Tek p5205 HV differential probe teardown. BTW, what are the red and brown wires? - Page 1
Forum section: electronics / testgear

author: onlooker
author_rank: Frequent Contributor
timestamp: September 28, 2014, 02:30:28 am
content: Well, there is not much to teardown other than showing 2 internal pictures, then ask a few questions and ideas.As it stands now, a tek p5205 differential probe (100MHz, 1000V, 50X-500X) in working order may cost several hundred dollars even in the second hand market. The 1103 probe power supply will cost a additional several hundred dollars.The alternative for someone with low budget is to get the ones that occasionally pops up on eBay that had all cables cut and without any accessories. But, it can go about $30~$50 a piece, or may be even lower.I opened one of such p5205. It looks like it used all off-the-shelf parts. The design also looked simple in contrast to the high original cost. I guess, the cost went into the professional design and the professional specs.To reconnect the necessary wires, I tried to find the schematics, but, I failed on it. It will be nice if someone can share the schematics. Otherwise, I will continue to understand the wiring from the PCB, do some testing and hopefully not to damage anything.Edit: bottom picture added.The back side of the PCB is not very interesting. The 1st picture is the upper side of the PCB. The HV wiring (left side) and the coax wring on the LV (right) side are simple to redo.The thin Black, Blue, Red and Brown wires are my concerns. I have identified that the Black and Blue wires are the -+15V main power supplies. When the -+15V are on, I can hear a brief beep and LED flash.More importantly, when one of the HV wire was touched, the LV coax showed the usual distorted mains waveform. This says that the device should be still functional.Currently I am trying to understand the roll of the Red and Brown wires. According to the instruction manual, it is likely related to input of the offset adjustment voltage. But, why two wires. Anyone know the answer?The official power supply 1103 also supplies +-5V. But they are not likely used in p5205 since p5205 have circuitry to split/convert the +-15V supplies to a pair of +-5V supplies.I am also thinking to reduce the attenuation from 50x-500x to 10x-100x since I am really just interested in the differential capability, not the HV capability. Any suggestions?As to the +-15V power supply, is switch mode supply good enough?The 2nd picture is with the HV side wired with the wires taken from a old CRT monitor.

author: MarkL
author_rank: Unknown
timestamp: September 28, 2014, 04:46:58 am
content: One of the wires is probably the input to the scope which tells the scope what attenuation factor to use for the channel, x50 or x500.Look for a fixed change in resistance to ground when you push the attenuator selector button.

author: MarkL
author_rank: Unknown
timestamp: September 28, 2014, 01:01:42 pm
content: Ok, I popped the lid on a P5205 "compensation box". First off, that's in quotes because there's no compensation in it. The coax goes right into the scope.Brown goes to the Tekprobe "Data" pin, which is the attenuation sense input (aka "readout" pin). It flips between 690 and 1140 ohms for x500 and x50 settings, but the probe needs to be under power for it to work.Red goes to the center wiper of a 1-turn 10k pot, and the ends of the pot go to +15 and -15. This is the offset adjustment accessible through the small hole in the compensation boxYou are correct on the blue +15V and black -15v.(Edit: Fix typo.)

author: onlooker
author_rank: Frequent Contributor
timestamp: September 28, 2014, 03:16:50 pm
content: Excellent and clear. And thanks MarkL. The next time google will be friend again for this info.For my power supply, I can now forgo the brown wire. It needs only 4 wires: one for GND, two for the +/-15V rails, and plus a wire for -1V~+1V offset adjustment. A piece of phone cord should work; A coiled cord can even wrap around the coax.I think there is also a pot on the p5205 PCB that does the offset adjustment during calibration. if I am willing to deface the device to expose the pot, I can further omit the offset adjustment wire to the power supply.To answer my own question about using switch mode supply, yes, I googled, in its TekVPI to TekProbe adapter, Tek was already using switching power to convert a 12V single rail to +/-15V dual rail. It is only a metter of if I can find one that works noise-wise. It should be no suprise since switching powers are used in powering scopes for some time.

author: 128er
author_rank: Regular Contributor
timestamp: September 28, 2014, 05:04:48 pm
content: Hi,bought four of the P5205 probes a few weeks ago for 50€. Now I'm planning a little powersupply like the Tek 1103.Almost all Informations are given in this thread. Nevertheless I add my hand drawn schematic to this thread.IIRC, the probe draws about 100 mA per rail (+15V/-15V).

author: onlooker
author_rank: Frequent Contributor
timestamp: September 28, 2014, 06:01:16 pm
content: You certain got better deal.I did further test on mine. It passed the "Functional Check" (probing mains as described in the manual). And yes, it is a good news that the power supply is not demanding. Mine draws 71mA steady.Thanks for sharing the drawing.

author: 128er
author_rank: Regular Contributor
timestamp: October 05, 2014, 10:35:02 am
content: Hi,would that be an adequate way to detect the attenuation over the data pin? Or is it to complicated, or did i miss something?Edit: VDD is +15VEdit²: Could I use an LM324 for the window comparator and the CC source instead of real comparators and an extra opamp? Would reduce the number of packages

author: David Hess
author_rank: Super Contributor
timestamp: October 05, 2014, 05:26:29 pm
content: The old Tektronix designs essentially did use a window comparator but with a lot more windows; the signals themselves used 15 volts of bias to generate 0 to 1 milliamps with 0.1 milliamp resolution.Later more resistance values were added to handle attenuation factors other than x10, x100, and x1000.

author: MarkL
author_rank: Unknown
timestamp: October 06, 2014, 02:00:56 pm
content: Quote from: 128er on October 05, 2014, 10:35:02 amI didn't analyze your circuit in detail, but I think your approach would work. Since you're only trying to differentiate between two resistance values, I think it could be simplified. And it could be really trivial if you use a comparator with a push/pull output, such as the TLC3702. See below (caveat: NOT built/tested).The real utility of the attenuation sense pin is to allow the attached scope to automatically adjust the V/div so that cursors and other measurements appear correctly. Lighting an LED can certainly be done instead, but isn't that a lot of extra trouble when you can glance over at the x50/x500 button?

