Test Equipment Anonymous (TEA) group therapy thread

[Vince]

Tek 180A update.


Just back from the local shop to get some ceramic disc caps, cheap, to allow me to keep trouble shooting the instrument while I am waiting for the proper Mica caps to arrive from Germany.

Guy didn't have 250pF, only 220pF or 330pF, so I bought a couple of each hoping one of these values would be good enough.

330pF no joy, too big, time constant of the RC network is too long, divides too much.
220pF does it, but not much headroom.
It really needs to be 250pF to work well it seems... so glad that German shop had 250pF. Can't wait to install them.

Anyway, so with a 220pF I got the second "Mica stage" let's call it that, to work just fine. That's the 500us setting.
Then next stage, 1ms, I had zero signal, flat line, clean flat line, completely dead.
So I thought hmm... not sure a leaky cap could cause that catastrophic a failure... I tested it "good" with the DMM at low voltage, spot on 250pF.
So I was hoping/expecting that even if it were leaky, I would at least get "something" going on on the scope screen...
So I rather imagined it would be a dead tube breaking the signal path. The coupling diode at the input, or the cathode follower at the output.
So I was about to swap tubes, but in the end decided to first replace the Mica anyway, go figure.
Well, what do you know, that fixed it  ! Nice markers showed up from the dead, and I was able to adjust the time interval just fine.
So here again a 220pF works well... but again not much headroom either, so still impatient to put the proper 250pF Mica in there.
Good enough for now though.

So that's cool. Those 3 Mica stages are all sorted now. Next stages use the "Bumble Bees " black Sprague Electrolytic, bar the very last stage, the 5 seconds one, because the Sprague caps had gotten too big by now (220nF 600V). So instead, that last stage uses a big 1uF 600V metal cased cap, made by General Electrics, screwed to the deck/chassis.

Anyway, so I am now testing the " Sprague" stages, let's call them that.

So first one is the 5ms one. It appears to work, however the time interval is completely out of wack : I can only adjust it from 6 to 12 ms, not 5.  So clearly the time constant of the RC network is way, way too long. So either the ' R ' or the ' C ' has drifted / increased quite a bit. Will check the resistor but of course I assume it must be the Sprague cap that's off.

I will look into that... later this evening. For now, need to go do some shopping before it's closed, need something to eat ! 

[med6753]

Vince, now you know why my mantra is all capacitors are suspect until proven otherwise. But it is very unusual for mica caps to fail. I don't think I've come across one. And while ceramic caps are usually very reliable I have seen failures with them.

Black beauties, paper, wax. Don't even test them. They are trash. And of course electrolytics. 

And we must not forget TANTS. 

[m k]

Hoefer Scientific PS500XT, pick up from Budapest, Hungary
https://www.troostwijkauctions.com/uk/electrophoresis-power-supply/03-40901-34448-8035255/


BTW,
earlier IBM made a problem here, had to scrap a device, no space.
Computer stuff, a chassis saved for something, Linotronic RIP 3, 18x16 inch single PCB Postscript to bitmap converter with a bit thick casing.
Had to weigh those side plates, 3,5kg a piece.
It's Papst fan was still starting with ~1W.

[mnementh]

Electrophoresis, you say...?

   ...the only fun I was able to have was torturing a lead in my pencil and a little tingle across a fingertip.

mnem
 

[med6753]

Here you go Brumby. This one's for you. More 7000 series plug-in goodness.  Military 7603N on bench 1 for some power up time replacing a 465B/DM44 and 475A. I gotta pull the center plug-in and clean the attenuator deck. It's very noisy.

The military 7603N has no fan and a linear PSU and gets damn hot in the back. Later versions of the 7603 did have a fan. Adding a fan would involve cutting the covers because they are louvered rather than a screen like the 7904. Not gotta happen.



Ain't I a stinker? Can't help myself. 

3 bays....  100MHz, I believe?  Hmmmm.   Beggars can't be choosers, I suppose.

How much for $hipping?

For some reason the military 7603N is only spec'ed to 65MHz. Why? Don't know. Other than some mechanical bits like different type covers and slightly different front panel it's identical to civilian 7603N. I would have to examine the vertical circuits carefully to determine if there really is a difference electrically.

