Re: MAX134CMH+D A/D Converter: Faulty or OK?
stj: a lot of components are SMD (SMT), but I may have to test/replace everything until I find the fault. I refuse to give up on this meter!
I've been trying to purchase an Evaluation Kit for the MAX134, but it is now obsolete and nobody has any in stock, that I can find. The model number is MAX134EVKIT#. The board has the MAX134 on it, a microcontroller with software and a LCD. It would be a good tool to get to understand the basics of a DMM.
Krisby
Member
Last Activity: 01-24-2021, 01:44 AM
Joined: 10-14-2020
Location: Bonville, NSW
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Update:
Some time ago I took delivery of a new MAX134 ADC and soldered it into the Protek 506 DMM. However, the DMM is still not working correctly; the fault has merely changed in it's characteristics! I thought perhaps I may have damaged the chip by exposing it to too much heat, but, then again, it may have been a reject dud chip to begin with!
I've now taken delivery of two more MAX134, as well as a practice PCB with a practice 44pin MQFP IC, so that I can perfect the soldering technique before attempting...Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Interesting website, that "elektroda".
Yes, I just have to wait until the new MAX134 shows up (assuming it is not junk). Cutting the pins off with small sharp side-cutters is effective, but I'm thinking of making a purpose-built 4 sided copper "iron" which I can melt the solder on all 44 pins at once, then pull the IC up & off with a bit of glue on a stick. Well, that's the idea.
redwire, I hope you are looking forward to an Alberta winter! I spent a couple days once up at Grand Prairie,...Leave a comment:
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Re: Protek 506 DMM Problem/Fault
Yes, we seem to find ourselves at the end of the road....
Thanks for the Evaluation Kit download.... it would be an interesting tool....
OK, I might pull out RN1 and see if it has any effect on pins 25-28. But pin 24 should not have any voltage on it when there is no voltage being tested at the meter's probes, alternating or otherwise. When I manually select the next range up (40V), the meter performs normally, so the problem lies with the 4V range. I just hope that the origin of the alternating voltage is not the...Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Thanks, redwire, for supplying that clearer schematic of the CPU (U1). Is there a clearer schematic image of the MAX134 (U2) and rotary switch connections to be found?
So, are you thinking now that there may be a fault within the CPU (U1)?
Curiously, I checked out the temperature function on the meter, and it was reading well over 200 deg Celsius for the ambient temp! By turning the temp adjuster VR4, all the way, I got the temp reading down to 159 deg C! Is this strange anomaly in any way relevant to the problem...Leave a comment:
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Re: Protek 506 DMM Problem/Fault
Have slightly adjusted VR2, and also turned to full lock in both directions, but there was no change in the symptoms.
I have ordered a new MAX134 from China, and will simply swap it for the old one. If that doesn't fix the problem, then it may well be the MCU.Leave a comment:
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Re: Protek 506 DMM Problem/Fault
Yes, the datasheet for the MAX133-MAX134 shows a pinout of the 40 pin DIP version, not the 44 pin MQFP (Metric Quad Flat Pack). The datasheet also shows a 44pin chip on page 18, but that version starts its numbering from the middle of the top, not at the top of the left hand row of pins like the one used in the Protek 506.
I have tested all 15 Zeners, and they all test OK.
Both PTCs read 500 Ohms, as per the schematic.
You have suggested to "slightly adjust VR2". VR2 is connected to the VREF at pin...Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
I get a reading of 0.2 Ohms between AGND and BATT(-)
Where does AGND and DGND come from, or go to?
On the schematic, there is an arrow coming from the DGND at pin 29 of the MAX134, pointing to a "cartouche" with some letters in it, but as it is on the crease of the original schematic, I can't read it.
I can't see on the schematic of the MCU, which pin/s are supposed to be supplying 5V.
I've tried to find a pinout drawing of the MCU, which is a Samsung S3F84DBXZZ-QXRB TQFP100,...Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
I don't know if it is relevant, but: When the meter is on the 4VDC range, and the display is alternating between showing 3.999V and 0V, if I short out X3 (connected to pins 15 and 16), by pressing my finger on the two leads sticking out the other side of the board, then the display stabilizes at 3.999V! When I remove my finger, the alternating voltage display returns. Pin 15 is named OSC1 and 16 is named OSC2, so, presumably X3 is an oscillator.
What, if anything, does it mean?Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Whoops! I've made a mistake! The Cathode of ZD15 is also connected to PTC2 and SG1.... when I pulled one of ZD15's leads off the board, that Zener tested normal. So, seems like there is no problems with the Zener Diodes.
