| Electronics > Repair |
| Tektronix TCP202 current probe repair - Schematic and suggestions needed |
| << < (13/18) > >> |
| MarkL:
Great! Glad you got it adjusted and it wasn't a more complicated problem. It's been a long road for you to find a working TCP202. Thanks for the heads-up on the 50-turn calibrator. I've always used a load resistor, but now we know what to expect from the calibrator. It doesn't seem like a very good accessory if the goal is calibration. |
| MarkL:
--- Quote from: esc on August 28, 2020, 08:16:14 am ---Glad I found this thread. I also have acquired a TCP202 in good condition. The probe "operates" but it doesn't "work". I did test it with DC 1A and the display seems accurate. Also tested with DC 50mA and it seems accurate, but I need to degauss to go back to the original 0 value - after the DC 50mA test the trace is about 10mA higher then 0 every time. This may be normal, not sure. The degauss works and so does the coarse zero (on the back of the probe head) and the fine 0 on the side of the plastic box at the BNC. The sine wave in AC looks ok, but it is smaller than it should be. At 10KHz is about 15% smaller, at 20KHz is the worst, 60% smaller and it recovers at 40KHz to 15% again, staying around there to the MHz range. The square wave response is very ugly. I measured the transformer in the head and I got the following values (compared to the previously posted measurements): +3V - -3V = 276 ohm - 176 ohm +3V - HALL1 = 183 ohm - 93 ohm +3V - HALL2 = 179 ohm - 92 ohm -3V - HALL1 = 189 ohm - 141 ohm -3V - HALL2 = 182 ohm - 141 ohm HALL1 - HALL2 = 110 ohm - 72 ohm COIL - COIL = 6.5 ohm - 6.5 ohm These are with the small PCB in the head disconnected. Are these still in range? Also, the electronics in the plastic box looks good, no visibly fried parts, and no sign of any repair. Attached some pictures. The load is a 100 ohm metal film resistor. Any help would be greatly appreciated. Thanks. --- End quote --- It's been a while since that post, but I had a chance to take my probe head apart and I made some measurements. I got the following values with the 6-pin connector disconnected and the sensor cold (after warm-up the Hall readings are different by about 10 ohms). There is a part number on the side of the sensor head "120-2032-XX". My measurements in [...] : +3V - -3V = 276 ohm - 176 ohm [347] +3V - HALL1 = 183 ohm - 93 ohm [211] +3V - HALL2 = 179 ohm - 92 ohm [227] -3V - HALL1 = 189 ohm - 141 ohm [246] -3V - HALL2 = 182 ohm - 141 ohm [259] HALL1 - HALL2 = 110 ohm - 72 ohm [154] COIL - COIL = 6.5 ohm - 6.5 ohm [6.5] Your Hall sensor is different by a fairly large margin. I can also say that the TCP202 Hall sensor uses +/-2V instead of +/-3V, measured at the 6-pin connector. This table, originally posted by user vtp, was for an A6302. And also different from the A6302, there are two 100R resistors in parallel on the -2V input on the TCP202 sensor head. On the degauss question... I also find that after measuring large DC currents it can leave the core slightly magnetized and show a small offset. It's normal. |
| vtp:
--- Quote from: MarkL on October 14, 2020, 05:22:17 pm ---I can also say that the TCP202 Hall sensor uses +/-2V instead of +/-3V, measured at the 6-pin connector. This table, originally posted by user vtp, was for an A6302. And also different from the A6302, there are two 100R resistors in parallel on the -2V input on the TCP202 sensor head. --- End quote --- Yes, the table I made was for A6302 head but the measurements I provided in the earlier post in this thread are from my TCP202. Looking at the schematics of the box, the head voltages are supplied directly from the probe interface +-5V to the head through a pair of 220R resistors. With 276 ohms between +-3V pins and 220R resistors from both ends to the +-5V supply I get 3.85 volts for the HALL element operating voltage. Close enough to your +-2V (=4V) measurement. Perhaps there are then different revisions of the probe - I do not have any 100R resistors in my probe head circuit board. There however are 2 paralleled 39R2 resistors and a 1u8 inductor in series with the coil circuit. Just to give a reference of a broken probe head, here are measurements from one A6302: +3V - -3V = 1834 ohm +3V - HALL1 = 1701 ohm +3V - HALL2 = 1987 ohm -3V - HALL1 = 347 ohm -3V - HALL2 = 626 ohm HALL1 - HALL2 = 470 ohm COIL - COIL = 5 ohm |
| MarkL:
Thanks for the clarification. I took apart my other TCP202 and measured it. Below are the measurements plus the others posted. My TCP202 #1 is newer, original purchase date unknown, and TCP202 #2 was purchased new 20 years ago. TCP202 #1 is marked "04 21 42 61" inside the potting compound, and TCP202 #2 is marked "99 21 18 34". I could believe the "99" is 1999, and maybe "04" is 2004. Just a guess. Both have the 100R resistors on a tiny PCB the female connector is mounted on. They're easy to overlook; photo below. The resistors are consistent with the diagram in the old "Tek Probe Circuits". Both also have the 39R2 resistors and 1u8 inductor. There's also a toroid wound as a CM choke that the two coil leads pass through before going to the resistors and inductor you mention. Readings in ohms "+/-3V" is actually +/-2V on TCP202 vtp esc MarkL MarkL vtp From To tcp202 tcp202 202#1 202#2 ex6302 ------ ------ ------ ------ ------ ------ ------ +3V -3V 276 176 347 287 1834 +3V HALL1 183 93 211 202 1701 +3V HALL2 179 92 227 200 1987 -3V HALL1 189 141 246 234 347 -3V HALL2 182 141 259 232 626 HALL1 HALL2 110 72 154 174 470 COIL COIL 6.5 6.5 6.5 6.8 5 How did your A6302 die? |
| vtp:
--- Quote from: MarkL on October 14, 2020, 10:56:55 pm ---Both have the 100R resistors on a tiny PCB the female connector is mounted on. They're easy to overlook; photo below. How did your A6302 die? --- End quote --- You are right. Thanks for the reminder on those resistors. I completely forgot about them. They also seem to be in A6302 heads as I have drawn the resistors on my notebook. I can't really recall but the broken A6302 I may have bought as non-working since I had one new element to replace the broken one with. I also have an old P6302 which died spontaneously. Measurements of the hall-element signals give a clue about what failed. In the A6302 example the probe head has a problem with +3V pin connection. In the broken P6302 the fault is even more clear, HALL1 pin has disconnected itself completely from the element as all HALL1 related readings give infinite resistance. Here is a nice basic introduction to Hall-sensor: https://www.electronics-tutorials.ws/electromagnetism/hall-effect.html and a picture from that borrowed below: As in the picture +-3V, or really the current supply pins, provide current to the element and Hall-voltage from the diverted charges appears at pins HALL1 and HALL2. Depending on what the resistance measurements show it is fairly easy to determine if the probe head is ok. Those signals are all available on the A6302 connector so the element can be checked without disassembling the probe. With TCP202 some disassembly is needed, at least to get to the wire to board connector in the compensation box. Of course there is the probe head PCB in between but that being faulty would be very good luck. |
| Navigation |
| Message Index |
| Next page |
| Previous page |