Is the CRT the same part number? Military means ruggedized and the a rugged CRT may not have the same performance as the standard one.

Good point. I'll have to check. I have a copy of the manual.

OK, I did some checking and the mystery is essentially resolved. The military contact for the OS-245(P)/U scope (7603N mainframe) specified that it have 2 vertical plug-ins AM-6565/U and one time base plug-in TD-1085/U. The AM-6565/U plug-in is the same as a 7A15A. The 7A15A has a B/W of 65MHz. However, you can use a higher B/W plug-in such as a 7A11 and achieve 100MHz. So the scope does have same B/W as the civilian 7603N. The TD-1085/U is the same as the 7B53A timebase.

CRT: The P/N specified is 154-0672-00. The civilian 7603 get 154-0640-00/05/10. The manual for the civilian 7603 also sez 154-0672-00 but for option 4 only. Not sure what option 4 is. Perhaps the mil version. So you might be correct that the military gets a "ruggerized" CRT but apparently keeps the 100MHz B/W. 

[ch_scr]

(...)

OK, I did some checking and the mystery is essentially resolved. The military contact for the OS-245(P)/U scope (7603N mainframe) specified that it have 2 vertical plug-ins AM-6565/U and one time base plug-in TD-1085/U. The AM-6565/U plug-in is the same as a 7A15A. The 7A15A has a B/W of 65MHz. However, you can use a higher B/W plug-in such as a 7A11 and achieve 100MHz. So the scope does have same B/W as the civilian 7603N. The TD-1085/U is the same as the 7B53A timebase.

CRT: The P/N specified is 154-0672-00. The civilian 7603 get 154-0640-00/05/10. The manual for the civilian 7603 also sez 154-0672-00 but for option 4 only. Not sure what option 4 is. Perhaps the mil version. So you might be correct that the military gets a "ruggerized" CRT but apparently keeps the 100MHz B/W.

Tekwiki says:
Standard: P31 phosphor, 8 × 10 divisions of 1.22 cm (Tek T7400/154-0640-00 tube); 15 kV acceleration (-3/+12);
Opt. 4 : P31 phosphor, 8 × 10 divisions of 1.0 cm (Tek 154-0672-00 tube); 18 kV acceleration
So.. a smaller tube with higher voltage? Might also indicate the tube does not limit the BW either?
Edit: Tekwiki further below says... Opt. 4 is "Maximum brightness CRT with reduced area"
Brightness seems like something you would want on the Mil-Spec one
Edit: I guess the 1cm/div is to make for easy measurement in 1:1 scale photos?
Edit again: Maybe the "faster" beam is harder to deflect? Have to admit to be a bit rusty on the whole CRT business...

[Peter_O]

Boat anchors are not that often offered at reasonable prices.

This guy was advertised 500 Euros with little reliable information about it's condition.
No risk, no fun. I pulled the trigger. 

Today arrived a substantial, but weak package, that managed to stay kind of in in shape during shipment.
I hoped for the best and schlepped it up to the 3rd floor.


Luckily there was no mechanical damange at all. The guy is in pretty good shape and very clean. It has the orgininal feets installed. It came with some SW disks.



It's an HP 35665A DSO from 1995.

And here comes the fun:
It has the swept sine option installed by licence, so I do not need to burn an eprom from the beginning to have some fun.
It passes all self tests.
The THD of the internal generator for 10.24 kHz is 0.037% which meets the magnitude of spec.



Winter has come back these days over here. Couldn't care less. Weekend is save. Nerd-save.   

[Robert763]

Hmm,
If I didn't already have a S331B and R&S FSH3 I'd be all over this:
www.ebay.co.uk/itm/265614422411?
Anritsu S332D hand held cable analyser, antenna analyser, spectrum analyser and receiver covering 25 MHz to 3 GHz.
No idea about the seller.

[Vince]

Tek 180A update :


Boy time flies when I work on this thing on the bench, it's already 01H30 almost ! Will be 2AM by the time I am done with this post.

Still not 100% fixed but getting there.

I have gone through each and every one of the 14 stages now, pulled all the Sprague electrolytic to measure them, all but one were off by +20% up to +100%, which made it impossible to adjust these stages for proper operation. Replaced them all with a mix / montage of random salvage plastic caps that I put on a tiny piece of vero board for convenience (no choice, the pins were extremely short, could only mount them on a board, not solder them directly to the ceramic strips), and that fixed it.

