New owner of Tektronix THS710A, Questions & Discussions

[BravoV]

Edit :
The original title was "Tektronix THS710A at $190, grab it ?" , updated since I already grabbed it and now questions and discussions at this handheld Tek scope.



The frequency of measurement activities using scope is getting more and more at switching power supply, even though I have a 1Kva isolation transformer. Yes, I'm aware the limitation of using an isolation transformer and know how to use it properly, its just I'm getting tired of using it and also its error prone. For sure when it comes to mobility factor using bench type scope + iso-tran. is practically zero. 

The condition of the Tektronix THS710A physically is at 95% as the seller claimed, comes with complete all standard accessories like two genuine Tek probes, the pouch, Tek DMM probes and manuals.

Another advantage point, I will be allowed to test and verify it physically, apart from the standard built-in diagnostic mode, since the transaction will be at the seller's place, I guess I will not be able to test it's measurement throughly, any hints or tips on this part ?

Although its only 60Mhz bandwidth and with 250 MSa/s at only 2500 samples  , am I on the right track if I trust the safety regarding it's isolation spec & design compared to cheap Chinese modern hand held scope which definitely have much higher specification on bandwidth, samples rate and samples size ?

Again, I'm not looking nor expecting to use it in troubleshooting anything else except for "common" switching power supply. At 60Mhz is "adequate" enough right ? cmiiw

Suggestions, comments & thoughts are welcome.

Illustration quoted from it's manual regarding the isolation design attached below.

[EEVblog]

60MHz is plenty for switchmode work.
Sounds like a bargain, grab it.
Yes, trust the Tek.
The proper isolated Tek probes are important.

[Fraser]

I own the THS720. The asking price is a bargain for a 710A in good working order ! They sell for around $1000 on e*ay.

Grab it. If you ever want to sell it you will get your money back on it or even a profit !

[Shock]

Factor in if the battery hasn't been replaced in a few years it's probably toast.  That may also work to your advantage when you ask that question. You can also check the date on it I assume it will have one.
http://ths710bat.blogspot.com.au/

[BravoV]

60MHz is plenty for switchmode work.
Sounds like a bargain, grab it.
Yes, trust the Tek.
The proper isolated Tek probes are important.

Our glorious leader  has given the green light, I feel confident now, thanks Dave. 

I own the THS720. The asking price is a bargain for a 710A in good working order ! They sell for around $1000 on e*ay.

Grab it. If you ever want to sell it you will get your money back on it or even a profit !

Great to hear another vote for confidence  , btw, any tips apart from the standard self test to verify if its working adequately without signal generator in hand ? Remember, I will be testing it at the seller's premises.

Factor in if the battery hasn't been replaced in a few years it's probably toast.  That may also work to your advantage when you ask that question. You can also check the date on it I assume it will have one.
http://ths710bat.blogspot.com.au/

Great info, thanks a lot ! 

Yeah, I'm expecting that, NiCd just can't last that long.

[marshallh]

I had a THS720A for a while. The official batteries are ludicrously expensive.

You can build an identical one with http://www.batteryspace.com/nicdbatterypack48v30ah4xcendtoendwithtabs.aspx
I used alum. foil to bring down the pos. terminal to the spring contact using a band of aluminum foil.
See the official battery for reference.

The scope has a trickle charger circuit built into it so tha'ts all you need.

[SeanB]

Simple test is to place a piece of wire in the input socket and look for a 50/60Hz hum signal. Will not be looking like a clean sine wave, but as long as it is the mains frequency and varies in amplitude as you move your hand closer or further away from the wire it is working. Sensitivity will need to be close to the max for this of course.

[PA0PBZ]

http://www.batteryspace.com/nicdbatterypack48v30ah4xcendtoendwithtabs.aspx[/url]

Nice, but $115 shipping is a bit too much for me 

[Fraser]

The original battery was toast on my unit but a newer one was supplied and that is still OK. I have looked into building a new battery as it is simple except for the unusual charging connection down the side of it. I have the batteries, heat shrink and self adhesive copper to make a copy. I recommend using self adhesive copper tape as it is possible to solder it where needed. I even considered modifying the DSO and connecting the charge wire to the positive battery terminal but decided it wasn't necessary.

