Tektronix TCP202 current probe repair - Schematic and suggestions needed - Page 1
Forum section: electronics / repair

author: AndersJ
author_rank: Frequent Contributor
timestamp: July 08, 2018, 10:06:29 am
content: The probe output is constantly at 2 Volts.Possibly the internal negative voltage is gone.I have double checked with other probes and other power supplies.I believe the problem is in the probe.Does anyone have a schematic diagram or suggestions?Thanks,Anders J

author: tautech
author_rank: Super Contributor
timestamp: July 08, 2018, 10:45:51 am
content: Have you got the manual:http://download.tek.com/manual/070954202.pdfCan't seem to find any repair threads on them.

author: AndersJ
author_rank: Frequent Contributor
timestamp: July 08, 2018, 03:50:46 pm
content: Yes, I have the users manual.No schematics unfortunately.

author: lukier
author_rank: Unknown
timestamp: July 08, 2018, 04:37:14 pm
content: Do you have any pictures of the internals, both the probe and the plug end?Maybe this way we could help. I don't have TCP202, but I have A6302 with AM503 and AM503B amplifiers, so maybe there are some similarities. AFAIR TCP202 doesn't have the 50 Ohm amplifier with ranges and whatnot that standalone units use and terminates into 1M straight into the scope and relies on the scope frontend on AC/DC and ranges.

author: AndersJ
author_rank: Frequent Contributor
timestamp: July 09, 2018, 08:31:23 am
content: Here is a picture of the opened compensation box.The SO8 next to the OP27 is damaged, and the part number is partially gone.The part number seems to end with "58", possibly prefixed by a "4".Could be a LM1458.Does anyone have a TCP202 they could open and verify this?

author: Giaime
author_rank: Regular Contributor
timestamp: July 09, 2018, 12:12:33 pm
content: Hi!I have one: you can find a pic attached. I confirm it's an MC1458

author: AndersJ
author_rank: Frequent Contributor
timestamp: July 09, 2018, 12:19:35 pm
content: Many thanks for your confirmation./Anders

author: KrudyZ
author_rank: Frequent Contributor
timestamp: July 09, 2018, 05:06:20 pm
content: Looks like a few of the SOT-23 parts are fried as well.

author: AndersJ
author_rank: Frequent Contributor
timestamp: July 09, 2018, 05:50:21 pm
content: I had not noticed those before, thanks.I have now found 2 that need attention.Giaime,can you take a close up photo so I can identify the two SOT-23 parts?

author: Giaime
author_rank: Regular Contributor
timestamp: July 11, 2018, 06:52:29 am
content: Hi! Here are some additional photos, hope they help:

author: AndersJ
author_rank: Frequent Contributor
timestamp: July 11, 2018, 09:48:07 am
content: Thanks Giaime,I cannot tell for sure how the SOT-23 next to the MC1458 is marked.It looks like it could be GJ1 or GJ or perhaps 6J1 or 6J,Can you try to see what it says, perhaps using a magnifying glass.I have not been able to locate a SMD part marked GJ1.I also tried 6J1 but cannot find that either.The closest one I found is 6J which is a N-ch fet 2N4391ora some sort of resistor network./Anders

author: Giaime
author_rank: Regular Contributor
timestamp: July 11, 2018, 11:55:27 am
content: Hi!1AM is easy, should be MMBT3904.The other one looks to me 6J1, could be MMBF4391 but it's not 100% guaranteed.

author: vtp
author_rank: Regular Contributor
timestamp: July 11, 2018, 04:13:41 pm
content: From my notes on TCP202 disassembly and reverse engineering for repair:6J = MMBF43911AM = MMBT390426 = MMBD1203Both JFETs are used during degauss. One is to isolate OP27 from the power amplifier (1/2 1458, BCP68/69), the other appears to enable degaussing oscillator (1/2 1458).

author: lukier
author_rank: Unknown
timestamp: July 11, 2018, 04:59:53 pm
content: Quote from: vtp on July 11, 2018, 04:13:41 pmWould you mind sharing some of this info? Some pictures from the back, maybe simplified schematics?I'm asking, because I don't like my AM503/AM503B amplifiers and I think it is silly to replicate scope frontend (ranges, AC/DC) and 50 Ohm amplifier there when there is one in the scope. Don't know why Tektronix went for it even in TCP300A (although allegedly there they've stopped using custom hybrid ICs).So I always wanted to somehow mod my A6302 probe to be more like TCP202 (although with LeCroy's interface preferably), but there is very little online on these devices and signal conditioning.I know very briefly how the DC probe works, studied old AM503 schematics a bit, but I'm not confident enough to risk damaging my A6302

author: vtp
author_rank: Regular Contributor
timestamp: July 11, 2018, 06:16:32 pm
content: Quote from: lukier on July 11, 2018, 04:59:53 pmMy notes are four pages written and hand drawn schematics and I do not have scans of those. Not that they would do much good as the whole thing is a bit scattered around those pages.But the operating principle is similar to other current probes. There is the head with its HALL-element and coil in the same magnetic circuit. HALL-element signal is differential input to the OP27 with 1k60s as inputs and 20k0s to GND/output. Then it goes trough 475R to one JFET that can disconnect the OP27 during degauss.If the sensed signal is allowed to continue it goes to input of 1/2 1458 which has PCB68/69 discrete output stage driving the coil in the probe head. This is used to compensate the field sensed with HALL-element. The other end of the head coil is filtered and brought out then directly to the probe output BNC-connector (at the bottom board). So the coil is in series with the PA and probe output. Gain of the PA looks to be set with 10k0/2k00 resistor divider and it is non-inverting. OP27 output is brought to the 1458 inverting input trough the said 475R and the JFET.The rest of the probe electronics are degaussing oscillator and power supplies. It uses +-15V and +-5V from the tekprobe interface.TCP202 head differs from others regarding few parameters, the coil DC-resistance is higher at about 6.5 ohms to make driving it with a smaller amplifier easier. A6302 and TCP312 coil DC-resistances seem to be around 2 ohms. These are not very accurate measurements, they were taken with a Fluke 87 from the element....To the OP, I do not quite understand how someone has managed to blow up those two JFETs and the 1458. The probe head may have touched live high voltage wire but even then it should have been limited to high current going trough ground shields. Unless there has been a breakdown in the head itself when you are looking at about €1200 repair (flat exchange fee from Tek - or at least was several years ago) due to unobtainium head.It might be a good idea to check the head.If you look at the head element from the connector end the pin out should look likeCode:_____| || ||OOO| pins top row|OOO| pins bottom row-----The pins being HALL2, HALL1, +3V on the top row and COIL, -3V, COIL on the bottom row from left to right. That +-3V is voltage in A6302, TCP202 may have different hall operating voltage but I will leave it like that here.Resistive measurement between pins:+3V - -3V = 276 ohm+3V - HALL1 = 183 ohm+3V - HALL2 = 179 ohm-3V - HALL1 = 189 ohm-3V - HALL2 = 182 ohmHALL1 - HALL2 = 110 ohmCOIL - COIL = 6.5 ohmYours may differ from these several tens of ohms. If something reads hundreds of ohms different or around kohm or open then you have a damaged head.The same way it is easy to check quickly if an A6302 is ok as those signals are all brought to the cable connector.

author: vtp
author_rank: Regular Contributor
timestamp: July 11, 2018, 06:21:18 pm
content: Just digging the notes again, TCP202 head HALL-element operating voltage comes from +-5V through 220R resistors in series with both voltages.

