| Electronics > Repair |
| [SOLVED] HP 34401a - Error 612, 613, 615, 617, 618, 619, 621 |
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| chihaxinh:
Hi Tin Ok let's me check all zenner and report for you soon ! Update: I check all zenner have voltage drop like datasheet, but CR201A ( 4.7V ) in Ohm current source have osic from -0.9V to 1.4V . And voltage drop on pin 7 U201-B have only 4.6xxV |
| robjpiel:
I have been working along with this thread trying to solve a similar issue that I have with my 34401a. Error codes only: 612 Ohms source current failed, 618 DC HV attenuator failed (no surprise here- I hit it with between 1100~1250VDC while in the DCV AutoRange, yes this was dumb but we got a new 34461 and now I'm trying to repair this 34401 for fun/learning experience/I want it for myself) Sorry to dredge up such an old thread but it has so much relevant information in it, and you all seem to be the only resource I could find out there with this kind of information. The meter does work in several other functions such as the DCV all except the 100V and 1kV range so I figure it is worth some time and attention. When it is in these two fried ranges it is not accurate at all on low V inputs and only registering 70% of actual higher up ie. a 1000 volt input will only read 700v. (It will not accept a new calibration this far out fyi- I tried this first) I first thought I blew up the 9.9M and 100k ohm voltage divider resistors in u102-A, but they are fine so I checked all the rest in: u102-C: 2k, 2k 2k-All Good u102-D: 20.57k, 5k, 50k, 500k, 1M-All Good. I checked all the voltages that I could (attached). I highlighted red only values with significant deviation from what the OP had (Zucca I believe) and in black I have additional readings in case they were to help me down the road, but most of my values turned out to correlate with TiN's working meter leading me to think this IC u102 may be OK?? Hoping anyway. Where my confidence stops is after checking u102-B I get 2k Ohm (pin11-14), 17.3k (13-14), and 84.8k (13-15)instead of 2k, 18k, and 180k. But I didn't really expect any values to be in tolerance since its still in the circuit and I'm measuring resistance which I know is fundamentally wrong to begin with. The second issue I found here is that my output Ohms Current test did actually have 0 current from the low terminal to the anode of CR202. I was measuring with a 77IV so I will try it again to confirm with a 3458 tomorrow I guess just to be sure. If anyone would like to call me an idiot for looking where I have been, and point me in the right direction that's obvious to you that would be much appreciated, or tell me those resistance readings in u102-B are OK since they are still in the circuit that would be cool too. Otherwise my next step was going to be to see if RV102 was having an issue only when it sees higher voltages and maybe the rest of the meter is working just fine after that point - but I will say I dont know how to check a -"Diode-Varistor 1.1kV" yet. Time to pull out my textbook I guess. Thanks in advance for any input you may have!!! |
| Dr. Frank:
--- Quote from: robjpiel on November 28, 2016, 06:43:10 am --- 618 DC HV attenuator failed (no surprise here- I hit it with between 1100~1250VDC while in the DCV AutoRange, yes this was dumb ... --- End quote --- I don't understand this expression.. What exactly happened? Did you apply 1250Vdc when in Ohm mode, or simply when in DCV / Auto mode? The instrument should withstand such overvoltages to some degree in both modes. --- Quote from: robjpiel on November 28, 2016, 06:43:10 am ---The meter does work in several other functions such as the DCV all except the 100V and 1kV range so I figure it is worth some time and attention. When it is in these two fried ranges it is not accurate at all on low V inputs and only registering 70% of actual higher up ie. a 1000 volt input will only read 700v. (It will not accept a new calibration this far out fyi- I tried this first) --- End quote --- Are 10Vdc, 1Vdc, 100mVdc accurate? I would have expected that you damaged these lower ranges by applying the overvoltage.. Anyhow, the overvoltage might have damaged the input path, somewhere in between the input jack, ESD circuit, relays K101, L101, K104 , towards U102-A, that is the 100:1 divider. I propose that you chose 1000V DC range, apply 10V to the input jacks, and measure with your 34361 in high Z mode at first the input voltage to U102-A, i.e. pin 1. If you don't see 10V, you have to check the components and PCB traces of the mentioned input path. If 10V