author: 128er
author_rank: Regular Contributor
timestamp: October 06, 2014, 03:12:11 pm
content: Quote from: MarkL on October 06, 2014, 02:00:56 pmThanks a lot for your input! The push pull solution is nice and would save me a comparator. But the TLC3702 and the LM393 comes with two comparators either way. So it's not that important to reduce the circuit to one comparator. Maybe just for kicks or minimalism.Quote from: MarkL on October 06, 2014, 02:00:56 pmI had the same thought while I planed the circuit. In the end my thought was: If I have the possibility to read out the data pin, then why not.It's not a lot of extra trouble and cost. Furthermore, the probes have long cables and can lay anywhere on the bench or in a switching cabinet. It's nice to have LED's in the power supply housing as a central point for fast indication.One more thing...After I saw your schematic with the voltage divider for the reference voltage. That was my first idea too. But the reference voltage depents on the supply voltage and it could be unstable. With my circuit i try to sense +- ~250 mV.Is the solution with the zener regulator as a reference overkill, seen from a practical point? The 7815 should regulate well enough, that it won't have any effect on the circuit.Probably I put too many thoughts at such a small thing.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 06, 2014, 04:17:39 pm
content: Quote from: onlooker on September 28, 2014, 02:30:28 amif you are well versed in "dividers matching" and "frequency compensation" then its possible. all you have to do is replacing the dividers in HV left section with "quality" components of the same sizes. otherwise dont do it, messing with attenuation is messing with differential capability/performance.Quote from: onlooker on September 28, 2014, 02:30:28 amif it doesnt screw the noise and CMRR performance.

author: David Hess
author_rank: Super Contributor
timestamp: October 06, 2014, 06:22:35 pm
content: Quote from: Mechatrommer on October 06, 2014, 04:17:39 pmEspecially do not do it unless you are prepared to recalibrate the AC and DC common mode rejection. Of course you may have to do this anyway if you change the probe leads.You may be able to adjust the attenuation on the output side which is low impedance but I would sure want a schematic before trying it which seems like a lot of work for a minor convenience. Why not just set the oscilloscope vertical input to a higher sensitivity?

author: MarkL
author_rank: Unknown
timestamp: October 06, 2014, 06:42:40 pm
content: Quote from: 128er on October 06, 2014, 03:12:11 pmPerhaps it might not be obvious as drawn, but it's really just a classic measurement bridge. It's not dependent on supply voltage variation.For example, if the +5V supply goes up 10% and throws off the 2.5V reference voltage by +10% on the - input, the measured node into the + input is also up by +10%. They track each other. The only things critical to this design is the tolerance of the resistors, and the offset voltage of the comparator (TLC3702 = 6.5mV max).You can work out the exact requirements for the tolerances, but we're trying to detect an almost +/- 25% change in resistance on the brown-to-GND leg of the bridge. There's a lot of leeway.One thing not obvious is that this circuit is operating off +5V and not +15V (so, yes, there's regulator not shown). 5V operating voltage is on purpose because from testing we know the resistance on the brown wire is not valid unless the probe is powered up. That tells you instantly there's some active electronics also on that brown wire and not just a switch with a couple of resistors. On a TDS3054, the brown pin was measured as +5V, so that's the only thing I'm comfortable with, without knowing what else is on the brown wire. Your current source has a compliance voltage > +5V on that pin. I don't know if that's safe or what effect it might have on the probe internals.In fact, that contact on the TekProbe interface, along with another, make up the connections for 5V I2C communication with some of the more expensive probes. That's why the connection is called "Data" (and the other "Clock"). The pin is multiplexed by the scope between the two functions of I2C and attenuation sense.And one additional thing, as you point out the TLC3702 is a dual comparator. If you're not using the other half you should connect one input high and the other low. It has extremely high input impedance and it's probably pretty easy for it to oscillate with open inputs. It's generally good practice to tie levels on unused gates on any chip anyway.QuoteSometimes the fun is in the designing and building, more than the final outcome!

author: 128er
author_rank: Regular Contributor
timestamp: October 06, 2014, 07:24:05 pm
content: Quote from: MarkL on October 06, 2014, 06:42:40 pmThat's a huge no go for +15V. Didn't thought of that, or missed it in the thread. Thanks again. One more power rail required. One thing leads to another . . .

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 06, 2014, 08:42:51 pm
content: Put in a zener to prevent that pin from going above 5V.

author: onlooker
author_rank: Frequent Contributor
timestamp: October 07, 2014, 04:19:24 am
content: Thanks for all the suggestions and comments. I think I will do the easy part first, that is, to do minimum rewiring to make it usable again.The first thing is the coax. I have just received some eBay version of RG174. Its small diameter is the reason for the choice. I need to have both the coax and the power wires go through the existing outlet.From an online coax loss calculator, for a run of 5ft of generic RG174, the loss is about 0.1dB@10Mhz and 0.4dB@100MHz (comparing to RG58 with <0.1dB@10Mhz and 0.2dB@100MHz).Is a generic RG174 good enough or I need to have a low loss coax? Additionally, is this 0.1dB vs 0.4dB difference enough of a concern?The other main part is the power. I did more tests. For a 50Mhz signal, the current consumption of the device is already more than 200mA, which is significantly more than that for a low frequency signal that I checked earlier.Lastly, two pictures are attached for the entertainment. The pictures are just quick checks of 10MHz aquare and triangle waveformss before (yellow) and after (red) P5205. They are not with proper termnation or best possible cabling; the square one looks particularly ugly.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 07, 2014, 10:02:06 am
content: Quote from: onlooker on October 07, 2014, 04:19:24 amno. by the right mind, you should concern more on the impracticality of the bigger RG58, which you cant do pretty much anything about. the major artistic side of it is "to make it work" by hook or by crook, 58 or 174. i think you are fine with 174, just recompensate if the result is not good, thats the biggest part anyway.... knowing your stuffsedit: btw thanks for the pcb picture of the probe. if you can post the back side of it i will appreciate it. from the signal capture... triangle wave got roll off at peak and bottom, thats normal due to BW limitation, at 10MHz, triangle still got so many harmonics which your probe cant show. second picture... too much ringing on both red and yellow signal. i'm suspecting reflection (or black magic) on yellow stuff. not sure how you test it.wait a minute, the yellow is original triangle signal and red is probe output? you have overcompesated proberedo again with proper termination.