author: lukier
author_rank: Unknown
timestamp: July 11, 2018, 06:49:59 pm
content: Quote from: vtp on July 11, 2018, 06:16:32 pmThanks! This is very appreciated.Now I get a better idea what's inside TCP202. It seems radically simplified from AM503A schematics (the most modern amplifier schematics available). There hall signal feeds MC34081P via 475 Ohm resistors, with non-inverting input grounded with 47.5K and inverting having 47.5K in the feedback loop + some RC filtering. Output from that goes via JFET (degauss disconnect) and feeds another MC34081P that drives multi stage totem-pole amplifier, with darlingtons doing the final push into the probe transformer. On both opamps there are input signals to adjust the offset, HALL_PREAMP_DC_OFS and PWR_AMP_DC_OFS, while TCP202 has only one knob. Degauss signal comes from amplified DAC output.In AM503A the second transformer output goes to the attenuatior and the rest of these duplicated scope frontend stuff. I'm glad to hear that in TCP202 it goes straight to the scope, without any termination inside the probe or similar stuff.What confused me in AM503A is that there is this FEEDBACK_LOOP signal that comes from Tek's custom made attenuator module into the line bettwen Hall OpAmp and PA OpAmp, adding something there for some reason.Now I might try some DIY, but still very careful, especially with this power amplifier output and fragile transformer

author: vtp
author_rank: Regular Contributor
timestamp: July 11, 2018, 07:28:10 pm
content: Quote from: lukier on July 11, 2018, 06:49:59 pmI was not very clear about this. There is some filtering and termination and even one trimmer in the probe box between coil output and BNC connector. So the coil comes to the probe box in a coax cable, goes through some filtering and four parallel termination resistors one of which has a trimmer in series probably to adjust the output amplitude/gain.Let me try to draw:Code:---R---| |------L----------L---------L------------------------------ output to BNC/scope| | | | | | | |R R R R R R R R+trimmer| | | | | | | |------ ------ -----------------gnd| |C C| |- gnd -I do not have component values for those except that the last L in chain is 10uH and has two 68R1 resistors in parallel to it (only one drawn above). Left is input from the coil.

author: lukier
author_rank: Unknown
timestamp: July 11, 2018, 07:55:35 pm
content: Maybe it is similar to the termination used in Tek's AC probes, like shown here:http://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdf(pdf page 69 and 70)

author: AndersJ
author_rank: Frequent Contributor
timestamp: July 14, 2018, 10:41:56 am
content: Hi all,I have replaced the visually obviously damaged parts.After that the probe behaviour improved, but it was not fully functional.The "undamaged" OP27 was uncomfortably warm so I replaced it too.After that, the probe seems to work.QuoteDuring the repair i noticed that the grey collar that mechanically locks the probe in place, was rotated 180 degrees.This means the probe will connect "backwards", possibly reversing power inputs, thus blowing the probe.This is normally not mechanically doable but with some ingenuity even the impossible might have happened.I don't know if this is the right explanation, but efter repairing it, I do not want to try that.Thanks for all help!/Anders J

author: Pic
author_rank: Newbie
timestamp: January 18, 2019, 05:39:33 pm
content: Thanks' to these posts I was able to fix my broken TCP202I did a short when I removed the probe from an unisolated 400V wire.I want to share some hints for everyone who did the same mistake.I exchanged the two SOIC-8 opamps. But it still did not work. Degauss, offset was working fine but the offset adjustment was quite sensitive. I figured out there was no voltage supplied to the HALL. The two 220R and two 1k resistors in series to the supply, next to the connector have gone high impedanze. I replaced them and now - everything is working again.Many thanks' to you folks!

author: Tantratron
author_rank: Frequent Contributor
timestamp: April 07, 2020, 05:54:46 pm
content: Hello,So far I've been using for most of my projects AC current probes P6021 and P6022 but lately I have new specific projects requiring DC-AC current probes.What is the global return of experience using these TCP202, are they quality, calibrated stable with little failure if used correctly ?Thank you, Albert

author: MarkL
author_rank: Unknown
timestamp: April 08, 2020, 04:39:42 pm
content: Quote from: Tantratron on April 07, 2020, 05:54:46 pmI think they are great probes. I have two of them, one is about 20 years old now purchased new, and the other one used about 2 years ago. I've had no performance issues with either of them.The only failure I can recall is that the older one developed a crack in the bottom plastic surrounding the core about a year ago. It hadn't quite reached the point of breaking off completely, and some plastic welder fixed it with no further cracking since then. I've seen several photos of used probes with this bottom piece missing, so it makes me believe it's a common weak point in the design.You might already know this, but being a powered probe, it does need a TekProbe II connection on your scope (or equivalent adapter), or an external power supply such as the Tek 1103.

author: Tantratron
author_rank: Frequent Contributor
timestamp: June 17, 2020, 02:11:42 pm
content: I've finally purchased one TCP202 probes from eBay in Austria, it came with a calibrate done by the vendor last week but for some reason, it does not work here in France.When I connect the probe to my TDS540C, the corresponding channel will shift automatic to 50ohms input impedance, it will display A (Amperes) instead of V (Volts).However when connected to a ballast source running at 250KHz, the signal is always zero plus it seems impossible to DC balance so no idea if the degauss works. The DC bias output stays always circa 20 mA flat.I've then tried connect the probe to my spare tek 1103 power supply adapter then my tek 2465, same story with no output whereas it should display circa 1.5A peak sinewave generator at 250 KHz.Do you know if the probe termination box circuits has some plug connector who could have moved or got loose during the shipment between Austria and France ?Any suggestions or guidance, thank you

author: MarkL
author_rank: Unknown
timestamp: June 17, 2020, 03:12:04 pm
content: I'm assuming you mean you can't get it to zero with the knob on the compensation box. Did you try the coarse balance adjustment on the underside of the probe body?See page 3 here:http://w140.com/tek_tcp202_instruction.pdfAlso sounds like you're not getting any signal out of it. Can you see any deflection with just a test DC current of 1A?

author: Tantratron
author_rank: Frequent Contributor
timestamp: June 17, 2020, 03:57:48 pm
content: Quote from: MarkL on June 17, 2020, 03:12:04 pmJust connected a DC load from then going up to 1A while the TCP202 clamped... no deflection at all on my TDS540C while pushing at different times the force trig

author: MarkL
author_rank: Unknown
timestamp: June 17, 2020, 05:29:13 pm
content: If it fails on both your TDS504 and the 1103, it sounds like it's the probe. You could also do one final check and do the 1A on/off test while measuring the output of the probe with a DMM. Also check the power supply pads on the 1103 TekProbe connector. Pinout is here:http://w140.com/tekwiki/wiki/1103Do either of the offset adjustments on the probe (not on the 1103) move the trace? Or change the DMM reading?There are two connectors inside the probe housing, and one inside the compensation box. Since it was presumably working before shipping, you could check to make sure that everything is seated properly.Be careful disassembling the probe head. There's a tiny ball bearing which can (and will) roll away unexpectedly. If you lose it, the jaws will not "click" closed.If you purchased the probe as "working", I would check with the seller before opening anything. They might not accept a return if you break any seals. And if it was supposed to be working and they don't want you to mess with it, I would return it.

author: Tantratron
author_rank: Frequent Contributor
timestamp: June 17, 2020, 05:43:20 pm
content: Thanks Mark for helping me.Could it be a situation that the trip from Austria to France would have created an internal connector loose via chock or vibration ?In the meantime, i've written to the eBay seller whom I now discover is a professional seller plus he works as a calibration technician to big company called TRESCAL Group (found his name on LinkedIn). What is wierd, this man is in the know of all these advanced and legacy testing gears plus he produced a calibration certificate on behalf my company.However one thing which annoyed me was the fact he said the probe to be in excellent condition but he never showed a picture where the internal jaw is partially cracked (see attached picture). Just hoping this will end OK because I've paid 500€ + 18€ shipment...Attached pictures I've sent him, you'll see my test using an induction lamp, my good old P6021 and P5210 then the flat output TCP202.Albert

author: MarkL
author_rank: Unknown
timestamp: June 17, 2020, 08:42:10 pm
content: Yes, I was suggesting that maybe a connector popped out during shipping, assuming the seller was being forthright. It happens.But metal parts around the core exposed, it looks like? If so, that piece of metal shielding is connected to ground when the jaw is locked. The broken insulator is supposed to protect you and your scope when measuring current through uninsulated wires.Besides the trouble with the functionality, that's a safety issue. Considering what you paid, I would return it as defective immediately.

