the lid it struck me that this thing was a major risk for lead paint. (70's... military... etc)A quick hardware store trip to pick up a lead tester confirmed the thing has heavily leaded paint on it. LovelyOff to buy a respirator before sanding impact points and covering the thing in several layers of yellow Rust-Oleum enamel.

author: Jimmy Rocket
author_rank: Newbie
timestamp: December 06, 2012, 08:33:21 pm
content: I've got one of these 339s that I'm trying to rehab and it's missing the power supply. I've been looking for one, but I'm not really sure what I'm looking for. Did yours come with the original cord?I've thought about re-wiring the front as an IEC jack but I'm curious about making sure I wire it correctly. Any chance you could help a brother out and let me know which pin is what?Thanks!

author: kallisti5
author_rank: Contributor
timestamp: December 11, 2012, 09:56:09 pm
content: Definitely!Mine came with the original power cable which was rotting and stunk. I ended up taking apart, cleaning up the solder points, soaking the connector in WD-40 then denatured alcohol (to remove surplus stank) and replacing the power cable with a nice shielded PC power cable.I'll grab the pin-out this evening and post here. (maybe with pictures as well) I would double check the ground pin to the case to make *sure* the pinout is the same. I tried to find a replacement before I figured out how it came apart.. and they seem * extremely* hard to find, you may want to just purchase another waterproof connector and replace it completely.I actually am planning on removing the unit from the metal case and using some heavy paint stripper on it to remove the lead paint... i'd recommend you do the same if you want to keep it long term (or if you have kids... the lead paint on these things seems stronger then they used on houses)

author: kallisti5
author_rank: Contributor
timestamp: December 17, 2012, 03:52:21 pm
content: Jimmy Rocket:Here ya go! Sorry for the delay (work's been pretty busy)I'd still confirm your ground pin goes to the case to make sure the pinout is correct for your scope. (You don't want to make the case live)

author: kallisti5
author_rank: Contributor
timestamp: December 17, 2012, 04:01:20 pm
content: Also, a picture of the stripped case.Went pretty well to be honest. Put stripper on, wait 2 hours, scrape paint off.Still need to strip the lid and it's infinite nooks + crannys though.