Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

Not me; I was the quintessential Rebel Without a Clue most of my life... I didn't turn into Squidward until I'd been in Texas a few years. Pretty sure that's not a coincidence. 

Hmm, no idea why this picture hits me:       

Donchoo know it!!! Sandy Cheeks is totally my girl!!! 

mnem
You know, right after Marceline...     

[med6753]

Holy complexity Batman! These are the Hi-Z/Lo-Z attenuator decks on the 485. Like nothing I've ever seen before. Anyway, needed to find out why Hi-Z (1MEG) is showing a roll off on a 5kHz square wave. So I fed identical signal into channel 1 and 2 and started scoping. Found it pretty quick. Base of Q56 looked good. Base of Q60 looked like crap. Thought Q56 was duff so swapped it with channel 2. No change. Turned out all that was needed was a tweak of C55 on the emitter of Q56 and now it's perfect. Mission accomplished. 

Before re-installing the covers going to connect the Heath IG-4244 Scope Calibrator and do a complete check out of Both Hi-Z/Lo-Z on both channels. Once that's done then change out the trigger/slope control.

[bd139]

Will reply to everyone later.

Clean, passes self test 34401A. Worth £325? Opinions.

[med6753]

Both channels check out excellent both Hi-Z input and Lo-Z input.

First pix is 10MHz square thru a 50 ohm feed thru terminator into the Hi-Z input. 2nd pix is direct coax into the Lo-Z input. I can now put the covers back on the attenuator decks and move on the the trigger/slope replacement. 

[tggzzz]

... and it is awesome that you could get that close to a Spitfire and a Harrier.

Many of our museums are like that.

For aircraft, goto Duxford (bonus points for arriving in a DC3 ) and RAF Cosford (and Maybe RAF Hendon, but I haven't been there).

Manchester's Science Museum has a superb Shackleton, a  Spitfire, MXY-7 Ohka (kamikaze), and a replica of Baby.

Another notable museum (Pitt Rivers) has real shrunken heads from the Amazon, mummified babies, and you can pull open the cabinet drawers.

And I won't bother to mention TNMoC yet again!

Ob SR71 porn at Duxford:

[Mr. Scram]

Will reply to everyone later.

Clean, passes self test 34401A. Worth £325? Opinions.

That’s about the going rate for a decent one. Paying less generally gets you a scrappy unit.

[bd139]

Yeah seems reasonable. Anything I need to look out for or preventative maintenance? Mains filters good?

I'm going to send it off immediately to Calmet for cal.

[tggzzz]

Both channels check out excellent both Hi-Z input and Lo-Z input.

First pix is 10MHz square thru a 50 ohm feed thru terminator into the Hi-Z input. 2nd pix is direct coax into the Lo-Z input. I can now put the covers back on the attenuator decks and move on the the trigger/slope replacement. 

I think you are right to move onto the trig/slope replacement.

I don't want to rain on your parade, but I don't think you have discovered just how nice the 485 can be.

I'd like to see something more like these...

Homebrew signal source 1ns/div




Homebrew signal source, 20ns/div (I believe the same scale as your photos)

 


1MHz cal out 100ns/div (recommendation is to use the rising edge only)

[bsdphk]

There are a lot of articles in the Bell Systems Technical Journal about all aspects of the first telephone cable under the Atlantic.

Archive.org has them.

I belive there are two whole issues dedicated to that cable, about 2-3 years apart in the middle of 1950-ies.

[med6753]

Both channels check out excellent both Hi-Z input and Lo-Z input.

First pix is 10MHz square thru a 50 ohm feed thru terminator into the Hi-Z input. 2nd pix is direct coax into the Lo-Z input. I can now put the covers back on the attenuator decks and move on the the trigger/slope replacement. 

I think you are right to move onto the trig/slope replacement.

I don't want to rain on your parade, but I hope the poor risetime and wiggles are due to whatever signal source you are using.

I'd like to see something more like these...

