Did you notice its doing it in a pattern? It goes: 0 5 0 5 0 5 0 5 pause, repeat. It's extremely consistent. Something in the logic is definitely doing it. Looks like it's timed with the refresh of the LCD too....
My guess would be it has something to do with the autoranging "leaking over", maybe even internally accidentally connecting the reference wrong. Its probably on the asic.
Brian I saw that too. It's static on the 5, but flashes the real reading four times quickly and then pauses on the 5. The period for one complete cycle is just slightly over 2 seconds (close to 2.2 seconds, maybe). Only the designers would know what on the processor might be cycling at this speed and with that pattern. Some auxiliary function is bleeding over and affecting the display output, but is otherwise leaving the critical functions unaffected. Another clue is that it is causing a display error on V and A settings, but is only causing some barely noticeable flickering on resistance and diode settings - again that might only mean something to the ASIC designers.
I like that you keep investing failures of "your" meters. Makes interesting videos and improves probably not this but multiple lines of devices. Keep on going Dave!
@@hotgluegunguy asside from the different chemistries of the batteries, one potentially charging/overcharging the other, and different material types mixing, and the potential to cause a fire, the actual current they are capable of is different also, resistances, allsorts, so who knows exactly what issues it could cause...
@@Ghozer I still don't see what damage it would cause here, as the batteries are not charged by the device. High series resistance could cause unstable operation, but I can't imagine it damaging the meter. I'm not saying you're wrong, I'm just curious as to why you arrived at that assumption.
Looks like it's generating some noise somewhere and it is trying to autoscale to the fast fluctuations in the noise. EDIT: So, it shows the correct voltage and toggles range. Then it can't be noise. I'm probably wrong. Definitely looks like a processing issue now.
I have one and I regret buying it. The first firmwares were slow and the recent ones tend to drift. The display hasn't got a lot of contrast (even at max setting) and there's no way to read the SD without taking it out of the meter. I recommend watching ru-vid.com/group/PLZSS2ajxhiQDDs_mWPLavaveGe0RGEw1M before ordering one.
@@henninghoefer Agree with you, I really don't like the 121GW. It messed up some measurements because of a low battery, and at that point you've just fucked up my confidence completely.
I had both types of EEVBlog meters (121GW and BM235). The BM lost all function of its buttons, and the 121GW I barely trust to measure DCV under 10 volts. The AC measurements are downright dangerous to trust when checking if an AC circuit has 110V/230V live voltage on it and trying to measure ripple on something like +24V DC is just impossible. The AC+DC measurements ranges are not specified in the datasheet. The fanboys at the EEVBlog forum thinks this is fine, as they know the inside of the meter by heart...that is NOT what I expect to need when I buy a DMM. I want a datasheet. I bought it from the KS campaign so naturally there was no datasheet at the time. I have learned my lesson, I will never again any instrument carrying the EEVBlog on it...But each to their own!
Since Dave has access to the company he should definitely get a replacement CPU and put it in. What if that does not fix it? Reasons to fix it: 1) You got to be very curious why the meters you sell died. 2) It will probably sell another 50 meters. 3) You can call it a tutorial on replacing SMD components.
I wonder why Dave doesn't put much time into his channel anymore. He said that this is his main job. So what else eats up so much time that he cannot do fundamentals or anything with some work behind anymore?
Yeah that's a glorious example of terrible marketing by Energizer! First thing I thought when I first saw Energizer "Eco" branded batteries was that they must be rechargeable cells. So I'm not surprised they've been mixed up with an actual Ni-Mh cell. But no, turns out they're just made of a whopping FOUR percent recycled materials. I'm not sure you could get much more disingenuous.
Is it possible its switching in a reference voltage for self calibration and the switching signal is not functioning? Or is there a pin on the ASIC that's pulsing at that frequency? Is there any ghost signal coming out of the input connections?
@@steverobbins4872 I was looking for the reference voltage, U2 looked like the candidate for being one. A scope probe on that, and a few on the power pins for the micro should sort out where the issue is.
@@station240 I couldn't agree more. Scope the shit out of that - Hook up a good meter right next to it, and just compare what is going on at various voltage-rails. (where you find deviations that rhythm of full-scale readings). My opinion is: having a non-broken copy of the device might be even better than having a schematic ;-)
4 года назад
Always very interesting videos. Thanks Dave for the time you spent for us. I just have a quick question : I saw on your PCB some resistors that is labeled RM in place of R. What is the meaning?
It's an interesting and very unusual fault, the fact that it is a repeating pattern makes it fascinating ! I would like to see a scope reading to measure the frequency of that pattern. Most of these guesses here show that most people really don't understand what they are seeing and either didn't watch the whole video or are assuming that Dave knows nothing about electronics and that he can't see what we can see in the video !
Just a random thought. But could there be a 5v rail connected to a mux? I assume it's in package package on die so there's not an external chip to replace but might that be doing it?
I bought a 235 directly from Brymen and 1 month after the warranty expired it developed a calibration error that prevent it from measuring any voltages. Shipped it back to Brymen and they re-calibrated it and sent it back - it did take about 90 days to get it back but at least they repaired it.
