Test Equipment Anonymous (TEA) group therapy thread

[TERRA Operative]

TEK 7603 restoration

See if this mod is installed and try it if not.. Apparently it reduces the fuzzyness which is a GHz range oscillation. It might help a little.
Shouldn't need much more than a bit of copper or brass strap.

https://w140.com/tekwiki/images/0/0e/7603mod36005.pdf

So I put two pieces of braid in  //, each insulated with heatshrink tubing. Blue tubing of course, because.. it's a Tek ! 
I don't know, I felt in the mood of using some colour..

So the result ? Well, scope still works and no smoke, so that's a good start. I would need to male a side by side comparison to be objective.. Which is not possible of course.
So I have to go with my memory here, of what it was like before I put the straps in place.  I would say it's better. Hardly "Tektronix sharp", but better enough that I think it exists and is not a placebo effect. So I will take that... thanks Terra for the link.

As I posted the info on the ground strap I thought of the solderwick braid trick, but I guessed you'd figure it out.

Looks like great minds do think alike after all.....


On my bench is still the TM506. I replaced all the pass transistors with TIP35C and TIP36C as a couple of the originals were blown, so who knows how much abuse the others took, and I got a bushel of TIP3xC transistors for a good price, so in they all went.
I had to turn them around and put them on little flyleads as the pinout was reversed, but that made the next step easier.
I have found that the NPN transistors often like to oscillate when testing them with my mainframe tester.
I don't know if this is a result of something about the mainframe tester or inherant to the mainframe design itself, but the PNP transistors don't do it and the design is exactly as per the original Tek design and the +Ve and -Ve sides of the test module are mirror images of each other, practically down to the PCB layout.


Noisy noise is too noisy... ENHANCE!


That doesn't look right! ENHANCE!


Woop, there it is! 4.7MHz!


This is what it's supposed to look like, from the PNP transistors.

I measured the oscillation at 4.7MHz, so I played with some ferrites and managed to kill the oscillation completely, so after a trip to akihabara to get more, the mainframe is mostly happy.
I ended up with two ferrite beads on the base of each NPN transistor (most transistors only needed one but a few were still marginal, so I put two on them all for good measure) and one on each PNP, just to be sure they won't oscillate in other load conditions.

Now, I said the mainframe is mostly happy...
The high-power compartment is being a bit stubborn still..
The PNP transistor os rock solid, but the NPN is still being naughty.
I added a few ferrites and it solved the 4-ish MHz oscillation, but now there's a 9-something kHz oscillation to kill too.
The maximum ripple is stated at 600mV, but the ripple is pushing it out to 650mV..


Well, at least it's better, but still not great.


ENHANCE! again and we see 9.4kHz.

So, next is to dampen that 9kHz ripple, I'm sure the 40cm long wires from the backplane PCB to the pass transistors located on the other side of the mainframe (good job on that one Tek engineers...) isn't helping things.
The usual 10-100 ohm series resistor on the base does nothing, 0.1uF cap between base and emitter makes it worse, and more ferrites has no effect as the ripple frequency is so low...

Looks like we fixed the oscillation due to the parasitics, but now we have a loop instability problem. Might need some RC network lovin' applied in a special place.

Gotta hunt for the solution this weekend..

[HenryFeng]

It was designed in the 70s which 2 layer PCB is still the state of the art, any fix is just patching by today's standard. Or you have to wait until the PC Era to get a more robust design.
 

TEK 7603 restoration

See if this mod is installed and try it if not.. Apparently it reduces the fuzzyness which is a GHz range oscillation. It might help a little.
Shouldn't need much more than a bit of copper or brass strap.

https://w140.com/tekwiki/images/0/0e/7603mod36005.pdf

Thanks !

So Tek was aware of the problem... yet they put that scope on the market anyway 
The guys in the marketing dept must have told management : " We have a narrow window to launch these new 7000 series of scope , it's NOW and not in 3 months ".
... "You can always improve it later, but it needs to go public NOW ".

Oh dear..

That board is easy to access from the side of the chassis, once you remove a large access door, so I had a go at it.

So I added a strap, well two, because the one shown in the Tek illustration is super wide, don't have that.
Best I could come up with in a hurry was to find a use for my 35 year old 15 meter roll of 3mm wide tinned solder wick !
Too coarse to work on your average electronic board, and too much of a thermal mass for my 50W iron to heat it up quickly.

So I put two pieces of braid in  //, each insulated with heatshrink tubing. Blue tubing of course, because.. it's a Tek ! 
I don't know, I felt in the mood of using some colour..

Given how old that braid is, needless to say solder doesn't stick to it any more... but if you heat it up long enough and use enough of ym long expired 30cc syringe of flux... you can bring it back from the dead...

So the result ? Well, scope still works and no smoke, so that's a good start. I would need to male a side by side comparison to be objective.. Which is not possible of course.
So I have to go with my memory here, of what it was like before I put the straps in place.  I would say it's better. Hardly "Tektronix sharp", but better enough that I think it exists and is not a placebo effect. So I will take that... thanks Terra for the link.

