Test Equipment Anonymous (TEA) group therapy thread

[srb1954]

I did notice that the inner conductor of the probe cable is solid wire - not stranded wire. I would have expected stranded wire used for something that had to take being moved around quite a bit over its lifetime. Hmmm ...

Most x10 scope probe cables have solid wire in them. It is not copper wire but a special resistance alloy to introduce some damping on reflections in the cable.

This alloy is a lot tougher than copper wire and doesn't break easily with flexing; I have never seen one of these wires break in the middle of a probe cable. If it going to break it is usually right at the termination end where it is crimped or soldered to the termination circuitry.

[TERRA Operative]

As for tonight's work, I just calibrated my Tek 2445 scope. I had already done a bit of work on it ages ago, maybe even have a video on it on my Youtube channel. Just a usual fan repair and Rifa replacement. Didn't bother with capacitors etc beyond that.

It adjusted perfectly and works really well. I am happy, should be easy to sell this one as fully working and calibrated/adjusted.   

I would be weary of buying one that hadn't had a PSU recap, someone on another forum bought one that had only had the X2 caps replaced (sold as recapped), it didn't last long before the PSU failed causing lots of damage. Casualties were the HV board, various op-amps on the A5 board, two CA3046 transistor array and the U950 hybrid and few others I can't remember. This took several months to fix, I ended up repairing the A5 board & confirming the defective U950, don't say you weren't warned. 

David

Alright, you convinced me. I dug through my stock of capacitors and found all but one cap ready to go. All United Chemicon caps too.

I know what I'll be doing tonight....  

[tautech]

Jason of Siglent NA received my email and is sending me a new probe. So, I'm impressed with customer service. 

Jason is a top dude and does all the NA Siglent videos.
We chat about things often as he visited NZ a few years back before we got to know one another.

Received a new replacement 200 MHz probe for the SDS2202X-E today. It does not have any noise issues when wiggling the cable. So I decided to take apart the original one to see if I could find any problems inside.

I disassembled the original probe. After inspecting the guts with a microscope, I failed to find any obvious issues. I really was certain that the cable connection was going to be the issue. Once taken apart, I placed it in a plastic 3D printed vise, and connected it to the calibration signal with a test lead. I could not get it to exhibit the original issue - the noise issues when the cable was wiggled (although it did pick up mains noise which was to be expected with the shield taken off). Perhaps some component was touching the metal shield that the PCB slides into?

Put it back together and it again exhibited the noise only when the cable was wiggled or pulled. I now thought it may be the connector at the end of the internal PCB. It connects to the probe pin inside the metal shield, which is not making good contact. That is why when it is connected to the signal via the clip lead the noise does not appear when wiggled.

Removed the plastic probe tip assembly from the metal shield. When I pushed it back onto the PCB end connector, it does not fit tight at all. The PCB end female has two small dimples in either side that are supposed to clamp to the male pin - they are not formed correctly and do not grab the metal as they should. This is what is wrong with these probes (that hopefully the sub-contractor has fixed).

I did notice that the inner conductor of the probe cable is solid wire - not stranded wire. I would have expected stranded wire used for something that had to take being moved around quite a bit over its lifetime. Hmmm ...

Interesting.
2 thoughts.
As the inner conductor is an alloy, has it tinned properly to the solder for a rigid perfect connection ?
It appears the probe coax is terminated with a crimp which one imagines also terminates the braid.

IME with these faults cable termination is the issue for which one doesn’t need to be a rocket scientist to see it must be one or the other of the above…….. but which ? 

[xrunner]

Interesting.
2 thoughts.
As the inner conductor is an alloy, has it tinned properly to the solder for a rigid perfect connection ?
It appears the probe coax is terminated with a crimp which one imagines also terminates the braid.

IME with these faults cable termination is the issue for which one doesn’t need to be a rocket scientist to see it must be one or the other of the above…….. but which ? 

Well my friend ... thinking about it today, why don't we just do this ...

Rebuild it.

I've never needed to do this to a scope probe but it should work out. I was able to un-squish (technical term) the crimp holding the shield enough to pull the cable out. The metal that was crimped takes solder very well. Since I don't have the crimping tool they used, I can tap the metal in a couple of places with a small punch when I re-do the end on the cable and want to hold it in. But to make damn sure it's electrically connected I think I'll also solder the braid to the metal. Any advice you guys have let me know before I go further.

