Brother industrial sewing machine repair / reverse engineering (repair success) - Page 1
Forum section: electronics / repair

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 02:32:04 am
content: This is a thread on my repair and reverse engineering project with a Brother industrial sewing machine.It started off with a question "Why does the polarity of oscilloscope probe matter?" then touches on mains earthing protection (or grounding, depending on where you live) in some good depth, then aspects of the project. And it goes on...I'm repairing another vintage industrial sewing machine (the other one ishere). I found something that I can't find an explanation for so would appreciate any help from you.I'm aware of the risk of blowing a piece of equipment by using an oscilloscope in the wrong way (particularly when using two probes), after having watched the vids from David. So I would not put the Earth clip of the probe to anywhere that is not connected to Earth in a circuit lightly. In this case however, it appears Earth is not connected to any point of the circuit, so it's safe to clamp the clip to anywhere I want as long as I'm using only one probe.I'm testing the output terminals intended to drive a solenoid. The circuit is a typical design, consisting of darlingtons, flyback diodes and associated power resistors.Without the load (solenoid) connected, when connecting the probe in one way, I can see a switching between ~40V DC and 0V, as a waveform on the oscilloscope, across the two pins. When I change the polarity of the probe to another way, the wave form becomes a flat line.What's going on here? Thanks for any insight.

author: Psi
author_rank: Super Contributor
timestamp: February 08, 2023, 02:48:40 am
content: Without the solenoid connected there may not be anything to switch on/off and so you might be measuring something that is now floating. Are you sure it's a push/pull driver that will function without the solenoid in circuit?Also keep in mine its not just earth connections you have to be aware of when deciding where it's safe to clip the scope ground.Neutral is connected to Earth at the house fuse box, so electrically they are the same wire.And of course phase has voltage with respect to both those as well.If the device has a transformer and you can see it's totally isolated from mains and the case is not earthed then it's probably fine to clip anywhere with a single scope probe.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 03:00:27 am
content: Quote from: Psi on February 08, 2023, 02:48:40 amIt's not a push/pull circuit or something like that. It's a digital circuit beautifully made without an MCU chip but with only logic gates (flip-flops). The existence of a waveform, with only the power on (but without any action on the pedal lever), is not expected and is probably a problem on its own. But now what baffles me is the different behaviour of the oscilloscope with different ways of probing the two pins.Yes, they are probably floating. But, if I understand correctly, notwithstanding the floating pins, the relative voltage difference should be correctly reflected between the two poles of the probe. And clipping the probe to one of the two terminals will set it to the ground potential anyway. Am I right here?And true, the behaviour is different when the load is connected (again no voltage differences or waveforms). I'm not sure if that is due to the existence of the flyback diode?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 03:03:41 am
content: Quote from: Psi on February 08, 2023, 02:48:40 amAre you sure about this? If this is the case, I will detect a positive connectivity with a multimeter between ground and neutral of a wall socket. Really?Edit: just checked this out - indeed neutral and ground of the wall socket are electrically connected. I still have not truly understood how ground protection of the grid works.Any recommendation of good resources about this? I watched videos of TPAI on YouTube, thought I understood, but obviously I have not.The good side of this is, this makes me understand (really?) why an isolation transformer is useful/important in repair jobs (I made one at one point by the way, though have not really used it).

author: srb1954
author_rank: Super Contributor
timestamp: February 08, 2023, 04:43:24 am
content: Quote from: max.wwwang on February 08, 2023, 02:32:04 amThe 2SD720 transistor cases, which are also the collector connections, don't appear to be insulated from their respective heat sinks so you should assume that these heat sinks are not grounded and you can't clip your scope earth lead onto them. Remember, for a standard scope, the earth clip is connected through to the mains earth connection. Clipping a scope lead to such a heat sink will likely short out an active signal.Assuming that your device has a mains power transformer it is best to connect your earth clip to the circuit common, which will be found on pin 7 of a 14-pin logic chip or pin 8 of a 16-pin chip. The heat sink of the regulator (the vertical one on the RHS) is also likely connected to circuit common (check with an ohmmeter) and could be safely clipped onto.If your device doesn't have a mains transformer then you will need to power it through an isolation transformer before you can safely connect your scope earth lead to the circuit common.

author: james_s
author_rank: Super Contributor
timestamp: February 08, 2023, 04:45:17 am
content: Quote from: max.wwwang on February 08, 2023, 03:03:41 amOf course they are. Every electrical system that I'm aware of around the world has neutral tied to earth somewhere. Here it's in the main panel, elsewhere it may be somewhere else, but it's always done somewhere. Neutral is a current carrying conductor, a load on a circuit may pull it up above ground at the point of use, sometimes as high as a few volts due to resistance of the wire. The protective earth ground is for safety only, it should never be carrying any current except in a fault condition, if a live wire contacts the housing of a metal appliance for example if it is grounded that will cause a short circuit and trip the breaker and prevent the housing from becoming live.If you're not 100% sure you understand all this, you shouldn't be messing around with non-isolated gear (such as a scope) and anything that is mains connected.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 05:04:06 am
content: Quote from: srb1954 on February 08, 2023, 04:43:24 amThanks! Yes, the case of 2SD720 is not isolated from the heatsink. That's why I clip the probe on it (it is connected to one pin of the output). Yes, I understand one pole of the probe (the little clip on the side) is directly connected to mains ground. That's why I was careful and checked that mains gound is not connected to any point of the circuit.Quote from: srb1954 on February 08, 2023, 04:43:24 amOne good thing is that I'm using a mains transformer to mock the power supply to this unit (30V AC), which is isolated. So I have not (hopefully) blown it by probing it with the scope.What looks like a voltage regulator (the one you refer to) is not a regulator, only another darlington (D633).

author: IanB
author_rank: Super Contributor
timestamp: February 08, 2023, 05:05:24 am
content: Quote from: james_s on February 08, 2023, 04:45:17 amThis is a digression, but not exactly true. There are some places that use the IT earthing system, where none of the live conductors are tied to earth. This is found quite commonly in Norway, for example. On the other hand, this means there is no "neutral" conductor, so in a way your statement is true. If there is no neutral, it cannot be tied to earth.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 05:12:16 am
content: Quote from: james_s on February 08, 2023, 04:45:17 amHow dumb I was!But anyway now I know (a part of it)!Just to understand this better (), is it the only reason for connecting neutral to ground (say, in the switch box) that the breaker will trip when a live wire touches the grounded metal case of an appliance? Certainly will do a bit more homework on this.

author: james_s
author_rank: Super Contributor
timestamp: February 08, 2023, 05:22:13 am
content: Quote from: max.wwwang on February 08, 2023, 05:12:16 amThere are multiple reasons to reference things to earth. One reason is common mode voltage. If the transformer feeding your house didn't have the secondary bonded to earth, it's possible you could get a high common mode voltage due either to capacitive coupling, or worse a leakage or short. In other words live and neutral could both be floating at 7200V or whatever feeds the primary of the distribution transformer. This is as you might imagine, a very bad situation.

author: tautech
author_rank: Super Contributor
timestamp: February 08, 2023, 07:11:02 am
content: Quote from: james_s on February 08, 2023, 05:22:13 am11kV in NZ is normal for last mile HV normally stepped down from 33kV used for medium rage distribution and it derived from 110kV or 220kV, our normal long range national grid voltages albeit we have some 400kV main trunk feeders from our hydro regions also.NZ and AU have a quite similar mains distribution network and share the same single phase socket for 230VAC mains and our 3 phase supplies are 415VAC normally with only an earth wire although some machinery that uses both 3 and single phase require a 5 core cable as it's not legal to use the PE as a neutral return despite them being bonded at the fuse/metered supply.Each 415VAC phase has that potential only to any of its accompanying 2 phases and they each are at 230VAC to mains ground/earth.2 phase supplies are quite rare here although it is sometimes used into high load domestic applications however a 3 phase supply is more common and good electricians can take some trouble to spread these 3 single phase loads onto each of the phases to keep with limits of our normal 60A max/phase supplies.Uprating a supply, even for just one phase adds significant cost to the daily line charges in NZ.For a rough idea, per phase we pay a little over $1/day with kWh rates levied on top for a 60A single phase supply.For some special applications Powerco's have offered reduced connection 3 phases of 20A/phase for near equivalent cost of a 60A single phase supply which offers the convenience of being able to continue to use small 3 phase equipment without the substantially higher cost of a 60A 3 phase supply.Attached is a pic of the label on a pole mount 50kVA 3 phase transformer installed near our dwelling yesterday replacing the 15 yr old 30kVA transformer that had developed a faults and continually blew its 3A HV fuse last week.Lucky there was another transformer close by that they could back feed us from until the replacement was installed.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 07:56:39 am
content: Thank you tautech. Interesting stuff about the line prices, the 60A current threshold, and the single/three-phase options etc. I never knew this before. Relevantly, at one point I wanted to have three-phase fed to my house for some small reason (which could hardly justify the cost) but didn't get it done (and no idea about the cost).These transformers (often ABB) around the corners of the streets in residential areas do attract my attention when I come across them.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 08:06:47 am
content: Quote from: james_s on February 08, 2023, 05:22:13 amThat's interesting. But I don't fully (or at all actually) understand common mode voltage.So this is probably a(nother) dumb question. Since neutral and protection earth (E or PE) are connected (at least at the position of the house switchboard), what's the difference if, after that switchboard, we use only two wires (L/N) and bond the metal case of all consumer appliances to N? This way, touching the metal case will not give you a shock (because it has the same potential as the ground), and a fault of live touching the case will also trip the breaker with the short circuit current. What's wrong with this arrangement? (Note: N is still earthed for the household, but only two wires are used for the sockets all around.)

