Test Equipment Anonymous (TEA) group therapy thread

[VK5RC]

I very kindly received a gift of a pair of HP 335 attenuators, Thanks Brian 👍 (fellow vk5 ham), the 0-10dB attenuator works well, but the 0—120dB had some gremlins.
Thanks to x-dev for hosting the manual, opening it up revealed previous mucking around. Some mis replaced resistors (wrong values) and some others burnt out. 7 needed changing. The resistor values needed are quite weird but I managed to get close enough (+/-1/2%) using some smd 1206 resistors I have in a kit and the helpful resistance calculator site https://www.qsl.net/in3otd/parallr.html
The only issue is that I have dropped the power loading, I estimate, from 1/2W to sl less than 1/4W. It tests accurately now from 1MHz  to 1GHz with a bit of bleed through at 1GHz at 100dB + attenuation.

[Wolfgang]

I didnt say your LCR is cheap, I said that the Chinese ones are cheap, obviously.

[Specmaster]

A few years ago when this whole Chinese LCR meter debate first kicked off there was a lot of folk slagging off the cheap Chinese ones and seeing as I already had a Chinese XJW01 meter that had already received a fair bit of flak from some quarters, despite it had been tested against a massive HP 4262A LCR bridges, it gave pretty good results which were within a couple of  % points of its readings for a fraction of its price.

That set me wondering about the accuracy of the ultra cheap Chinese ones, so I then purchased a cheap Transistor tester that did caps, ESR etc as well and while the readings on capacity was around 5-6% off from the readings of the XJW01 it was still reasonable enough that it was suitable for most work, seeing as the average cap used in consumer grade equipment is going to be in the realms of 20% tolerance, the ESR values were much closer to the more expensive meter.

Next I purchased one of the other types of Chinese testers, which could be brought either with a clear perspex case or open as populated board with no protection and that again proved to be a perfectly acceptable tester and fell between the XJW01 and transistor tester and TBH is now my go to tester for most things because it can test loads of devices, Caps, Inductors, resistors, transistors, diodes, dual diodes, MOS and SCR etc and can also test SMD parts and correctly identify pin outs as well.

The XJW01 is a 4 wire device and so will produce more accurate results, but it is a much less versatile device the other 2 cheaper devices, so does not get much these days.

[Swake]

Does it happen to you too that you buy some older broken equipment to make a quick flip because you think/know you can repair it but then you don't want to sell it anymore because it is 'insert whatever excuse here' ?

Is this a sign of mild addiction that a therapy can still correct or am I waaay too deep in this now?

[Vince]

I fear the answer is the latter not the former. Welcome to the club...

[factory]

None of the various LCR or capacitor meters (or DMMs with cap ranges) at work could agree on capacitance readings, probably because of different test frequencies used, they were all calibrated using the Fluke 5500A.
The one I used the most was the AIM LCR databridge, which has probably been destroyed by SIMS metals by now, so down to the un-calibrated Escort cap meter hidden in a draw.

David

[factory]

...snip...

So I replaced those caps on the vertical amp board, and the readout board. Problem now is that there are so many wires and cable attached to the readout board, it's such a mess in there, that the board has  10 pin socket I can't find a cable for.... and OTHO I have a 5 pin cable that I don't know where it goes to.. so maybe it goes to that 10 pin socket but which of the 10 pins does it plug to... hmmmm.... I think I didn't take enough pics.... will check anyway. Also, that 5 pin plug is no more : its plastic disintegrated ( a disease in this scope I notice... strange), and I am left with just bare crimped terminates flapping around in the breeze, fun... no.  Did I say I hated '70s scopes ? Yes I did. Well I just said it again anyway....

Are there any similarities between that scope & the R7903 for the readout board? just acquired one earlier today at the Radioactive sale in Nantwich, along with a Tek 545, one of the 76xx storage scopes, a HP 8007B and a Macaroni TF2008/1 signal generator. I was trying not to buy anything big, but completely failed when my brother turned up to help.  Total spend on TE was £140, also picked up lots of parts.



David

[AVGresponding]

I didnt say your LCR is cheap, I said that the Chinese ones are cheap, obviously.

They are surprisingly non-shit. I wouldn't trust them for serious measurements, as they can be a bit inconsistent, which I suspect may be due to variations in contact resistance, but they are pretty useful for getting an immediate pinout on a transistor without having to look it up, for example.

The readings it gives are close enough to serious, calibrated TE, that it's definitely worth the money, and I can live with the fact it has trouble understanding certain transistors (unijunction ones confuse it, iirc, though that might have been fixed in later firmware versions) for its general usefulness in giving quick go/no-go answers on most caps, diodes, and transistors.

[Vince]

...snip...

