Test Equipment Anonymous (TEA) group therapy thread

[McBryce]

Been poking at things again this weekend.

Replaced the capacitors in the PSU in my TDS220 scope, noticeably less noise on the trace with no signal now.

Also, had a go at one of my FG504 20MHz Function Generators. It isn't turning on, and I found it had a popped C122B1 SCR in the +25V PSU board. Thanks Peak DCA75 component tester!
The parts list in the manual says 2N4441 for this part, but it looks like they are both obsolete of course, but I found I can get an 8P4SMA part from Akihabara that looks like it's a close enough match to work.

Apparently I might have 2N4442 (slightly higher voltage rating) if that helps.

David

If you can scrounge up two you could send all the way east (both my FG504's have popped the same part..) I love you long time with some Paypal action.

Any idea why they both failed the same way? the thyristors are part of the OVP crowbar circuits.

The good news is I have six parts labelled 2N4442, bad news is Mr Peak doesn't recognise any of them, according to the datasheet on the web, the gate trigger current is typically 7mA, the DCA75 should be able to check between 8mA & 12mA, no idea why it doesn't like them.  The parts look suspicious, the leads are tinned (mostly) & the part number area has been resurfaced, could they be relabelled used parts?

David

Those pins look seriously oxidised. Maybe try cleaning the pins first?

McBryce.

[m k]

If you mean 100 MHz then yes as I wrote above, according to TekWiki, 100 MHz it is...

Did you do what BU did?

I'm quite sure your post didn't have pictures when I answered, but anyway.
Yes, obviously 7603 and not 7103.

[m k]

"ground” is a convenient fantasy

One pic from last weekend at the Maker Faire in Hannover ...  Pic is from my dear fellow Denis

We have prefix grounds, one is flower pot ground.
It's different than any signal ground, sometimes like a protective earth.

[Robert763]

On testing the 2N4441s.
These are fairly insensitive devices and can have hold currents up to 40mA. This is outside the specification of the DCA75 which only works with sensistive SCRs and TRIACs. The specification says <12mA trigger and hold current so a 2N444X is unlikely to test on a DCA75.

[TERRA Operative]

Went past Akihabara at buy the Peak SCR/Triac tester, but alas, none in stock...

So I put one on order. Should arrive between 4 days and 2 weeks they said.

[tggzzz]

"ground” is a convenient fantasy

One pic from last weekend at the Maker Faire in Hannover ...  Pic is from my dear fellow Denis

We have prefix grounds, one is flower pot ground.
It's different than any signal ground, sometimes like a protective earth.

And, of course, not all grounds are at the same potential.

Basically "ground" is a fiction, but a fiction that is convenient and useful in a limited domain.[1]

The limits deserve to be understood, since they are interesting and important in practical circumstances.

[1] another way of putting it is that "all models are wrong, but some models are useful".

[factory]

Any idea why they both failed the same way? the thyristors are part of the OVP crowbar circuits.

The good news is I have six parts labelled 2N4442, bad news is Mr Peak doesn't recognise any of them, according to the datasheet on the web, the gate trigger current is typically 7mA, the DCA75 should be able to check between 8mA & 12mA, no idea why it doesn't like them.  The parts look suspicious, the leads are tinned (mostly) & the part number area has been resurfaced, could they be relabelled used parts?

David

So here's a weird thing... My DCA75 also can't figure out the 2N4441's from the older FG504 here either. Just says 'no component detected' like yours.
BUT, of the C122B1 SCR's used in my later FG504 instead of the 2N4441's, it says one is ok, but the other is bad.

Both power supply PCB's exhibit the same faults, so I assumed the 2N4441 in the older PSU that is in the same location as the bad C122B1 in the newer PSU must be bad, seeing as the DCA75 said nope. But from your measurements, it might not be that simple...

My Chinese T4 tester roughly agrees with the DCA75, saying both 2N4441's are resistors, the bad C122B1 is a resistor and the good C122B1 is a transistor (close enough).