I also noticed that the display at power up does not move and up erratically any more... well it might come back later who knows, but for now I don't see an ounce of it any longer, so I will take that as well !   We will see in the longer run.
Maybe the various connectors just needed to be reseated / cycled..

Also replace more caps!

I found 4 electrolytic caps on that board. No alu ones, but 4 dipped tantalums, the old variety with colour bands and dots on them. All the same value it looks like, though I don't know what value that is... need to google how to decode the markings. So I could replace those I guess.

And check for drifted high value carbon composite resistors in HV circuits and replace as needed (I replace almost all carbon composite resistors with metal film by default these days, besides those in HF signal path where some care is required).

Will look at the HV section later on, but I fear it might not be feasible as access looks to be... impossible. I mean I can't even SEE where the HV stuff is located  in that chassis !    That's definitely not promising to me...


23H45.... 

[factory]

TEK 7603 restoration

...snip...

I found 4 electrolytic caps on that board. No alu ones, but 4 dipped tantalums, the old variety with colour bands and dots on them. All the same value it looks like, though I don't know what value that is... need to google how to decode the markings. So I could replace those I guess.

And check for drifted high value carbon composite resistors in HV circuits and replace as needed (I replace almost all carbon composite resistors with metal film by default these days, besides those in HF signal path where some care is required).

Will look at the HV section later on, but I fear it might not be feasible as access looks to be... impossible. I mean I can't even SEE where the HV stuff is located  in that chassis !    That's definitely not promising to me...


23H45.... 

Here is the missing tant color code info, that Tek forgot to put in the 7603 manual. The stripe on the side is the voltage coding & polarity marking.




David

[Vince]

Thanks Dave.

OK... so that dot shows the polarity and voltag rating.... all 4 caps have identical markings, so all 1uF 50V... which is.... annoying.... real.... annoying, given that two of them decouple the 50V supplies... zero headroom, wow.... playing with fire here...

Looks like 50V was the highest voltage rating available, according to that table, but they could have at least put two caps in series couldn't  they ? 

Looking at the schematic, the amplifier runs on the +/- 15V supplies. The +/- 50V is used only to drive the deflection plates. So yes I guess any imperfection in those overstressed tantalum caps will transfer straight to the trace on the screen... so worth replacing those caps indeed.

Just looked at my two local shops. They both have cheap dipped tantalum (just don't ask for a datasheet or who makes them, I guess...), and well, both shops have only 35Volts caps max....  hmmm.... OK. So I will put two 2.2uF 35V caps in series to get about 1uF 70V. 45 cents each and local pick up down town... it's within my budget 

Though to be honest it would be mayb cheaper to order them from that other local-ish shop (40 miiles away). 5 Euros shipping... might actually be cheaper than wasting 3 hours to endure teh traffic jams to get to town center and back, wasting lots of petrol and wearing out teh clutch brakes and suspension and engine at every of the many many many many... countless speed bumps, one every 100 meters or so... it's a  French disease...  I think I will soon buy an old Jaguar just so I can ride over the speed bumps like on a magic flying carpet.

Anyway, so I guess these caps will be replaced early next week then. That will be one more thing out of the equation.

[TERRA Operative]

If the tants are just for power supply duties, why not replace with electrolytics with decent voltage rating headroom?

[tautech]

If the tants are just for power supply duties, why not replace with electrolytics with decent voltage rating headroom?

That's certainly a viable option but Low ESR or not ? Not is what I would pick and if anything fast was needed parallel it with a ceramic.....trouble is sometimes you don't have the room which is why tants were selected in the first place. 

[Vince]

If the tants are just for power supply duties,

Aren't they always for decoupling power rails anyway ?! 
EDIT : oh no not always I guess... only 99% of the time. In that QUAD 303 pwoer amp I am workign on, I replaced two dipped tantalums, they were used as AC input coupling caps. I guess that's the exception that confirms the rule..

why not replace with electrolytics with decent voltage rating headroom?

I don't know, it did not even occur to me TBH... dipped tantalums are still readily available and cheap so why chance it  ? I am nowhere near as clever as the engineer who decided to use them 

I don't master the subtleties that lead to choosing tantalum or aluminium in this specific application. How will one or the other affect the noise injected to the plates...

Well, I will tell you what. Given how cheap these caps are, and how easy to access that board, I will try BOTH options, and see if there is any difference in quality of the trace, and if there is, I will just go with whatever type of cap works best. Sounds like a plan ?

So as I understand it, the aluminium caps would nee dto be 2 or 4 times the capacitance of the tants ?

So let's say  I use 3.3uF instead of 1uF.

[tautech]

So let's say  I use 3.3uF instead of 1uF.

I'd go higher to 10 or more.
YMMV

[BU508A]

So let's say  I use 3.3uF instead of 1uF.