So I replaced those caps on the vertical amp board, and the readout board. Problem now is that there are so many wires and cable attached to the readout board, it's such a mess in there, that the board has  10 pin socket I can't find a cable for.... and OTHO I have a 5 pin cable that I don't know where it goes to.. so maybe it goes to that 10 pin socket but which of the 10 pins does it plug to... hmmmm.... I think I didn't take enough pics.... will check anyway. Also, that 5 pin plug is no more : its plastic disintegrated ( a disease in this scope I notice... strange), and I am left with just bare crimped terminates flapping around in the breeze, fun... no.  Did I say I hated '70s scopes ? Yes I did. Well I just said it again anyway....

Are there any similarities between that scope & the R7903 for the readout board? just acquired one earlier today at the Radioactive sale in Nantwich, along with a Tek 545, one of the 76xx storage scopes, a HP 8007B and a Macaroni TF2008/1 signal generator. I was trying not to buy anything big, but completely failed when my brother turned up to help.  Total spend on TE was £140, also picked up lots of parts.

David

Wow, congratulations on your latest purchases..   

The R7903 ? No idea about its readout board... I know absolutely squat about 7000 series scopes, I am learning as I go with the one I've got here...
All I can say is that yours looks pristine... very clean and with ivory buttons that look ivory not dark yellow like mine... so I am a bit jealous...

Readout board if I had to guess, would get luckier with the other 7000 scope, the desktop one, as it looks like it uses the same vertical and horizontal plugins that my scope does, so maybe the readout boards and interconnect are identical. Nice thing being, in this form factor the readout board is readily available : just pop the side panel and the board is right there smiling at you.... whereas in my rack mount scope, that board is a major PITA to get to and remove.

[Vince]

OK I figured how to reconnect my mystery cable, thanks to the schematics, the one pic I took of the board in place before disconnecting the wires, and the high-res pic I just found on Tek Wiki. Thanks Tekwiki.

Board is now plugged back. I have more problems now : nothing at all appears on the screen.... no readout, no traces, not even a spot, a fussy blob somewhere.... nothing.

With these old machines it's always one step forward one step back ! 

More troubleshooting is required.... never a dull moment with these machines...

[Vince]

TEK 7603 saga

OK the display is back.

To cut the story short, was my fault again of course. When I plugged the vertical amp board after recapping it, turns out I bent the center pin on two of the coax cables.
I hate these bastards, because they are quite stiff, take some force to plug them, and you can't "feel" if the pin is inserted properly or not. So both pins were bent 90°
Luckily I could straightened them and insert them properly this time. Display is back, all 4 traces are there and look nice, the recap helped a bit I think. I am happy with the traces now, it's good enough.

I still had problems though : the readout would not show up... turned out I swapped two 5 pin connectors... readout shows up now.

While playing with these two connectors a grey and a brown one, I noticed interesting things :

1) The problem I had with the trace looking very noisy "inside" the trace itself, like it were a flashing dotted line or something, that would manifest it self at slowish sweep speeds and gradually disappear as you crank up the speed... well I noticed that if I disconnect the grey connector (live), the readout disappears and the traces magically heal ! They look perfectly "solid" and clean, as you would want / expect ! No more funny business going on "inside" the trace !

2) Dim trace issue at fast sweep speeds. I noticed that when I unplug the other connector from the readout board, readout disappears AND I get a very significant boost in trace brightness !


So basically these two issues are not issues then, it's just an unfortunate downside of having the readout feature !
I love the readout feature, but not sure I love it as much now I know it makes my traces look crap and dim ! 
If at least we had a switch on the front panel to disable the thing when we want to...

Anyway, that was interesting.

However I am still not done : I still have a problem with the readout... there is not horizontal sweep for them... doesn't work. Vertical is OK which is why I know readout is there : I get a small vertical segment at the top and bottom of the screen.
So I need to fix that... I guess it must be my mystery connector again... maybe I didn't plug it the right way after all... even though the info I found looked unambiguous 
Or maybe it's one of those pesky coax cables again that I bent.... hopefully it's something simple like that.. probably is...

[Vince]

OK fixed it, it was indeed again a bent coax pin... one of the 5 present on the readout board.

So I guess that was the lesson of the day. Watch out when you deal with these old Tek coax connectors... it's all too easy to bend them. and not even notice it

[srb1954]

So basically these two issues are not issues then, it's just an unfortunate downside of having the readout feature !
I love the readout feature, but not sure I love it as much now I know it makes my traces look crap and dim ! 
If at least we had a switch on the front panel to disable the thing when we want to...

You can turn the readout intensity (small light grey knob in the top RH corner) down to minimum.

Anyway, that was interesting.

However I am still not done : I still have a problem with the readout... there is not horizontal sweep for them... doesn't work. Vertical is OK which is why I know readout is there : I get a small vertical segment at the top and bottom of the screen.
So I need to fix that... I guess it must be my mystery connector again... maybe I didn't plug it the right way after all... even though the info I found looked unambiguous 
Or maybe it's one of those pesky coax cables again that I bent.... hopefully it's something simple like that.. probably is...

Temporarily put a vertical plug-in into the horizontal slot and see if the readout display re-appears in the horizontal position. This will allow you to determine if the horizontal plug-in or the main frame is at fault.

