US MIL Spec Scope / Based on HP1707B

[kallisti5]

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 HP1707B

http://www.ebay.com/itm/380485571993

I 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.html

Everyone online seems to want $175+ for the them.. so the $74 USD didn't seem *that* steep.

 Thanks!
  -- Alex

[kallisti5]

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/full

Good thing they are on the DC input and not the AC input.

[SeanB]

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.

[amyk]

They look like globs of toffee... were they cylindrical like the ones below when intact?

[PA0PBZ]

I've seen coils like that dipped in 'chocolate', so if they conduct just leave it like it is, it's probably original.

[tekfan]

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)

[free_electron]

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 ...

[PA0PBZ]

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 ...

Yeah, I can see a nice combination too!*

_{* hint, it's not the scope}

[SeanB]

I think she might be an OAP now...............

[kallisti5]

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.

Yeah... 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.

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)

Wow!  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 idea 

EDIT: 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)

[kallisti5]

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)

The device shown in the pictures on the right, and below, is certainly not the most representative of the 1700 series of oscilloscopes. But it is nevertheless an interesting and symbolic example of the HP special production responding to military requirements.

The AN/USM-339 is the ruggedized version of the HP 1700B. It is a lightweight, portable oscilloscope specifically designed for the rugged requirements of military operations. Operation in dusty environments cause no problem due to the lack of ventilating holes, which allows the 1700E to pass the Dust Test of Method 510. Procedure I of MIL-STD-810. In fact, the 1700E can operate in chemical plants, refineries or many other locations where corrosive or adverse atmospheres may be present. The environmentally designed construction makes it very difficult for any contaminants to get inside the oscilloscope.

This unique ability to operate in an adverse environment is made possible by the extremely low power consumption of the standard 1700 Series oscilloscopes. When operating on ac line power, these oscilloscopes consume less than 25 watts and when operating on dc line or optional internal battery pack, power dissipation is only 18 watts. This means that no vent holes are required and the oscilloscope can be tightly sealed with little concern for internal heat buildup. The majority of the internal components are designed to operate at only 10 to 20 per cent of their maximum rated power which assures high reliability. The lack of ventilation holes also increases measurement reliability by reducing short term dc drift caused by transient ambient temperature changes.

Neat!  That definitely answers some historical questions.

[kallisti5]

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.  Lovely    Off to buy a respirator before sanding impact points and covering the thing in several layers of yellow Rust-Oleum enamel.

[Jimmy Rocket]

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!

[kallisti5]

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)

[kallisti5]

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)

[kallisti5]

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.