Quadtech 1880 Milliohm eter calibration procedure - Page 1
Forum section: electronics / testgear

author: HalFoster
author_rank: Frequent Contributor
timestamp: August 12, 2019, 03:06:49 pm
content: I have a Quadtech 1880 milliohm meter that I would like to calibrate but I can find nothing out online as to the exact procedure.So far, it seems to be:1) Turn unit on2) Move calibration switch to enable position3) Unit shows "0", short probes and press the "Man/Ext" key - unit does call.4) Press "Man/Ext" again, unit shows required reference value. Connect to probes, press "Man/Ext" - unit does cal5) Continue steps 3 & 4 through 1.9M range; unit resets.6) Move calibration switch to disabled.7) Cycle power, done.What is happening is that after this, meter only reads somewhat correctly if the measured value (1st digit) is in the lower part of the current range. A value of 1.5 milliohms, 1.5 ohms, 1.5 K or 1.5M measures correctly; values of 4 milliohms, 4 K, 6 milliohms cause erratic readings.Question is, it this due to a bad cal or are there hardware issues with the meter. If I knew for sure the exact calibration procedure, it would at least help me to know where to start troubleshooting.TIA,Hal

author: Kleinstein
author_rank: Super Contributor
timestamp: August 12, 2019, 05:13:14 pm
content: This sound a bit like a hardware problem, like a wrong current source causing the source to drive into saturation.With a militohm meter, I would suggest using 4 wire technique. So the short may be not just connecting 2 wires. Or closing Kelvin probes together. There are special 4 way shorts. Other wise the sens wires should be connected, the drive wire should be connected and some wire / resistance between the 2 pairs.

author: Shock
author_rank: Super Contributor
timestamp: August 12, 2019, 05:35:02 pm
content: Contact distributors or manufacturers for the schematic, service manual and calibration info whatever they can provide. Manufacturers often include test points or short points to confirm the test equipment agrees with itself and is operating correctly.You mentioned erratic measurements, does this mean reproducible fluctuating measurements or reproducible inaccurate measurements? There is a big difference between the two.Are you using the original kelvin leads sold with the device as it may be similar to my micro ohm meter which has two 100k resistors between each drive and sense.First you must rule out the components under test to ensure they are not complicit in the inaccuracies, then if it's not try and include offsets in your calibration to see which way the inaccuracies swing. You might be able to characterize where it is occurring. Obviously you should be able to produce reproducible measurements regardless of accuracy or drift in ranges.Probably about that time you might want to scope the calibration procedure and during normal measurements to see what is different. Also you can verify the power supply noise/ripple and general component quality. Normal warnings about connecting the scope ground clip to a circuit that is not isolated/floating or at ground potential apply.

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 08, 2021, 08:13:53 am
content: HI there, I was wondering what happened with the issue you were having with your quadtech 1880?I just got one and it seems it is not reading anything. I zero it out. but it keeps reading the same values (-.5522 to -.5421) no mater what is connected to it.where you able to find any schematics or a service manual for it?

author: beanflying
author_rank: Super Contributor
timestamp: January 08, 2021, 08:18:29 am
content: This is what I have for the 1880. Mine works great btw

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 08, 2021, 09:47:22 pm
content: thank you for your reply,I have those manuals . they are basically the user manual and the brochure. I need the service manual if it exists with schematics and or pictures of the big flat board inside.

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 08, 2021, 10:26:28 pm
content: Sorry again, I am just figuring out this blog. I was replying to your massage in a different way. so you may have several reply.I have the manual and brochure.I need either the schematics or a few pictures of the board setting flat in the unit.on mine it looks like someone had modified it for their use.there are 2 snipped wiring of 5 wiring that extent from the rear of the test lead connector to the board. snipped off wiring connect to the right of the connector on a couple of diodes. and a few resisters around the board looks like done after the manufacturing. I could send you pictures if you want.I need pictures of a good unit please.thank you

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 08, 2021, 10:30:12 pm
content: you ever got that quadtech 1880 calibrated and working?

author: beanflying
author_rank: Super Contributor
timestamp: January 09, 2021, 03:07:57 am
content: Sounds like your unit is the same as mine internally and was a 'factory bodge'These photos should be easy to compare against yours for a start. I will leave the top off mine for a couple of days if you want any voltages measured or photos elsewhere on the board.