 

[tautech]

Interesting.
2 thoughts.
As the inner conductor is an alloy, has it tinned properly to the solder for a rigid perfect connection ?
It appears the probe coax is terminated with a crimp which one imagines also terminates the braid.

IME with these faults cable termination is the issue for which one doesn’t need to be a rocket scientist to see it must be one or the other of the above…….. but which ? 

Well my friend ... thinking about it today, why don't we just do this ...

Rebuild it.

I've never needed to do this to a scope probe but it should work out. I was able to un-squish (technical term) the crimp holding the shield enough to pull the cable out. The metal that was crimped takes solder very well. Since I don't have the crimping tool they used, I can tap the metal in a couple of places with a small punch when I re-do the end on the cable and want to hold it in. But to make damn sure it's electrically connected I think I'll also solder the braid to the metal. Any advice you guys have let me know before I go further.

 

 

Can you rebuild it in such a way that it can be soldered later if/as necessary ?
Doing this could better point out the earlier failure point which don't appear to be the inner conductor based on the healthy layer of tinning on it.

I can't help think as it's a low % braid cover and therefore easy to miss braid strands with the dimple crimps. 
Your findings might suggest the makers need to retool to add more dimples into the crimp.
Otherwise all continuity checks out okay ?

[xrunner]

Can you rebuild it in such a way that it can be soldered later if/as necessary ?
Doing this could better point out the earlier failure point which don't appear to be the inner conductor based on the healthy layer of tinning on it.

Don't think so. The metal that was crimped is already cracking and I don't think it will hold a good crimp again. I don't even have the tool for it - whatever it was.

I can't help think as it's a low % braid cover and therefore easy to miss braid strands with the dimple crimps. 
Your findings might suggest the makers need to retool to add more dimples into the crimp.
Otherwise all continuity checks out okay ?

It did but I've taken it apart as you see. Now I have a new issue I was unaware of. The center conductor wire will not take solder. 

I've tried everything including flux meant for plumbing and the special wire will not accept solder.

I have since researched it this evening and I see others commenting on that fact on other sites. Now look at the previous picture again of the center wire apparently soldered to the PCB. Or ... is it just sitting in a "blob" of solder simply making contact by existing in the blob? I'm beginning to think it is.

So I'm stuck and I would like advice from the crowd. 

[tautech]

 
Don't worry laddie, no way I missed that it was plonked in a pool of solder and that's what I believe you should repeat using minimum heat and maybe some 2% silver solder which is lower temp too if you have some.

I should really get some of the dud probes I have here and experiment with them.....some wet days coming and our house will be empty of visiting family come tomorrow. 

[Neomys Sapiens]

Don't worry laddie, no way I missed that it was plonked in a pool of solder and that's what I believe you should repeat using minimum heat and maybe some 2% silver solder which is lower temp too if you have some.

I should really get some of the dud probes I have here and experiment with them.....some wet days coming and our house will be empty of visiting family come tomorrow. 

That is close to what I would have tried. Maybe use a glass fibre burnisher on the wire directly before your next try and use additional flux - but SnPbAg is the way to go!
And pre-tin both the screen strands and the inside of the ferrule, but remove most from the latter. Then, only when you have achieved a good center connection, heat this assembly and feed in a tiny bit more solder.

[Neomys Sapiens]

After having been asked to tidy up my office a bit, I started with removing some sample boxes from TI and AD, consolidating their contents and carrying them home. Lots of various OPAs and TPS linear regulators to record in the componnts list...ugh. Finally done. I have succeeded to noodle several 'Enhanced Product' variants out of the TI guys. But the limit to Quantity = 2 from AD sucks severely. One has to pester them repeatedly for the same parts to make them usable.
 

[BU508A]

@Neomys

One of these are available for 10 Euro in Ebay Kleinanzeigen:

[syau]

So, it seems one of my TM5006 mainframes has had a fit and blown out two IRF840 transistors in its past life, I also had to replace a few popped resistors that died due to the dead-short MOSFET's, they put on a show when I replaced the fuse and powered it up..

The other mainframe that I'm keeping needs a new mains input filter/fuse holder/voltage selector ,   so I'll grab a freaking expensive Schaffner FN372-6-21 to replace it, it looks to be a direct replacement 
with all the correct terminals.
Hopefully this one wont pop in my face when I turn it on.... 


