Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

mnem
 

[med6753]

Been noticing for a while that my "problem child" 465B/DM44 has been exhibiting peaking on fast rise time pulses. So today I was determined to find the cause or bust. Traced the entire vertical pre-amp board all the way to the bandwidth limit switch and it was OK. Right at that switch and then to the delay line is where it went to crap. Issue with the B/W limit switch? Nope...it's fine. Had me puzzled for a while then decided to jump ahead into the vertical output board. Bingo. See pix. All those unmarked pots on the Vertical Output board. Careful tweaking revealed the culprit. But somehow it manifests it's way back. Dunno how I guess that's the mystery surrounding high frequency circuits. But now it's fixed.





In other news.....the capacitors for the RCA scope should FINALLY be delivered tomorrow.

[Martin.M]

  looking for new oscillators... 

I found in the bay this apparatus



fine for the weekend 

[Kosmic]

Same here by TDS420, 

Other TDS420A with damage input hybride (overvoltage)
Swapping of Hybride , which  is soldered, is hateful  jobs.
Then is one other hybride dead, oh no, fucking again heavy desoldering:  I take plier and knack him. It is out. It is out!!

Funny, in my case it's also a piece of equipment from Tektronix (Tek 2794) from the same era with the same surface mount 10uF caps. They definitly had a problem with that batch 

[Martin.M]

Matt, bec. you are owner of a 523B you can calibrate for me the 200cd 

[worsthorse]

Now I just need to find someone locally that has a good calibrated DMM so I can calibrate my new calibrator and then calibrate all my DMMs. 

And so it begins...

ha! it actually began when i learned what a level sine generator was for after acquiring one by accident.

It wasn't as inexpensive as I would like but much less expensive than they are currently seem to be going for. I lost out on one a couple of weeks ago that cost almost as much being sold without any testing.

Now I just need to find someone locally that has a good calibrated DMM so I can calibrate my new calibrator and then calibrate all my DMMs. 

As your calibrator exceeds the digits on your Fluke you obviously NEED 6 1/2 digits + 

Seriously given you are in the USA and that you now have a calibrator consider a one time calibration of the Fluke then apply that known back across your gear using the new Calibrator as part of that. The costs in the USA are typically a lot better than in Oz for example.

This is what I have been doing with my recently calibrated 34401A and 34461A using the pair of them to improve the level of confidence as I go over the other Calibrators and references I have. Next years plan will at this stage get only one of them re calibrated do an initial check against the other then go over the fleet again. Yes it is a circular Rabbit Hole 

*sigh* i already have one foot hovering over that rabbit hole as i thought about having the 8800A or 3478A calibrated to use to calibrate a DIY voltage (up to 100V) source that I could use to calibrate all the other DMMs around here.

As your calibrator exceeds the digits on your Fluke you obviously NEED 6 1/2 digits + 

There you go pushing drugs again. 

Seriously given you are in the USA and that you now have a calibrator consider a one time calibration of the Fluke then apply that known back across your gear using the new Calibrator as part of that. The costs in the USA are typically a lot better than in Oz for example.

This is what I have been doing with my recently calibrated 34401A and 34461A using the pair of them to improve the level of confidence as I go over the other Calibrators and references I have. Next years plan will at this stage get only one of them re calibrated do an initial check against the other then go over the fleet again. Yes it is a circular Rabbit Hole 

With my considerable cross-checking the level of confidence here is 98-99% WITHOUT 6.5 digits. 

I've considered that, too, except I don't know which instrument should be the starting point as the "precision voltage sources" I own, other than the DMM CheckPlus don't have a reliable calibration and don't go high enough (and the CheckPlus is only 5V).

That said, I don't need 6.5 digits. For anything. I could paint over all the digits after x.xx on all of my calculators and meters and be perfectly happy.   

[madao]

Matt, bec. you are owner of a 523B you can calibrate for me the 200cd 

No, i have  HP 523C , not B-models 

[med6753]

I've considered that, too, except I don't know which instrument should be the starting point as the "precision voltage sources" I own, other than the DMM CheckPlus don't have a reliable calibration and don't go high enough (and the CheckPlus is only 5V).

That said, I don't need 6.5 digits. For anything. I could paint over all the digits after x.xx on all of my calculators and meters and be perfectly happy.   

For me it was to purchase another 8800A and bring it into the fold and hopefully it would confirm my findings.

It confirmed that the AD584-M references hadn't drifted.
It enabled me to repair my other 8800A and then confirm that it's calibration was good.
It confirmed that the 8050A that I was using as a bench reference was in cal and accurate.
And it confirmed that the now deceased 8810A was a drifty piece of crap. 