To test the input amplifiers you need nothing more than a 1.5V battery. Set the DSO to DC input and apply a positive input and then a negative input. If it deflects 1.5V, it is likely that the unit is working OK. These are well made units but the LCD can show its age in terms of contrast. Still very readable though.

[Jay_Diddy_B]

Hi,

I can show you how I made my battery for a THS730A. The batteries for the THS710, 720 and 730 are the same.
The original battery was constructed from 4 NiCad C cells.

I found 4 Sanyo NiCad batteries with tabs welded to them. I soldered the tabs together to put the four cells in series. The tricky part is the positive terminal, this must be connected to a metal band around the bottom cell. I used thin brass metal for the connections. The brass is easy to solder.

I held the whole assembly together with tape.

Here are the pictures:






Jay_Diddy_B

[SeanB]

Nice, I was looking to do the same for some Maglite battery packs, but decided the simpler thing is to just toss the 20 year old pack, gut the charger and replace the pack with a cylindrical lithium cell pack, using the spare space to install the charge controllers and LED drivers. just means I will have to draw some circular PCB's to stack in there. Long term project though, I have enough torches just the Maglites look so nice aside from the poor battery chargers.

[BravoV]

@SeanB & @Aurora, thanks for the advices, btw I brought 9V battery and it helps as expected, yes, done deal and it has a new home & owner now.

@Jay_Diddy_B, thanks for the battery shots, really appreciate it.

I think I got the whole shebang, complete with all those hooks, probe's accesories made by Pomona & Mueller, heck, even the multi-colored rings for the probe id are still sealed in the plastic. The lcd backlit is also still really bright, looks like the previous owner rarely used it and still looks so new, no even a scratch at the scope body and the screen is still shiny. And even the DMM probe tips are still protected with the rubber caps.

The battery confirmed dead as expected, the scope was tested using the AC adaptor and works flawlessly. Now new homework to do, buy new C or AA cells and mod the battery pack.

Again, thanks to all for the suggestions and comments given. 


Few eyes candies attached of my shiny THS710A below, freshly captured.

[qno]

Good job.

I also have 2 of them. A 720 and a 710.
What is the software version?

Need some more info? Check out

http://warped.org/tek/

I use a program Wintek32 to capture screenschots to the pastebuffer.
You can paste screenshots directly into your MS-Word research report.....

[BravoV]

qno, thanks for link  , damn, I didn't know there is a fan page for these Tek portable scopes. 

Firmware version is 1.11 dated back 1997, is there anything that I should aware of regarding this version ?

Photos of the power-on diagnostic screen, and screen of detail firmware version attached below.

[BravoV]

Just thinking out loud about the battery replacement, obviously buying the genuine replacement is NOT an option for me. 

Say we're not discussing and forget for a while the troubles of making the tube with it's unique contact points, protection circuit against charging the battery while its inside the scope and etc, has anyone ever thought of using rechargeable Li-Ion cell as an alternative replacement for this really pricey battery ?

Fyi, I can get a genuine Panasonic 18650 Li-Ion cell with 3.1 AH capacity (NCR18650A) at $11/pcs, while the genuine Tek battery replacement for example at Element14 cost $195, go figure. 

The Tek standard battery is just a stacked of 4 C sized NiCd cells rated at 2.8 Ah, and as the manual stated, the scope has approx 2 hours of "continuous" use from a fully charged battery, realistically from I gathered around the net is about 1.5 hours. Meaning the average current consumption only at 1.4 A, which is still within safe region say for a common 18650 Li-Ion cell.

Of course with the "assumption" that the scope will terminate the discharge when the NiCd cells are reaching at 0.9 Volt/cell (3.6V), and this low volt threshold level should be compatible with the Li-Ion safe discharge voltage level, cmiiw.