author: Tantratron
author_rank: Frequent Contributor
timestamp: June 18, 2020, 08:15:32 am
content: The seller did not respond to my query sent yesterday so this morning I declared the issue to the eBay protecting system. He now accepted to refund me so I will ship back the probe. He claims to have tested the probe, that it worked prior shipping so my oscilloscope to be the problem. Anyway he did not comment on the other issue you have raised regarding the lack of isolation inside the jaw having in mind his eBay add said excellent condition.One last question, my TDS540C does self-switch to 50 ohms, DC and displays A (Amperes) instead of V (Volts) once the TCP202 is inserted then locked into of of its Channel input. Do you know if the electrical self-recognize this TCP202 probe by the TDS540C is just passive coded electrical connector or is managed by some active electronics in the probe internal PCB's.What is certain, no signal comes from this probe wether connected to a valid 1103, a valid TDS540C (I've tried all 4 channels) and there is a safety issue inside the jaw system. If some of you have such probe to sell and in good working condition, let me know since I need this probe along my actual tek P5210 to perform testing on behalf the University of Toulouse.

author: Weston
author_rank: Regular Contributor
timestamp: June 18, 2020, 09:43:45 am
content: That sucks that the probe you bought was a dud, best of luck in getting that resolved.I bought a working TCP202 off ebay in good condition in the beginning of march for $450, its really weird how ebay prices have almost doubled since then, I wonder what causes such price trends.From what I know, the read out is done via some standardized resistor value on one of the tekprobe pins. On the internet at large / eevblog forum there are tables of what resistor corresponds to what readout.

author: MarkL
author_rank: Unknown
timestamp: June 18, 2020, 03:06:58 pm
content: I'm sorry the purchase didn't work out for you. I'm sure there's one out there somewhere with your name on it.The TCP202 has a 24C02 EEPROM in the compensation box which is read by the scope. I2C is used on the TekProbe II interface.Probes with readout pins have a resistor that will set the scale multiplier, but I'm not aware of any values that will make Tek scopes change the units or termination to 50R.

author: Tantratron
author_rank: Frequent Contributor
timestamp: June 19, 2020, 02:26:59 pm
content: Quote from: MarkL on June 18, 2020, 03:06:58 pmInteresting to know that the TCP202 has a digital I2C serial bus to communicate between the probe part number and the digital scope. I guess same design (24C02 EEPROM with I2C bus) inside my high voltage differential probe P5210.Would you have a document or datasheet which details the precise signal mapping of the TekProbe output pins, there 4 pins on the left and 3 pins on the right then the BNC connector (GND and signal) when inserting inside say my TDS540C front panel ?

author: MarkL
author_rank: Unknown
timestamp: June 19, 2020, 08:35:20 pm
content: Quote from: Tantratron on June 19, 2020, 02:26:59 pmI have a P5205 and it does not have an EEPROM. The x50/x500 button changes the resistance on the "data" pin closest to the flange on the BNC collar. So, it changes the scale on the scope like the old-style probes. The 50x position is 1126R, but interestingly the probe needs power to set 676R for the 500x position. There must be a little bit of electronics involved with the readout pin.QuoteIt's an undocumented interface, but there's some info here:http://w140.com/tekwiki/wiki/Tekprobe_BNC_connectorA better resolution version of the pinout is here, along with some info on the evolution of Tek connectors here:https://download.tek.com/document/TekVPI.pdfAnd someone has an adapter board with labeled pad functions:https://www.eevblog.com/forum/circuit-studio/example-project-tektronix-tekprobe-adapterbreakout/msg1201386/#msg1201386If you search around the net there's various reverse engineering projects.I like TekProbeII probes because now that Tek's patent on it has expired (US4708661A), other major manufacturers are offering adapters to use Tek probes on their scopes. There's no need to re-buy all your expensive active Tek probes if you move to another scope manufacturer (well, minus the cost of the adapters).

author: Weston
author_rank: Regular Contributor
timestamp: July 03, 2020, 11:34:56 pm
content: I don't think I ever explicitly check the square wave response on my TCP202 when I got it, so I am unsure if this is a new issue or an old issue, but I have realized the square current step response is quite bad on my probe. It almost seems like a HF/LF compensation issue, but there is no way to adjust that. Here is a waveform where I compare against at CT-2 current probe.This has to be a defect, right? No way this is acceptable behavior for a commercial probe. Given that the probe works down to DC the hall effect sensor is still good.Right after degaussing before it jumps to the correct DC level the response looks more compensated. Could something have damaged the JFET that isolates the degaussing circuity from the amplifier? I have inspected the PCB and everything seems visually fine. I am pretty close to just replacing every IC on it that I can identify.

author: tautech
author_rank: Super Contributor
timestamp: July 03, 2020, 11:42:00 pm
content: Why is the trigger level outside the waveform ?

author: MarkL
author_rank: Unknown
timestamp: July 04, 2020, 08:12:19 pm
content: Quote from: Weston on July 03, 2020, 11:34:56 pmI have some non-flatness with my TCP202, similar to yours but not as extreme.Do you have 50R termination on in the scope? I never used an R&S scope, but I don't see an indication of the termination. Or maybe using an external terminator?What do you get with different input frequencies? Does it eventually flatten out with lower frequency?If it helps for comparison, below are some screen shots measuring the current from a signal gen output into my scope's Ch1 with internal 50R termination set. The TCP202 is attached to Ch3 with a Tekprobe II adapter which sets 50R automatically on the scope. I'd like to tweak the probe to be a little better, but as you point out there are no adjustments, except for the offset and gain. The TCP202 specs provide a very wide berth for "System Aberrations 10% p-p", but I think your probe should be doing better than you show.The AM503 service manual has some good background on how all these DC current probes work in relation to combining the signals from the Hall sensor and AC transformer. It may help you understand where to dig. Perhaps there are some factory selected components in the TCP202 that could be tweaked.

author: Weston
author_rank: Regular Contributor
timestamp: July 04, 2020, 09:30:53 pm
content: I am using an external 50 ohm load, I have already checked everything in relation to the tekprobe power supply, scope, and load.I saw the "System Aberrations 10% p-p", so guess this is technically in spec? I guess I am just surprised its so bad. Talking about this issue with a friend got them to check their AM502 + A6302 and they were seeing a similar response, although not as bad. Based on that + your measurements I guess its just bad compensation and not any damage to any of the active parts. I wonder if something drifted over time.It just seems to be some mid-band weirdness, its better at LF or HF. I measured a bode plot today using a 50 ohm shunt.I will have to read through the AM503 manual and see if I can figure out any ways to tweak the compensation networks, thanks for the advice!

author: Tantratron
author_rank: Frequent Contributor
timestamp: July 05, 2020, 04:54:18 pm
content: Quote from: Weston on July 04, 2020, 09:30:53 pmOne issue or explanation, this is a hybrid technology probe where they mix or fuse the hall sensor with the current sensor outputs. Normally tektronix design should compensate actively and passively the effect to get it much less that 10% otherwise what is the point to pay so much.Similar topic happens with Rogowski coil where you cascade or hybrid three types of integrator (two passive and one active)...So far I've never owned any hall-Transformer probe plus as mentioned before I got unlucky with a purchase on eBay-Austria. I've been refunded thanks to PayPal protection but do you guys confirm acquiring TCP202 is still good investment for laboratory use now we find this non-flat bump response ?For years I've been using P6021 and P6022 but these are only AC probes with incredible performance... the DC-AC philosopher stone is not easy to design or find !

author: Weston
author_rank: Regular Contributor
timestamp: July 06, 2020, 09:38:16 pm
content: I spent what is probably too much time this weekend fiddling with the TCP202. I reverse engineered a good portion of the schematic and took a lot of measurements (as a side comment, this board is really weirdly routed, did they use an autorouter or something??). The pulse aberrations are due to the nulling amplifier, nothing in the passive output network of the TCP202 seems to have relevant time constants.As previous comments have said, the hall effect amplifier is amplified by a OP27 and then further amplified and buffered by a MC1458 + PNP/NPN stage. The schematics for the AM503 and the AM503A have a similar configuration. One thing I noticed was that those units had adjustable feedback on the nulling amplifier output stage and had a R + C feedback network on the hall effect amplifier stage. The TCP202 actually has two sets of unpopulated pads for what I assume is a R + C feedback stage.I took some interesting waveforms from the TCP202, it is clear that the nulling amplifier is under damped. Here is a capture of the input current (green) probe output (blue) output of the nulling amplifier (orange) and output from the hall effect sensor ( yellow) (orange and yellow should be inverted).I guess if I took bode plots of a lot of things I could calculate more optimal feedback network values, but I already sunk more time into this than I wanted to and was getting tired of it. So instead I just iterated through possible tweaks of the two feedback networks. I tweaked the feedback resistor on the output stage, lowering it from 10k to 4.3k and that seemed to make the biggest improvement. Installing a 140p + 83k network on the unpopulated pads seemed to contribute a small additional improvement, lots of changes there just made the waveform worse, including RC corner frequencies used in the AM503 and AM503B.I changed the current level, so the scales do not exactly align, but you can see the waveform is now greatly improved!I assume manufacturing tolerances on the hall effect sensor lead to a range of gain values, so it seems to make sense that by changing the loop gain elsewhere I could improve the step response. The hall effect resistance in my probe seems to be lower than typical, I after the 220 resistors that drop the voltage from 5V to the hall effect sensor I was only reading ~+-1.8V instead of the +-3V others were mentioning. I think this may be related to why changing the loop gain was beneficial in my case.