Homebrew signal source 1ns/div




Homebrew signal source, 20ns/div


1MHz cal out 100ns/div

Trust me. It's the source, not the scope. The IG-4244 does a decent job but it ain't perfect. The traces I got on this 485 are identical to what you would see on a 475A, 2465, and the 50 ohm input 7A24 on the 7904.

[factory]

The paper in oil caps are usually pretty stable. But only at low voltages ( <200V). They punch through over time on high voltages so I'd be tempted to replace them. However when they punch through they actually reduce the capacitance significantly so you can test if they are knackered with an LC meter. If they're not, leave 'em.

Main problem on replacement is that high voltage high value polypropylene film caps, the usual replacement, are pretty expensive.
-snip-

Oil filled caps in general are pretty reliable. But keep in mind if they pre-date the 1970's (most do) chances are the oil is PCB. If they do let go you'll need a Hazmat team to clean up the mess.

Given that 200V isn't even a mosquito bite in these units and that these caps are likely from the very early 50s if not 40s it seems to me it's best to just bite the bullet and buy the replacements when I can. I can get 10 8uf 1100V for $34 and connect two in series for each desired capacitor replacement. $77 for a complete recap on both units, the 618B eating most of that.

HP 618B was introduced in 1952;
https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1952-09.pdf
But your 618B will be later than that as the front panel has the updated knobs, less fuses and no power socket.
Looking at the catalogues they change around 1956/7.

David

P.S. Just spent the last couple of hours sorting two dozen manuals (bought from the seller I got the 5280A from, after negotiating a much lower price for a job lot) into the three four boxes I now have for manuals.

[Mr. Scram]

Yeah seems reasonable. Anything I need to look out for or preventative maintenance? Mains filters good?

I'm going to send it off immediately to Calmet for cal.

No calibration batteries or anything as far as I’m aware. They’re fairly modern devices. The earlier units can have unobtanium VFD components so make sure the display is good. Fading segments are a nuisance and leaking segments mean you’re in trouble.

[bitseeker]

Yeah seems reasonable. Anything I need to look out for or preventative maintenance? Mains filters good?

I'm going to send it off immediately to Calmet for cal.

Run full self-test and verify no error codes. If you have a voltage reference, check if the meter is drifty. Measure some resistors to make sure the current source is OK.

If yours has both red and black banana jacks, you have the newer VFD drivers. If they're all red, you likely have the unobtanium version. Check for segments, decimal points, or indicators being on when they're not supposed to. That's the first sign of the driver going bad.

I haven't done anything to my 34401A or 34410A since I bought them. They're pretty bullet proof. No major capacitor leaks or the like that plague these. Just the old VFD drivers that sometimes go bad.

No calibration batteries or anything as far as I’m aware.

Correct. No calibration battery to die on you.

[bd139]

Thanks both - much appreciated.

Shows self test pass, seller has a 14 day returns policy and it's a later model.

Worst case I can return it and it'll bounce for more than that 

Edit: I now own a 34401A. That spider was radioactive and gave me TEA spending powers 

[med6753]

Edit: I now own a 34401A. That spider was radioactive and gave me TEA spending powers 

Does that mean you are now going to spin webs and leap between buildings? 

[Mr. Scram]

Thanks both - much appreciated.

Shows self test pass, seller has a 14 day returns policy and it's a later model.

Worst case I can return it and it'll bounce for more than that 

Edit: I now own a 34401A. That spider was radioactive and gave me TEA spending powers 

Congrats. They’re spiffy machines. They’re the industry benchmark for a reason.

[bd139]

Finally getting around to rest of the replies now...