@@Yrouel86 Yeah, I think so too, I dont see a skid mark on the pcb near that wire. So probably flux.. My bet is an internal fault of the prosessor and that flashing 5 four times, then pauses and repeats consistently. Is some sort of fault indicator. Like maybe the eprom has corrupted somehow. It's weird for sure
@Dave if you can, try giving it a re-flash. What's the betting of a random bit flip in the firmware that causes a jump to the wrong part of code or some crap?
Maybe a stupid suggestion, but could it be the most-significant bit (MSB) of their custom ASIC going weird? IDK how they make their ASICs or what each of the pins does, but maybe a bond wire somewhere that's related to the MSB is faulty. Not that I've ever heard of them failing, but it's all I can think of. The randomness makes it look like a floating pin or something.
Its not random. On voltage anyway. Its a regular sequence of 5 pulses. its four pulses showing the correct reading then the 5th pulse just shows the max range. edit: the other ranges have a pattern too but different from voltage.
Can you measure the input to the logic side to see if something is feeding 5v into it? Although this kind of failure doesn't explain the A/mA weirdness to me. I'm brand new to electronics, green as grass, so I'd love to learn more about this, and if this develops into anything. Will scoping any of the logic test points (if there are any?) help at all? I'm probably talking complete nonsense, but I'd love to see more diagnosis of this.
Internal bondwire fracture - maybe on something related to the voltage reference. Making just enough contact to supply a reference, then draws current and the failed junction goes non-linear, add a tiny amount of capacitance and it oscillates?
Could you test this with some percussive maintenance while the thing is powered and see if anything changes, or is everything kind of set in stone with the packaging? Would be curious to know if this is a viable diagnostic method.
Maybe ESD damage to the micro. Might be worth scoping the meter supply and comparing its current draw against a known good one. If the chip is damaged, its supply current may be higher.
You must have another scrap unit around that you could swap the processor with just to see if that cures it. it doesn't matter about calibration as you are unlikely to put the unit back in to service. It would just be good to see it through to the end.
My theory is the LCD driver is damaged. The segments change each time the processor refreshes the display, more often when measuring resistance than when measuring voltage. It looks like some bit of some internal counter (frequency divider or memory address counter) has a short to memory area of first digit's segments.
Do the eeprom chips carry any write data. I had an incident where a character byte was accidentally written to the wrong address on an eeprom and it caused the display to output the wrong character when called. Just something to check.
I have a 25q series EEPROM with similar weird behaviour, it bit flips at MSB every exactly 16 bytes sent. It was used as a font lookup table memory and a particular character on the display changes, as Dave's multimeter does. I exchanged emails with the manufacturer several times and they refused to believe that their EEPROM was delivered as faulty, they carefully test them, etc. The EEPROM was delivered with factory programmed fonts and I never used it. Just plugged it in my flash reader and bootloaded the fonts in my code. I had instantly saw the weird glitch, with exact repeatability. I copied its content in a blank EEPROM and it works flawlessly. It's not my circuit design fault, as the manufacturer claimed.
I had a fault in a scope, where a rubber key was stuck inside and made a permanent contact. Couldn´t be seen from outside. So the reaction on any input was weird. Check all rubber keys for correct operation.
If the measurement is spot on, could it be the communication between the processor and the lcd? if it's an spi or i2c, could the processor be reading the values correctly but experiencing noise when sending that over to the lcd controller? 5 is 0101 in binary btw
Shot in the dark here - Is the reference crystal on spec? Can they be fractured internally yet still 'function' ? Will replacing the crystal still require re-calibration?
the way the 5 flashes from 5 to 0 is almost like some sort of error code.. like it flashes 4 times then pauses then flashes 4 times and so on. almost like the check engine light on a car
Hi, I've had a *very similar problem* with APPA305. Reason was, it somehow managed to erase its' own calibration EEPROM. Because I got it free with this error and it had some decent amount of counts, I decided to dig into this. It took me several hours to reverse engineer eeprom data mapping, and in the end, I've mapped all calibration data (I think except of temperature) and recalibrated it.
Definitely look like exceeded range measurement due to different ASIC chip properties in this particular multimeter or it can be software bug too. I'm curious are this glitch is only BM235 specific or it affect all BM2xx line? I ordered BM257s at yesterday and hope it will not show these funny 5-s.
It could be a problem with the voltage reference. Or it could be an op-amp with a cracked solder joint or feedback resistor somewhere. Those are the only 2 things that could shoot the reading to the roof and back I would guess.
Both fuses good? Voltage spike perhaps trashed the asic driving the display? I had a Uni-T that someone blew the fuses which caused a voltage skip that got past the input protection and took out the main IC. Spot on except it had all the wrong ranges. Replaced the IC and it's been perfect.
Just guessing. It is showing the correct voltage intermittently, so the downstream of the ADC is ok. It is weird how the display is messing up which may show an electrical issue, like voltage leaking on a line, or dropping. It could be some kind of ADC communication breakup which is going to the max value.