Any other thoughts about this idea just in case I missed something here ?

[Fraser]

I considered alternatives but have a distrust of DIY Li-Ion as I am not familiar enough with the batteries needs.

I personally planned to take a much easier and IMHO safer route. I bought four C size high capacity Ni-Mh batteries which have higher power density than the original Ni-Cd cells. The Ni-Mh cells are the easily available retail type that have the protruding nipple top. They fit in the THS-720 battery tube fine.

To charge them without the daft hardware around the cells, all you need to do is open the DSO and rum a jumper wire from the tubes side (charging) contact to the tubes positive contact. This has little risk and is IMHO safer than the original design. So why did Tektronix use such an odd battery design ? My kind side says it was to prevent people trying to charge alkaline cells that were placed in the battery tube. My less kind side says it was a measure to prevent users buying replacement batteries from a normal battery supplier    The battery is nothing special at all, it is just the charge contact that makes it different to COTS 4 x C cell battery packs.

IMHO using the method I have detailed above is the simplest, quickest and least damaging to the DSO's standard build. Nice high capacity C cells will give a longer run time. It is easily reversed by removing the jumper wire. replace my one working battery, it will be the modification that I employ.

[qno]

The software did not change very much.
Just some extra functions
Zoom when in multimeter mode.
Trigger on the multimeter input.

Manuals should be on the net somewhere Haven't checked..

[BravoV]

I personally planned to take a much easier and IMHO safer route. I bought four C size high capacity Ni-Mh batteries which have higher power density than the original Ni-Cd cells. The Ni-Mh cells are the easily available retail type that have the protruding nipple top. They fit in the THS-720 battery tube fine.

If you're done making that, share it please.

I've considered C size Ni-Mh too, like using high capacity 5000 mAH Imedion brand battery from Powerex, the problem I see is the trouble of charging them, this new generation NiMh batteries wont react too well if using slow charging method, minimal at 0.5 C in order to detect full charge state, meaning a whopping 2.5 A Ni based charger that DIY route is a must.  Most commercial NiMh charger out there maxed out at 2 A, and only for AA size, not C  or must be really hard to find . Currently I just can not afford the trouble in building this dedicated 4 C cells high capacity NiMh charger at the moment.

Since AA size charger is almost everywhere, I'm also thinking to use the AA to C adapter like below photo, stack and stick 4 of them, while maintaining the open and close mechanism for battery replacement, and do some modding at the gap inside the case with cable from the top and route it to the positive contact band made by a copper strip outside like Jay_Diddy_B's work.

[BravoV]

The software did not change very much.
Just some extra functions
Zoom when in multimeter mode.
Trigger on the multimeter input.

Manuals should be on the net somewhere Haven't checked..

Which version is that with that extra features ?

I guess with this old generation scope, updating the firmware by user is not possible without cracking up the scope right ?


What manuals are you talking about ?

[Fraser]

I am no expert on the latest Ni-Mh chemisrty but your suggestion that a charge rate of 0.5C minimum comes as a bit of a surprise.

I have charged modern Ni-Mh C cells at currents as low as 100mA and achieved a full charge. The capacity was tested with a CBA III battery discharge analyser (constant current load)  It was my understanding that fast charging cells meets the needs of the consumer but does reduce the cells life span. Historically, the best charge upload to a Ni-Mh cell has been a low current over a long time frame, followed by trickle charge current to maintain charge at 100%

The RC world do treat batteries in a very different way to 'normal' consumers. They want fast charging and peak perfromance in terms of available current and duration. They are willing to cook their batteries to achieve this in competition use. An RC racer would laugh at me slow charging a battery. They tend to charge at 1C or even 2C !

[BravoV]

I am no wexpert on the latest Ni-Mh chemisrty but ypur suggestion that a charge rate of 0.5C minimum comes as a bit of a surprise.