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 08:48:54 am
content: I still don't know why the scope behaves differently when I flip the polarity of the probe.

author: tautech
author_rank: Super Contributor
timestamp: February 08, 2023, 09:07:24 am
content: Quote from: max.wwwang on February 08, 2023, 08:48:54 amThe probe Reference lead is at mains ground potential therefore it shunts any signal to mains ground as srb1954 previously said.Everyone calls them a ground leadwhich indeed they are however as the waveform is referenced against it, it should more correctly be called the Reference lead.Where you can come unstuck is with isolated channel scopes where each/every Reference lead is isolated from all others and on instruments of this type you can swap leads/probe tips willy nilly just as you might with a DMM.When the Reference lead on a normal grounded scope pulls the signal down you have the cheapest option of using 2 probes and Maths settings of A-B and just probe a reference point and a POIorget a differential probe which for a few 100 allows you to probe much wherever you need to with 2 properly isolated from mains ground clips.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 09:29:37 am
content: Thank you tautech. But I don't think I fully understand why the ground lead will shunt the signal in one way but not the other. Can you enlighten me on this?I was also about to come back and report some new findings.I said before that when the solenoid was connected, I was unable to detect any voltage across the same two pins both ways. I suspect it was due to the existence of the flyback diode.Along this line, I've tried with a dummy load of a 30 Ohm (more than double the resistance of the solenoid) pure resistor. This will not bring the diode into function.With this setup - with the resistance load connected - I am now able to detect the same, but stable, voltage both ways (with of course opposite polarities) with the scope.Any thoughts on this new information?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 08, 2023, 09:33:06 am
content: Quote from: tautech on February 08, 2023, 09:07:24 amWould love to have one of these isolated scopes. Is this the standard feature of modern models? If so, this may be a good reason to get a newer one!Alternatively, still with the same old scope, can I do the same thing (nearly) with the scope isolated with an isolation transformer?

author: tautech
author_rank: Super Contributor
timestamp: February 08, 2023, 10:38:39 am
content: Quote from: max.wwwang on February 08, 2023, 09:33:06 amNo, each channel's Reference lead is still at the same potential. (commoned)In reality there are few truly isolated channel DSO's on the market as it is an expensive design.Tek I think TDS models are isolated channel but very small memory for what is expected in a DSO today.Others and Siglent do some but due to their cost many use a handheld DSO as for at least one channel they provide isolation from mains ground.However the cost of true isolated DSO's might scare you eg the new Siglent 2ch 100MHz SHS1102X is $2650NZD but it does offer some impressive capabilities:https://www.eevblog.com/forum/testgear/new-x-model-siglent-handhelds-coming/https://int.siglent.com/products-overview/shs1000x/Quote from: max.wwwang on February 08, 2023, 09:29:37 amYou were lucky.In the modern DSO we can easily invert any channel to null values from swapping leads.

author: srb1954
author_rank: Super Contributor
timestamp: February 08, 2023, 10:52:17 am
content: Quote from: max.wwwang on February 08, 2023, 09:33:06 amIt is a very bad idea to power an ordinary scope through an isolation transformer. If the ground lead, or the exposed ground barrel, of a scope probe gets connected, intentionally or accidentally, to a live circuit all the exposed metalwork on the scope also becomes live and a major shock hazard!For the same reason you should never cut the earth wire on the power lead to the scope.

author: IanB
author_rank: Super Contributor
timestamp: February 08, 2023, 06:13:23 pm
content: Quote from: max.wwwang on February 08, 2023, 09:33:06 amNot with an isolation transformer, but I think you can do the same (nearly) with a differential probe. I think Dave sells one, for example, if they are still in stock. With a differential probe each probe is equivalent and neither is grounded. Therefore you can use them to probe two active points in a circuit without risk of upsetting the circuit under test.

author: james_s
author_rank: Super Contributor
timestamp: February 08, 2023, 06:46:12 pm
content: Quote from: max.wwwang on February 08, 2023, 08:06:47 amCommon mode voltage is an offset relative to something, usually ground, that is present on both conductors. For example if a 240V line had a hypothetical 1kV common mode fault, that would mean that neutral was sitting at 1,000V and live at 1,240V.As I mentioned earlier, neutral is a current carrying conductor. Due to the current passing through it, the resistance of the wire will result in some parts of it being pulled up above ground, possibly by several volts or more. The other issue is that a neutral fault (open circuit) would then result in the cabinet of the appliance floating at mains voltage when no other fault exists. The idea of a protective earth is it is a fallback, no matter what else is going on, any exposed metal should be at earth potential. You're standing on the ground too so you'll be at the same potential and won't get a shock. There is no possible fault condition that is likely to result in protective earth being live.

author: TimFox
author_rank: Super Contributor
timestamp: February 08, 2023, 07:56:19 pm
content: Quote from: james_s on February 08, 2023, 06:46:12 pmAlthough a real "neutral" is connected to "ground/protective earth" at some point in the building, due to substantial current flowing in the neutral (white in US) wire between your outlet and the breaker/fuse box where that connection is made, you can have a few volts of AC between the relevant contacts of your outlet when measured with a normal AC voltmeter.Common-mode definition: if you have any two voltages A and B, both measured with respect to the same point (for example, the PE contact in your outlet), then by elementary algebra you can define"D" = difference = differential mode = A - B, and"C" = common-mode = (A+B)/2Thereafter, you can compute A and B from the measured D and C: A = 2C + D and B = 2C - DEdit: correction after comment below: 2A = 2C + D and 2 B = 2C - D.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: February 09, 2023, 04:30:54 am
content: Quote from: tautech on February 08, 2023, 10:38:39 amNot the TDS models, they are very baseline. It's the TPS models. And the Tek portables (THS710/720 and the newest one, whose designation I forgot) There is at least one from Gould too (was also sold by Siemens).

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 09, 2023, 06:13:47 am
content: Quote from: tautech on February 08, 2023, 10:38:39 amOh, that's disappointing.I thought you said "you can swap leads/probe tips willy nilly just as you might with a DMM".I don't understand yet why making DSOs isolated and each channel independent is so difficult.Quote from: tautech on February 08, 2023, 10:38:39 amWhat do you mean I was lucky?Do you mean what I got will not repeat if I do this again?I understand with a scope that is not isolated, i.e. is earthed, the ground lead will pull the signal down. But the problem is, why is there a stable voltage when I probe both ways, with a dummy resistive load connected?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 09, 2023, 06:21:44 am
content: Quote from: srb1954 on February 08, 2023, 10:52:17 amI think I understand what you are saying here. That's the purpose of the earth wire. I only came up with the idea of isolating the scope with a transformer in this discussion - I thought the whole point is, to get more freedom in probing, temporarily disconnect the PE connection, which can be either on the equipment under test or the scope itself.The risk you are saying is real. But my follow-up question is, if we DO need to use the isolation transformer for the reason of testing (say with the equipment under test), the same risk will exist with the equipment. We can only take extra care to compensate such an increase of risk. The same holds for isolating the scope (which is actually less likely to fail, because the equipment is faulty in the first place). This means no extra increased risk in isolating the scope when using a transformer IS necessary.Am I missing anything here?Yes, I am. Refer to reply #41 (answer to question 2) for detail.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 09, 2023, 06:42:06 am
content: Quote from: IanB on February 08, 2023, 06:13:23 pmDifferential or isolated, I think they are the same thing, aren't they?But differential does not sound very expensive (maybe it is?), whereas according totautech, isolated scope is difficult to make and expensive? Why is this?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 09, 2023, 06:53:11 am
content: Quote from: james_s on February 08, 2023, 06:46:12 pmThanks for explaining; that's very kind. Now I know what it means.Quote from: james_s on February 08, 2023, 06:46:12 pmThat makes sense. I need to take time to think about this a bit more. It looks like simple but is actually quite tricky (at least to me). It is probably related to the 'principle' of single fault assumption.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 09, 2023, 06:56:47 am
content: Quote from: TimFox on February 08, 2023, 07:56:19 pmThanks. That's clear and helpful. But I think you mean:A = C + D/2B = C - D/2

author: IanB
author_rank: Super Contributor
timestamp: February 09, 2023, 06:58:04 am
content: Quote from: max.wwwang on February 09, 2023, 06:42:06 amYou will have to decide what "expensive" means for you:https://www.eevblog.com/product/hvp70/