Time to get a Mouserkey order underway I think...

Solder those freaking expensive mains input filter/fuse holder/voltage selector is messy as you need to desolder the old one and hook up the wire to the new one through the opening.

[McBryce]

@Neomys

One of these are available for 10 Euro in Ebay Kleinanzeigen:

Link?

McBryce.

[PA0PBZ]

Link?

https://www.ebay-kleinanzeigen.de/s-anzeige/messgeraet-yokogawa/2323443215-168-20774

[TERRA Operative]

So, it seems one of my TM5006 mainframes has had a fit and blown out two IRF840 transistors in its past life, I also had to replace a few popped resistors that died due to the dead-short MOSFET's, they put on a show when I replaced the fuse and powered it up..

The other mainframe that I'm keeping needs a new mains input filter/fuse holder/voltage selector ,   so I'll grab a freaking expensive Schaffner FN372-6-21 to replace it, it looks to be a direct replacement 
with all the correct terminals.
Hopefully this one wont pop in my face when I turn it on.... 


Time to get a Mouserkey order underway I think...

Solder those freaking expensive mains input filter/fuse holder/voltage selector is messy as you need to desolder the old one and hook up the wire to the new one through the opening.

I'm lucky with this equipment that the old input filter thing had mostly fast-on connectors, only two soldered wires.
On the replacement I'll be able to use the Fast-on connectors all round, so it'll be easy this time.

[ch_scr]

So, it seems one of my TM5006 mainframes has had a fit and blown out two IRF840 transistors in its past life, I also had to replace a few popped resistors that died due to the dead-short MOSFET's, they put on a show when I replaced the fuse and powered it up..

The other mainframe that I'm keeping needs a new mains input filter/fuse holder/voltage selector ,   so I'll grab a freaking expensive Schaffner FN372-6-21 to replace it, it looks to be a direct replacement 
with all the correct terminals.
Hopefully this one wont pop in my face when I turn it on.... 


Time to get a Mouserkey order underway I think...

Solder those freaking expensive mains input filter/fuse holder/voltage selector is messy as you need to desolder the old one and hook up the wire to the new one through the opening.

I'm lucky with this equipment that the old input filter thing had mostly fast-on connectors, only two soldered wires.
On the replacement I'll be able to use the Fast-on connectors all round, so it'll be easy this time.

Beware, on the filter I bought, the links from line filter to fuse input (that come pre-installed) were not only non-isolated, but one was also loose, like a slip fit on the lug!
In fact, it was more held in place by the short, bent wire itself - I originally removed them to put at least some heatshrink for insulation, wouldn't even have noticed otherwise

[TERRA Operative]

Ooh, thanks for the heads-up! Will check it when it arrives.



In TE news, the 2445 has just had all PSU caps replaced and it still boots! It's all fully adjusted and working perfectly too, so happy days there.

Next on the bench to be adjusted is a 2467, I lost the cal data when I messed up with the backup to the backup battery (yep, score one to doing it with mains applied I guess. damnit. Well, I was young and stupid! ), one pin on the battery I soldered to on the PCB was not a battery terminal pin (just there for mechanical support), so poof went the cal data.... 

It happened two years ago and I stuck it on the shelf with a sulky face to await my accumulation of the needed equipment to calibrate and adjust it.
Now that time has come, so it will be made whole in the next few days. 
I also found that Tekwiki has -09 firmware roms where my unit has -06 (now uploaded to Tekwiki too), so I burnt a set of replacement EPROM chips (keeping the originals safe for now) and stuck them in. Still boots to the 'you dun fk'd up, no cal data' error so so-far so-good.

The next after this will be the 2467B, the crown jewel of my analogue scopes. Not sure if I'll keep these two 2467 scopes yet. The MCP screens are cool, but they're delicate and have a limited lifespan so I have to be careful with them, and anything I'd use them to utilise their capabilities, I'd just as soon boot up the TDS784D or TDS794D.

I think in real-world use, a 2465B is much more day-to-day useable. Maybe I'll keep the 2445 for now, sell the rest of the analogue scopes and see if a decently optioned 2465B pops up one day.

[xrunner]

Before I repair the cable end of the defective scope probe, I want to get the loose connection at the probe tip fixed so I don't have to work with it while the cable is attached.