author: onlooker
author_rank: Frequent Contributor
timestamp: October 08, 2014, 12:34:21 am
content: Ok, a picture of the bottom side is just added to the 1st post. The PCB has visible middle layer(s).Yes, I will try RG174 1st, though the little leftover of the original cable shows it was more close to RG58 in size.And yes, the P5205 output is closer to the true waveform shape; the yellow traces were taken before P5205 with an x10 probe having its tip touching one of the input terminals of P5205.And yes, I found the problem, I did not use the probe GND connection since I mistakenly thought the GND connection was already there. In fact, it was indeed there, but it was in the form of a big ground loop going from the FG GND to the scope GND. This loop dumped the yellow traces and caused the delay of the yellows.After connecting the probe GND to another one of the input of P5205, the views are much better. Again the yellows are at the input of P2505; and the reds are at the output of P2505. Now the yellows are ahead of the reds.Anyway, I think, if nothing else, these pictures showed that 1). the waveforms are centered well enough without needing any additional offset compensation (though for small signals, the offset is more pronounced); and 2). the amplitudes are roughly right.BTW, I did not like the forced mental math with the x50/x500 attenuation settings. This is also a good motivation to change it to x10/x100 later.

author: MarkL
author_rank: Unknown
timestamp: October 08, 2014, 01:54:50 am
content: Quote from: onlooker on October 08, 2014, 12:34:21 amDoes your scope not support manually entered attenuation factors? Surely it must have x1 and x10, but not x50 and x500? (Sorry, I don't recognize the make/model from your screen shots.)

author: onlooker
author_rank: Frequent Contributor
timestamp: October 08, 2014, 02:05:48 am
content: Right, it has only x1, x10, x100 and x1000. It is the now "infamous" Owon SDS7102. Ok, I can do divide by 2 or multiply by 5.

author: MarkL
author_rank: Unknown
timestamp: October 08, 2014, 02:40:25 am
content: You could go in the other direction and make it x100 and x1000 by doing a simple divide by 2 (with compensation) on the coax side to the scope.If your plan was to modify the input side of the probe, this alternative preserves the CMRR and other input characteristics.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 08, 2014, 03:01:34 am
content: agreed, making divider on the output is much less risk. looking at your picture, 50X is unterminated, simply adding proper 50 ohm termination at dso end you'll get 1/100X output (@ 50X setting) and 1/1000X (@500X setting), set your dso to suit, no need mental math

author: MarkL
author_rank: Unknown
timestamp: October 08, 2014, 01:34:30 pm
content: Yes, this works to a first approximation and a simple 50 ohm pass-through terminator can be used. However, be aware of this from the probe specs:QuoteSo, a compensated divide by two attenuator with an impedance greater than 50k is needed if you want to stay accurate. You could use a couple of 25k resistors as a divider, or you might even be able to get away with a single 1M and rely on the 1M inside the scope. In either case you'll need an adjustable cap for compensation across the resistor, around 5 to 25pF. If you put the arrangement in the probe box instead of at the scope you'll need even more pF to compensate for the cable.There's no information I can find that says exactly *which* specs are invalidated if you go with 50 ohms (I suspect accuracy with max signal input), so in reality the above may be overkill for your purposes. I would say try the 50 ohm termination with various signals that you typically measure to see if it works well enough.(Edit: Ohms symbol didn't make through cut/paste from specs. Changed to "ohms".)

author: David Hess
author_rank: Super Contributor
timestamp: October 08, 2014, 07:42:26 pm
content: Quote from: MarkL on October 08, 2014, 02:40:25 amQuote from: MarkL on October 08, 2014, 01:34:30 pmWhat I find really odd about this discussion is that such a device used to exist!Oscilloscope input "normalizers" are used to adjust the input capacitance of the vertical inputs of an oscilloscope as well as the compensation of the input attenuators but these normalizers also function as compensated precision divide by 2 attenuators. I have a couple of them in my collection of calibration instruments.Quote from: MarkL on October 08, 2014, 01:34:30 pmThe accuracy of the 50 ohm termination will degrade the calibration. The high voltage differential probes I am familiar with specify two different attenuation factors depending on if their output is terminated into 50 ohms or not.

author: MarkL
author_rank: Unknown
timestamp: October 08, 2014, 07:59:53 pm
content: Quote from: David Hess on October 08, 2014, 07:42:26 pmI figured there had to be; this didn't seem like such an unusual situation. But I couldn't find any to say, "Here, buy this!" Thanks for the pointer. Is there a compensation adjustment on a "normalizer"?QuoteRight. I'm expecting the P5205 won't be able to swing to the peaks of its specified output with 50 ohms and the waveform will get squashed.

author: David Hess
author_rank: Super Contributor
timestamp: October 08, 2014, 08:19:54 pm
content: Quote from: MarkL on October 08, 2014, 07:59:53 pmYes, it is not shown in the photo because it is on the bottom but there is an access hole for the trimmer capacitor.In practice they were compensated against one channel and then used to adjust the compensation of the other channels and all of the input attenuator sections. They could also be used to compensate multiple oscilloscopes against each other so probes could be moved between them easily. A x10 probe may be used to do the same thing but it will have 5 times more attenuation of the test signal which may or may not be a problem.QuoteThe waveform will certainly be halved but if they designed it to drive a 50 ohm transmission line to its 100 MHz bandwidth, I doubt it will have problems besides that.