Hmmm, I wonder if we just have all bad 2N444x's between us (unlikely) or maybe I need to go buy a Peak SCR100 SCR/Triac tester when I get paid next?.....

Ok I missed the max values in the datasheet, I guess none of mine are typical examples. 
Guess I could manually test them.
We had a GEC (I think ??) test set for diodes/thyristors, it could test at several gate currents and higher voltages, can find anything on the web for that tester.

Those pins look seriously oxidised. Maybe try cleaning the pins first?

McBryce.

Maybe I didn't word that very well, the leads looked to have been tinned (aka dipped in solder bath).

David

[TERRA Operative]

Looks like the Littelfuse MAC15x series Triacs are a pretty close match to the 2N444x series with a nice bit of overhead current/voltage rating to boot. Cheap and plentiful on Digikey, so I might grab some of those and see what they perform like.

https://datasheetspdf.com/pdf-file/74617/MotorolaInc/2N4441/1

https://www.littelfuse.com/~/media/electronics/datasheets/switching_thyristors/littelfuse_thyristor_mac15m_d_datasheet.pdf.pdf

[Vince]

If you mean 100 MHz then yes as I wrote above, according to TekWiki, 100 MHz it is...

Did you do what BU did?

No, not at all.

I'm quite sure your post didn't have pictures when I answered, but anyway.

No, as I always do, I attach all my pics before posting my message. there is zero reason for doing otherwise. So yeah, I can guarantee that all my pics were attached..

However, as for INLINE images, well, singular here, of course since this feature is borken as yuo know, the only work around is to first post your message without them, then click on the thumbnail of the pic(s) you want to inline, then edit your message and copy/paste the URL of all the pics, one by one, and one by one select them to add the "IMG" tag around them. So this takes a minute or so to do.
So it's possible that you did not see the inline image if you checked my message litterally within the first few seconds of me posting it....

Yes, obviously 7603 and not 7103.

Oh boy thanks for that ! I scrolled back for some reason yes, I kept mentioning 7103 everywhere instead f 7603 ! 
Now fixed 

[Vince]

The time-base plug-in in a vertical slot shouldn't cause any trouble. The 7000 series is very versatile and some people use this configuration with a time-base in vertical slot to generate rasters for television display purposes.

Oh thanks for that ! That's excellent news indeed !!! 
What a relief ! 

In refurbishing any 7000 series scope you should pay particular attention to any tantalum bead capacitors, which are used fairly extensively in these models. Tektronix at the time did not derate their operating voltage and consequently they have a strong tendency to suddenly fail short and cause damage to surrounding circuitry. Any wet tantalum capacitors (in the silver cylindrical cases) are generally safe from sudden shorts but they occasionally leak their acid electrolyte causing extensive damage to PCBs

Oh that's bad.... tantalum caps are so very expensive, it there are so many of them, it's gonna bankrupt me 
Well I will power it up on my dim bulb tester to keep it from frying, in case some tants are already shorted, and go find them... and I will see about doing all the others as preventative maintenance.... need to assess the cost of this advnture... also in terms of man hours... I mean I had a quick look at the internal pics of the beast in Tekwiki, and it looks jam packed, compared to my type 5111.

[TERRA Operative]

I can get the dipped tantalum capacitors cheap in Akihabara. Maybe I can send you some.
Only the dry-slug tants are stupid expensive (The wet slug ones are pricey, but they can usually be replaced with electrolytics), normal dipped ones aren't.

Too bad shipping big stuff overseas is so expensive, I want to get rid of my 7704A with 7A26, 7D15, 7B71 and 7B70 plugins.

[Vince]

Me is after one of thoe THS Portable Tek scopes one day.... used to cost 750 / 1500 Euros here, but looks like the crisis has made sellers more reasonable evntually ?

This 200MHz 1GS/s model costs only 250 Euros  !

https://www.leboncoin.fr/bricolage/2221285019.htm

Still far from having recovered financially so even at that price it's a no-no, but it's nice to see prices on these puppies drop quite a lot !