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 09, 2023, 07:01:35 am
content: Quote from: IanB on February 09, 2023, 06:58:04 amThanks. Aha, this reconciles now. It is indeed expensive.It does not seem like something trivial.

author: james_s
author_rank: Super Contributor
timestamp: February 09, 2023, 07:13:11 am
content: If you keep an eye on ebay you might get lucky, I have two different Tektronix HV differential probes that I don't think I paid more than $100 each for. There are also DIY projects if your needs are basic which for this application I think they are. In concept a differential probe is very simple, the devil is in the details if you want more than a few tens of MHz but something like a 20MHz differential probe is probably something you could build fairly easily.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 09, 2023, 07:15:56 am
content: Due to this discussion, had some read into the earthing systems. It's good learning. But in reading this reference (Earthing System & Protection in Low Voltage Installations), I don't quite understand the difference between the TT system and the TN-C system. Since there will normally be local earthing at the installation, they look the same to me (Figure 12 and Figure 16).In Figure 16, I've added the green dash line for the local bonding between N and PE.Another observation, the diagram for TN-S (Figure 11) in this reference is different from the diagram for the same TN-S system in this reference (EARTHING: YOUR QUESTIONS ANSWERED) ("TN-S", which I think is correct).The topic of earthing/grounding is actually very complex and interesting.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 09, 2023, 07:17:18 am
content: Quote from: james_s on February 09, 2023, 07:13:11 amThat's good to know. Thanks. I never knew this before!

author: james_s
author_rank: Super Contributor
timestamp: February 09, 2023, 07:26:20 am
content: https://hackaday.io/project/169390-a-10x-100mhz-differential-probehttps://resources.altium.com/p/differential-oscilloscope-probe-project

author: tautech
author_rank: Super Contributor
timestamp: February 09, 2023, 08:15:40 am
content: Quote from: max.wwwang on February 09, 2023, 07:01:35 amIt is if you value your life !We try to keep a few of the infamous DP-25's in stock and can easy whip NZ RS pricing by some margin.http://www.pintek.com.tw/productDetail/land-ctop-2/index/pscsn/17072/psn/19265

author: tautech
author_rank: Super Contributor
timestamp: February 09, 2023, 08:26:55 am
content: Quote from: max.wwwang on February 09, 2023, 07:15:56 amTT is the NZ system where the PE/N is bonded at the pole/distro transformer with its own PE peg field and again at the customer installation, meter board and if separate the breaker board too.Typically just one PE peg is used and both at meter and breaker boards the PE and N are tied together.This image is a good find.

author: TimFox
author_rank: Super Contributor
timestamp: February 09, 2023, 03:09:06 pm
content: Quote from: max.wwwang on February 09, 2023, 06:56:47 amOops--I stand corrected. I need more caffeine in my algebra. I'll add a note to my post.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 05:00:11 am
content: Quote from: tautech on February 09, 2023, 08:26:55 amFrom this 1993 NZ code of practice (NEW ZEALAND ELECTRICAL CODE OF PRACTICE For POWER SYSTEMS EARTHING) now still available on WorkSafe website (I have not got into the detail of it yet), and a post from what appears to be a NZ hardcore expert (TT Earthing Systems - Interest by New Zealand), it appears the system in NZ is (or was) MEN (Multiple Earthed Neutral), but was considering a transition to the TT system. From what you are saying, it seems like this transition has been done at certain point?Quote from: tautech on February 09, 2023, 08:26:55 amGlad to hear you like it.Just keep in mind it's not the original one, it has been adapted by a dumbass (that's me).I added the green dash line.For the original one, you will need to go to the reference above.

author: IanB
author_rank: Super Contributor
timestamp: February 10, 2023, 05:03:46 am
content: Quote from: max.wwwang on February 10, 2023, 05:00:11 amIf you add the green dash line, it's not TT anymore. Why would you do that?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 05:17:04 am
content: Quote from: IanB on February 10, 2023, 05:03:46 amWas not trying to correct an 'error', was only trying to illustrate what I was saying -- if, according to what was said by someone above that almost everywhere there is such a connection, then I couldn't see a difference between the two systems (TT, and TN-C). I've highlighted this above to avoid misleading.By the way, do you mean in TT system, N is not tied up to PE in the household switch box?

author: IanB
author_rank: Super Contributor
timestamp: February 10, 2023, 07:25:19 am
content: Quote from: max.wwwang on February 10, 2023, 05:17:04 amYes, exactly. That lack of a connection is what characterizes a TT earthing system. If you were to make such a connection it would be against code and it would no longer be a TT earthing system.You can find a description of all the different arrangements here:https://en.wikipedia.org/wiki/Earthing_system

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 07:26:10 am
content: The original question (puzzle) is still not answered (explained) satisfactorily (to me at least). That is ---[Open question 1]Why turning the leads of the probe around will hide the signal (about 40V peak, when the load is not connected)?Note:1) when there is load (a dummy pure resistive load), this phenomenon does not exist, a signal can be detected both ways (though without fluctuation but rather stable +/- about 40V).2) the circuit under test is fully isolated from the mains and mains PE.Another question that has come out of the discussion and has also not been satisfactorily answered ---[Open question 2 --- edit: this has been partly answered]When an isolation transformer is needed in a repair job, which I understand is usually connected to the equipment under test, can the isolation transformer be used between mains and the scope to achieve the same effect of isolation?According to the contributors to this discussion ---This was probably once used by experienced people decades ago. Butis definitely dangerous so must be avoided, particularly because of the availability nowadays of isolated scopes and differential probes which make this dangerous trick unnecessary.The major risk is that, by doing this, when you clip the ground lead of the probe to a point in the circuit of the device under test (DUT) that has a voltage above the earth (say 110V, DC or AC), the metal case of the scope, as well as the ground lead of other probes of the same scope with become live as well (at the same potential). This is not only a threat to your own safety but also to people around you, people who o rescue you (in case the worst case eventuates), none of who would likely be aware of this hazard.The key is that this does not require an earth fault inside the scope. This risk exists with a scope in fully working order without any fault because of the way scope (that is not an isolated type) works. This is different from using the isolation transformer with the DUT, in which case the metal case of it will not become live unless there is an earth fault inside it (that is, contact of the live wire with the metal case).Yet another question related to earthing system is ---[Open question 3 --- edit: this has now been answered satisfactorily]In the TT system is there a connection at the household end between N and PE as indicated with a green dash line in the figure below?A big, fat, firmNO. In TT system, there is no such direct connection in the household switch box.Furthermore, in the five earthing systems described in the IEC 60364 standard, which are TN-C, TN-S, TN-C-S, TT, and IT, only TN-C or TN-C-S systems have a direct connection between N and PE at the consumer end (usually in the household switch box).

author: james_s
author_rank: Super Contributor
timestamp: February 10, 2023, 07:28:25 am
content: Quote from: max.wwwang on February 10, 2023, 07:26:10 amNo! Do not ever do this! People have been shocked and even killed this way. it can result in the entire scope becoming live.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 07:32:09 am
content: Quote from: james_s on February 10, 2023, 07:28:25 amThanks, can you please elaborate, and respond to my questions (or counter argument) in reply #24 above?

author: james_s
author_rank: Super Contributor
timestamp: February 10, 2023, 07:34:53 am
content: No, sorry, I can't give you an entire EE education, some of this you're going to have to figure out on your own.

author: IanB
author_rank: Super Contributor
timestamp: February 10, 2023, 07:35:36 am
content: Quote from: max.wwwang on February 10, 2023, 07:26:10 amThere may or may not be, it depends on the local electrical code. But in most localities the protective earth and neutral conductors are indeed electrically bonded on entrance to the property. They may, or may not, also be connected to a ground rod.

author: tautech
author_rank: Super Contributor
timestamp: February 10, 2023, 07:55:55 am
content: Quote from: james_s on February 10, 2023, 07:28:25 amCertainly such a practice is very dangerous however with the normal isolation transformer with a pass through PE it really achieves little as each probe's reference lead is still bonded to mains earth therefore supplying the DUT via an isolation transformer makes far more sense.Take that PE away and you have a floated scope, something that was done by experienced users decades ago however today it is universally frowned upon and I imagined outlawed in many businesses.Today we have differential probes that remove the danger of needing to connect to an elevated reference point for not much coin at all, certainly far less that the cost of a funeral.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 08:43:55 am
content: Quote from: james_s on February 10, 2023, 07:34:53 amFair enough!Will do my homework.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 08:52:47 am
content: Quote from: tautech on February 10, 2023, 07:55:55 amI think I get all that you are saying here.True, there is no point in isolating a scope but still tying its PE separately to the mains earth. As you said, that still puts the ground lead of the probe at the ground level which will likely short circuit whatever is above or below the ground level of DUT.Aha! Are you saying in the good old days experienced people used to use this trick?! It sounds like this is not entirely a dumb idea then!Don't get me wrong, I now know the existence of potential probes and isolated scopes. I am also not desperately trying to put my life in danger. I am just fiercely attacking the problem (and in the meantime grilling you guys) and trying to distil the essence out of it for the sake of knowledge and deeper understanding.I'm not going to walk away satisfactorily with an advice "you should do this not that" but without knowing/understanding WHY.