I'd go higher to 10 or more.
YMMV

I'd use 4,7µF/100V/105°C Jamicon electrolytic capacitors and in parallel 1206 X7R 100nF/100V SMD ceramic capacitors from Vishay.
This should do the trick.

[DC1MC]

Sorry for spamming this thread, but is a little project important for me and I know that the people collective experience here is way longer than a millennium  , so kindly please go to the thread here and help me chose the MCUs of that project:

https://www.eevblog.com/forum/projects/improved-performance-5v-arduino-nanomega-compatible/

Some of you know me, even personally and know that I'm (mostly) a non-BS, straight person and I've tried to help when I could, now I will appreciate a bit of support 

Cheers,
DC1MC

[TERRA Operative]

My Tek 2467 scope is now calibrated and fully working, yay! The calibration process isn't the most user-friendly thing, and a few steps weren't described very well, but I was able to figure it out ok.

I also have a 2467B so the 2467 just needs reassembly to be put on the 'to sell' pile.



Aaannnddd, the Tek AWG510 Arbitrary Function Generator is adjusted now too. This thing is a monster! Waaaayyy big, so it's off to be sold too.

I've decided I want a HP 3458A eventually, so I need to accrue coin.

[TERRA Operative]

And now it's time to get the spare TM5006A mainframe working.. I got two rack mount TM5006A (I'm using one) and one TM5006, so two of these will be sold to make space. They are rather large...

I already replaced a couple blown transistors and associated burnt resistors just the other day, but I just now found a faulty LM339 that I replaced from my spare parts stock and now the thing actually puts out its voltages as expected with no load.
However.... when I load it up on my test load bank as per the manual, the voltages collapse. booo.

So, I've basically traced it down via a process of elimination to the PWM controller chip, an SG3525.

Annnd no-one in Japan seems to have one in stock..  Anyone here happen to have a spare SG3525, UC3525 or KA3525 laying around?

[Zoli]

...
Anyone here happen to have a spare SG3525, UC3525 or KA3525 laying around?

Most important part: what package?
Disclaimer: I don't have one, but in a week I can dig out a DIP-16 one(tested working).

[TERRA Operative]

Looking for DIP-16

Ha, I'll be in Canada for a few days in a few weeks actually, wanna come drop it off in Yellowknife for me?

[Zoli]

Looking for DIP-16

Ha, I'll be in Canada for a few days in a few weeks actually, wanna come drop it off in Yellowknife for me?

Or maybe you want to fly down in the greater Vancouver area? Anyway, if there's no offers this week for replacement, next weekend I will extract the one in case; and tomorrow I will confirm if it's possible.

[TERRA Operative]

Looking for DIP-16

Ha, I'll be in Canada for a few days in a few weeks actually, wanna come drop it off in Yellowknife for me?

Or maybe you want to fly down in the greater Vancouver area? Anyway, if there's no offers this week for replacement, next weekend I will extract the one in case; and tomorrow I will confirm if it's possible.

I will have a layover in Vancouver... Gonna go stock up on some me-sized clothes at a McArthurGlen outlet store. Clothes run like 3 sizes small here in Japan, and 28cm is about as big as shoes get (I'm size 31)...


Need something from Japan? We can do an exchange. hahahaha

[Zoli]

Looking for DIP-16

Ha, I'll be in Canada for a few days in a few weeks actually, wanna come drop it off in Yellowknife for me?

Or maybe you want to fly down in the greater Vancouver area? Anyway, if there's no offers this week for replacement, next weekend I will extract the one in case; and tomorrow I will confirm if it's possible.

Looks like no need to cannibalize that one, since LCSC has the SG(ST) and KA(onsemi) in stock, beside the usual second source(Xinluda, HGSemi, etc.) ones.

[factory]

A quick HP blanking decade counter IC update, the PCB layout is done with four layers.



David

[Vince]

Now it's official, Dave is a big fan of Deep Purple ! 

[tautech]

Now it's official, Dave is a big fan of Deep Purple ! 

Who isn't ?

[BU508A]

Now it's official, Dave is a big fan of Deep Purple ! 

Others are (not me of course!) fans of Mireille Mathieu. 

Purple PCBs are usually coming from OSHPark.

[Gertjan]

Factory:
My comliments for your very nice work! 

[Vince]

Now it's official, Dave is a big fan of Deep Purple ! 

Others are (not me of course!) fans of Mireille Mathieu. 

Purple PCBs are usually coming from OSHPark.

Have 45 years of experience with French people. Have never met a sngle one who was a fan of Mireille.

However compared to the music that's been coming out here for the past 25 years, I think I would rather listen to Mireille, honestly.

But I shouldn't even be posting this, I am late for work...

[m k]

Not France Gall, eh.

[dl6lr]

Others are (not me of course!) fans of Mireille Mathieu. 

At least she can sing. She is a very professional singer with a very good voice. Quite some years ago, I saw her in a talk show. And just there she began to sing, no orchestra, nothing. Clear, crisp and struck every note, that was amazing. Nevertheless, I would not buy a record of MM.

BTW: DEEP PURPLE ROCKS!