author: MarkL
author_rank: Unknown
timestamp: July 07, 2020, 12:24:17 am
content: Quote from: Weston on July 04, 2020, 09:30:53 pmI dragged out my old AM503 + A6302 and looked at that too. I think it has a bad core or a bad mating between the transformer surfaces. Squeezing the surfaces improves a 10% overshoot problem by several percent. So, mechanical problems can cause bad waveforms too.Quote from: Tantratron on July 05, 2020, 04:54:18 pmThe small level of non-flatness I'm seeing in my TCP202 was surprising. I guess I'm going to have to temper my opinion of this probe a bit.However, I'll also say that in the 20 years I've been using it I never noticed it. The resulting waveform was always close enough to what I expected to see, and I never required a high level of precision.The aberrations may be a good question for the TekScopes mailing list on groups.io. I also don't know if the behavior is typical of other manufacturers' DC current probes.

author: Weston
author_rank: Regular Contributor
timestamp: July 07, 2020, 01:47:39 am
content: I always considered these probes the gold standard in current sensing so it is a bit discerning to see this behavior. I am still trying to figure out if my probe is within specs or is defective. Based on what others are seeing, if this is the case I am surprised its not a well known thing. I guess, similar to how I have not noticed until now, most people do not probe square currents where this behavior is most evident?In favor of the argument that these probes are all that bad, this post shows the weird crossover behavior in simulation;https://www.eevblog.com/forum/testgear/p6042a-tek-current-probe-replacement-circuits-an-61-lineartechnology/msg3085619/#msg3085619On the other hand, upon taking apart my probe and making sure that the surfaces were clean and in contact with maximal force, I was able to reduce my LF overshoot by a just barely perceivable amount. I have heard that the cores are fragile, it may be possible that we all have at least slightly damaged transformers with these ebay acquired probes.The research group I work in has some more modern current probes based on the same architecture. Next time I am in lab I will have to test and see if I can observe similar behavior.

author: MarkL
author_rank: Unknown
timestamp: July 07, 2020, 06:51:21 pm
content: I think you're right that most people are not usually looking at perfectly square current waveforms. I know I'm not, which is why I never noticed. Nevertheless, I still think it's a good test of the probe's signal integrity.My TCP202 was purchased new by me in 2000 and has never been mistreated.The A6302 was an ebay purchase, along with two AM503's. The A6302 has the same behavior on both AM503's, so I'm going to say the issue is with the probe. The AM503 has four compensation adjustments, but none can bring the output flat. Or even affect the waveform significantly, for that matter. I'm going to have to go through the official cal procedure for both of them.I have a second TCP202 which I will retrieve and test. It was purchased from another user on this forum in the Buy/Sell section a couple of years ago. It hasn't seen as much use, but again I never noticed anything because I wasn't testing square current waveforms with it. It's a newer version with a black cable instead of gray, and the serial number is on a tag on the cable instead of on the probe. But it's still labeled as a TCP202.I may also try swapping the comp boxes on the two TCP202's to see if the issue moves.It's also interesting to note there's no response flatness in the verification procedures or specifications for either the TCP202 or A6302/AM503. Only BW, rise time, and DC accuracy. You could have a completely bizarre waveform and still meet the verification (and still be within 10% "aberrations").The Agilent/Keysight N2893A (15A/100MHz) is similar in ratings to the TCP202. The specifications are even sparser. Accuracy is +/-1% of reading +/-1mV (DC or 45 Hz to 66 Hz), and rise time 3.5ns. They include a Bode plot showing (typical) flat response out to 10MHz and then a rolloff to -3dB at 100MHz. The amplitude scale is in 10dB increments, which is hardly enough precision to show anything interesting.If anyone else has a DC current probe from Tek or another manufacturer, it would be great if you could take a few minutes to test it and post a screen shot or two of a square current waveform. It could help answer the question if non-flatness is par for the course, or if all of us so far have messed up probes.

author: MarkL
author_rank: Unknown
timestamp: July 07, 2020, 08:19:44 pm
content: Ok, here's some screen shots.Since I mentioned it, first up is the A6302 overshoot. Screenshots included of normal pressure and then significantly more pressure applied to the transformer halves. The surfaces are absolutely clean, and under a microscope everything looks perfect. Maybe there's a tiny crack in the transformer core where it's potted that I can't see.Second up is some screenshots with the newer TCP202 that I purchased used two years ago compared to the older TCP202. At a low frequency it's absolutely flat. I couldn't ask for much better than that. But a closer look at the edge reveals a ringing problem, and by the looks of it at *two* different frequencies. Great. It's still within +/-10% aberration, but barely.All three current probes are clamped onto the same wire. The order doesn't affect the waveform shapes. All the differences appear to be introduced by the probes, and confirmed by the shot that also includes Vin (scope measuring across the 50R load which is creating the current draw). I must admit it's a bit disappointing.

author: MarkL
author_rank: Unknown
timestamp: July 08, 2020, 12:46:20 am
content: Here's some more screen shots of a couple other DC current probes, again clamped onto the same wire as the TCP202/AM6302 tests above.The first is an A6303 which is rated for 15MHz/100A and is also used with the AM503 amplifier. It has three tweakable compensation adjustments on the probe body and it's possible to get the response very accurate to the actual current. The rise time is showing a BW of only 13.5Mhz so a little more tweaking is in order. Perhaps an examination of what these pots do can be applied to the the TCP202 and/or the A6302.I'm not for a moment suggesting anyone use the A6303 for small circuit probing. The thing is huge. I was interested in seeing its response since it uses the same Hall/transformer design.The second is an Aim-TTi iProber 520 which is rated for 10A but is only 5Mhz. It's normally used open-ended to measure current in PCB tracks, but also comes with a horseshoe shaped attachment (presumably ferrite) to capture the flux around a wire. It uses a fluxgate magnetometer instead of a transformer/Hall device. It has a completely flat response apart from some settling after the edge.That's it for me. I'm out of DC current probes. Screen shots from other DC current probes from Tek and other manufacturers welcome for comparison.EDIT: Oops - had the iProber set on 500Hz BW limit. Screenshot fixed.

author: esc
author_rank: Newbie
timestamp: August 28, 2020, 08:16:14 am
content: Glad I found this thread.I also have acquired a TCP202 in good condition. The probe "operates" but it doesn't "work".I did test it with DC 1A and the display seems accurate. Also tested with DC 50mA and it seems accurate, but I need to degauss to go back to the original 0 value - after the DC 50mA test the trace is about 10mA higher then 0 every time. This may be normal, not sure.The degauss works and so does the coarse zero (on the back of the probe head) and the fine 0 on the side of the plastic box at the BNC.The sine wave in AC looks ok, but it is smaller than it should be. At 10KHz is about 15% smaller, at 20KHz is the worst, 60% smaller and it recovers at 40KHz to 15% again, staying around there to the MHz range. The square wave response is very ugly.I measured the transformer in the head and I got the following values (compared to the previously posted measurements):+3V - -3V = 276 ohm - 176 ohm+3V - HALL1 = 183 ohm - 93 ohm+3V - HALL2 = 179 ohm - 92 ohm-3V - HALL1 = 189 ohm - 141 ohm-3V - HALL2 = 182 ohm - 141 ohmHALL1 - HALL2 = 110 ohm - 72 ohmCOIL - COIL = 6.5 ohm - 6.5 ohmThese are with the small PCB in the head disconnected. Are these still in range?Also, the electronics in the plastic box looks good, no visibly fried parts, and no sign of any repair.Attached some pictures. The load is a 100 ohm metal film resistor.Any help would be greatly appreciated. Thanks.

author: esc
author_rank: Newbie
timestamp: August 30, 2020, 01:45:05 am
content: Sine wave picture at 20KHz.The two traces are supposed to be identical for the 100 ohm load (20mA/Div and 2V/Div).

author: esc
author_rank: Newbie
timestamp: August 30, 2020, 01:46:03 am
content: One more at 10KHz.