author: Psi
author_rank: Super Contributor
timestamp: February 10, 2023, 08:56:17 am
content: Putting an isolation transformer on a scope or other test equipment is can be somewhat acceptable if you understand what side effects it creates and why it's so dangerous, and you take adequate precautions , like using test equipment with no exposed metal and only using 1 probe.The main issue is that if you isolate the scope and then clip the scope ground lead onto 110/220 phase (or any HV source.)Then the scope case and all metal terminals are now LIVE !!!And of course if you put CH1 gnd clip onto a HV source then all the other scope probe ground clips are also now LIVE!!You can see why it's so dangerous and it requires such extreme care, and why its killed many people.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 08:57:07 am
content: Quote from: IanB on February 10, 2023, 07:35:36 amSorry, though it should have been clear enough (with "TT" in the figure), I could have included "in the TT system" to make it clearer (have done now). Do you mean,specifically for the TT system, that is still the case? If so, why are other people saying there is no such connection in TT, and there is indeed no such connection in many references that I mentioned above?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 09:09:50 am
content: Quote from: Psi on February 10, 2023, 08:56:17 amThanks. Of course whoever using an isolation transformer should know what they are doing. Agree with all you said. That's exactly my counterargument in Reply #24. By using an isolation transformer with the DUT, we must know what we are doing as well --- because by isolating, we have taken away the safety protection provided by PE deliberately.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 10, 2023, 09:21:26 am
content: Quote from: IanB on February 10, 2023, 07:25:19 amThanks. That's been covered now along with a handful of other resources.

author: tautech
author_rank: Super Contributor
timestamp: February 10, 2023, 09:49:10 am
content: Quote from: max.wwwang on February 10, 2023, 08:52:47 amThis is where we walk the tightrope of informing how it was once done when EE's didn't commonly have the tools to do it more safely or expanding on what was and still is, a mortally dangerous practice.None of want it on our conscience after explaining in detail such practices so we universally advise strongly against it.Now that's not to say many of us haven't done it but in doing so we realise how dangerous it actually is.As I now have stocks of differential probes you won't catch me doing floating measurements again.

author: gf
author_rank: Super Contributor
timestamp: February 10, 2023, 11:10:55 am
content: Quote from: Psi on February 10, 2023, 08:56:17 amThe same also applies to battery powered scopes, though, except for isolated ones. In fact they are equally unsafe per se as a floating bench scope, but nobody cares.

author: alm
author_rank: Super Contributor
timestamp: February 10, 2023, 12:17:18 pm
content: Quote from: gf on February 10, 2023, 11:10:55 amThat's why reputable brands like Fluke and Tektronix have fully isolated inputs, isolated BNC jacks and probes with insulated reference leads on their battery powered scopes.

author: 2N3055
author_rank: Super Contributor
timestamp: February 10, 2023, 12:43:29 pm
content: Quote from: alm on February 10, 2023, 12:17:18 pmAs do R&S, Keysight, and Siglent isolated scopes..

author: IanB
author_rank: Super Contributor
timestamp: February 10, 2023, 02:29:41 pm
content: Quote from: max.wwwang on February 10, 2023, 08:57:07 amIn a TT system,there is no connection between protective earth and neutralat the consumer premises. If there is such a connection it is not a TT system, it is something else such as a TN-C-S system.When I say there may be such a connection, it means that such places are not using the TT system. For example, there is usually (always?) such a connection in North America, but this also means that North America is not using TT.

author: james_s
author_rank: Super Contributor
timestamp: February 10, 2023, 06:42:53 pm
content: Quote from: tautech on February 10, 2023, 09:49:10 amIt's a lot like driving drunk. Lots of people have done it and lived to tell the tale, technically it's still possible to do, but nobody is going to suggest you do it. It's needlessly dangerous both to yourself and anyone that happens to be nearby.

author: tautech
author_rank: Super Contributor
timestamp: February 10, 2023, 08:15:38 pm
content: Quote from: james_s on February 10, 2023, 06:42:53 pmExcellent point James, the risk to others that might attempt to rescue an electrocuted person from a hazardous situation.....wouldn't be the first time innocent parties have paid the ultimate price when helping others.

author: james_s
author_rank: Super Contributor
timestamp: February 10, 2023, 10:31:51 pm
content: Quote from: tautech on February 10, 2023, 08:15:38 pmOr somebody who happens to walk over and twiddle with the scope not realizing it's floating, or move it out of the way to reach something, or brush against it while walking by, you might say you'll always turn off the power when walking away but it only takes one mistake. More than once I've managed to leave a burner on the stove on when I'm done making dinner. Humans make mistakes.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 11, 2023, 01:07:19 am
content: Quote from: james_s on February 10, 2023, 10:31:51 pmMakes good sense. I need to do a bit more homework on the subject of isolation transformers. Vaguely understand it but probably not fully.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 11, 2023, 01:18:31 am
content: Quote from: IanB on February 10, 2023, 02:29:41 pmReally appreciate your patience here. It's now crystal clear now. So it is --For TT systems, there is no (never) direct connection in the household switch box between N and PE.I believe this is correct because this aligns with two (possibly more) references mentioned above.So if I understand correctly (as always, please correct me straight if I'm wrong), in the five earthing systems described in the IEC standard, which are TN-C, TN-S, TN-C-S, TT, and IT,only TN-C or TN-C-S systemshave a direct connection between N and PE in the household switch box.I believe this is the most accurate statement so far in this discussion with regard to this subject. Edit has been made inReply #41for easy reference of people who might be reading and are interested.Any of you who have contributed if don't mind, can please move to that post and make sure I'm not making any mistake, misunderstanding, or misinterpretation, there.

author: tggzzz
author_rank: Super Contributor
timestamp: February 11, 2023, 09:38:57 am
content: Quote from: james_s on February 10, 2023, 10:31:51 pmBoth of those have happened to me. In the latter cases (plural) I kick myself. In the former I gave a verbal kicking to the Dunning-Kruger-candidate perpetrator who ignored safety instructions, making sure that everybody knewwhy/howit was potentially lethal.No harm has occurred, so far.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 11, 2023, 09:08:53 pm
content: Quote from: tggzzz on February 11, 2023, 09:38:57 amThanks for sharing your experience. That's the reason why I try hard to understand that it is a bad idea, should be avoided, and (more importantly) why --- and sharing this with whoever comes by.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 12, 2023, 09:26:37 am
content: Carefully probing and testing. It's slow and no progress here.Another strange thing I don't understand --- when probing a checkpoint on the board (with GND lead clipped on the negative of the 37V DC rail, which is believed to be, or may be considered as, the common GND of the circuit), I got two straight lines on the scope: one 0V another 12V DC.Do you have an explanation for this? Only one channel is being used and on display. Thanks for any help.

author: tggzzz
author_rank: Super Contributor
timestamp: February 12, 2023, 11:08:31 am
content: Quote from: max.wwwang on February 11, 2023, 09:08:53 pmYou are welcome.It is always a pleasure to see someone that thinks, asks important/good simple questions, and listens to the responses. That isn't guaranteed

author: james_s
author_rank: Super Contributor
timestamp: February 12, 2023, 06:52:40 pm
content: The scope is not triggering properly, either the sweep is the wrong speed or the trigger setting is wrong for the signal that is there.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 12, 2023, 10:20:02 pm
content: Quote from: james_s on February 12, 2023, 06:52:40 pmThanks, James.I traversed all the stops of the speed (time/div) dial (along with the different settings of other related trigger switches/dials), but failed to get a meaningful display of signal. In the meantime, using a fluke DMM, I got 1.17V AC and 3.90V DC readings across the same two spots.

author: james_s
author_rank: Super Contributor
timestamp: February 12, 2023, 11:49:34 pm
content: What happens if you turn down the sweep speed very slow so you can watch the dot moving across the screen? It's an analog scope so the vertical position of the dot is directly controlled by the voltage at that instant in time. The only way you can get two parallel lines is if the beam is sweeping across at both voltage levels in succession.