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 10, 2021, 04:47:38 am
content: If you wouldn't mind can you please take pictures of all around that board please and send to me. Pictures you sent looks the same as mine so far. On mine there is a few more places that look bodged.

author: beanflying
author_rank: Super Contributor
timestamp: January 10, 2021, 05:03:16 am
content: Overall and three separate ones for a bit more detail. The tight hold on a service manual and calibration service for these now older models is completetime they pulled their heads out of their ....

author: beanflying
author_rank: Super Contributor
timestamp: January 10, 2021, 05:03:53 am
content: part 2

author: HalFoster
author_rank: Frequent Contributor
timestamp: January 10, 2021, 09:04:16 am
content: Still no luck on the correct procedure by me. Mine has/had the same bodge (I changed the connector to a standard DIN to facilitate making new test cables) - I had been wondering if that was factory or not.Hal

author: beanflying
author_rank: Super Contributor
timestamp: January 10, 2021, 09:10:38 am
content: The bit of recent trawling I did indicates the use of a custom 0.019. 0.19. 1.9set etc for $2k+ I have also looked and searched in the past for the Original Manufacturer "Chen Hwa Tek" with no success. Chroma the now brand owner seem to want to tie the units to return to them only so they can gouge you for $ instead of helping with an older model.

author: beanflying
author_rank: Super Contributor
timestamp: January 11, 2021, 01:45:55 am
content: Naked Bum shot for BobbeBob of the front panel PCB connection area.

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 11, 2021, 04:51:11 am
content: Thank you. I took some smaller pictures Hopeful these will make it through.would you mind taking more pictures from the back as many as you can please.thank youkind RegardsBob

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 11, 2021, 04:55:26 am
content: more pics of the mine, modified one.

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 11, 2021, 04:57:07 am
content: more pics of the modified one

author: beanflying
author_rank: Super Contributor
timestamp: January 11, 2021, 05:06:20 am
content: Interesting BodgeAcross the large Pad R26 where mine has the 110W resistor on the chassis with wires going to it yours has what looks like a 1/4W resistor? What is the value on it might give a clue as to what some of the other bodges were setting out to achieve

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 11, 2021, 05:08:56 am
content: you got to see the bodge work on mine. I sent a bunch of pictures. the real mess is in the rear.I was planning to remove all the add on component and fix the cut traces to see what happens. I will leave the ones that match Beanflying boards.just waiting for a few more pics.

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 11, 2021, 05:10:45 am
content: The value seems to be 100K,Brn, Blk, Grn, Gld

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 11, 2021, 05:12:47 am
content: Or is it 1m ohm?

author: beanflying
author_rank: Super Contributor
timestamp: January 11, 2021, 05:18:22 am
content: 1 Meg. Without tracing the circuit out or trying to sort out your rats nest from photos at a very rough guess they were trying to reduce the test current or change the range able to be tested by the unit while maybe making use of its tolerance/sorting functionality?

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 11, 2021, 05:43:23 am
content: I just double checked. it is a 100K.I figured I will just remove everything they added and reconnect the traces, Add the same resister you have on yours. if I see signs of hope, them will think of calibration.I am open to suggestions thought.

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 12, 2021, 07:54:31 am
content: Hi, I was wondering if it is not too much trouble for you, at you convenience, Please send some more picture of the back side of the PCB. I need enough pictures to be able to see the entire PCB back side. please.thank youregardsBob B

author: BobBeBob
author_rank: Regular Contributor
timestamp: January 14, 2021, 05:34:09 am
content: Hi, any luck getting a few more pictures from the back of the PCB please?

author: BobBeBob
author_rank: Regular Contributor
timestamp: February 21, 2021, 09:30:38 am
content: Hi There,any luck with those pictures please?