As it seems that the MAX134 A/D Converter has a fault within it, and I have ordered a replacement, is it likely that the MCU also has a fault? I hope not, because the Samsung MCU has umpteen pins and is probably expensive.Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
I have tested, [I]in situ[/I], all 15 Zener Diodes named as such on the boards of the Protek 506 DMM, with the diode test function of my other meter. With the exception of two, they all test "GOOD" with the breakdown voltage within limits and when the test probes are reversed, they all test "OPEN".
The two anomalies are named on the board as ZD12 and ZD15, which test "Good" in both directions. Maybe that test result is because of other componentry that they are connected to.
...Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Adding to what I have said above, my understanding is that, measuring from BATT(-), I should see around 6V at the AGND (input COM, pin 30) and about 4V at DGND (pin 29), but I'm getting 0V and -1.9V respectively.
I think that before I noticed this fault with the meter, I had tested the output of a DC to AC inverter, which was about 240V AC. This may have caused the problem, because I had not manually set the appropriate range, relying on the meter to auto-range.
I shall test all Zeners mentioned by redwi...Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Thank you redwire for expanding upon the workings and the power/voltage requirements of the MAX134 ADC IC. I've printed out what you've said so I can study it in detail and see if I can make some relevant voltage measurements.Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Pin 30 is named COM and it shows a voltage of 0.00V, and Pin 29, DGND, is showing -1.9V. On the other side of the IC, Pin 9 is also DGND, and it also shows -1.9V What does it all mean?
I don't understand what you mean, redwire, when you say, "Check the power +V to AGND is 3.0V". If AGND is the COM at Pin 30, then the voltage would be 0V, how could it be 3.0V? I've got the negative test lead of my other meter attached to the GND of the subject meter, and I am probing with the positive test lead, so if I probe anything...Last edited by Krisby; 10-18-2020, 12:19 AM.Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Actually, I am now seeing 2.99V at pin 25. All the associated components with the subject IC test OK, so I presume that the voltage at pin 25 must have its origin within the IC. The same goes for pin 24, which should be at 0V when no voltage is being measured at the probes, instead of alternating between 1.8V and 0V. Curiously, if a voltage less than 4V is measured at the probes, The LCD display will alternately show (at 4Hz?) 3.999V and the actual voltage being measured. 3.999V would be at the top of the 4V range, so it seems to be an...Leave a comment:
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Re: MAX134CMH+D A/D Converter: Faulty or OK?
Hello redwire: Thanks for responding.
I hope it's not the MCU that is at fault. I emailed MAXIM regarding the MAX134, but they weren't all that helpful, though they did concede that the MAX134 ADC could be at fault. I emailed Protek, the manufacturer of the Protek 506 DMM, and they sort of agreed that the fault may lie within the ADC IC.
I have two of these DMMs, and that's why I know that the MAX134 pins 24-28 should be at 0V when there is no voltage being measured. I can only assume that the voltages on...Leave a comment:
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MAX134CMH+D A/D Converter: Faulty or OK?
Hello Badcaps.netters,
I have a problem with a DMM, where there is a malfunction with the 4V measuring range, and the diode test function. The meter has a MAX134CMH ADC IC in a MQFP-44 pin format. See pinout diagram and schematic diagram of DMM circuit below.
When there is nothing being measured on the 4V range, pins 24-28 should be at 0V, but instead pin 24 has a voltage that alternates between 1.84V and 0V, and pin 25 has a steady 2.5V. Pin 24 is the input from the positive test probe lead, and pins 25-28 are connected to attenuator switches inside the chip, and... -
Protek 506 DMM Problem/Fault
Hello badcaps.net Forum People,
I have a Protek 506 DMM which has a problem with the Diode Test Function and with the 4V range of the Voltage Measuring Function. I have posted this on three other forums, but have not been able to find out the source of the problem.
It seems that the Diode Test problem is linked with the 4V range Voltage Measuring problem, so I shall just focus on the 4VDC range to simplify things.
When I select the DC voltage function on the rotary switch of this DMM, the display alternates between showing 3.999V and 0V. If I test a... -
Re: New Members - please post your introductions here
Hello! My name is Chris B. and I use the username of krisby, which is very clever of me, ha, ha! I am interested in all aspects of electronics, but I am a permanent beginner. My current project is upgrading my home solar power system, using recycled Li-ion cells for energy storage. I used to make simple battery charge controllers using Op-Amps as voltage comparators, but then I tried to make one using an Arduino Uno, but was not successful. Could have been a problem with the messy prototype set-up & breadboard. I shall try...Leave a comment:
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