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 03, 2020, 09:54:26 am
content: Quote from: MarkL on July 04, 2020, 08:12:19 pmYou might remember that I did purchase few months ago a TCP202 to a eBay-Austrian but it was not working plus the jaw was partially broken so got lucky PayPal reimbursed me. This time, I finally acquired to Belgium a TCP202 along with a 1103 and P6243 where all work except the TCP202 would fail the compensation test on my TDS540C.I've carefully balanced the DC offset after de the degauss, the TDS540C and the probe been running at least 20min. However there seems to be a response flatness issue, please see attached two pictures taken this morning.What do you think and what would be the procedure to have a better flatness when 1KHz square current loop is sensed ?I'm still on my learning curve of the TDS540C use and many options. Do you know if the probe compensation output of the TDS540C and the probe calibrator are standard or precision 500mV and 500 mA references ?Thanks, Albert

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 04, 2020, 07:20:39 am
content: Earlier this morning, I thought to try leaving into open the probe jaw (see picture) and noticed then upon not easy or stable thumb pressure or slight movement the probe would display a flat square response. It is very unstable mechanically where the slightest movement would loose the correct response, then I did run the TDS540C probe compensation which this times shows a PASS status (see picture).When I inspect visually the jaws, the external probe it seems quite neat so what failure or mechanical issue causes the probe to not work correctly when the jaws are CLOSED but the current-transformer with Hall sensor would tricky work when OPEN ?

author: KrudyZ
author_rank: Frequent Contributor
timestamp: October 04, 2020, 03:00:48 pm
content: The earlier versions of Tektronix current probes had a home brew looking switch assembly in it made from stamped metal pieces to let the amplifier know if the slider was closed.I'm not sure if they kept that "great" design in the TCP202, but that's where I would be looking.

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 12, 2020, 02:57:45 pm
content: Here is a status on my attempt to calibrate-repair the TCP202.First I've completely de-constructed the probe head to observe any visible issue then re-constructed the probe, so far I did not see any problem (electrical or mechanical) which could explain the non-flatness response when sensing a 1KHz square signal (see attached some pictures of the de-construction).After that, I decided to connect a 100W incandescent lamp to the 230Vac-50Hz grid then probe with my P5210 and my TCP212, see pictures again where everything seems OK.So if we go back tony initial test, see both pictures where I'm using the tektronix 015-0672-50 calibrator 50 turns current loop, how can we obtain better flatness and rise time speed !I've not opened yet the termination box of the TCP202 but do you think the circuit has some tuning or calibration to solve the issue ?

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 12, 2020, 03:09:01 pm
content: P.S. regarding the tektronix 015-0672-50 calibrator 50 turns current loop, does anybody knows the schematics or circuit... does the calibrator really generates a super fast rise and fall 1KHz signal from the TDS front panel ?P.S.2. If someone owns the same tektronix calibrator and same TCP202 connected to a TDSxxx oscilloscope, could it be possible to make the same test which I did earlier to check the resultant waveform ?

author: MarkL
author_rank: Unknown
timestamp: October 13, 2020, 04:45:45 pm
content: It seems odd that you would get a perfect waveform when the jaws are not locked CLOSED.In your photo of the disassembled probe, are you showing all the parts?There should be a coil spring inside a metal sleeve which forces the upper sliding piece forward, and there should also be a tiny ball bearing. The ball bearing is important. It puts pressure on the wavy piece of spring metal to make sure the sliding transformer piece is seated firmly against the lower transformer. It's also the thing that "clicks" when you move the lever to the CLOSED position. Does your probe click?Also make sure the wavy spring metal is in the correct orientation.Screen shot from the TCP202 Instruction Manual attached: spring metal thing (10), coil spring and sleeve (2) and (3), ball bearing (12). I'm pointing these out explicitly in case someone else before you lost them. You may not know they're supposed to be there.

author: MarkL
author_rank: Unknown
timestamp: October 13, 2020, 05:08:00 pm
content: Quote from: Tantratron on October 12, 2020, 03:09:01 pmLooking at the compensator output circuit I wouldn't call it "super fast", but it should be faster than what you're showing on the TCP202.It doesn't seem likely it's the calibrator output but you can verify it's shape with a voltage probe.Schematic snippet fromhttp://w140.com/tekwiki/wiki/TDS540

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 13, 2020, 06:58:43 pm
content: Quote from: MarkL on October 13, 2020, 04:45:45 pmYes I did forgot to take pictures of the tiny ball, the spring assembly and metal sleeve... but there were there and later when re-assembling the probe head I did put them all together as shown in the service manual. Of course the initial issue was not resolved !Quote from: MarkL on October 13, 2020, 05:08:00 pmToday I've measured the resistive impedance and the inductive impedance of the tektronix calibrator, the values are 42 ohms and 85 microH so I really wondered if maybe the problem could be the calibrator speed (kind of slow 50 turns transformer). What you show is part of the TDS540C front panel circuit which generates the signal output whereas my concern is the external calibrator 015-0672-50 where the TCP202 will sense the current connected to the TDS540C.So later today I've built a quick and dirty test fixture, see the first picture where I connect the High Voltage output BNC of my PG506 to my Q&D box which is connected to a 50 ohm coax load. At the same time, I sense the voltage output to Ch 3 and display Ch2 the output of the TCP202.The good news now is that the TCP202 does respond very well with sharp rise and sharp fall at different 50% square signal (100Hz, 1KHz, 10KHz, 100KHz and 1MHz), see attached pictures.Then I've made a very high sampling rate to show the transient (see last attached picture) which is less than 10ns so this proves the probe works good BUT the problem seems to be a gain mismatch. I've tuned my PG506 to make 5V as shown on my TDS540C so if my 50 ohms load is precise I should get around 100mA but in average I get more circa 103mA or 104mA.As you see on the pictures, I've removed the top box of the TCP202 amplifier-compensator but I do not understand how to remove the bottom box. It seems to adjust the gain, one needs to access the bottom of the TCP202 box and maybe this will solve the problem.So either the TCP202 calibrator fixture is partially detuned or my TCP202 needs a gain adjustment to meet the PASS test of the TDS540C.It would be interesting to have someone post the circuit of the TCP202 to see if this makes sense or if someone could run its TCP202 with the 015-0672-50 calibrator to see the waveform, if if PASS or FAILThank you

author: MarkL
author_rank: Unknown
timestamp: October 13, 2020, 10:40:40 pm
content: Quote from: Tantratron on October 13, 2020, 06:58:43 pmThe bottom of the comp box is a friction fit. You can gently wiggle the black piece of plastic that is part of the BNC assembly out of the bottom. Then you can separate the two boards and undo the insulating tape around the bottom board as needed to get access to the pot. The coax going into the BNC is a Peltola connector and unplugs if needed.

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 14, 2020, 08:14:51 am
content: Quote from: MarkL on October 13, 2020, 10:40:40 pmI'm still not sure to properly understand how to safely access the gain adjustment part. I wonder if there is not a physical issue, see attached one picture showing my partial deconstruction of the compensation box. It seems unless I'm wrong that both half plastic covers have been mounted incorrectly or opposite when comparing to page 33 of TCP202 instruction manual.When removing the the top cover catches, I see directly the DC offset pot and the de-gauss button which should be the other way. How should I remove safely without any breaking both PCB's, how to unplug from the Tekprobe to re-assemble correctly the all unit ?What is wierd, the previous posthttps://www.eevblog.com/forum/repair/tektronix-tcp202-current-probe-repair-schematic-and-suggestions-needed/msg1663601/#msg1663601shows an installation similar to my probe but does not corresponds to what tektronix instruction manual states...By the way, the page 33 does mention that the gain of the probe must be with +/-2% for the TDS oscilloscope compensation routine to work so I guess that was my initial issue (FAIL compensation routine) and not a flat response issue.

author: MarkL
author_rank: Unknown
timestamp: October 14, 2020, 02:26:07 pm
content: I'm not seeing the difference between your probe, the manual, and the previous photo you reference. It doesn't look opposite to me. Can you mark up the photo and point it out? Maybe I'm just being dense.Below is my comp box disassembled. The black plastic that forms the BNC assembly is just pushed into the bottom cover. It's a very tight fit, but it does come out. It is not glued or fastened by any other means.If you're working on the two boards, you can also unplug the Peltola connector to untangle the cables a bit. The white connector can also be unplugged, but it too is a tight fit. The brown piece of plastic in the photo is just insulating tape around the bottom board that can be undone partially as I've done, or remove it if you want. Just make sure you put it back.But I think you should be able to get to the gain pot without removing the bottom anyway by pushing the top board out of the way. You can probably shove the insulating tape to one side or poke a small hole in it to get to the pot.