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 12, 2021, 09:23:24 am
content: Hi it's me again, sorry to bother you. But I was wondering if you would send me a few more pictures from the back of the board of the quadtech 1880 please. pretty please.I have a picture here from you but I need more to the right of the board. the pictures you send are is very nice and clear but I wish I had some more images of the back.I am attaching some thermal images of my board which indicate a short I think on U29, which on yours is a OP77EP, But on mine is a LTC1052CN8. I have a 0P77 on order and will be replacing and will look for any change.Also below chip U31 is a resister I want to guess is R51, (the number is under the piece and not able to read it), on one side the resister traces out to U30 pin 5. well, there is what appears to be a Zener Diode next to it. I want to know if the resister and the cathode side of the zener diode are connected in the back of the board. this is one of the reasons I need more pictures of the back of the board please.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 12, 2021, 09:47:56 am
content: Hi, so I seem to found a short on U29, which is a OP77EP on you board but on mine is something else. I attached thermal images for viewing. ordred the OP77EP, we will see what happens.I could use some more pic from the back of the board.one reason I need more pictures is because I need to see if the resister in below chip U31 which one side of it traces out to pin 5 of chip U30, is connected to the zener diode cathode side. it looks as if the trace on mine was scrapped off in the back.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 12, 2021, 09:48:54 am
content: more thermal pics

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 12, 2021, 09:50:13 am
content: more thermal pics

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 13, 2021, 03:33:13 am
content: 279 F. I think the measurement is within 0.2 C accurate. but as soon as I took U1 chip out of socket the heat went away and the rest of the chips turned on with normal on.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 13, 2021, 03:46:57 am
content: After undoing the birds nest and soldering several cut traces. I think I did it correctly. though not sure if the cathode of zener diode next to R53 is connected to it or not. I connected it. Ran out of patience, crossed my fingers, plugged the unit in and turned it on. No sparks but, It was still not making any measurement. it was stuck on 4.232 M ohm. it was stuck on that number in every range but decimal was moving. before undoing the birds nest the unit was stuck on 5.5xx M ohm, That's when I decided to get the short finder for dummies out, the thermal camera. I was not looking for a short but just wanted to see what is on. And yes, there was a short there. But, unfortunately, I did not take a before thermal picture. So, I don't know if removing the birds nest and connecting R53 to the cathode of the zener next to it caused this issue or was it this way before. If anyone has picture of the back side of the board I would appreciate it if you could send some clear pictures of the backside of the board of quadtech 1880. thanks.Bob

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 13, 2021, 05:10:21 am
content: sorry everyone for multiple posting the same. I just figured out there are other pages to the threads. figuring out EEVblog is like the first day driving on the opposite side.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 13, 2021, 05:20:25 am
content: Ok, my apologies, I think I made a few mistake, let me just make a quick correction.U29 I think is the chip that has the short, it is OP77EP.R51 it appear to be the resister that I would like to see if it is connected to cathode of the the zener diode next to it. these 2 are next to U31 pin 1.any info is helpfulthanksBob

author: rafik
author_rank: Contributor
timestamp: February 28, 2025, 05:03:44 am
content: Hello everyone,I am a humble electronics enthusiast. I know I still have a lot to learn, but this time, in exchange for knowledge, I would like to contribute to the forum.Attached to this message, I am sharing the electronic schematic of the Quadtech 1880 and the programming manual. I know this will be useful to someone, and I am happy to share it.Best regards, 73!PS: I know this is not the right forum for this message, but well... If anyone knows which are the 5V, -5V, 15V, and -15V pins on the power supply of the TDS744A, it would help me a lot.73!

author: rafik
author_rank: Contributor
timestamp: February 28, 2025, 05:06:33 am
content: It did not upload properly.

author: BobBeBob
author_rank: Regular Contributor
timestamp: February 28, 2025, 05:16:35 am
content: Thank you I can use that manual.Regarding your question power rails for tds744a. unfortunately I do not know. But tek forum maybe helpfully. And I think there may be a tek forum on yahoo as well.I will keep you in mind and if I come across useful info on tds740a, will pass it along.Thanks again

author: HalFoster
author_rank: Frequent Contributor
timestamp: February 28, 2025, 09:53:55 am
content: Re the 744a - TekWiki should have what you are looking for:https://w140.com/tekwiki/wiki/TDS744

author: HalFoster
author_rank: Frequent Contributor
timestamp: February 28, 2025, 09:55:42 am
content: @rafik - Thank you very much as well for the schematics; I need to dig my unit out and look at it again.Hal

author: rafik
author_rank: Contributor
timestamp: February 28, 2025, 04:55:09 pm
content: Hello,I appreciate your quick replies. I will review the information provided.Best regards! 73!

author: BobBeBob
author_rank: Regular Contributor
timestamp: February 28, 2025, 08:49:25 pm
content: Do younhave a non working 1880 quadtech unit?