So me happy and 6.5 digits is just excess noise. 

[SeanB]

I fetched up two capacitor decades on ebay -from UK:



Does anyone know the companies shown on the plates?:



Different sellers, different auctions.
One for £24,99 and the other one for £19,99.
Nobody seemed to be interested in those. They both were a buy now offer that had already run several days.

I tested them with my HP 4362A LCR meter and they both are within their 1% spec!   
The larger one with the 50pf to 160pf vernier was offered 'for parts or not working' and it was indeed.
But nothing serious: One capacitor connector was broken what could be fixed with a little soldering job.   

i picked up some "standard" capacitors and some resistance decade boxes from that same manufacturer, from the scrapyard. Decade boxes of course have some well cooked resistors inside, 1% metal film 0.3W, so I should get around to replacing the cooked decades on them. Capacitors are pretty nice, made up from stacked metal film ones inside, and trimmed with some mica capacitors to get an exact ( 1% ) value, though I very much doubt they do drift with temperature, as they are for school lab use. Also got some other equipment as well, but had to not take the motor test benches, there were just too many things, and they were too heavy.

[Martin.M]

Matt, bec. you are owner of a 523B you can calibrate for me the 200cd 

No, i have  HP 523C , not B-models 

and the 521 is a 5 digits, the 523B a 6 digits counter

[tggzzz]

I've considered that, too, except I don't know which instrument should be the starting point as the "precision voltage sources" I own, other than the DMM CheckPlus don't have a reliable calibration and don't go high enough (and the CheckPlus is only 5V).

Use whichever is most stable, which often means the oldest.

[factory]

Matt, bec. you are owner of a 523B you can calibrate for me the 200cd 

No, i have  HP 523C , not B-models 

and the 521 is a 5 digits, the 523B a 6 digits counter

The 523C (nixie) or 523D (neon column) electronic counters are the newer versions of the 523B, either would do the job fine.



David

[Kosmic]

Well, I was wondering why I was not able to see anything bellow 1GHz on the SA I'm currently fixing.

This is the frequency response of the limiter. In Cyan the noise source and in White the same noise source via the limiter.



There is something like 20dBm attenuation in the lower frequency range. The good news is that the mixer sitting just behind the limiter is fine. Someone probably did a big mistake and connected some high power source on the input. The limiter did it job and died protecting the rest of the instrument.









P.S: Please excuse the crappy microscope pictures. I need to find a better one.

[mnementh]

I think this may take a wee bit longer than a "Go fix myself a sandwich..." break...

mnem
*toddles off to ded*

[DaJMasta]

There is something like 20dBm attenuation in the lower frequency range. The good news is that the mixer sitting just behind the limiter is fine. Someone probably did a big mistake and connected some high power source on the input. The limiter did it job and died protecting the rest of the instrument.

Possible, but if you haven't already, worth checking the solder joints to the connectors and such carefully - a little break in a conductor can make a pretty convincing high pass filter.  Could even be a cheaper fix than replacing the limiter!

[Kosmic]

There is something like 20dBm attenuation in the lower frequency range. The good news is that the mixer sitting just behind the limiter is fine. Someone probably did a big mistake and connected some high power source on the input. The limiter did it job and died protecting the rest of the instrument.

Possible, but if you haven't already, worth checking the solder joints to the connectors and such carefully - a little break in a conductor can make a pretty convincing high pass filter.  Could even be a cheaper fix than replacing the limiter!

Good to know, but unfortunately, the solder joints are fine. I should have mentioned the attenuators. They were horribly burned. Probably absorbed most of the energy.

[DaJMasta]

Ouch, those indeed don't look healthy!

[med6753]

Ouch indeed. Crispy Critters. 

[bd139]

Hold my beer while I connect this scope to the lightning rod on the building?

[med6753]

Modern day Ben Franklin? 

[Cubdriver]

Modern day Ben Franklin? 

I'm using a 10:1 probe - what could go wrong?   

-Pat

[VK5RC]

You fools, you connect the scope to an isolation transformer and all will be ok!

[bd139]

Yeah this one will do it:

[VK5RC]

I NEED one of those!
Now where can I put it?

[McBryce]

Yeah this one will do it:

Looks like part of a Megavolt inverter. @VK5RC: You'll usually find them somewhere close to an underwater DC connection between countries. You might need a decent trailer to get it home though. Maybe something like this?

McBryce.