I've sent a PM to a few people with today's science museum trip gallery in it. There are 342 images so I don't want to post the link here otherwise my transfer will get eaten in 2 minutes by robots/scrapers. If anyone else wants to have a look, PM me and I'll send you the link. Preview:

Spacecraft, measurement, electrical items, dangerous flying machines, robots, old transistors and valves/tubes, time standards, vintage computers, crypto machines, enigma communications, old radios, amateur radio equipment from the dark ages, a bit of the moon, big scary transmitters, telephones and exchanges, supercomputers, old mobile phones, historic computers, calculators, jet engines, aircraft, difference engine, gold plated bbc micro and a wannacry infected laptop. Some captures of info cards but most if it is a case of playing guess what it is

Not much TE in there. There's an Advance oscilloscope lurking in one photo however. Slightly disappointed by that

I FINALLY finished slogging through all of that this morning... very interesting, the collection of tube-era transatlantic cable repeaters; something I'd always been curious about. Also the recreation of the Marconi broadcast station from London... and it is awesome that you could get that close to a Spitfire and a Harrier. Was that the Gen1, that they used to call the "Flying Coffin" due to its crash history? And the exploratory spacecraft... I took a 3-day trip down the DAWN/DS1/Ion-Drive rabbithole alone... 

Thank you very much for sharing!!! 

Glad you enjoyed. Not sure which Spitfire that was in there unfortunately. It was at the top of the building and I'd walked about 5km by then so got a little fast on the photos thus skipping the signs  . Dawn was one of the coolest missions NASA ever did - followed that one to the conclusion. I can imagine how pant pissingly cool it was for the team to get this photo out of the mission: https://upload.wikimedia.org/wikipedia/commons/4/4c/Occator_crater.jpg

Donchoo know it!!! Sandy Cheeks is totally my girl!!! 

Furry alert  ... at least it's not MLP and clopping, something I accidentally stumbled across the other day 

Does that mean you are now going to spin webs and leap between buildings? 

I'm going to grab the cobwebs from around my living room ceiling and fall to my death 

Nice one on the 485 there - you hit the jackpot 

Congrats. They’re spiffy machines. They’re the industry benchmark for a reason.

Indeed. Been after one for a while but other priorities get it the way usually.

Picture of actual meter

[bitseeker]

Thanks both - much appreciated.

Shows self test pass, seller has a 14 day returns policy and it's a later model.

Worst case I can return it and it'll bounce for more than that 

Edit: I now own a 34401A. That spider was radioactive and gave me TEA spending powers 

It'll definitely bounce for a pretty penny. Welcome to the 34401A club. A not oft mentioned feature is the speed of the continuity function.

[bd139]

Yes I read about that. 300 samples/second apparently 

[BU508A]

Regarding the 34401A:
I can second all said that, have one of my own.
It is sitting on my bench and mostly the first choice to measure something.

Check the VFD if it is dim (was all said) and check the front and the rear connectors.
There is a relais switch inside it which can fail sometimes.
a good check is with a well-known resistor (check it with 2- and 4-wire)
and to shorten the inputs (2- and 4-wire).

This, and with a passing self-test you can be very confident to have a good unit.

Good choice to buy one.   

Edit: meant switch

[med6753]

Yes I read about that. 300 samples/second apparently 

And this for the cob webs. 

[Mr. Scram]

It'll definitely bounce for a pretty penny. Welcome to the 34401A club. A not oft mentioned feature is the speed of the continuity function.

Of course knowing bd139 he'll flog it in 2 months time, buy another in 7 months time, sell that one in 9 months time and end up with a K2000 somewhere next year.

[BU508A]

It'll definitely bounce for a pretty penny. Welcome to the 34401A club. A not oft mentioned feature is the speed of the continuity function.

Of course knowing bd139 he'll flog it in 2 months time, buy another in 7 months time, sell that one in 9 months time and end up with a K2000 somewhere next year.

And, finally, he'll end up with a 3458A which he will compare all day long with a 8508A? 

[Mr. Scram]

And, finally, he'll end up with a 3458A which he will compare all day long with a 8508A? 

He'll end up with a 3458A which gets flogged as soon as all the capacitors have been replaced. Many digits confuse penis finger primate.

[bitseeker]

Yep, and then buy a whole stable of 6.5-digit meters since he didn't really need 8.5.

bd's ears must be burning up right about now.