author: rafik
author_rank: Contributor
timestamp: March 01, 2025, 03:25:26 am
content: Hello BobBeBob,That’s right, my dear friend. I spent some time trying to repair it, but I put it aside for now as I have a lot of work. I bought it at a flea market for less than $10, but it's missing the kelvin clip.It has a fault that presents as a long beep from the buzzer and a red LED indicating a HI failure. Initially, it lacked 5V, so I replaced the 78L05, which improved the situation somewhat—the buzzer now sounds for a few seconds, but the red LED remains on.Do you think this could be due to the missing measurement cable? The LM317 on the heatsink gets hot, and I suspect too, some BUZ11 transistors might be shorted. I'm not sure; I need to dedicate more time to it.Thank you for asking. 73!PS: Would you be able to advise me on which Kelvin clip is compatible? Your advice would be of great help. It’s definitely worth repairing—I plan to use it for short detection.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 01, 2025, 04:55:16 am
content: I have 1 working unit and 1 not working. I had the non working unit for several years. I gave up trying to fix it. Then I got lucky with a working one for just over $100.Make sure yours has not been customized for specific jobs. That is what I though had happened to my non working unit. It might have then also been broken. There cut traces and reconnection in multiple places. The large resister with heat sink was also missing....If you need me to measure anything off of the working unit and report back to you just let me know. The kavin leads, you will have to make yourself.I would convert existing to short banana leads so you can connect other leads to it.There are a few different tools for short finding and microphone meter is one.

author: rafik
author_rank: Contributor
timestamp: March 01, 2025, 05:22:51 pm
content: Hi,Thank you for offering your help, I really appreciate it. My unit is intact, except for the resistors connected to the Kelvin cable connector, which seem to have been modified. Additionally, about five BUZ11 transistors have been replaced with other components. I will install the original ones.I will do my best to make a Kelvin cable, although I have no idea what type of cable to use or its proper length. I would appreciate any advice on this.Best regards.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 01, 2025, 11:14:42 pm
content: Sure. Let me know if you need me to check mine out for info you may need.kavin cable, check this out for a basic kalvin test lead. He is good and answers questions as well.https://youtu.be/w9hvT0428jc?si=51Z5y3_7adDkD_szYou also want a needle point Calvin test lead as well. But you would have to figure out how to connect them to your unit.I would suggest making a short extension to convert the quadtech 1880 plug to banana plug for your unit.To tell you the truth mine quadtech 1880 is on the shelf. I don't have a lead for it either. I got a different micro ohmmeter on the bench. But I would mine getting the quadtech 1880 ready for use.

author: rafik
author_rank: Contributor
timestamp: March 02, 2025, 05:14:27 pm
content: I appreciate your kind help. I watched the video, thank you, this is very interesting. However, while browsing the web, I found two types of Kelvin clips, but the issue is that the connectors are different; they have 5 pins, but they are female connectors.By the way, do you happen to know what type of connector is used in the Quadtech?As for your unit, you should now be able to repair it since you already have the schematic. I am attaching the images with this message.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 02, 2025, 07:46:50 pm
content: I will check to see if the pictures you sent have the same connector as the quadtech 1880.Like I said, mine been selved for a while no, and I don't remember exactly what fits it. I can do that in a day

author: rafik
author_rank: Contributor
timestamp: March 03, 2025, 03:02:24 pm
content: Hello, thank you for your message.Well, the Quadtech does not have the same connector; it is different from the one in the photo. However, I plan to change the connector if I can find a male one, but I don't know its model.

author: HalFoster
author_rank: Frequent Contributor
timestamp: March 03, 2025, 03:10:25 pm
content: If I remember correctly i just replaced mine with a shielded 4-pin DIN plug and jack.Hal

author: rafik
author_rank: Contributor
timestamp: March 04, 2025, 02:50:42 am
content: Hello, thank you for your message. Yes, the connector has 5 pins. I’m wondering what pin 5 is for. In what order are the pins connected? That information would be very helpful to me.Best regards.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 04, 2025, 07:46:31 am
content: 5th pin is ground. If you've seen the original lead for this unit there is a lone black Alligator lead beside the 2 kalvin.I think it connects to either end of the DUT. It's common in hi accuracy ohm and lcr meters. Some ohm meters have thermocouple as well. Plus other bells and whistles I don't know about.What I remember is the 2 on the left 1 is sense and the other is voltage and the 2 on the right 1 is sense the other is voltage.I don't remember which side is L and which is H. Not sure if it matters.As long as the 2 on the left go on one lead and the 2 on the right go on the other. The midle is ground.I haven't had a chance to look at mine yet. Work is demanding all of my time these days. And what free time I get is spent watching short videos on the bowl.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 04, 2025, 07:58:26 am
content: In schematics 1st page top left is the lead out, I think.I think this is personal massage so there is no option to load pictures. I did a screen shot but cannot load .