I have never done that before, but I had no choice but come up with that solution. I actually quite like it, it's very convenient. This way you can easily make any mix  / montage of caps in // or series comfortably on the bench,  until you get the desired voltage rating and capacitance value, then solder two bits of wires to it, and solder it easily in the instrument as if it were a single long legged component. Will not hesitate doing that again. It looks ugly but it saves your bacon and makes your life / soldering so much easier and cleaner.

There was ONE stage that worked properly from the get go... and surprise surprise, this particular one was NOT using a Sprague cap. From a distance it looks like one, but it's not. It's got white lettering and branded " GOOD-ALL ". No I am not making this up, see picture !    "Good" it was indeed, stage worked perfectly so I left that cap alone ! For now at least. I am still in "debugging" mode, not in "Restoration / finished product "mode... just yet. All I care for now is to get the thing working properly, to trouble shoot / diagnose any problem it has. Then will clean and tidy every thing up once everything is tested and working.

Ceramic strips : bad luck, one of them broke a corner    The bit is still held in place by the solder in the notch, so it's functional no worries, but it sucks ! I would like to glue it back together.. I wonder what kind of glue could put ceramic together again ? Super glue ? But would it survive the occasional heat of a soldering iron ?! 


So now all but two stages work :

- 10ms stage : worked fine once I had replaced its cap, but a few minutes later go figure, it failed.. partially. Lemme explain

A) User output on the front panel shows zero signal, flat line.
B) BUT, the next stage DOES work ! We know what that means... since every stage has two outputs, one that feeds the front panel and another that feeds the next stage internally, each with its own cathode follower... that probably means the cathode follower for the front panel, just died... so will do some tube swapping to figure it out.
C) the nest stage (50ms then) works BUT when I play with the trim pot to adjust it, I notice that it can be adjusted in increments of 5ms not 10ms ! That not normal !
That means that the defective 10ms stage does not divide the frequency, it just forwards the 5ms signal straight to the 50ms one. This could be potentially be due to the time constant being out of whack, so small that it passes every 5ms markers instead of only one in 2. So, that might mean that the cap I just put.. died short circuit ?! Tested it.. no, still fine. So need to trouble shoot that... first tube swapping, if not, well proper probing and trouble shooting will have to follow...

- 1s stage

Similar problem as above !
So hopefully once I find the problem for the 10ms stage, the other stage will be fixed similarly....



Anyway, making good steady progress, getting there....   

[syau]

Tekwiki says:
Standard: P31 phosphor, 8 × 10 divisions of 1.22 cm (Tek T7400/154-0640-00 tube); 15 kV acceleration (-3/+12);
Opt. 4 : P31 phosphor, 8 × 10 divisions of 1.0 cm (Tek 154-0672-00 tube); 18 kV acceleration
So.. a smaller tube with higher voltage? Might also indicate the tube does not limit the BW either?
Edit: Tekwiki further below says... Opt. 4 is "Maximum brightness CRT with reduced area"
Brightness seems like something you would want on the Mil-Spec one
Edit: I guess the 1cm/div is to make for easy measurement in 1:1 scale photos?
Edit again: Maybe the "faster" beam is harder to deflect? Have to admit to be a bit rusty on the whole CRT business...

7603 is a great unit, big screen, can use with curve tracer or spectrum analyzer plugin with excellent result.

Managed to score a NOS 154-0841-00 as spare 

[Zucca]

Opening the box reveals this: A spanking brand new piece of TE in its original box.

Not the best idea to post it on the 1st April. 

[Zucca]

Italy (@180°)... I miss my home now...

[Zucca]

It's an HP 35665A DSO from 1995.

Nice puppy, do you plan to use it for audio circuit analysis?

[Neomys Sapiens]

Italy (@180°)... I miss my home now...

Well, that last RIFA did surely smell like the Etna on an active day combined with one of Neaples' most unsavoury neighborhoods. Should I clad it in  bit of red/white/green foil and send it to you? 