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 14, 2020, 05:03:39 pm
content: Hi Mark, many thanks for the guidance where now I've fully de-constructed the compensation box, cut part of the insulating tape to access the gain potentiometer per guidance.As you can see on the 2 pictures, my PG506 with my homemade current loop 50 ohms fixture along with the TCP202 trimming pot got it to a better gain calibration. Not perfect as a real test gear but then I've run the calibrator...the test is PASSplus we can finally see the calibrator was not supposed to generate an ultra-wide flat square (it is a 50 turns transformer).Again many thanks where I'm this time on the road to discover, use in my plasma test lab the TCP202 current probe versus my previous P6021 and P6022.Albert

author: MarkL
author_rank: Unknown
timestamp: October 14, 2020, 05:10:44 pm
content: Great! Glad you got it adjusted and it wasn't a more complicated problem. It's been a long road for you to find a working TCP202.Thanks for the heads-up on the 50-turn calibrator. I've always used a load resistor, but now we know what to expect from the calibrator. It doesn't seem like a very good accessory if the goal is calibration.

author: MarkL
author_rank: Unknown
timestamp: October 14, 2020, 05:22:17 pm
content: Quote from: esc on August 28, 2020, 08:16:14 amIt's been a while since that post, but I had a chance to take my probe head apart and I made some measurements. I got the following values with the 6-pin connector disconnected and the sensor cold (after warm-up the Hall readings are different by about 10 ohms). There is a part number on the side of the sensor head "120-2032-XX". My measurements in [...] :+3V - -3V = 276 ohm - 176 ohm +3V - HALL1 = 183 ohm - 93 ohm +3V - HALL2 = 179 ohm - 92 ohm -3V - HALL1 = 189 ohm - 141 ohm -3V - HALL2 = 182 ohm - 141 ohm HALL1 - HALL2 = 110 ohm - 72 ohm COIL - COIL = 6.5 ohm - 6.5 ohm [6.5]Your Hall sensor is different by a fairly large margin.I can also say that the TCP202 Hall sensor uses +/-2V instead of +/-3V, measured at the 6-pin connector. This table, originally posted by user vtp, was for an A6302. And also different from the A6302, there are two 100R resistors in parallel on the -2V input on the TCP202 sensor head.On the degauss question... I also find that after measuring large DC currents it can leave the core slightly magnetized and show a small offset. It's normal.

author: vtp
author_rank: Regular Contributor
timestamp: October 14, 2020, 07:01:58 pm
content: Quote from: MarkL on October 14, 2020, 05:22:17 pmYes, the table I made was for A6302 head but the measurements I provided in the earlier post in this thread are from my TCP202. Looking at the schematics of the box, the head voltages are supplied directly from the probe interface +-5V to the head through a pair of 220R resistors.With 276 ohms between +-3V pins and 220R resistors from both ends to the +-5V supply I get 3.85 volts for the HALL element operating voltage. Close enough to your +-2V (=4V) measurement.Perhaps there are then different revisions of the probe - I do not have any 100R resistors in my probe head circuit board. There however are 2 paralleled 39R2 resistors and a 1u8 inductor in series with the coil circuit.Just to give a reference of abrokenprobe head, here are measurements from one A6302:+3V - -3V = 1834 ohm+3V - HALL1 = 1701 ohm+3V - HALL2 = 1987 ohm-3V - HALL1 = 347 ohm-3V - HALL2 = 626 ohmHALL1 - HALL2 = 470 ohmCOIL - COIL = 5 ohm

author: MarkL
author_rank: Unknown
timestamp: October 14, 2020, 10:56:55 pm
content: Thanks for the clarification.I took apart my other TCP202 and measured it. Below are the measurements plus the others posted.My TCP202 #1 is newer, original purchase date unknown, and TCP202 #2 was purchased new 20 years ago. TCP202 #1 is marked "04 21 42 61" inside the potting compound, and TCP202 #2 is marked "99 21 18 34". I could believe the "99" is 1999, and maybe "04" is 2004. Just a guess.Both have the 100R resistors on a tiny PCB the female connector is mounted on. They're easy to overlook; photo below. The resistors are consistent with the diagram in the old "Tek Probe Circuits".Both also have the 39R2 resistors and 1u8 inductor. There's also a toroid wound as a CM choke that the two coil leads pass through before going to the resistors and inductor you mention.Readings in ohms"+/-3V" is actually +/-2V on TCP202vtp esc MarkL MarkL vtpFrom To tcp202 tcp202 202#1 202#2 ex6302------ ------ ------ ------ ------ ------ ------+3V -3V 276 176 347 287 1834+3V HALL1 183 93 211 202 1701+3V HALL2 179 92 227 200 1987-3V HALL1 189 141 246 234 347-3V HALL2 182 141 259 232 626HALL1 HALL2 110 72 154 174 470COIL COIL 6.5 6.5 6.5 6.8 5How did your A6302 die?

author: vtp
author_rank: Regular Contributor
timestamp: October 15, 2020, 08:04:06 am
content: Quote from: MarkL on October 14, 2020, 10:56:55 pmYou are right. Thanks for the reminder on those resistors. I completely forgot about them. They also seem to be in A6302 heads as I have drawn the resistors on my notebook.I can't really recall but the broken A6302 I may have bought as non-working since I had one new element to replace the broken one with.I also have an old P6302 which died spontaneously.Measurements of the hall-element signals give a clue about what failed. In the A6302 example the probe head has a problem with +3V pin connection.In the broken P6302 the fault is even more clear, HALL1 pin has disconnected itself completely from the element as all HALL1 related readings give infinite resistance.Here is a nice basic introduction to Hall-sensor:https://www.electronics-tutorials.ws/electromagnetism/hall-effect.htmland a picture from that borrowed below:As in the picture +-3V, or really the current supply pins, provide current to the element and Hall-voltage from the diverted charges appears at pins HALL1 and HALL2. Depending on what the resistance measurements show it is fairly easy to determine if the probe head is ok. Those signals are all available on the A6302 connector so the element can be checked without disassembling the probe. With TCP202 some disassembly is needed, at least to get to the wire to board connector in the compensation box. Of course there is the probe head PCB in between but that being faulty would be very good luck.

author: esc
author_rank: Newbie
timestamp: October 15, 2020, 08:35:20 am
content: As for my measurements, after taking the probe head apart, I realized that my probe head has a newer transformer, designed for the TCP305 PN 120-2032-XX.The transformer has 04-20-44-40 on it. Maybe that's why the discrepancy is there.

author: MarkL
author_rank: Unknown
timestamp: October 16, 2020, 01:50:31 am
content: Your 120-2032-XX is the same part number as my TCP202 #1. Within Tektronix part numbers, the NNN-NNNN are the main part number, and the -XX is usually the revision. According to the TekWiki page, the last number could also be a quality or a speed grade.But given that these both came from TCP202 probes with the same ratings, I think it's less likely that the same major part number would have such different resistance readings, and by implication that the problem is elsewhere other than the Hall sensor.So at the moment I think the Hall sensor is the prime suspect. However, I can't come up with a good explanation of the strange frequency response. Maybe the lower impedance has affected parts of the active circuitry that it's connected to.Instead of just resistance, I will see if I can come up with an out-of-circuit dynamic test or two so you can compare to your Hall sensor.vtp: Thanks for the nice pictorial on the Hall effect.