Same for the TDS220 that used to fetch 300+ Euros and sell instantly regardless of condition... now you routinely find them at 150 or so, and even at that price they don't sell all that quick. Sometimes takes 3 days for them to go.

[TERRA Operative]

I want one of those too, but they usually sell for more than my impulse buy limit for something that old with that bandwidth.

[Vince]

I can get the dipped tantalum capacitors cheap in Akihabara. Maybe I can send you some.
Only the dry-slug tants are stupid expensive (The wet slug ones are pricey, but they can usually be replaced with electrolytics), normal dipped ones aren't.

Thanks !  I will wait to receive the scope and see just how many tants there are in there.... and price it locally. Then we can work out if it's cheaper to pay for shipping from Japan !
It probably will be cheaper, since a small padded enveloppe would be enough, and hopefulyl regular enveloppes don't cost too much to send, even from Japan. I don't know...

Too bad shipping big stuff overseas is so expensive, I want to get rid of my 7704A with 7A26, 7D15, 7B71 and 7B70 plugins.

No worries, keep everything around please... we can just add that to the palette that will carry my future TDS 784D ! 

[AVGresponding]

I want one of those too, but they usually sell for more than my impulse buy limit for something that old with that bandwidth.

You don't buy those for the bandwidth, you buy them for the independently isolated channels. I have (courier allowing) a TDS784C arriving tomorrow, might want to pick your brains re PPM

[capt bullshot]

I'd recommend to go for one of these instead of the THS7x0:



It's missing the DMM, but can do everything else better than the THS ones.
Don't ask for the price, it was stupidly expensive, but I wanted one (mostly for the isolated channels, they really come in handy sometimes) ...

[duckduck]

I'd recommend to go for one of these instead of the THS7x0:



It's missing the DMM, but can do everything else better than the THS ones.
Don't ask for the price, it was stupidly expensive, but I wanted one (mostly for the isolated channels, they really come in handy sometimes) ...

I see that this model has an optional battery pack. That is very handy. What are isolated channels? Does that mean that the ground connection on each channel isn't connected to the others?

I did read the manual (quickly) to see if I could find the answer: https://download.tek.com/manual/071144105web.pdf

EDIT:

Also, I didn't see this model in the TekWiki: https://w140.com/tekwiki/wiki/Main_Page

[AVGresponding]

I'd recommend to go for one of these instead of the THS7x0:



It's missing the DMM, but can do everything else better than the THS ones.
Don't ask for the price, it was stupidly expensive, but I wanted one (mostly for the isolated channels, they really come in handy sometimes) ...

There's an immense difference in price; also they are less portable. Both of these matter to me, but might matter less to others of course.

I see that this model has an optional battery pack. That is very handy. What are isolated channels? Does that mean that the ground connection on each channel isn't connected to the others?

I did read the manual (quickly) to see if I could find the answer: https://download.tek.com/manual/071144105web.pdf

EDIT:

Also, I didn't see this model in the TekWiki: https://w140.com/tekwiki/wiki/Main_Page

Yes, each channel ground is isolated independently. They are especially useful for probulating SMPS because of this.

[TERRA Operative]

I can get the dipped tantalum capacitors cheap in Akihabara. Maybe I can send you some.
Only the dry-slug tants are stupid expensive (The wet slug ones are pricey, but they can usually be replaced with electrolytics), normal dipped ones aren't.

Thanks !  I will wait to receive the scope and see just how many tants there are in there.... and price it locally. Then we can work out if it's cheaper to pay for shipping from Japan !
It probably will be cheaper, since a small padded enveloppe would be enough, and hopefulyl regular enveloppes don't cost too much to send, even from Japan. I don't know...

Should be around 700-800 yen for a small box (Think the physical size of a 3.5" HDD) weighing a few hundred grams. Maximum size for the cheap 'small packet' service is up to the size of about a tissue box, max weight of 2Kg. Gotta go by boat though due to Corona... The last thing I sent to France just arrived last week and took 3-4 months.