[Vince]

Oh thanks for that ! 

It works ! Looks like when you turn the readout intensity control all the way CCW, the scope detects this condition and disables the readout, because when I do that instantly all the "crap" disappears from my traces and they look clean again, yeah !   So Tek did think of it, cool.

This scope is getting better by the day.

Now one thing that would make it even cooler is if I could figure out how to use the dual time base to display ALONG with the main time base.
So far I have only been able to display either the main time or the delayed one, but not both at the same time 

But looking at the pics on Tekwiki, which appears to use the same plugins I do, it is possible to display a "combined" display like this :

I want my scope to do that... will RTFM the TB plugin  again...

[Vince]

EDIT : no, the scope does not "detect" when you the brightness control is all the way CCW in order to disable the readout....there is a switch that's all.. but I didn't know it at first because the scope is so old and unloved before me, that the switch was very stiff, so I assumed I was fully CCW but I was not.... OK I hope that switch is not sealed and I can get some contact cleaner in there.

[Vince]

YES !!!

I finally got what I wanted !

RTFM'ed the mixed sweep. It's supposedly easy : just pull the little red "CAL" knob.... which I did but I could not get it to work no matter what !

I really was running out of ideas, this was supposed to be simple and it should be Vince-proof, I thought.

So I swapped the plugin for another one, since I have two identical TB plugins.

Well what do you know, it works just fine now, as you can see ! 

Turns out the first plugin has a defective red knob. When you pull on it it does not come out as much as it should, by a long shot, like 5mm at least. It's also very stiff to turn.
So it probably needs some contact cleaner and some mechanical adjustment somewhere perhaps. Will look into that tomorrow maybe.

For now it's 23H15, time to go to bed, week-end is over and finishing on a wonderful note.

Was a productive week-end for this scope, very happy.

Still needs some little things looked at, but the bulk of the work is done I think, it's almost there. I am starting to enjoy this scope 

[Wolfgang]

I just added a modified PD16K10 that does 10kHz, 1kHz, 100Hz and 10Hz instead of 1kHz, 100Hz, 10Hz and 1Hz.
Sourcecode was sent to Tom.

[TERRA Operative]

Those little Tek coax connectors are great aren't they? 
They are called Peltola connectors after the guy who invented them.

https://w140.com/tekwiki/wiki/Peltola_connector

They are nice and compact, and work great once you get them plugged in, but that's the trick....

I much prefer SMB connectors for push-on coax connectors, but the Peltolas are somewhat cheaper to produce, so economics and bean counters win again.... 

[DC1MC]

Those little Tek coax connectors are great aren't they? 
They are called Peltola connectors after the guy who invented them.

https://w140.com/tekwiki/wiki/Peltola_connector

They are nice and compact, and work great once you get them plugged in, but that's the trick....

I much prefer SMB connectors for push-on coax connectors, but the Peltolas are somewhat cheaper to produce, so economics and bean counters win again.... 

And then we have these:
https://www.ebay.co.uk/itm/281702938081

[Brumby]

I was trying not to buy anything big, but completely failed when my brother turned up to help. 

Which is as it should be   

Total spend on TE was £140, also picked up lots of parts.

Nice. 

[Ice-Tea]

As promised. Pretty niffy.

[timeandfrequency]

Hi Ice-Tea,

Funny feature on this unit : the small plastic axle at the bottom of the black knob can be pushed to lock both knobs together (one for each channel).
So the ranges of both channels keep synchronized.

The top LED scale with 110 dB span that gives a ballpark of each input level is really cute too.

[Ice-Tea]

Yep. A lot of though went into this design ☺️

[Vince]

Those little Tek coax connectors are great aren't they? 
They are called Peltola connectors after the guy who invented them.

https://w140.com/tekwiki/wiki/Peltola_connector

They are nice and compact, and work great once you get them plugged in, but that's the trick....

I much prefer SMB connectors for push-on coax connectors, but the Peltolas are somewhat cheaper to produce, so economics and bean counters win again.... 

Thanks for the link Terra, interesting ! 

I feel better somehow now... I thought that my dislike for these things was solely due to my incompetence, but apparently no, others dislike them as well...

For sure they must have been cheaper to manufacture than... anything else. Just an eyelet soldered in the PCB, and a piece of folded sheet metal and that's it.
No precision machining involved....

Well actually you could say it's a "plus"... I mean it makes the design resilient. I don't think I would have been able to straighten an SMA center pin once it had been bent 90°.. and hope that it would work.

I think the Tek design had some merits in this regard. I think it would have taken only a minor modification of their design to make it more "reliable" : modify slightly the shape of the eyelet on the PCB, to extend it with a conical shape, like a tiny funnel, so as to guide the center pin 100% reliably into the eyelet. I will rent a time machine and talk Tek into doing that...

[Wallace Gasiewicz]

The Taiko Denki Connectors are also a pain in the butt.
Kinda the same type of cheap connector