author: MarkL
author_rank: Unknown
timestamp: October 08, 2014, 08:22:03 pm
content: Quote from: MarkL on October 08, 2014, 07:59:53 pmDid a quick test and this is correct. Instead of the output swinging 6.2V Pk-Pk (measured; 5.2V is the spec), I only get 2.8V Pk-Pk with 50 ohm termination.A side effect of 50 ohm termination, which I didn't expect, is that the overrange LED does not light. It's obviously looking at its own output to determine overrange and the level never gets high enough. So, 50 ohm termination with this probe is not a good thing.Edit: Since the source impedance is 50 ohms, 2.8V is actually not too far off expectations.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 09, 2014, 04:29:08 pm
content: make active 1/2X divider or 5X amplifier with an opamp then as suggested by the OP earlier.

author: MarkL
author_rank: Unknown
timestamp: October 09, 2014, 05:33:49 pm
content: Not sure I saw that suggestion, but why would you want to start adding active components? Plus added complications of DC to >100MHz?The question I was trying to answer was if a simple, widely available, 50 ohm terminator could be used. A: It can, but there's a tiny amount of non-linearity on max signals, and you lose the overrange light. Or, to stay in compliance with the probe output specs, build something passive with 1 or 2 resistors and a trimmer cap.

author: onlooker
author_rank: Frequent Contributor
timestamp: October 10, 2014, 12:24:30 am
content: Right, I did not mean to add my own active components. The talk about x100/x1000 (/2) or x10/x100 (5x) was to say that, after all, mentally dividing by 2 or multiplying by 5 may not be that bad, though from the beginning, I did contemplate about what might be possible by some simple unofficial adjustments of the current PCB to reach x10/x100.If at all possible, x10/x100 (5x) is more preferable than x100/x1000 (/2) since it reduces the attenuation that the device currently has and smaller signals will likely be less noisy (yes, small signal after P2505 appeared to be a lot more noisy).As you guys had mentioned, x10/x100 can be done by rearranging the voltage divider at the HV side, then, at the expense of de-rating the HV performance (but, how much de-rating, 5 times worse? I do not have a quick answer). Or, is there any room in the x50/x500 calibration pots on the PCB?On the other hand, as I mentioned earlier, for now, I am just trying to make it usable with minimum effort. My eBay adventure just failed. The RG174 I got was junk. The shield has probably less than 60% coverage, that resulted to significantly high signal loss. The new hunt for lower loss RG174 is in progress and the price is likely more than double.

author: 128er
author_rank: Regular Contributor
timestamp: October 23, 2014, 06:51:37 pm
content: Little progress with my P5205 probes.Today I had some time and etched a pcb to easier test my (supposedly) broken P5205 probes. As I said, bought them cheap on Ebay. It seems that they come from some sort of lab. They all have "defective"-stickers with a short failure description on them. On two of them is written: "generates voltages that are not plausible", and on the other: "x50 range defective".At the moment I can only test them with my variable isolation transformer. Actually no chance to test them to full Bandwidth. Maybe at work I can find some (reasonable) high frequency power stuff.But...In both cases, they work fine (with my limited test conditions). Only the x50/x500 switch looks dodgy. You touch the switch slightly and the probe output goes nuts.I don't expect to find these switches somewhere. Have to look. Has anyone ever observed the same issue?Have two more probes to test. But not this evening.

author: David Hess
author_rank: Super Contributor
timestamp: October 23, 2014, 07:05:54 pm
content: Quote from: 128er on October 23, 2014, 06:51:37 pmAre you referring to the three push-button switches?From your picture it looks like the body of the switch easily comes apart so you can clean the contacts and put it back together. What kind of switch mechanism do they use inside?I have had rubber dome switches with a carbon conductive surface and gold plated contacts which just needed cleaning. My guess is that they were contaminated during cleaning to remove flux but took years to fail.

author: 128er
author_rank: Regular Contributor
timestamp: October 23, 2014, 08:26:12 pm
content: Quote from: David Hess on October 23, 2014, 07:05:54 pmYes.That's not my picture, but no matter.All Switches, at all probes working fine, except for the x50/x500 switch (probably the most actuated of all three switches). However, I opened the switches. They were perfectly clean. A little metal spring contact shorts two carbon contacts to close the switch. I had to bend back the spring contacts. Obvious, they were worn out over the years.Extreme fiddly work.Thanks David for the hint!