author: srb1954
author_rank: Super Contributor
timestamp: February 13, 2023, 12:03:12 am
content: Quote from: max.wwwang on February 12, 2023, 10:20:02 pmIt is probably a pulsed waveform so the DVM is measuring the DC average of the pulsed waveform.It looks like you have your scope configured for auto trigger, which is not suitable for triggering off slowly varying waveforms.Slow the sweep speed of your scope down to 10ms/div or slower. Select NORM trigger and INT source. Adjust the LEVEL control and polarity until you get a stable waveform display.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 13, 2023, 12:23:52 am
content: Quote from: james_s on February 12, 2023, 11:49:34 pmWhen I turn the dial CCW (towards greater time per div), the two lines first start to flash (when the dial is at 5 ms/div), then look like shooting from LHS to RHS (on the same voltage levels), then become two dots moving at the same direction in an increasingly slower speed. Nothing special is observed. Thanks.Quote from: srb1954 on February 13, 2023, 12:03:12 amThanks. Indeed I was using auto trigger (though the source was internal). Tried what you suggested but the same remains.But anyway, with more patience, more combinations of the "Level" knob and the "SWP VAR" knob, I finally got a meaningful sweep (with time/div set at 100us/div or less, and still with auto trigger mode -- the same for normal). It's a square waveform between 0V and 12V (or so) with a period of 44us or so, which is about 23kHz.Thanks for the help! This 12V or so DC voltage is the same, or similar, voltage for the Vdd pins of all the logic chips. Does this ring a bell with you?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 13, 2023, 05:00:00 am
content: Some tiny progress. I think the signal detected is ok.It's a "checkpoint" on the board (cp2, a metal stud on the LHS of the top logic IC in bay #6. Refer to the photo). It goes to pin #5 of a TC4011BP chip - a Quad 2 Input NAND Gate. Pin #5 is one of the two input pins of one of the four(4) NAND gates. According to the datasheet, the voltage range for inputs is from 0 to V_DD. V_DD is about 11V (pin #14). That is about right.Also, (a little bit) excitingly, this (input) signal --- its frequency --- responds to the pedal movement. The frequency increases when the pedal is pressed forward. This makes sense. This is the first meaningful response to the pedal action I detected from the circuit so far. This means at least the pedal sensing module is working (though not necessarily in full order). The opposite is unlikely but this has to be demonstrated by readings or test runs.Attached is the component side of the board I'm talking about. There is another board of similar size, and a third small board for pedal movement sensing, all enclosed in one single beautifully made metal control box.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 14, 2023, 09:08:34 am
content: Trying to trace down where the issue is. I start from the output side, that is the connector going to the clutch solenoid. It's supposed to output 37V or so voltage, either stable or switching. Refer to the upper left corner of the further updated photo.The base of the darlington for this, RHS of the two big ass power transistors, is fed by an upstream transistor (the RHS one of the two, RHS of the letter 'A' on the PCB), whose C&E lie between the 11V rail and GND, with transistors on both sides. Its base (B) goes to one end (upper end) of a resistor ladder (highlighted with a blue rounded rectangle). I suppose the analog signal comes from this ladder which in turn comes from the logic chips, with the ladder working as a DAC. However, the bottom end of the ladder goes to a TC4011BP chip, pins 1&2, which are the two inputs of one NAND gate, not an output pin (as I hoped).I would appreciate any help here working out this part of the circuit, particularly the ladder and the logic chips around it.

author: james_s
author_rank: Super Contributor
timestamp: February 14, 2023, 08:18:21 pm
content: It would be much easier to follow if you draw a schematic of the area in question.If you can identify which output(s) of the logic chip control the device you're trying to test then it should be straightforward to determine if those outputs are doing what they're supposed to do. Then test the transistors using the diode check feature on your multimeter.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 14, 2023, 08:52:37 pm
content: Quote from: james_s on February 14, 2023, 08:18:21 pmHave started to make schematics of this part, still need more time to broaden the territory (will update). Checked the related transistors (including the darlington) with the diode mode of DMM. They appear to be ok. The solenoids' connectivity is also ok --- i.e. motor side is good.By the way, in terms of circuit diagrams, whatfree onlinetools do you guys use/like, just in case? This one is drawn with the Digi-Key's "Scheme-it" app.

author: james_s
author_rank: Super Contributor
timestamp: February 15, 2023, 12:40:10 am
content: It would be more clear if you put all voltage sources at the top and ground at the bottom but that's pretty good for a beginner schematic.I use KiCad personally but there are lots of suitable tools out there.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 15, 2023, 04:18:26 am
content: Quote from: james_s on February 15, 2023, 12:40:10 amVery good advice. New version with more territory now ...Earlier I was tracing where "??" is, which now does not seem to be the source of the signal, because it goes to the input pins of a logic gate (not an output pin). So the investigation needs to be wider. Still more to be added.Quote from: james_s on February 15, 2023, 12:40:10 amThanks!Quote from: james_s on February 15, 2023, 12:40:10 amThanks. Will try it out and find out what suits me best. KiCAD looks like a very good one. Scheme-it has export option for it. The only downside is that it's not online (install-free). I guess really good ones still need to be installed locally? Only with the first time trial of Scheme-it, it quickly proved too limited.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 15, 2023, 07:21:54 am
content: Clearly KiCAD is a serious tool. It's cool, though a bit too heavy for me now (but too heavy is better than too light and inadequate). That's great.A quick redraw of (roughly) the same thing here (I didn't find a way to load or import the files exported from Scheme-it, so redid it from scratch). Obviously, this will be ugly.One thing I need to figure out now isthe configuration of a resistor network (ladder). It has a label "IHR-4-103 JB" and 8 pins.I couldn't find its datasheet (probably that's common for resistors?). Is it likely to be configured the way shown in this schematics (which is taken from the part lib), or may be a so-called R-2R ladder? This is sortedhere.

author: james_s
author_rank: Super Contributor
timestamp: February 15, 2023, 07:26:50 am
content: Quote from: max.wwwang on February 15, 2023, 04:18:26 amAll real software has to be installed. Web based toys have their place but rarely in the professional realm. I have a strong dislike for software that is stuck within the constraints of a browser.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 15, 2023, 07:42:56 am
content: Quote from: james_s on February 15, 2023, 07:26:50 amAgree.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 01:08:49 am
content: Did more tracing. It quickly becomes exponentially more complex and beyond what I can manage because of the logic gates. Also tried starting from another simpler (I thought) end, but the size of the problem grows the same way. Maybe it will be a failure. Or maybe let it sit for some time ...

author: james_s
author_rank: Super Contributor
timestamp: February 18, 2023, 02:04:01 am
content: Well before you spend too much time working out what all the logic does, is the output of the last gate doing anything? It shouldn't be hard to determine if the problem is the logic or the power stage.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 02:09:59 am
content: Quote from: james_s on February 18, 2023, 02:04:01 amTrue. That’s also what’s in my mind. I’m going to use a dummy load and trace up by simulating the working of the transistors by shorting their collectors and emitters and going upstream to see if they behave the way they should without getting into the rabbit hole if the gates (they are not difficult at all, only interconnected into a complex web!).Thanks man for your ongoing support here!

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 03:46:03 am
content: Had another go from the starting point -- testing the single board without it connected with other boards. The power source is on this board.Tested below (one at a time). In each case, the solenoid works correctly --1) Short C/E of Q1 (power transistor)2) Short C/E of Q2, which brings Q1 into action (closed between C/E)3) Manually bring pin 6 (output) of U1 to +11V (output of U2 is low, so Q3 is open between C/E), this will turn on Q2, then Q1.Now it goes to logic (and the rabbit hole). For U1/6(X1) to be high, U1/3(A1) or 5(C1) must be low (A1=B1). This then goes on ...

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 04:23:35 am
content: This however brings the voltage comparator C271C (said to be the direct replacement of LM311) to my attention, because for the solenoid to be powered, its pin 7 (output) but be low (turning Q3 off) at least for some time in a cycle. I guess this guy can be the weak spot of the whole thing. Gates are robust, resistors and transistors in this area are all ok.What's the best way to test if it's ok without taking it out? Its BAL and BAL/STR pins are N.C. And LM311 is new to me (will have a close look at its datasheet).With a bit of poking around, it appears it is doing alright. When the voltage on pin 2 (+) is higher than 3(-), it gives a high (5V) on the output pin (7), otherwise a low (0V). I think this is the expected behaviour of it.

author: tautech
author_rank: Super Contributor
timestamp: February 18, 2023, 06:08:37 am
content: Quote from: max.wwwang on February 18, 2023, 01:08:49 amOnly because you are doing it the hard way !For heavens sake just use a gate symbol and enumerate it with with the device # and pin #'s.Each IC has xN gates and power pins that don't even need be visible as being an IC everyone knows it need power and decoupling caps. Smart layouts have the decoupling caps the same # as the IC; C9 belongs to U9.In a complex design all gates are broken out from an IC only layout as we can follow it better and the PCB CAD program is quite smart enough for schematic layouts like this not to worry it one little bit.A bit of additional guidance here:https://resources.pcb.cadence.com/blog/jbj-unpacking-logic-as-it-is-used-on-a-printed-circuit-board

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 06:59:15 am
content: Quote from: tautech on February 18, 2023, 06:08:37 amTrue, it's a hard way. But even with a smart(er) way, as what I did at the beginning (post #79), things were not much better.But I know, it's a long way to go before I can draw schematics in a professional way (or close)!One question, which CAD programs are smart enough to recognise the separate gates in schematics and integrate them into individual chips when doing PCB? Keen to know.