[Zucca]

Deanna huckt an Dütscha Koch, ar seyt "Ich kann Dich mitnehmen bis nach Mellau von da an
Musst du schauen wie du selber weiterkommst und jetzt steig ein und mach das Fenster auf
Es stinkt" ja reg di ned uf Zefix!!

[mansaxel]

Now snowing, and I have to go out. Bah!

(Only "Bah!" because it's enough snow to be a nuisance, and not enough to be fun.)

Don't drive your BMW in snow, unless you are prepared to laugh or cry a lot.
(press on DSC button and DTC (Dynamic Traction Control) active helps to not get stuck, long press on DSC button it is not suggested... on public roads)

In our internal trainings they tough us "Remember, there is no restore button after a crash".

We've had a used 4WD V70 for about a year now, and apart from it needing the annual suspension overhaul ( They EAT suspension parts, especially those with rubber in) badly, it's been very good.  Recently we were out for a walk in the forest. The parking space in the nature reservation where we went, is on the north side of a hill, surrounded by high spruces and pines and so very seldom sees sun. The snow had been compacted by cars and then solidified to ice. No snow left at all in the forest, just this ice square for cars. And it is sloping. I tried to park sideways, but found that the rear of the car slid downhill as soon as I stopped. Reevaluated and parked front downhill, on a small patch of gravel, for one of the wheels. People fell over as they got out of their cars.  The 4WD got us out without wheelspin when we were done.

[mansaxel]

First foray into TE today: 8060A fuse replacement.

The fuse is a Bussmann BBS3 or equivalent, which (as a Littelfuse variant) can be had in 10-pack from Mouser for about 8€30 a piece, ex VAT, and while the 10-pack would get me above the 50€ free shipping threshold it's still a lot of money.

Found a NOS pair in Italy for 2€ plus 10€ shipping, so took my chances.

Arrived yesterday, and fitted today. Result: The 8060A is within 1µA of the DMMCheck reference, untouched.   

Went over mA ranges on the 8020A and 8022A too, and they're within, say, 10-15µA.

DMMCheck AC frequency mini-rant: I still feel a bit annoyed at having to check the frequency of the AC signal to understand where I am. While the 8060A shows nice results at both 100Hz and 10KHz, the lesser meters get all wonky at 10KHz.    If one's not prepared for the frequency switching (every time you select AC the frequency is changed, so to go from 100Hz to 10K, select DC, then AC, but you still have to measure the frequency unless you KNEW you were on 100Hz... ), nasty surprises loom.

When one depends on meters to check for absence of lethal voltages (as I do, frequently) I want predictable results. My Fluke fetish stems largely from this, because they won't lie or make up results.  But if I ask them to measure something they can't, they're going to present strange readings.

[Peter_O]

It's an HP 35665A DSO from 1995.

Nice puppy, do you plan to use it for audio circuit analysis?

Not seriously, no. My hifi preamp, which is an old 2002 design, has and THD of 0.0025%, which is 10 times lower than the limits of the HP, if I understand it right.

It's more about understanding the concepts in general and getting kind of hands on to support that. I'm sure, most or all measurements could be done with my Siglent DSO, but having a device dedicated to this area of application with that level of perfection of the user interface and documentation is nice to get things ordered in my mind.

As an application I plan to get a bunch of guitar pickup piezos, solder some FET amp together and see, if I can understand hifi furniture resonances, etc. But it's just a playing field.

[BU508A]

Italy (@180°)... I miss my home now...

Well, that last RIFA did surely smell like the Etna on an active day combined with one of Neaples' most unsavoury neighborhoods. Should I clad it in  bit of red/white/green foil and send it to you? 

Do you mean by any chance Mount Vesuvius which is in the neighbourhood of Neaples as well as the Phlegraean Fields?
Mount Etna is on Sicily.

[Ice-Tea]

Not too shabby...

[m k]

Electrophoresis, you say...?

   ...the only fun I was able to have was torturing a lead in my pencil and a little tingle across a fingertip.

mnem
 

It's 200W max.
It also has a timer so remembering is not so essential.

https://www.eevblog.com/forum/buysellwanted/hoefer-scientific-instruments-ps500xt-500v-variable-dc-power-supply-_serviced_/

Here last minute offers to London started from 26€.
(possibly with self pedaled propels)
Since transport seems to be always an issue maybe I'll start traveling with empty and hard core luggage.