author: onlooker
author_rank: Frequent Contributor
timestamp: November 17, 2014, 03:40:15 am
content: I have done a few things since the last update. These include---- Came up with a power supply that is light and cheap;---- Fitted connectors on P5205 for power supply and output signal;---- Some performance tests about the power supply and the P5205.The 1st picture shows the overall set-up.----------------------------------1). P5205: connectors for power supply and signal outputThe high voltage input had fitted with HV wires before this round of experimenting. But, I still need some HV accessories. They are expensive and relatively rare. Other than this, the wiring was more or less usable.As for the low voltage output, I settled with a simple solution: just fit a female BNC to the existing short coax left on the P5205. For connecting to the external power supply, a short cable with a micro USB female jack was used.Though the signal output and the power connection are on the low voltage side, I may later still like to have some silicone shroud to cover the exposed metal for, in case, the P5205 has to move around in HV surroundings.-----------------------------------2). Power Supply: The constructionThe power supply I ended up to use was a "DIY" hybrid type and quite simple: a SMPS pre-regulator followed by a linear regulation stage.The pre-regulator SMPS was one I already had. It was unregulated and speced as 12V and 1.5A, though, the ripple can be quite high. The low cost of $1.50 made it disposable for experimenting. The other important consideration was that its half bridge topology with the typical center tap full wave rectification secondary can be easily modified to have +/- rails. For my use, I would only need up to about 0.2A per rail and, for such load, the modified SMPS supplied +/-13.2V.For the linear regulation part, a $5 small dual rail 317/337 board rated to 1A was used. The board was adjusted to output +/-10.5V. On the board, the spots for rectifier diodes were fitted with 2 inductors taken from burnt out CCFL bulbs to form PI filters.Now, there are two important questions: 1). Will the power be clean enough at the required load level; and 2). The P5205 was speced to use +/-15.0V power. Will a +/-10.5V supply be adequate?----------------------------------------------3). Power Supply: The noise measurementsAC differential measurements were taken at different test points with the P5205 as the load (100mA) and also for a resistive load (230mA). Of particular interest were the results at the power output.With a HP3457A, the 2 rails showed readings of 0.13mVAC and 0.18mVAC at a 230mA load respectively (short leads reading=0.1mVAC).On the scope, the +10.5V output did not show any noise above the noise floor; while the -10.5V rail output showed the worst at the (2mV/div, 20MHz limit, 1x probe) setting and it is shown in Picture #2.The common mode (and radiated) noise was tricky to measure and my noisy scope just added the difficulty. Nevertheless, the comparative picture (#3) can still show the level of such noise. In this measurement, the ground lead of the probe was unused; while the measurement was taken with the probe tip touching the PS ground. The comparison was between whether the PS was plugged into the mains.-------------------------------------------4). P5205: The performance testsThese were aimed to provide quick (non-exhaustive) answers to 2 questions: a). Is a +/-10.5V PS a good enough replacement for a +/-15V PS; and b). How usable is a P5205 for "small" signals.For the first question, a concern was that the reduced supply voltage may lead to waveform clamping for full range signals or it may lead to reduced band width of P5205. Up to now, I only did the clamping test.For the 50X setting, P5205 is speced for a voltage range of +/-130V. To test the clamping, the mains (with a +/-170V range) was used as the signal source and no visible and measured difference in the waveforms was observed comparing using the +/-10.5V supply with a +/-15V supply.On the other hand, I think being over range for the 50X setting when using mains did show a slight different waveform than that for the 500X setting (Picture#4) and the difference was independent of the supply voltage (10.5V or 15.0V). It was also more interesting to see that the mains waveform was not very "sine".As for "small" signal tests, a ~10MHz square wave with Vpp ~= 0.7V was used. Picture #5 shows a comparison among the "original" (without P5205 involved), and the P5205 input/output. With using P5205, the signal was 50 Ohms terminated at the P5205 input; While for the "original", the 50 Ohms terminator was on the scope input.Two things are worth to note here: a). To get stable waveform from the P5205 output, my scope needed to set at average=16 samples; and b). There are excessive ringing when using P5205. Can these ringing be reduced? Then, maybe, my scope and cabling are to blame here?

author: David Hess
author_rank: Super Contributor
timestamp: November 17, 2014, 03:53:19 am
content: Quote from: onlooker on November 17, 2014, 03:40:15 amIf you needed to use averaging then the noise level seems high.The frequency of the ringing may yield a clue about the cause but I cannot see it accurately on your image. Is it 130 MHz?Was the differential probe terminated into 50 ohms on the oscilloscope?

author: 128er
author_rank: Regular Contributor
timestamp: November 17, 2014, 08:02:30 pm
content: Quote from: onlooker on November 17, 2014, 03:40:15 amCan't remember which parts of the circuit use the +/- 15V. But IIRC the +/- 15V input is directly followed by two adjustable linear regulator, one for +5V and the other for -5V. And they power most of the probe circuit. Have to look in one of my probes.Quote from: David Hess on November 17, 2014, 03:53:19 amDon't know if the OWON is capable of 50 Ohm termination. But the probes are specified for 1 MOhm input impedance.But it is nice to see that the thread is not dead. I have worked a little bit on my Tekprobe PSU at the last weekend.I like Onlookers idea. It is more like a stand alone solution, instead of my brick like Tektronix 1103 cloneA few pictures of my PSU . . .

author: onlooker
author_rank: Frequent Contributor
timestamp: November 18, 2014, 01:24:14 am
content: QuoteYes, that should be about right.QuoteMarkL had already quoted the manual earlier: The scope end must have an impedance > 50kR. Or as 128er mentioned, 1MR should be fine.128er, Your 1103 clone looked quite authentic and nice.QuoteThe output is speced to be +/-2.6V. So, in theory, it is possible that a +/-5V supply is all needed, though a few chips on the PCB can work up to +/-15V. In any case, it should be an interesting item to followup on. If true, the requirement for the PS is further reduced.

author: David Hess
author_rank: Super Contributor
timestamp: November 18, 2014, 06:34:51 am
content: Quote from: onlooker on November 18, 2014, 01:24:14 amI am thinking that the original cable had a compensation box on the end and was made from wire similar to x10 probe cable with a resistive center conductor to dampen reflections. If that is the case, then modifying the new cable to work into a 50 ohm termination may be necessary to get full 100 MHz performance.The 130 MHz ringing may be from the reflections along the length of the new cable and not anything to do with the probe end.

author: onlooker
author_rank: Frequent Contributor
timestamp: November 18, 2014, 12:07:13 pm
content: I would quote MarkL again about the "compensation box" of P5205 that connects to the scope:QuoteAlso, my P5205 had about 5" coax left. The core was made of multi strand silver(?) plated copper wire like RG400.Then, the manual says: "Output Type: Single-ended Source Impedance of 50 ohms drives 1 M ohm oscilloscope input". That is, yes, the scope end will reflect, but the scope would never see it since the P5205 end has a matching impedance and will not reflect back the reflection. This is what was meant by "single-ended".The square wave picture I posted earlier also showed that the output of p5205 followed the input "closely", including the ringing. That is, the ringing should be from the input of P5205. My input cables are about 20cm in length that are shorter than the original cables which are 30cm. I should expect less ringing?The problem is that the manual did not spec the ringing. Maybe they should spec it in some way since the manual did have pictures showing extra ringing as an expected result of using P5205 and adviced to twist the input cable pair.