author: tautech
author_rank: Super Contributor
timestamp: February 18, 2023, 08:10:37 am
content: Quote from: max.wwwang on February 18, 2023, 06:59:15 amMost.IIRC you can drop individual gates part of the whole package but they must be U*Pt1, U*Pt2, U*Pt3 etc and each will have different pin numbers.Here you need consult datasheets to ensure pin and gate numbers match for each IC.It becomes much more fun when getting to do the PCB layout as to make routing easier sometimes we swap gates to make trace/track layout easier.From the link I posted earlier is your basic Quad AND package but with gate #'s unspecified for which you can develop you own theme and/or create your own model to use in schematics.There is also the old trick of creating NETS and NET labels so to not actually have physical schematic connections but instead virtual connections buy way of named NETS.Once you assign a NET label to any 2 or more connections any PCB CAD program will sort it out.I use an old cracked copy of Altium Summer 09 but sadly I have less time for layouts and such now business has grown.It's one hell of a lot of fun and a real challenge to lay out a good PCB and not at all too hard to make a better job than those commercially done as they make no effort at all for any ease of rework.They might be more compact but what a bitch to have to work on !And a thought just to mind, you might learn heaps by spending a little time in here:https://www.eevblog.com/forum/eda/

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 08:22:40 am
content: Quote from: tautech on February 18, 2023, 08:10:37 amGreat. Then I presume KiCAD is one of them. Only became aware of it here from James. I think it's the one I'm going to stick with -- it's free and open source, yet powerful as far as I can see for now.If the answer is indeed yes, and if you have the answer to this next question, and if it's a short answer, how is this typically done in KiCAD?Quote from: tautech on February 18, 2023, 08:10:37 amRoughly get the idea. True, there can be many ways I think. And different app may have different tricks.I think EDA means "Electronic design automation", as suggested by Google?What does "NET" mean here?I see it in KiCAD but don't know what it is.Quote from: tautech on February 18, 2023, 08:10:37 amBusiness growing is good! Nowadays there are wonderful OS and free tools readily available. That's great!Quote from: tautech on February 18, 2023, 08:10:37 amIndeed it's great. Thank you!

author: tautech
author_rank: Super Contributor
timestamp: February 18, 2023, 02:02:25 pm
content: NETS take 2 forms, user specified in the form of a power NET or schematic NET added to make the schematic tidy or to take part of the design to another sheet/page.The other form is developed automatically by the CAD program when schematic components are connected and when converted to a PCB layout.In reality every connection between any 2 points is a NET, some which are user named and the remaining named by the CAD program normally with reference to one of the component pads that make up that NET.This becomes the trace name and all are added to a NET list.Component pads can be told to connect to a specific NET to prevent violations which are commonly triggered when placing a test point onto a PCB trace after the PCB is generated.You do this in component properties dedicating pad connection to specific NETS.Kicad should have all this functionality.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 09:00:47 pm
content: Thanks. It will take time and practice for me to fully understand. I guess NET is an acronym? What does it stand for?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 09:14:03 pm
content: Some progress, though it's peripheral.The synchroniser had not been connected when doing all the tests previously. I thought the motor should function without it. Just to be more sure, I took it off the head unit and hooked it up with the board.It's essentially three hall sensors, I believe, with another tiny PCB with something I'm not sure about yet. Shown in the photo (only hall sensors are visible).What happened first was even worse. The signal at CP2 was gone. Measuring with DMM, the power rail for +11V is even pulled down to GND. With further investigation, one of the sensors is gone --- with Vcc and GND pins shorted.So, one bad boy is caught.What's interesting is, by disconnecting the faulty sync (or with it connected but only with the bad sensor isolated), there is still +11V on that rail, i.e. it does not seem to have been destroyed by the short circuit due to the bad sync module.I don't know how the +11V DC is generated yet, though I'm pretty sure it must come from the +37V source. I guess a Zener diode and a transistor must be a part of that circuit. Shorting that supply would probably not destroy the Zener (it should still be working because this voltage is still available). But I'm not sure if the transistor(s) will have blown.Can we say for sure just by reasoning that, given there is still +11V DC there, the whole circuit providing that voltage must be ok?Not by reasoning but by measuring, the 11V DC circuit is ok. It survived the short-circuit caused by the sync module, or it features short-circuit protection by design.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 10:46:45 pm
content: Now trying to decipher the +11 power supply and investigate its health. What is this guy in the middle with two orange bands and two gold rings?

author: tautech
author_rank: Super Contributor
timestamp: February 18, 2023, 10:55:01 pm
content: Mr Google says 3.3 Ohm 5%https://kiloohm.info/resistor-4/orange-orange-gold-gold

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 11:14:47 pm
content: Quote from: tautech on February 18, 2023, 10:55:01 pmMy goggle dittos. Ah, it did not came to me that gold is not only for tolerance but is also a valid colour for digits (gold and silver for '-1' and '-2' zeros, respectively!). Thanks.So, the +11V DC PS looks like this. Does it make sense at all? Excuse my ignorance of schematic conventions (but please do let me know how I can make it better).

author: tautech
author_rank: Super Contributor
timestamp: February 18, 2023, 11:28:00 pm
content: Quote from: max.wwwang on February 18, 2023, 11:14:47 pmIt looks to me missing another ground connection somewhere. You might need to buzz it out.BTW, good use of 36 and 11V NET labels.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 18, 2023, 11:47:07 pm
content: Quote from: tautech on February 18, 2023, 11:28:00 pmGood spotting. One trace hidden by an ugly lump of glue (or something like that). Added. Now it makes sense for the Zener to clamp the output voltage. Its spec should be 11VplusQ1/Vce. Not completely getting how this works, or if there is any other error here producing the schematics, yet.Quote from: tautech on February 18, 2023, 11:28:00 pmReally? I just grabbed whatever looks right without knowing what it was.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 19, 2023, 12:28:16 am
content: Tried hard to get the sense of it. That does not work (Q1 will not be turned on). This one should be correct.Only this way will Q1 turn on. It seems it has good short-circuit protection by design?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 19, 2023, 01:08:22 am
content: A bit more tidy-up.One question to think about is ---If the +11V rail is shorted to GND (as what has happened), what Q2/Ve will be? Will it be low enough not to blow R4 (3.3 Ohm)?(I know it is not blown and is ok.)Also, to make this small schematic professional, I guess the +11V rail should use a different symbol to indicate it's not an input from an external PS but rather the output of the +37V source. What's the appropriate way in EDA?

author: tautech
author_rank: Super Contributor
timestamp: February 19, 2023, 03:27:14 am
content: Quote from: max.wwwang on February 19, 2023, 01:08:22 amRev 2 was fine with 2 Gnds, just fine. While you think you've made it neater with Rev3 it's actually harder to follow.For simplicity to follow use NET labels whenever necessary in order not to cross any wiring.+11V is a power NET and it don't matter a damn if it's devived locally or remotely. You might add a text box saying "From Sheet 1" or something.If you want it better designated use a different symbol for the supply and load parts of power NETS.Your Kicad surely has different symbol options other than the arrow which might better indicate data/analog signal flow.Altium, the one I use uses a T with the NET voltage above it but we do have choices in even the selection of power NETS. Signal path NETS are different and like power NETS can be named.Which brings me to another point I forgot to make earlier....try to lay out a schematic like this:Signal flow from left to right. Positive NETS at the top and GND NETS at the bottom.....although they can be placed within the design.It's also useful to drop a text label or 3 amongst schematics with a single or 2 word description of that part of the circuit. Eg, PSU, Reg, Timer, Vref and so on. There's no need to go overboard but later it can be useful for debugging.Do carry on...........

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 19, 2023, 05:37:32 am
content: Quote from: tautech on February 19, 2023, 03:27:14 amI'm afraid I have to agree. It seems tighter/neater but clarity is lost. That's a good point, clarity and easy-to-follow has higher priority. Here we go, rev 4, which I believe is even better than rev 2.Clarity is more important than formal neatness.Quote from: tautech on February 19, 2023, 03:27:14 amTrue, this is closely related to clarity because crossing but not connected lines increase cognitive load ---use NET labels to minimise crossing lines.Quote from: tautech on February 19, 2023, 03:27:14 amThe point here is ---include right amount of comment/annotation.Quote from: tautech on February 19, 2023, 03:27:14 amSignal/power go from left to right, top to bottom --- be intuitive.Quote from: tautech on February 19, 2023, 03:27:14 amWill do.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 19, 2023, 07:25:28 am
content: Known broken parts can be ordered early because it take a long time to arrive. So the broken hall sensor is taken out of the plastic housing. It has such marking on it:N3006(first line) /SK046(second line).Now one (peripheral) obstacle to overcome --- I could not find any place online where it is available.But this should not be an unclimbable mountain. I only need to find one that has a TO-92 form factor, the same polarity, and accepts high supply voltage (11V plus some margin).