author: MarkL
author_rank: Unknown
timestamp: October 16, 2020, 09:52:31 pm
content: Attached is some frequency characterization for the Hall sensor. And although you don't seem to be having a problem with the higher frequencies, I also did the coil up to 1MHz since I already had the sweep set up.The Hall sensor was supplied by +/-5V with each leg in series with a 220R resistor, as previously described by user vtp. I also confirmed I have the 220R resistors on both my probes. The output voltage was measured differentially across the two outputs. The outputs have an offset above ground of about +236mV, and between them about 4.7mV. No load was placed on the output except the probing. A test of a 1k load did not affect the output significantly, so it seems the Hall output is a fairly low impedance.Likewise, the coil output was measured differentially across its two outputs, but because it's floating it won't matter if you do it single ended. The coil output was loaded with a 50R resistor. I don't know if that's the actual impedance seen by the coil, but at least it will serve as a basis for comparison.The signal generator was set to 16Vpp with offset 0V. One leg of the output was looped through the probe transformer halves and terminated in a 50R load.I don't have a Bode plot on my scope, and I didn't feel like writing one. So, what you see horizontally is a full sweep at the noted start and stop frequencies, and then a closer look at the start, stop, and 3dB point. The scope has an RMS ratio function between two traces, so it was easy to find the 3dB point by spinning the horizontal delay until the ratio was down 3dB from the maximum. The sweeps include 20kHz, which is where you were having the most severe drop-off.The DC response of the Hall sensor was 44.4mV/A, measured at 1A.Hopefully this info will help you evaluate your Hall sensor.One thing you should check, if you haven't already, is that your TekProbe interface has all the +/-12V and +/-5V supplies working. You could also verify the Hall +/-2V supply at the head. But given the lower impedance of your sensor, it's probably going to be low.Also make sure the Hall and coil are isolated from the sensor's metal shell.EDIT#2: Ever have one of those days? I discovered my connection to the 50R load was bad throughout the AC measurements. I've removed all the previous screen shots and re-posted updated full sweeps for the Hall and coil, both 100Hz to 100kHz. I didn't mention it before, but it should be obvious the frequency on the X-axis is logarithmic.I'll just tell you the numbers derived instead of posting all those detailed screen shots again:Frequency at reduced signallevel from maximum (Hz)-3dB -6dB -10dB------ ------ ------Hall 2.3k 4.0k 8.1kCoil 2.3k 1.3k 775Hall @ 100kHz = -21dBCoil @ 100 Hz = -24dBThe sweep envelopes now look right and the numbers make a lot more sense.

author: esc
author_rank: Newbie
timestamp: October 17, 2020, 06:36:40 am
content: Thanks MarkL for the info.Since your transformer in TCP202#1 and mine are both the same part 120-2032-XX, the resistance measurements should be close, and they are not. So I agree, it is likely that the Hall sensor in my transformer is the problem. The interesting part is that my probe measures DC accurately. Maybe the small resistance between the +3V and -3V and the two 220R series resistors causes a too small supply voltage for the Hall sensor, and even though it "works", but causes the anomaly at 20KHz?

author: Tantratron
author_rank: Frequent Contributor
timestamp: October 17, 2020, 07:12:59 am
content: Quote from: esc on October 17, 2020, 06:36:40 amIf you have an anomaly circa 20KHz, this could be related to the electronics amplifier and mixer, namely the 2 responses (current transformer and hall sensor) which are fused or hybrid. If you look the service manual of the A6302 and AM503A, it mentions the cross over region. It seems clear visually that the TCP202 probe head is same technology or design than the A6302, maybe check more circa pages 3-6 of the manual. In the case of the TCP202, the compensation box contains the amplifier and probably the crossover electronic management.System Behavior in the Crossover Region: When the frequency of the current being measured is in the vicinity of the crossover region (approximately 20 kHz), part of the measurement appears at the Hall device and the other part appears across the coil. The waveforms in Figure 3 8 illustrate how these two components combine to make the total measurement. Waveform (a) shows the current being measured. The fre quency of the current is in the crossover region of the probe. Waveform (b) shows the low frequency bucking current produced from the Hall device output. Waveform (c) shows the high frequency component that is induced directly into the coil from the current source. Waveforms (b) and (c) are summed together in the probe coil and amplified by the AM 503A amplifier. The amplifier output is connected to a measurement instrument, such as an oscilloscope, where a waveform similar to waveform (d) appears. Waveform (d) conforms to the original signal shown in waveform (a).

author: Mrnt
author_rank: Contributor
timestamp: December 06, 2020, 07:16:53 am
content: I picked up a used TCP202 and I am not sure if this is me being thick, but it only seems to measure positive DC current ie it seems to accurately measure dc when flowing in the direction of the arrow on the probe but if I reverse the current direction, the probe only measures approx -700mA no matter what current is measured. Is this normal?I have not tried AC yet and nothing appears scorched inside the head.

author: MarkL
author_rank: Unknown
timestamp: December 06, 2020, 04:02:48 pm
content: The probe should have a symmetric output for AC and DC signals. I don't think it's likely to be something in the probe head. Maybe one side of the Hall driver is not working.You could start by checking the power rails in the comp box. A convenient place is on the little white ribbon that connects the TekProbe connector to the main circuit board. The ribbon pads on the circuit board are numbered starting from the end where the probe cable enters:1: GND2: -15V3: -5V4: +15V5: +5VTaking a look at a high frequency AC signal (like >1MHz sine) could also be enlightening, since the Hall driver should be out of the picture at that point.EDIT: Fixed description for pin 1.

author: Mrnt
author_rank: Contributor
timestamp: December 06, 2020, 07:53:05 pm
content: Thanks Mark for your prey response! It look like the voltage while not exactly a you listed are within the +\- 2% pc for the Tekprobe connections:At the white ribbon0-14.9-5.1614.824.96Trying at 1.5Mhz AC with approx 10v pp into 50 ohm the current waveform was fairly smooth, correct amplitude and symmetric about 0 mA. Unfortunately I do not have a higher current source.I notice that there is a different opamp on this board from the other pictures I have seen - an OP275.Any thought as what to look at next?

author: MarkL
author_rank: Unknown
timestamp: December 07, 2020, 12:12:13 am
content: Those voltages are fine. It was worth checking to make sure one of the rails wasn't completely missing.My older probe has OP27 and MC1458, but the newer one has OP27 and OP275 like yours.Have you done the coarse balance procedure on the underside of the probe? What kind of a range do you get for the coarse adjustment? Does it also bottom out at -700mA? For comparison, my newer TCP202 can be adjusted from -7.9A to +6.1A (or in volts: -0.79V to +0.61 into 50R). My older probe has a much lower range of -1.6A to +1.1A.If it does bottom out, I think a general approach would be to start working backwards from the Hall power amplifier which includes 1/2 of OP275 and the BCP68/69 SOT-223 driver pair (see vtp's earlier post). One approach would be to vary the coarse adjustment back and forth to find who's responsible for the amplifier falling out of operating range. Possible probe points would be the emitter and base of the BCP68/69 pair, and examining the OP275 output and inverting and non-inverting inputs.A few other simple voltage checks might also be in order. On the white connector on the main board, they are numbered 1 to 7 (same order as the ribbon connector):1 - 0V (Black to bottom board)2 - Varies with DC signal/offset (White to bottom board)3 - Hall power -2V4 - Hall power +2V5 - Hall 1 0.206V6 - Hall 2 0.259V7 - Center tap on course adj. pot, varies +/-2V5 and 6 will vary depending on the specific Hall device, but should be close to each other.I don't have any specific suspicions in mind related to this connector; just gathering data.Without a schematic and without resorting to shotgun parts replacement, you're probably going to need to do some reverse engineering. I haven't done any of that for the TCP202, but I can help with voltage comparisons from a working probe.

author: Tantratron
author_rank: Frequent Contributor
timestamp: December 07, 2020, 05:22:01 am
content: Quote from: Mrnt on December 06, 2020, 07:16:53 amHave you press the degauss button as a start ?

author: vtp
author_rank: Regular Contributor
timestamp: December 07, 2020, 10:10:49 am
content: Quote from: Mrnt on December 06, 2020, 07:53:05 pmPerhaps checking if the OP27 is ok? There should be about zero volts between plus and minus inputs. You can also check if it gets railed in operation. In any case since only half of the signal gets amplified properly your fault most likely resides in the amplifier circuit.The attached may help.