BTW,
I'll take back that earlier voltage reference drift.
It doesn't drift, it's just ambient temperature dependent, maybe 0,05mV/3C around 20C.

[TERRA Operative]

Time to join the club. Had this one for a while now but never got around to even turning it on.
I think I'll fix it up to sell it off, seeing as I have the TDS784C now.

First step, figure out why the intensity is stuck at full blast...

[med6753]

Time to join the club. Had this one for a while now but never got around to even turning it on.
I think I'll fix it up to sell it off, seeing as I have the TDS784C now.

First step, figure out why the intensity is stuck at full blast...

Yea, have fun. It's not a simple HV circuit like a 500 series. All that stuff like the intensity and grid bias are on the Z Axis board with lots of transistors and other assorted stuff that could go wrong. 

[Vince]

Tek 180A update :


OK quick update, making progress.

I just fixed the 10ms stage.

I swapped tubes and no joy. Well it was the easy thing to try first.

Checked the value of every resistor. A few are slightly off tolerance but nothing that would cause catastrophic problems like I am witnessing. So I let it pass.

So I fired it up and started to check waveforms.. yes, real troubleshooting at last, yeah !

It confirmed the symptoms I was seeing yesterday :

- Output to the front panel no signal.. so it's not a wiring or switch problem, there is ACTUALLY no signal, and we know it's not the tube at fault since I swapped them with that of a know working stage.

- Output wired internally to the next stage does work, but sends pulses/markers of the wrong interval, that of the previous stage, 5ms, instead of the 10ms this stage is supposed to produce.


Schematic shows waveform on one side of the timing cap. We are supposed to have pulses of the correct period, 10ms not 5, but I get 5 not 10, so it's wrong.
Amplitude of the pulses is also 3 times smaller than it should.

There is no waveform given for the other side of the cap, so I probed the next stage, working, instead. One side showed spot on what the schematic said, what I just described. So I was happy indeed that I could take this stage as a reference point... so, I probed the other side of the cap, and I got a cycling charging exponential as you might expect. Amplitude also about 100V+

So, back to the defective 10ms stage, I probed the other side of the cap and... no exponential. Instead, I get the exact same signal that I get on the other side of the cap !
Huuu........ if we get the same signal, 100%, on both side of whatever component.... that means it's.... basically.....  A SHORT !!!!   
WHAT ?! How could my cap be short ! I tested it just fine at 3.2nF before soldering it in !
So, could it be that it's leaking, and so bad that it acts like a short under operation ?
The evidence is there anyhow, electrons don't lie !

So, as a quick sanity check, I removed my cobbled together film cap, and put the old Sprague cap in place.
I mean it reads 50% high but at least it was behaving like a cap, and the stage was working fine with it.... not much headroom when adjusting the trim pot, hence why I replaced that cap, but still, I could get it to work fine.

So, put it back in there, and presto, the stage is back in business and waveforms are what they should be  !!


SO ! Tough luck for me cap wise !!!

The famous "never fails" Mica... that reads spot on with a DMM but is leaky as hell to the point of keeping the stage from operating.... and now a modern(ish, salvaged) film cap that also read fine with the DMM but short out in service !!! And that old Sprague that beats them all and DOES work ! 

Murphy is out there and kicking for sure !! 


So, now the next defective stage as I said last night, is the 1s stage, which exhibits the same symptoms.
so of course I checked my film cap but here it seems to work fine : I do get my charging exponential, with good amplitude, on its relevant pin.
So the source of the problem must be something else.


Stay tuned.

[Vince]

Time to join the club. Had this one for a while now but never got around to even turning it on.
I think I'll fix it up to sell it off, seeing as I have the TDS784C now.

First step, figure out why the intensity is stuck at full blast...

Yea, have fun. It's not a simple HV circuit like a 500 series. All that stuff like the intensity and grid bias are on the Z Axis board with lots of transistors and other assorted stuff that could go wrong.

You are supposed to ENCOURAGE / SUPPORT your fellow TEA friends, NOT make them depressed and want to dump their TE for parts cheap on Ebay !

Terra, don't listen to the old Smurf, just grab the schematics and start probing around !!!