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 21, 2023, 05:36:20 am
content: Was wondering where the square wave signal comes from. I think I got the answer now. It involves a UJT (uni junction transistor), which I didn't hear of before. It's at the top left corner of the schematic. This part of the signal generator is almost identical to figure 8-c in the datasheet, which is different from the more commonly seen (that is 8-a), but is specifically recommended for this transistor.Its output signal goes to an inverter, as one stage of buffer, then through another AND gate (effectively another stage of buffer). Then there is a stable square wave on check point 2-CP2. Pot R302 is for the adjustment of the frequency.I think the purpose of R306 and R307 (RHS of the inverter) is to set a mid-point (about 6V) for the signal before the analogue to digital conversion.Some questions for those who are experienced and have interest in analysing (or appreciating) this circuit.1. What's the purpose of R303 (area B1, RHS of 2-CP2)? I know it does not hurt. But is there any significance here? There is no such thing deep in the web of the gates.2. What's the magic going on here in the way the A798 chip (top right corner highlighted) is wired up? This IC consists of two PNP transistors; they are hooked up in an intriguing way.Will do a bit more poking around and see if all is working.

author: james_s
author_rank: Super Contributor
timestamp: February 21, 2023, 07:55:51 am
content: UJTs are cool, they were once common, used for flashing lamps and generating tones and such back in the 70s. You don't really see them much these days.

author: tautech
author_rank: Super Contributor
timestamp: February 21, 2023, 08:10:11 am
content: Quote from: james_s on February 21, 2023, 07:55:51 amI've only seen them in 2 applications, a now elderly electric fence controller (1 pulse/s) and in a SCR phase control in a 180A single phase welder.The welder used a pair and a RE schematic is attached.BTW, Max, that schematic was drawn using MS Office Visio and saved as a Doc in which one of its libraries was quite useful for electronics.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 21, 2023, 08:41:23 am
content: Quote from: james_s on February 21, 2023, 07:55:51 amTrue, it seems so easy to use, and has plenty of applications. But strangely, it's said to be obsolete now!

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 21, 2023, 08:43:45 am
content: Quote from: tautech on February 21, 2023, 08:10:11 amThanks. That's one of its common uses --- phase control.

author: tautech
author_rank: Super Contributor
timestamp: February 21, 2023, 09:12:24 am
content: Quote from: max.wwwang on February 21, 2023, 08:43:45 amVery interesting thing to get the SCR's balanced and when I was taught by a EE Prof how to float a scope.BTW, that welder was west Auckland designed and built.Triacs are much simpler to use with a controller IC and another welder I fixed some years back used an Alternistor, a specialised form of Triac.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 21, 2023, 09:34:59 am
content: Quote from: tautech on February 21, 2023, 09:12:24 amWill have a closer look and think. Alternistor is again new to me. How many new things not known to me are out there?!

author: tautech
author_rank: Super Contributor
timestamp: February 21, 2023, 09:58:03 am
content: Chill out Max, we can't know everything ! I certainly don't but knowing there is more to learn is what's so exciting about electronics.

author: james_s
author_rank: Super Contributor
timestamp: February 21, 2023, 06:14:29 pm
content: Quote from: tautech on February 21, 2023, 08:10:11 amI have a flashing red beacon that came off of an old forklift that uses one. I've seen them in a handful of old hobby circuits too, I think the 555 took over a lot of their applications when that came out.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 21, 2023, 06:57:05 pm
content: Quote from: james_s on February 21, 2023, 06:14:29 pmThat probably explains it. I’ve seen a lot of talk about 555 ages ago.

author: tautech
author_rank: Super Contributor
timestamp: February 21, 2023, 08:14:24 pm
content: Quote from: james_s on February 21, 2023, 06:14:29 pmThe welder we brought new that had UJT's was an 80's design but required pulse transformers for the phase control circuitry isolation and sufficient drive via the pulse transformer to drive the SCR gates.Dunno but guessing 555 would not have the drive to do that.

author: TimFox
author_rank: Super Contributor
timestamp: February 21, 2023, 10:21:32 pm
content: I think the 2N2646 unijunction and its equivalents are easier to interface to an SCR than would be a 555, but the 555 is far more flexible for general-purpose timing and oscillation.I believe that when the 555 came out, some scoffed that it was superfluous since you could do the same thing with a handful of components (instead of one).

author: tautech
author_rank: Super Contributor
timestamp: February 21, 2023, 11:00:00 pm
content: Quote from: TimFox on February 21, 2023, 10:21:32 pmYes at one time pulse transformers were quite common however Triacs removed much need for them.A pair of reversed bias SCR's and their phase control Gate waveforms are a wonderful thing to see.That welder ran so much nicer when the SCR phase control was properly balanced.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 22, 2023, 04:40:05 am
content: Quote from: tautech on February 21, 2023, 11:00:00 pmAs far as I know, TRIACS allow current both ways whereas SCR only one way. But don’t quite get why the need for transformers is removed by them?True, probing with a scope and actually seeing what’s going on out there is fascinating.On your earlier point on balance of two UJTs, sure, even if it was not nicer from the welder perspective, it still feels better with a balanced and symmetrical wave form above and below 0V.

author: tautech
author_rank: Super Contributor
timestamp: February 22, 2023, 11:27:46 am
content: Quote from: max.wwwang on February 22, 2023, 04:40:05 amUnlike a SCR reverse biased pair for AC phase control a Triac gate is zero crossing referenced I believe which negates the need for a pulse transformer.See these devices and datasheets.https://www.hestore.hu/prod_getfile.php?id=5680No current sense required for a welder if the set point is correctly set. (max rated current draw)A high current Alternistor in substantial airflow on a decent heatsink completes the phase control:https://ie.rs-online.com/web/p/triacs/1106594This pair using U2008B was just too easy for a repair I did on a mates 180A welder that had been parked atop some obstacle shoving a grille into a bottom mounted fan stopping it which fried the Alternistor. The previous DIP16 control IC was no longer available so a U2008D was carefully shoehorned into the same PCB footprint with a couple of cut traces and wire links for the welder to give further decades of use.I'm sure there are even better solutions available today.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 26, 2023, 12:06:03 am
content: Quote from: tautech on February 22, 2023, 11:27:46 amSo it seems Alternistor is only another name for "snubberless TRIAC". Good to know.Substantial progress has been made on two fronts --- chasing down the culprit (though the battel is not yet conclusive) and deciphering the working of the entire circuit and the machine. The aims now are two-fold: 1) to get the thing back and running; and --- more importantly --- to fully understand how it works. I will not be too disappointed if the first goal ends up a failure now.I said before this is a beautiful machine. It now looks even more beautiful than it was before. Without an MCU, its program is literally hard wired so is completely transparent. No secret is hidden whatsoever.Details to follow...

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 27, 2023, 05:13:12 am
content: A very strange thing that I've never come across before.Accidentally I think I found one fault on one board just by holding it in hands, turning around and closely inspecting (because I need to work out the rat nest across the components).In doing this, I noticed a very light but distinct clicking (metallic) sounds when turning the board, definitely because of the flexing of it due to its weight (this is when it's held in only one hand), and due to the (very light) forces imposed on it by my hands. Because there are no moving parts on the entirely board, there must be a crack somewhere, either in a trace or a component, or somewhere else.Strange enough, having done whatever I can do (including with a magnifying lens), closely combing through every square mm of each side of the board, I just cannot find where exactly the crack is. By holding one part each time and repeat, I think I located where the problem probably sits --- inside a resistor. There is no sound when it's lightly pressed (or touched) when turning. My explanation is that the sound is either eliminated by pressing it (causing the gap to close) or the sound it largely dampened. That said I'm still unable to observe any relative movement between parts of it (such as between a pin and its body) when bending the board slightly, nothing whatsoever. So I cannot be 100% sure.What else did I do with it? Tried to measure the resistance of it with too alligator clips on its two ends --- the reading is correct: 6.8k. What's more interesting is that, after doing this, I cannot get the same sound again!The only explanation I can come up with is: the use of alligator clips on its two ends -- due to the weight of the clips and the wires --- its two ends have been bent slightly closing whatever gap there existed before.Because this fault is so evasive, if I take it off, by applying heat and force, it's very likely it looks perfectly good.Not in a haste to take it off yet because first I'm still not very sure about this and second, there is much more test and investigation that need to be done. Even if it's faulty, there are probably more problems somewhere because its role here is still quite peripheral --- it's related to another solenoid not related to the motor.In the photo, it's the smaller resistor starting with a blue band at LHS of a transistor.