author: Mrnt
author_rank: Contributor
timestamp: December 08, 2020, 06:13:39 am
content: Thanks for all the help! I should get some more time to work on it in a day or two.Meantime another possible symptom - since I have not used one before I am wondering what typically appears on the scope when you hit the degauss button? I have found that I need to degauss it regularly (and somewhat tweak the balance fine tune) to get it be close 0 when not measuring. However I also noticed that when I press the degauss button there is a fairly large ac like waveform briefly displayed - is that normal? I thought I read somewhere in this thread that the amplifier and hence scope input was supposed to get switched away from the sensor when degaussing happened.

author: Tantratron
author_rank: Frequent Contributor
timestamp: December 08, 2020, 07:03:14 am
content: Quote from: Mrnt on December 08, 2020, 06:13:39 amIt is normal and healthy sign, pressing the degauss button will generate a low frequency decay signal... attached extract of service manual of the AM503A where the TCP202 is roughly same theory of operationDEGAUSS_SIG Simulates a 160 Hz pseudo exponentially decaying sine wave function during the current probe degauss cycle. DEGAUSS_SIG is generated at the VA and VH outputs of U370, which are also used to coarse and fine adjust the HALL_PREAMP_DC_OFS control line.This stair stepped waveform is first filtered, to remove high frequency com ponents, and then amplified. This signal is initiated as part of the probe degauss/autobalance routine.Figure 3 10 shows a rough view of the degauss waveform before and after filtering. Each burst contains approximately 256 cycles and the amplitude of the filtered waveform (at pin 1 of U353A) is approximately 3 V. The degauss signal goes to the power amplifier.

author: Mrnt
author_rank: Contributor
timestamp: January 08, 2021, 12:05:00 am
content: Thank you so much @vtp for the schematic and layout! It turned out to be the BCP69 transistor at the output of the amplifier board, however it took a long time to figure that out because I started with the OP27 which generated an asymmetric output for equal +ve and -ve DC input currents at the probe (which confused me greatly), and then worked my way through to the end.If I understand correctly, the output of the amplifier board passes through the coil on the probe and then on out to the input of the scope, so the magnetic core of the scope forms a feedback loop from the coil to the hall detector and on to the input of the amplifier board. Presumably because the output of the amplifier board was only ever generating a positive output then that was why the OP27 generated the asymmetric output.I'm attaching a schematic of the board inside the probe in case in helps someone else.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: May 13, 2022, 09:47:50 am
content: Unfortunately, I'm out of luck. I bought a TCP202 on ebay hoping to get it repair. Contacts from the output of the hall sensor have infinite resistance to power supply and to each other.Has anyone tried ordering the transformer separately?

author: Amphion
author_rank: Contributor
timestamp: June 02, 2022, 05:24:24 pm
content: I wanted to add something to this conversation that may be overlooked. I recently purchased a later model A6302 probe off e-bay. It seemed to be mostly working, but had AC overshoot that seemed too much. I finally figured out that the problem was with the core not mating perfectly, even though it would look like it was from casual observation. (The mu-metal housing looked to be perfectly mating, but the core itself was not).It seems apparent that these probe cores are made by potting the ferrite in the mu-metal shield using a soft epoxy, and then the mating surfaces (mu-metal and ferrite) are ground/lapped flat/planar as one unit. I have much experience with epoxies and suspected that the epoxy had shrunk with time, pulling the core a little further back into the mu-metal housing, creating a gap between the ferrite surfaces. This is especially a problem with softer epoxies that have plasticizes in them.Taking the probe apart I confirmed with a straight edge under the microscope that the core was indeed slightly below the surface of the mu-metal housing. I then starting lapping the cores, abrading the mu-metal until I could see that I was contacting the ferrite. I started with 600 grit sandpaper, working toward 1 micron diamond lapping film (used for polishing fiber optics) in multiple steps, all done on a flat glass surface.After all this, the AC overshoot is nearly completely gone and the probe is performing to my expectations.Some notes for "young players" on lapping, you have to have good technique!:-You must be aware of how/where you're applying pressure as you're dragging the probe core across the sandpaper/lapping film, or you will put a tiny but meaningful convex curve in it. The ends or sides will get lapped a little more as the lapping drag force creates a tilt force and you have to compensate for this. I actually had to do some final lapping with half the core off the edge of the film to remove this small convexity I had put in the middle of it. Under the microscope I could see that I had a tiny tiny bit of a teeter totter thing going on, and it was affecting the performance of the probe.-The ferrite is very brittle/frangible. Microscopic grains will come off, and then when you drag back over them they will take more grains out, leaving a rough surface in the ferrite. Consider this in your technique. I ended up lapping under a stream of water to wash the debris away.-I was surprised by the probe sensitivity to this mechanical fitup. It's been talked about before, but I don't think it could be overstated. I was seeing effects that would be measured in microns.-This process is not for the faint of heart and I don't recommend it for everyone!I have attached a picture showing the small core pullback I'm talking about. Unfortunately this picture is half-way thought the process. I didn't think to take one at the beginning, so you're only seeing about half the gap here.

author: MarkL
author_rank: Unknown
timestamp: June 02, 2022, 10:57:35 pm
content: Thanks, Amphion, for the great insight. I will have to look at the core mating on my A6302 that has overshoot.Did you find it was just the lower core? Or did you have to do both?Do you have any before/after waveform captures?I've also done a fair amount of fiber polishing, but it was many years ago.

author: Weston
author_rank: Regular Contributor
timestamp: February 03, 2023, 05:53:02 am
content: I noticed that my P6021 current probe had a scratch on the mating surface causing a poor LF response. Given my issues with the response on the TCP202 I decided to buy some lapping films and try polishing the transformer mating surfaces on both. As Amphion described I could see that the epoxy had receded, leaving the core surface slightly recessed.I have not lapped anything before, so my process may be a bit off, but it had enough of an impact where I am convinced this is the main, if not only problem. I was not able to get the core face mirror shiny, but got it smooth enough to check flatness using optical interference fringes, and I think I got it all flat to ~1um or so.Reference waveform in white and waveform after in yellow. Still some aberration but a decent improvement. Not sure if I am going to give lapping the cores another shot or just let it be. Similarly, I was able to bring the LF -3dB point on the P6021 closer to the spec than in was, but still not meeting the value.

author: Jitterbit
author_rank: Newbie
timestamp: February 07, 2023, 03:17:32 pm
content: Seems an NE5532 would be a lower-noise substitute for the 1458, if you're replacing that.

author: Amphion
author_rank: Contributor
timestamp: February 10, 2023, 08:30:45 am
content: Quote from: MarkL on June 02, 2022, 10:57:35 pmI apologize I didn't see this until now. I'm not super active on here and I'll have to figure out if there is a way to turn on notifications on topics??It's been a while now, but as I remember both halves needed lapping, but one was worse?? I wish I had before/after waveform captures, that would have been good to post... I might have some that unfortunately started halfway though the process, not showing how bad it was. I'll try to remember to look on that scope next time i'm in my lab.

author: iso14000
author_rank: Contributor
timestamp: October 08, 2024, 06:38:06 pm
content: Hi all, I'm not very active on this forum, far much on a french one, but global level forbid me to post my request on it.sorry to rise up this topic (and my bad english)I've just bough a used TCP202 as defective on 3bay for a buntch of euro, and indeed it is in failure...nothing looks fried into that, the global behaviour is ... an oscillator.does somebody have a schematic to dig into?best regards

author: iso14000
author_rank: Contributor
timestamp: October 09, 2024, 04:37:43 pm
content: so ridiculous I am... schematics are simply above....

author: iso14000
author_rank: Contributor
timestamp: October 12, 2024, 02:52:39 pm
content: Hi,I found some difference with VTP's schematics. (thanks sir , your work is awesome!)by taking two pictures and precisely match them with Gimp , I redraw the schematics.In my case , a 10resistor was out of specs , and was glowing in the dark, I chase it with my IR camera.By changing it, global behaviour is OK.there are still some mysteries for me :-what stands for X2 et X1 , they are SOT23 with "28" marking.?-what is the purpose of T7 et T4?I cannot see the oscillator activated when I push the degauss button