author: MarkL
author_rank: Unknown
timestamp: November 18, 2014, 02:34:41 pm
content: Quote from: onlooker on November 18, 2014, 12:07:13 pmAll the clues you point out correctly conclude it's 50ohm coax and not special resistive coax.Plus, I'll also add that the 5205 can be used with the 1103 power supply, which you extend to the scope using 50ohm coax.And to put the question to a final rest, I took the cover off mine and measured 0.1ohm from the BNC center pin to the cable termination solder joint in the 5205 main box.In one measurement, you're showing ringing on both the input and output. If you disconnect the 5205 from the dual banana adapter, do you still see ringing on the input coax?

author: free_electron
author_rank: Super Contributor
timestamp: November 18, 2014, 03:36:57 pm
content: Quote from: 128er on November 17, 2014, 08:02:30 pmthat's a nice metal box. who makes that ? i like the punched noches to slide the board in.schematic of the supply ?i am sitting on a bunch of 6247 diff probes and their active counterparts but no 1103. and 300$ is too expensive for that stupid thing.By the way, these probes are not made by Tektronix. Tek installs their own pigtail on it. The probe itself is made by Pintek. it is sold under many brand names. Agilent , fluke Tek , BK precision : they all have this probe in one form or another , all made by Pintek.Same goes for all those current probes out there. only tek has their own. almost any other brands are rebadged hioki's.Agilent scope probes are made by PMK in germany ( only the old infinium probes were an in-house job )

author: David Hess
author_rank: Super Contributor
timestamp: November 18, 2014, 04:19:26 pm
content: I forgot about the description of the original coaxial cable and compensation box.What kind of cable was used on the input side?

author: 128er
author_rank: Regular Contributor
timestamp: November 18, 2014, 07:10:04 pm
content: Quote from: free_electron on November 18, 2014, 03:36:57 pmBought that case here:http://www.eibtron.com/epages/eibtron.sf/en_GB/?ObjectPath=/Shops/eibtron/Products/754-5979Also available on RS:http://de.rs-online.com/web/p/gefahrstoffschranke/7545979/I don't know who the original manufacturer is. Top, bottom and side covers are steel. Front an rear panels are aluminium.Quote from: free_electron on November 18, 2014, 03:36:57 pmIs attached.JP1-6 are header connectors for LED's. Two indicates that the +/- 15V are present. And two for each channel to show the attenuation factor for the channel.Didn't heard of PMK electronics before. For those who are interested:www.pmk.de/en/

author: MarkL
author_rank: Unknown
timestamp: November 18, 2014, 07:59:36 pm
content: That's a really nice job on the power supply.All you need to do now is add the offset controls and, with a reasonable price, you could clean up selling them as Tek 1103 replacements.

author: onlooker
author_rank: Frequent Contributor
timestamp: November 19, 2014, 12:49:20 am
content: For those interested, currently on Ebay there is this 4 P5210 for $100+shipping BIN.http://www.ebay.com/itm/Lot-of-3-Tektronix-P5210-High-Voltage-Differential-Probes-1-EA-Tektronix-P5200-/151481910071?pt=LH_DefaultDomain_0&hash=item2345068337

author: onlooker
author_rank: Frequent Contributor
timestamp: November 23, 2014, 05:02:06 am
content: I did more tests to determine the power supply requirements. These were done by measuring the signal amplitude reading on the output of 5205, as a function of the power supply voltage.1). Power supply dependency of bandwidth:A sine signal of 100MHz and Vpp of a couple volts was connected to the input of the 5205.For supply changing from 15.0V to 9.0V, the signal output stayed flat at about 2.6V. When supply further reduced to 8.0V, the signal output was dropped to 2.45V, or a 0.5dB attenuation.2). Power supply dependency of signal clamping:For this test, the mains voltage with its voltage range of +/-170V was applied to the input and the 5205 was set to the 50X setting which has a speced voltage range of +/-130V.The waveform amplitude and shape stayed the same for the supply varying from 15V to 10V. When the supply further dropped to 9.0V, the output voltage clamped about 7% and other artifacts started to show up at the peaks of the waveform . Considering that 170V was a ~30% over range signal, I would guess an in-range signal should not show clamping for a supply of about 9V.Based on these tests, I think a supply voltage between 10V (or 9V) to 15V should work fine.

author: free_electron
author_rank: Super Contributor
timestamp: November 24, 2014, 02:05:52 am
content: http://www.chevalgrp.com/sa_series.phpthats the cases

author: 128er
author_rank: Regular Contributor
timestamp: December 18, 2014, 12:55:32 am
content: Hi all!Just wanted to show you my finished PSU for the P5205 differential probes that I have. It works fine.The labeling is made with self adhesive letters. Sticks quite well. The LED's seems a bit dim, but that is due to the camera flash. The brightnes is good. Not too bright, so that it is irritating on the bench.The BNC connectors are okay. I had prefered some sort of front panel BNC's with crimp connection. Or one of those front panel BNC's with a plug on the rear side (couldn't find a picture at the moment). But none of my usual suppliers had them (for a reasonable price).But all in all I'm quite happy with the thing.The last thing left to do, is to properly connect alle enclosure parts with the PE. And maybe change the screws on the front panel, to some nice looking round head with hex socket.Thanks to all who had replied to this thread and gave some good infos.

author: Fluxed Matter
author_rank: Regular Contributor
timestamp: January 22, 2015, 12:15:21 am
content: Just picked up the P5205 for cheap off fleabay and it arrived yesterday and have a couple of questions.The first thing is how do you remove the enclosure and get at the pcb? Been trying to figure it out without destroying the case. Do you just pry it open?Love the power supply 128er! Do you have the image for the probe board available? I would like to etch one up for the PS I will build.I picked the probe up and it has a few calibations stickers on it from '08 but someone wrote bad in permanent marker on both sides. It came complete with cables and connectors on both ends. Hoping to get this working because I been wanting a probe for power supply work.