author: rafik
author_rank: Contributor
timestamp: March 05, 2025, 03:44:52 am
content: Hello BobBeBob,Thank you for your message. Sorry for the distraction, yes, everything is in the schematic. Anyway, I appreciate your explanation.I will carefully review the connections. Right now, I am quite stressed with work. As soon as I have some free time, I will dedicate some time to my unit. I will take some measurements, too. I will try reparing this unit.Thank you for your time. 73!

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 05, 2025, 08:59:43 pm
content: Ok great, in the attachment schematics pages are upside down. If yours is not upside down, then 1st pg button right.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 05, 2025, 09:04:24 pm
content: Here you go

author: rafik
author_rank: Contributor
timestamp: March 07, 2025, 02:04:48 am
content: Hello, I will check the circuit and the unit over the weekend since I can take a break on those days. I will let you know what I find.Best regards.

author: rafik
author_rank: Contributor
timestamp: March 10, 2025, 03:28:57 am
content: Hello BobBeBob, I've checked the unit and all the voltages are correct. I'm still getting a FAIL-HI error, and the display shows "Incorrect Range Setting." The op-amp U28 is heating up, so I'm going to test it with the oscilloscope. The strange thing is that pin 4 measures 7.89V positive. I'll figure it out once I test it. Do you have any recommendations? Thanks in advance. 73!

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 10, 2025, 10:08:42 am
content: No, I don't have any info off hand on that unit. I use a chroma 16502 on the bench, which is starting to actup. The quadtech 1880 is on the shelf for spare backup.I can measure that ic and report back to you. Did you have ground lead on the same IC grn pin?Do you have a curve tracer or huntron tracker? How about a thermal camera to do a Thermal scan?

author: rafik
author_rank: Contributor
timestamp: March 11, 2025, 10:31:22 pm
content: Hello BobBeBob, sorry for the late reply. Thank you very much for offering your help. Regarding the instruments you mentioned, I don't have them yet. However, I did a basic functionality test of the OP77 op-amp, and it is failing. I'm sending you an image of the measurement on the scope. I'll try to get a new one. We'll stay in touch. Reards.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 13, 2025, 06:10:56 am
content: OP77 is that the one in front of the board mid section? if so I think I replaced that one on my first quadtech 1880, the non working one. it didn't help me. I remember it because it was just too expensive. but yours might be the one. though, I did not do a scope test on mine. to tell you the truth I don't think I had a working scope back then.but on another note, if you want to repair circuit boards and you are series about it. A Huntron must be on your bench. to be specific a Huntron ProTrack with a Scanner, it will set you back a couple of Ks, but will pay for itself in no time. or if you got the dough Huntron 3200s at 12K.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 14, 2025, 10:29:17 am
content: Hi, measured OP77. All measurements are refferenced to ground earth.Pin 1: 11.61 VDC / Pin 2: 0.85 vdc / Pin 3: 0.85 vdc / Pin 4: -12.08 VDC / Pin 6 4.95 vdc / Pin 7: 11.67 vdc / Pin 8: 11.61 DCVoltages were prety stable.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 14, 2025, 10:31:58 am
content: Here more pics

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 14, 2025, 10:34:36 am
content: More pics

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 19, 2025, 01:54:01 am
content: I have had the unit open for any question you may have. But I dont want to keep it open for too long. It'll be put it together and on the shelf in a few hours.

author: rafik
author_rank: Contributor
timestamp: March 19, 2025, 03:30:17 pm
content: A thousand apologies, BobBeBob. I'm swamped with work, but thank you so much for the info; it's really interesting. As soon as I find a little bit of time, we'll talk. I still haven't been able to buy the OP77, but I'll get to that too. Greetings.I'm going to work.....