[Vince]

4 months ?! 

Well.... that's OK... it's about the time it takes me anyway, at the best of times, to fix my old junk !

So it's just fine with me ! 

[Specmaster]

TTI / Thurlby Thandar came through on the TG1034 function generator.
Got an email with both operating and service manuals this afternoon. Turns out the rotary control is working OK. Use is not intuitive though. You have to press the Deldts buton and the the parameter button for the parameter you want to adjust.
Easy once you know how. Nice little generator, it will be my main one, well two actually as it hs two generators in one box.
Anyone want a Wavetek 274?

Yep, that's why I have so much of their gear in my line-up, last time I checked I had 15 of their gear and all but 1 item is fully working and in use on my bench, the other is sitting in my repair queue. I find it so refreshing to find a company that is willing to still support its old models well. 

[tautech]

I'd recommend to go for one of these instead of the THS7x0:



It's missing the DMM, but can do everything else better than the THS ones.
Don't ask for the price, it was stupidly expensive, but I wanted one (mostly for the isolated channels, they really come in handy sometimes) ...

Yet a selection of differential probes is the better long term option as you can use them on any scope.

[srb1954]

In refurbishing any 7000 series scope you should pay particular attention to any tantalum bead capacitors, which are used fairly extensively in these models. Tektronix at the time did not derate their operating voltage and consequently they have a strong tendency to suddenly fail short and cause damage to surrounding circuitry. Any wet tantalum capacitors (in the silver cylindrical cases) are generally safe from sudden shorts but they occasionally leak their acid electrolyte causing extensive damage to PCBs

Oh that's bad.... tantalum caps are so very expensive, it there are so many of them, it's gonna bankrupt me 
Well I will power it up on my dim bulb tester to keep it from frying, in case some tants are already shorted, and go find them... and I will see about doing all the others as preventative maintenance.... need to assess the cost of this advnture... also in terms of man hours... I mean I had a quick look at the internal pics of the beast in Tekwiki, and it looks jam packed, compared to my type 5111.

I would do a resistance check on all supply rails to check for shorts before powering up, just to be sure. I am not sure that a dim bulb tester would fully protect your scope against a shorted tant.

Since it is really only the tants on the supply rails that need replacement, and with the major advances in component technology since the 7000 series was designed, you could probably replace most of the suspect tants with modern low ESR aluminium electros for a substantially lower cost and no degradation of performance.

I suggest you post a query on TekScopes@groups.io - there will be plenty of advice on there from people who have already been through the tant replacement exercise.

[DH7DN]

"ground” is a convenient fantasy

One pic from last weekend at the Maker Faire in Hannover ...  Pic is from my dear fellow Denis

Epic 

[Carl_Smith]

Me is after one of thoe THS Portable Tek scopes one day.... used to cost 750 / 1500 Euros here, but looks like the crisis has made sellers more reasonable evntually ?

I've wanted one of those since I used one at a job a long time ago in the 1990's.  I worked at an electric forklift manufacturer.  The drive motors used separate field and armature windings and the field current direction was controlled by an H bridge to reverse motor direction.  So you can't look at the field current at the same time as anything else because when the field reverses direction your scope ground lead is now connected to a 36V battery that can put out a few thousand amps and that tends to not go well.

But with isolated channels you can just put one channel on the field winding and one on the armature (which is also not ground becuase it's low side switched) and just watch the voltage to both no problem.

You might think that is not a common probing situation, so I have a more likely one.  Watching voltage to both windings of a bipolar stepper motor on your 3D printer. 

Anyway, I've been watching eBay for like 6 months and in the US it seems like any of them that are actually in working order and come with the original type probes still go for over 300 dollars.  I also hesitate to bid on any that don't show a good picture of the BNC connectors.  They are plastic (for safety) and are often damaged.  And they are molded into the case so it is not practical to replace them.

I let one by that looked like it was almost new in box.  The original box was also included.  But it was around $400.00...