are present on the input, check pin12, if the divided 100mV are correct. If not, the input multiplexer, pin 8 of U101-B may have been damaged. --- Quote from: robjpiel on November 28, 2016, 06:43:10 am ---I first thought I blew up the 9.9M and 100k ohm voltage divider resistors in u102-A, but they are fine so I checked all the rest in: u102-C: 2k, 2k 2k-All Good u102-D: 20.57k, 5k, 50k, 500k, 1M-All Good. --- End quote --- I assume, that you unsoldered U102, before making these measurements? --- Quote from: robjpiel on November 28, 2016, 06:43:10 am ---I checked all the voltages that I could (attached). I highlighted red only values with significant deviation from what the OP had (Zucca I believe) and in black I have additional readings in case they were to help me down the road, but most of my values turned out to correlate with TiN's working meter leading me to think this IC u102 may be OK?? Hoping anyway. Where my confidence stops is after checking u102-B I get 2k Ohm (pin11-14), 17.3k (13-14), and 84.8k (13-15)instead of 2k, 18k, and 180k. But I didn't really expect any values to be in tolerance since its still in the circuit and I'm measuring resistance which I know is fundamentally wrong to begin with. --- End quote --- Correct, you will only get the proper values by unsolder U102... Very probably, U201-B is damaged, pushing current from its + input into the node between Q201 and pin4 of U102-D. This low bias OpAmp in many cases already, fails after years, or maybe the overvoltage killed it, as the 100:1 divider is sitting in the same package U102. Anyhow, replacing U201 probably will solve this problem. --- Quote from: robjpiel on November 28, 2016, 06:43:10 am ---The second issue I found here is that my output Ohms Current test did actually have 0 current from the low terminal to the anode of CR202. I was measuring with a 77IV so I will try it again to confirm with a 3458 tomorrow I guess just to be sure. --- End quote --- That may also be caused by a failed U201-B Frank |
| robjpiel:
Thank you Dr. Frank, Yes- To cause the problem I applied 1250VDC to the meter while in DCV Auto range. (I was testing the 1KV output of insulation resistance testers (meggers), normally they only put out 1050vdc and when I tested a dozen of the new fluke 1507 they were putting out over 1200vdc and without thinking twice I had tested 8 in a row and then they started reading 800vdc. Went back and checked the units that had just read 1250 and they too were reading 800vdc. Verified the problem with my meter calibrator, and tried to recalibrate the 34401 with no luck. Then I ran the self test and got the codes.) Yes- the 10VDC, 1VDC and 100mVDC all are 100% accurate (0-full scale). -Every ACV range is 100% accurate as well. -Resistance ranges are all good until I get up to the 10MOhm range (which reads 9x higher than it should) Believe it or not I actually did not de-solder the IC for any of these measurements. I Do not have the equipment yet to do so. I am ordering some soon so that I can enhance my repair capabilities to SMT and ics. But while I had it open I probed it anyway and all those resistance values were dead on until I got to u102-B. As soon as I get some equipment to desolder this IC I will check u102 properly. Current Output Over the Resistance Ranges All check Good 100Ohm 1.010407mA/7.90V 1kOhm 1.010403mA/7.912V 10KOhm 100.71440uA/8.185V 100kOhm 10.09959uA/8.422V 1MOhm 5.060033uA/8.439V 10MOHM 0.505691uA/5.0719V 100MOhm 0.505714uA/4.820V Below is what I have gotten so far for voltage readings going to the divider. The voltage up to R122 is 10.000V after it drops to .8V going into u102 pin 1 then then STEPS UP to 8V. ? I feel that means R122 may be open? I checked the Resistance across it (while in circuit) and it reads .22GOhm. I piggybacked a 6.19K decade resistor over R122 and This 100V and 1kV range all works fine. (I'll need to recalibrate it when I get the replacement R122 installed) Excellent!! THANK YOU VERY MUCH FOR YOUR HELP SIR! I'll post back after if it is not 100% -Rob |
| Kleinstein:
R122 might need to be a special resistor, e.g. fusible or higher peak voltage rating. If this resistor burnt, the root cause might have been arcing in the relays directly following it (e.g. during switching). Trouble with high Ohms readings somewhat points to possible excessive leakage. So it might be a good idea to check that too (e.g. 1 to 10 M resistor across input in the 1 V or 100 mV range, alternatively observe charging of a small (e.g. 1 nF) low leakage cap). |
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