I'm not a battery expert too, its just there are too many "convincing" references that agree the only reliable method to determine when a  NiMH cell has reached full charge state is using the Negative Delta Voltage detection (NDV) method. But using NDV method, the cell must be charge minimal at 0.5 C rate.

Again, there are too many references on the net, picked and quoted few crucial points regarding the charge rate on NiMH cell from this popular web site that is specializing in battery.

• The NDV method to measure full charge shows only a faint voltage drop, especially when charging at less than 0.5C.
• It is difficult, if not impossible, to slow-charge a NiMH battery. At a C rate of 0.1 to 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full-charge state accurately and the charger must depend on a timer.
• At a sufficiently low charge rate, NiMH can remain totally cool and yet suffer from overcharge.
• NiMH cannot absorb overcharge well ...

Read the rest yourself here -> Battery University : Charging Nickel-metal-hydride

[Jay_Diddy_B]

Hi,

I agree with BravoV. I have been involved with the design of several Nimh chargers. The biggest challenge with Nimh is determining when the batteries are charged.

The biggest single problem is caused by not using enough charging current.

The Linear Technology LTC4010 datasheet gives some insight into charge termination methods.

Link to datasheet:http://www.linear.com/product/LTC4010

If you don't use enough charging current you do not see the negative dv/dt and you do not see the rapid change in cell temperature.

Jay_Diddy_B

[Fraser]

Thanks guys. I have learnt some important information here. I have a bank of Ansmann XBase Delux chargers that I often use to charge my batteries and that unit permits charge currents as low as 100mA and I must admit that I have seen some false triggering of the charge endpoint on occassions when I have dilaied in a lowish current for a high capacity NiMh cell. All very interesting stuff.

I have always been a little concerned with what I call 'Fast Charging' i.e. less tha 8 hours as I mistakenly believed that the batteries preffered more gentle handling and I wanted to avoid cell overheating as well.

Thanks again.

[BravoV]

Noob questions just to make sure before I toast this fine scope or worst injured/killed my self, cause all this time I never even dream of using a scope to probe directly at mains voltage, btw the mains at my house is 220V (single phase).

From the scope's manual :



Since my activities only at home on my bench and no heavy machineries in my house, so its safe to categorize my electronic activity is in CAT II environment, right ? cmiiw 


Now, this is the "10X" standard probe's specification included with the scope package.



Even I though I have not try it yet, and to be honest I'm still abit scared to do it , its clear and there is even an example in the manual that we can poke it directly at the mains line. Remember, this is a 10X probe.


Next, the scope's input specifications.




Now, questions ... 

- At the scope spec above (1), in CAT II environment, the scope's input should be safe to be connected "directly" at mains ?

- At point (2), say we're using rated accessories, what and why the concerns regarding this earth ground vs common ? There is no exposed metal/conductive parts starting from the scope's body, BNC connectors and down to the probe, except at the tip and the scope's ground alligator clip (Common).

- Point (3) at the channel to channel commons with such low voltage limit, what kind of situations that must be avoided before breaking this limitation ? Example or worst case scenario please.

- Say I just want to monitor and observe low frequency signal directly at mains, maybe just in few Khz range (< 100Khz) and with max 20Mhz BW filter turned on. Is it safe to use the DMM probe at the scope input like below photo ? Remember, since this is direct connection, hence no attenuation what so ever (1X probe), and at the scope there is a menu to select the probe at 1X or 10X. Fyi, the banana to BNC adapter is fully isolated, high quality stuff from Philips/Fluke, and that DMM probes + hooks are the standard accessories from this Tek's scope for it's DMM function, and its manufactured by Mueller.

[Jay_Diddy_B]

BravoV,

The special feature of the P6117 probe is that the BNC connectors are insulated on the outside. The way the probe body is shaped it harder to touch the ground lead.

The rating published by Tektronix are all about the benefits from having this insulated BNC connector.



For example if you have two regular BNC cables connected, the safety limitation is from the safety hazard presented by having the two exposed (un-insulated) connectors.

What is the mains voltage in your area?


Jay_Diddy_B