Please refer to the attached picture - the bottom item is the female connection on the probe PCB, the top is an example of a female 2.54 mm header crimp part. Again, the problem here is that the pin which slides into the probe PCB connector (bottom part in the picture) is just way too loose.

The defect is that the dimple which you can see has not been formed properly, it isn't deep enough. There is one on the opposite side also. The pin just sits in there loose and only by some slight misalignment does it even touch the metal. This is why just barely moving the PCB by pulling on the cable can cause signal loss at the other end.

I'm investigating options, which include making the dimples deeper, finding a new female pin from various part bins, and even using the 2.54 mm header female. It doesn't fit as-is, but would easily if I pried it apart just a little bit. It would grip very easily and well. All it has to do is slide on one time and shouldn't have to be taken apart again.

[Robert763]

Just received another 'scope  A real high perfomer and very expensive - or maybe not.
A Scopex 4S6. This is a 1980's low end service / educational model. All transistor apart from the CRT. 6MHz single channel.
On eay "not working" but shown with a stationary blob on the screen. Maiden bid won it for under £10 including postage 
Plugged it in and sure enough a stationary blob. controls have some effect but there is also a smell of warm transformer  . Opening it up showed an additional small transformer screw in the bottom. As suspected a filament transformer indicating a insulation breakdown in the original. Not looking good 
No manual in any of the usual places, but odly enough th schematic of the powersupply and CRT was used in a book on 'scopes by Ian Hickman. Quck checks showed LT about right, HT (unregulated) low but no ripple. big clue. The LT, HT and EHT windings are all in series with lower end connected to chassis. EHT uses a capacitive coupled voltage doubler.  Easy to isolate by lifting one of the capacitors, I didn't want to dig the EHT probe out. A quick check showed HT is now correct. Checked the rectifiers, two pairs of 1N4007s in series, and two were reading about 100mV both ways on the Fluke 8060A diode check. Two new diodes and it's all working  . Whole bunch of red Plessey electrolytics in it but they all look good and check out OK. Case is blue textured vinyl coated steel. A quick spray with foam cleaner and scrub with a nail bush and it cleaned up nicely.
Nice little basic 'scope with bright sharp trace. Might use it for a 'scope clock.

Robert.

[xrunner]

I attempted to fix the original female connector by making the dimples deeper, but I could not get a result I liked. So I went with the option of replacing it with a female header pin which is shown in the pic. All I needed to do was enlarge the opening a bit. The results are good. It slides on tightly and the metal fingers grip the pin very nicely. That issue is now fixed, and I'll move on to the other end and work on attaching the probe cable.

[Robert763]

So I had the little Scopex 4S6 sat next to me on soak test and heard a noise. looked over and it was back to a blob on screen ans a strong smell of cooked resistor 
So whipped the covers off and a 1/W 100R resistor between the rectifier and smoothing capacitor for the 280V EHT had smoked. Capacitor checked out OK and the rectifier, a 1N4007, diode checked OK. However a check with an insulation tester showed it was breaking down. All unplugger and ready to work on I picked it up and the damm EHT bit me. Nasty white burn on finger tip 
The 1N4007 was the same odd package (rounded ends to plastic body) as the EHT ones. All of those have now been replaced and 'scope is working.

[xrunner]

I set up a test to compare the resistance of the repaired probe to an original probe of the same make. This simply checks the resistance of the inner conductor - nothing more - from BNC to probe tip. As I had to redo the inner conductor in the solder "blob", I wanted to make sure it was OK.

I removed the original solder blob (presumably unleaded) and replaced it with electronics silver solder. As I found out, the inner wire alloy does not "wet" like a copper wire. I just exists in that solder blob.

The resistance of an original probe is shown on the Fluke and the repaired probe on the Rigol. Looks OK so I'll move on to fixing the braid to the crimp connector.

[Wolfgang]

Now it got me as well. The rabbit did its TEA job:

https://electronicprojectsforfun.wordpress.com/finally-i-was-caught-in-a-tea-rabbit-hole/

 

[Peter_O]

I have a small 'had to be bought' on my table.

What is your best method to get 40 years of gunk out of HP knob grooves?

[ch_scr]

I have a small 'had to be bought' on my table.

What is your best method to get 40 years of gunk out of HP knob grooves?

Either sopay water or isopropyl alcohol and an old toothbrush.

[AVGresponding]

Though sometimes, only a new toothbrush will do...