author: tautech
author_rank: Super Contributor
timestamp: February 27, 2023, 05:57:00 am
content: Quote from: max.wwwang on February 27, 2023, 05:13:12 amYup, an old trick when assessing a faulty PCB is to bend and flex it while listening for the telltale clicks or a crack which while you've identified there is one, finding it can be an entirely different matter !We could of course go over it with a DMM and while components are in circuit and can give misleading measurements any that measure higher than bands/markings suggest must first be removed and checked.I had a PCB some years back from a sorta modern welder that had been carelessly dropped/tipped in a workshop and then refused to work.Initial diagnosis was easy, a small PCB mount transformer that powered the control PCB despite being cable/zip tied down had dragged a PCB pin from its housing breaking the primary winding deep in the potted transformer case a repair was not possible however it was a common voltage, pinout and construction that another was sourced from RS for a straightforward replacement resulting in a successful repair......well so I thought !When it came back I found a cracked solder joint on a SMD passive and a reflow remedied it again......so I thought !Returned again with an intermittent.....goes sometimes, sometimes not.... and based on previous finding it was obvious the PCB had suffered severe flexing when the initial damage was done to the transformer that some some substantial Sherlock Holmes'ing was required to beat it.This PCB fair crackled and clicked when flexed and reflowing several joints shut it up some but never completely fixed it.Even careful study with a good magnifying headset couldn't identify further cracks but it still clicked and cracked when flexed.As it was only some 150x150mm but mostly SMD I decided to reflow each and every solder joint by hand to near MIL spec...you know perfect fillets and all that.Never saw it back again !

author: max.wwwang
author_rank: Frequent Contributor
timestamp: February 27, 2023, 06:55:44 am
content: Ok, so I was not alone! With some little experience before, now I got a good appreciation of the magnitude of impact of the seemingly very trivial forces and fluctuation of forces, such as due to weight, heat, vibration, handling etc etc.Yes, there was definitely a good deal of Sherlock Holmes'ing going on. I was reluctant to take it straight off not only because I don't want to break things that were not faulty but also really want to clench the dirty hands when they are misbehaving! I was irritated if not insulted.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 01, 2023, 07:28:27 am
content: With strenuous effort, I think I've transformed all the PCBs into schematics, except for one module, which can be treated as a simple black box --- its behaviour is well defined.It seems more strenuous effort is needed to detangle this huge net. There appear no obvious winning strategies other than re-arranging, transforming, labelling signals with meaningful names, isolating parts of the circuity that are relatively independent or have relatively clear functions, keeping notes, etc etc.Take this part as an example, although it's already a hugely reduced/simplified application of the chip (with Aout/Bout/Cout/Dout all NC), it's still insanely complex --- perhaps too complex to decipher by human brutal force.The datasheet of TC4516BP is very vague to me (perhaps crystal clear to experienced). But at least I've figured it out (the working of the chip, not this circuit!) by staring into the timing diagram.

author: srb1954
author_rank: Super Contributor
timestamp: March 01, 2023, 08:53:19 am
content: Quote from: max.wwwang on March 01, 2023, 07:28:27 amIt will be easier to understand the operation of the chip in this circuit if you redraw the TC4516 symbol to put its inputs on the LHS and outputs on the RHS. Group the signals together with their associated control functions wherever possible. e.g. the PRE/EN signal is associated with the parallel inputs Ain - Din.If you still can't decipher the operation of the chip you may get a better description or diagram from another manufacturer's data sheet - the 4516 is a standard CMOS chip available from many other manufacturers apart from Toshiba.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 01, 2023, 09:32:51 am
content: Quote from: srb1954 on March 01, 2023, 08:53:19 amThanks. The difficulty at first is that it's not explicitly stated D/C/B/A are formed into a 4-bit counter. But this was figured out by carefully examining the timing diagram.Yep, redrawing the symbol more organisedly is a good idea!

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 04, 2023, 04:45:55 am
content: By redrawing the symbol and re-arranging ..., it becomes much clearer. The bottom two gates (U31B & D) are simply an RS latch. The only difference is that the "prohibited condition" for a normal RS latch is not a problem here because there is no complement of it as another output (so no logical problem). I've included the truth table on the LHS of it.So signals from 4 sources come in and become the 4-bit preset number (c0) of the counter (counting up), which, once preset, will count up until it's full (reaching 16, i.e. after 16-c0 clock pulses), when carry-out will be set (and all the bits reset). Since there is a bar on the top of C_OUT, which I think means it's the invert of C_OUT, so at that moment C_OUT' (I'm using "'" for a bar) will become L.The way the magic initial count c0 is set is really difficult to decipher. Just to make this a little closer, I've figured out at least what the input bits are. For this I need to start from the genesis of the clock signal.It starts from a square wave generator comprising a UJT, the frequency of which can be adjusted at run time through human interface (pedal action). This pulse signal, along with an ENABLE signal (as I understand it), feeds into a 4040 12-bit counter --- only 7 bits are used as a series of pulse signals for output. The lowest bit Q0 has 1/2 of the frequency of the (enabled) input signal (because it flips, from L to H or H to L, once in one cycle of the input). Next one Q1 has 1/2 of the frequency of Q0, and so on, until Q6 (the 7th bit).These 7 pulses signals go through a series of gates (AND, OR, etc.). When reaching the 4 input ports (bits) of 4516, I've figured out the formulas for all of them (noted on the top). I've also visualised these series of signals and the result of the formulas, as well as the value of the 4-bit number, in Excel. So you can get an idea of --- suppose RESET is L, i.e. at the moment of presetting the initial count --- the likelihood of c0 being non-zero (highlighted in green) and its value (be it zero or not). (Also shown is the result of c0 for another 4516, 2-3C.)Whichever of these c0 values is set (when the CLOCK signal is H), it will count up upon every clock pulse, and --- as soon as the count reads 16 sends out a carry-out signal (inverted) --- unless RESET becomes H, at which point it will start over again.(After this 4040, the Q1 signal feeds into the LCK pin of other logic chips, so I'm now naming it "CLOCK".)While this seems closer, it is still a huge maze to navigate.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 04, 2023, 05:20:58 am
content: While doing this vault-cracking exercise, another progress (or rather realisation) has been made.Last time when a bad guy was caught --- that was a shorted hall sensor --- there was a big oversight of me.It was a "peripheral" fault. Indeed, it would be, if it was only the sensor not working. The fact is, the sensor is not only not working, it has brought down the whole +11V power rail. One beautiful thing is that, the 11V power source is able to handle short circuit of its loads without any drama. But I should have realised this was not a peripheral fault anymore.So, now I suspect it was the ONLY fault, because the machine once worked well, but only without any sign of life (except for the motor, which is fed directly from the mains) after that. There was even no response to the manual back-tack (BT) switch or the knee switch, which normally would respond regardless of the running status of needle. With the +11V rail down, it's highly likely they are down, because it's unlikely the states of them do not go through ANY of the gates (which all rely on the +11V rail).Having realised this, simulation of closing these two switches is done (with hall sensor module disconnected, i.e. +11 V rail up), using dummy loads in lieu of the solenoids. +37V was detected for both scenarios (this is different from when the machine was down). So, very likely the machine will be back and running if I put everything together, and will be in full working order as soon as the faulty hall sensor is replaced.Of course, the lurking crack fault of one of the boards (now without a trace) will probably still be a problem at certain point.I'm now not hasting to put it back though, when it's wieldy and conveniently laid out on the desk --- so I can do a bit more probing and safe-cracking (it's still a looong way to go). Fingers crossed, hopefully this will not cause any new problems!

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 04, 2023, 07:44:00 am
content: Another part of the big puzzle I've partly figured out but hope I can get any input from here, is a part of the synchroniser, which I believe is the head unit speed sensor. Along with the three hall sensors (one is gone), there are other three wires going to a small board close to the centre (a hole). In side the hole, rotating with the needle mechanism, is a donut-shaped magnet. In the static condition (nothing moving), the resistance measurements between the wires resemble two 0.5k Ohm resistors between Black/Brown and Brown/Grey. These are drawn in the circuit (lower half). In whatever way, I believe the rotation of the magnet will induce a (net) potential in way of where a battery is shown. This induced potential will then be sensed by the V comparator and, depending on whether the speed is too high or too low, pulses are output on the top right corner through the gates.My question ---Does anyone have an idea of what exactly this speed sensing mechanism is (and what the small PCB is doing), assuming my assumptions are correct?(In the photo "Magnets", the other magnet than the donut-shaped one, is of course the one that works with the hall sensors.)

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 04, 2023, 08:29:09 am
content: There is another thing about this circuit that baffles me. I've drawn up the timing diagram of the signals (outputs and transistor states). Among the signals, only N2-6B-4-sync and N2-6B-11-sync are visible to external. If my timing diagram is correct, their responses to the too high or too low speed are the same --- either rising to high (-4) or falling to low (-11), then return (to low/high). So how can the user of the signals be able to tell whether the motor needs to be driven faster or braked down?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: August 29, 2023, 05:10:25 pm
content: Refer to message #127 and photos there, finally an update. After receiving the replacement hall sensor through snail mail from AliExpress and having it replaced, I put things together and had a test. Everything works now!

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 20, 2023, 08:23:33 am
content: Quote from: max.wwwang on February 10, 2023, 05:00:11 amNo, NZ and Australia are still using theMEN(Multiple Earthed Neutral) system, which -- according to theElectricity (Safety) Regulations 2010-- "is a New Zealand variant of the internationally definedTNCsystem". The standardAS/NZS 3000:2007 Electrical installations(known as theAustralian-New Zealand Wiring Rules) also includes a great deal of detail of the MEN system.