author: onlooker
author_rank: Frequent Contributor
timestamp: January 22, 2015, 12:45:43 am
content: The case was fastened with four screws. You can access the screws by lifting the top plastic sticky sheet cover. You need only to lift it at each corner just enough to see the screw well. A sharp knife can be used to do the initial lifting.

author: romantao
author_rank: Contributor
timestamp: January 22, 2015, 03:44:06 pm
content: @Fluxed Matter, I think i was overbid by youdamn!I'll keep waiting for my right to buy one myself!

author: Fluxed Matter
author_rank: Regular Contributor
timestamp: January 22, 2015, 03:51:03 pm
content: @romantao, I was out bid on 3 others before winning this one!

author: romantao
author_rank: Contributor
timestamp: February 09, 2015, 10:03:43 am
content: Hi!Anyone knows a reference for the probe switches ( teh ones for attenuation/ overrange and bandwidth)They have this inscription on the side 0113 201, but from it found nothing relevant...Two of mine are kind of funky...regards

author: 128er
author_rank: Regular Contributor
timestamp: February 09, 2015, 06:07:11 pm
content: Quote from: romantao on February 09, 2015, 10:03:43 amI had the same problem. Couldn't find any switches like them. But I repaired all switches at my four probes.Remove the grey cap from the switch by pulling it off. Then carefully remove the top half from the switch by bending the plastic latches on both sides. Remove the white top half slowly to avoid a mess inside the switch (spring and steel wire for the latching function). Be carefull in the end, that you put all back together as it was. You can put the red piece backwards in the white top cover. And you'll not be able to close the casing of the switch.Now the important part. You have two springy metal pieces inside. They get actuated by the red piece and shorting the contacts together. They wear out over time, because their shape gets flatter. The result is bad contact and all sorts of weird signals comming out of the probe.I have tried to illustrate that in the last picture, where you can see the cross section of the contact pieces. The one that is worn out, is less in width. The challenge is, to bring the contact piece in it's old shape. I have done that with my fingers. I repaired twelve switches. Several switches I had to open twice. Because it's a bit tricky to bend the pieces in the right way, so that it makes good contact.Man, I hope that is understandable. Very difficult to describe such a fiddly thing in a foreign languageP.S.:Good luck!

author: romantao
author_rank: Contributor
timestamp: February 09, 2015, 06:52:03 pm
content: Eheh! I know what you mean when you lack some technical terms in a foreign language!I manage to fix themI left the probe on during all day after compensating its gain and offset (internal trims).The differential gain is accurate now.However ... (there's always something wrong...) i'm noticing that under 500x the offset keeps running up once i close the case. That's not happening with the 50x. Even if i under-compensate while i have open case... as soon as i close it the offset keeps rising till 400mv approx.Is this a normal behaviour and i Just need to trim it using the compensation box? This way, depending on which attenuation range i'm working, i'll have to do different offset of the 50x and 500x range.Noticed that the lm317 and 337 get a little warm but they are putting around + - 5.1V respectively

author: Shock
author_rank: Super Contributor
timestamp: May 02, 2015, 07:36:32 pm
content: I have a Tek P5205 and I'm thinking about converting it for an analog 100MHz scope with 1MR input.Is the general consensus?Blue +15VBlack -15VBrown won't be used in my situationRed is the zero compensation for low voltage measurements.Since I don't have the power supply for it I was thinking of just of mounting a DC socket and the 10K zero compensation pot at the LV end of the probe which will need some new holes made.Is there any potential pitfalls anyone can see in doing this, will the power need shielding or twisting or interfere with the LV signal? It's got to be better than running it up to the scope, right?

author: 128er
author_rank: Regular Contributor
timestamp: May 02, 2015, 08:20:30 pm
content: Quote from: Shock on May 02, 2015, 07:36:32 pmYes!Quote from: Shock on May 02, 2015, 07:36:32 pmYou mean, fitting a DC socket and the 10k pot in the probe case? Why not. But the probe needs symmetrical +/- 15V. Or do you want to mount two DC sockets? I am not able to understand it at the moment

author: Shock
author_rank: Super Contributor
timestamp: May 02, 2015, 11:38:19 pm
content: I was thinking about drilling a hole for the DC supply (3 pin socket for +15V, -15V and GND). The DC supplies GND pin (not mains earthed referenced at the supply itself) then connects to the LV signal cables coax GND on the PCB (which is mains earth referenced at the scope). Then for the zero compensation put a 10K pot across the 15V rails and connect the Red to the wiper. Is that correct?

author: EvanShultz
author_rank: Newbie
timestamp: May 17, 2015, 11:46:55 pm
content: Cheers! First post!Hi Shock, yes that's the correct connections based on the schematic posted earlier. It should work fine.I just finished tracing the circuitry in the big probe box. I need to simulate a few things to make sure it all works, and I want to confirm the circuitry in the small box that goes into the scope, but so far it all looks correct and makes sense. Stay tuned...