Swap the asic (processor) with a good meter and see if it fixes it. Might be an internal fault in the asic, perhaps even reflashing it, if possible, with new firmware would fix it.
When I saw this, I wondered if the design has a auto-cal, or sanity check circuit, that’s executed on boot up. I can imagine a built-in circuit, like BIT, that switches the input between ground, 5V, etc. If the control signals for such a circuit went berserk, it might cause these symptoms.
Lower trace resistance due to the extra solder metal, I think Dave made a video about that practice. P.S. found it ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-L9q5vwCESEQ.html
@@sysghost ah, I see which one you meant. Hmmm, I know only two other reasons, but the traces don't look like that would apply here... (1. to improve heat conductivity to air, 2. acting as guard traces/rings, actively driven to the same potential as they are guarding, to get very high insulation/ultra low leakage from other parts of pbc, e.g. ultra low current/charge measurements => leakage flows over the PCB into these traces)
I was going to buy one of these, but I got no reply to my question on the EEVBlog Store, or on the eBay listing. So, I figured that support communication would probably also be nonexistent. So, didn’t end up getting one.
@eevblog2 I would probably take another meter out of the scrap bin and swap the processor. Not too many pins so shouldn’t take too long I don’t think. Would be interesting to see if it persisted, might be the silicon.
Maybe there is something wrong with the screen you use to watch this video, or you are just as blind as Dave himself. That is not a half dead battery, that is a rechargeable NiMH battery. It's just a different chemistry.
Not that it matters, but what firmware is in that meter? I noticed the RM1, RM2, RM3, and RM4 positions on the PCB. They look like option jumpers. I wonder what would happen if you played with them. I have two of the BM235 meters and they have different firmware revisions. That is one thing about the 121GW over the 235. Easy update of the built-in firmware.
1.check OP amps input stage. 2. check Ref. Voltage input stage (ref diide). 3. clean the contakts of the rotary switch (oxyde). 4. Glitch in the memory or cpu register?. 5. re-solder pins specially Opamp and mpu.
Dave, check the EEPROM. Read and check its contents several times. I have a 25q series EEPROM with similar weird behaviour, it bit flips at MSB every exactly 16 bytes sent. It was used as a font lookup table memory and a particular character on the display changes, as your multimeter does. I exchanged emails with the manufacturer several times and they refused to believe that their EEPROM was delivered as faulty, they carefully test them, etc. The EEPROM was delivered with factory programmed fonts and I never used it. Just plugged it in my flash reader to check if their fonts are fine and bootloaded the fonts in my code. I had instantly saw the weird glitch, with exact repeatability. I copied its content in a blank EEPROM and it works flawlessly. It's not my circuit design fault, as the manufacturer claimed. Maybe you have similar issue.
My first guess on seeing its behavior, and the fact it happens in any mode, is that it has dual ADCs that it alternates between to get measurements and one of them is not working anymore for some reason.
Probably a stupid solution, but have you tried connecting it in parallel with another multimeter? Maybe it's working fine but leaking power to the measuring side somehow?
Seems like a internal silicon issue to me. Not sure how the main processor and LCD driver communicate and the format of display data, but it could be just a display data corruption considering it only affects the most significant digit and in a repeatable way.
Possibly get a new asic and solder that in. As everyone said it is flickering at regular interval. Atleast putting a new one would eliminate some faulty silicon
Why is this video posted on the secondary channel? I usually don't watch EEVblog2, but this one seems perfectly suitable for the main channel that I'm subscribed to.
It could be a both programmatical and hardware error. Because the digit 5 blinks with a constant pattern. (It blinks 4 times then stops for a while) Why don't you replace the MCU to see if it helps?
My thought as well. Meters traditionally use a charge or discharge ramp with a counter, imstead of the SAR ADCs in signal processing. Maybe a fault in that ramp circuit could make zero look like full/half range, with or without a 50% bias circuit.
I'm not sure if' it's affecting the other digits, since you didn't connect up anything to measure, they show as zeroes (with the least significant digit 'bobbling'). Measure, say, 1.234 volts and see if it alternately displays "1.234" and "5.000"
I'm looking to buy either the BM235 or the 121GW, just not sure which to get. I mostly do some Auto/Home DIY and minor electronics repair, nothing too deep.
The BM235 is an excellent meter. I have 3 (one at home, 2 at the office) and they're the first meter I tend to reach for. If you need more advanced functions then the 121GW is good, but I generally prefer the BM869S or a bench meter in those cases. The 121GW is pretty impressive for feature set vs size.
My other theory is a short circuit on the zebra stripes connecting the display to the board. My meter alternately displays 0.000 and -0.000. Maybe in this Brymen there is a short circuit between the driver lines of the minus symbol and the G segment of the first digit.
So here I was, thinking it was a range overflow issue (+1, 0, then -1 manifesting as 5000), but noooo... you had to go and rain on my parade, saying it's a 6000+ count meter, at the end of the video!! :D (totally j/k)