author: abulafia
author_rank: Newbie
timestamp: June 05, 2017, 02:42:58 pm
content: Hi guys,Just for the interested parties here is R/E schematics from a P5205 (non A).Also to answer the buttons question, they are almost identical to Digikey itemhttps://www.digikey.com/product-detail/en/c-k/PVA1EEH11.2NV2/401-1132-ND/417713(same manufacturer)Best regards,Bogdan

author: walter76
author_rank: Newbie
timestamp: June 13, 2017, 03:30:46 am
content: Very useful post, it helped a lot in fixing a P5205 that was scrapped.The probe was marked as no-good and its showed a huge offest (around -2V) that could not be recovered by acting on the adjusting trimmer.It took some time to discover that the switches of the DG444 (U150) were no longer isolated each other: acting on R160 & R165 was partially successful in recovering the offset, until the scope suddenly switched to another scale!I removed U150 (obsolete) and I used a small 12V relais I found in my junk box: one switch to short R145, the other one to select between R160 & R165 according to the x50/x500 scale.Just move R155 to be in series with the wipe of R165, then most of the lands for U150's pins can be conveniently used to connect the relais.I hope this could help somebody else having the same issue.Walter

author: Dbldutch
author_rank: Regular Contributor
timestamp: November 01, 2017, 07:33:54 am
content: Just for kicks, while trying to understand how the various differential probes work, I used LTspice to model the input attenuation using the schematic provided byabulafiain an earlier post.Interesting to see that the higher frequency response is probably used or can be used to extend the bandwidth.I'm wondering why Tek used two identical 18R21/10-90pF in parallel???Enjoy!

author: Hydron
author_rank: Super Contributor
timestamp: November 01, 2017, 09:40:58 am
content: At anything higher than a few MHz the model would need to include input cable parasitics (L&C) and source impedance to get an accurate model of the frequency response. As the leads can move around (thus changing the parasitics) the response will be all over the place well before 100MHz, let alone 1GHz.

author: Dbldutch
author_rank: Regular Contributor
timestamp: November 02, 2017, 12:21:33 pm
content: Thank you Hydron for the comments, and I agree, but that was not my intention.I was interested only in the rather unusual front-end section and wanted to get a feel for the three things that stood out for me in this design. Tek engineers generally do that with good reason, and I wanted to try to understand why.First the relatively low parallel HF capacitors of 2.2pF, (only 1.1pF in total) which makes the front-end much more sensitive to parasitic or stray capacitance. In all the other designs I have found a minimum of 4pF in total, which is about a factor 4 more and so is 40x the typical 0.1pF for parasitic or stray's instead of only about 10x more.Second, the attenuation factor due to the 4M vs 6K81, which drives the rather odd LF compensation circuit with the strange, for me at least, dual parallel trimming section with R/C networks. In simulating the circuit, I found that the value of the LF 60.5pF I arrived at is extremely sensitive (I also used MC analysis), and the whole front-end is not flat. All the other attenuation designs I looked at can be easily calculated, and when simulated are flat.Third, the interesting circuit to adjust the CMR (2x 100K and a 25K trimmer). In all the other designs I found, the engineers use a 100-500 Ohm trimmer between ground combined with the two attenuation resistors (here the 6K81), which not only adjusts the CMR, but also the attenuation factor. I like the Tek method better, so I'll use that for my own design.I'm looking forward to get more comments about of this interesting circuitEnjoy!Paul

author: Tantratron
author_rank: Frequent Contributor
timestamp: September 06, 2020, 02:57:27 pm
content: This thread is quite old but maybe since then some of you do have a document explaining how to service manual or calibrate the P5205 which would be similar to the P5210 which I'm discussing in this threadhttps://www.eevblog.com/forum/testgear/repair-tektronix-p5210-high-voltage-differential-probe/msg3220840/#msg3220840Thank you in advance, Albert

author: Olexandr
author_rank: Newbie
timestamp: April 14, 2022, 12:31:52 pm
content: I want to repeat the scheme of this device for my own use, but the scheme lacks the denominations of almost all capacitors, based on this I want to ask everyone who has such a device to help me, you need to measure and indicate which capacitors are there.

author: richipedia
author_rank: Contributor
timestamp: May 08, 2022, 03:44:17 pm
content: Just in case somebody needs it: here are some nice pictures of the P5205 PCB's top and bottom sides.

author: minifloat
author_rank: Contributor
timestamp: December 30, 2022, 10:13:08 pm
content: Quote from: 128er on November 17, 2014, 08:02:30 pmA year ago or so, I got a pair of P5205 HV probes fairly cheap, without noticing the TekProbe supply needed. Yikes!I did not want to cannibalize the probes - being inspired by @128er, I made my own.Hacktronix- simple ±12V- no ±5V nor offset rubbish- some 3D print parts- mains filter waiting in the parts drawer- contact plate made with Dremel, drill press and carpet knife, out of a salvaged PCB with huge ground planes- mains xfmr salvaged out of a phone system- housing made from a salvaged MEADE battery charger- ...If someone needs the shroud, I can share collada or stl files.Thanks for all the information shared in this thread!Attached you find some pics.br, mf

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: December 30, 2022, 11:35:46 pm
content: Quote from: minifloat on December 30, 2022, 10:13:08 pmPlease put the shroud .stl here:https://www.eevblog.com/forum/testgear/replacement-knobs-feet-and-fittings-for-test-equipmentWould help me much with a TekProbe breakout box!

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 31, 2022, 07:22:49 am
content: Quote from: minifloat on December 30, 2022, 10:13:08 pmif BNC cable from that PSU output to scope is long, you risk reduced signal integrity (reflection), if its me, i will make an adapter from tek BNC input directly to normal scope's BNC output with power pins socket on the side, so PSU is external device with wires connecting to the adapter (which will be connected directly to the scope) much like tek 1141a diff probe with external 1142a psu module.

author: minifloat
author_rank: Contributor
timestamp: December 31, 2022, 09:38:53 am
content: Quote from: Neomys Sapiens on December 30, 2022, 11:35:46 pmdone so:https://www.eevblog.com/forum/testgear/replacement-knobs-feet-and-fittings-for-test-equipment/msg4611142/#msg4611142Quote from: Mechatrommer on December 31, 2022, 07:22:49 amYes I know - the P5205 requires the scope inputs to be set to Hi-Z.I am using 30cm of BNC cable after my box, since I placed the Hacktronix supply right below my 'scope.Using the original Tektronix 1103 supply with lengthy cable at the output would lead to the same problembr, mf