40,000 Count Multimeter under $50 - HoldPeak HP-770D

[LooseJunkHater]

It initially drifted a lot. I replaced the LM385 with an ICL8069A and it got worse. Replaced the LM385, cleaned the PCB, removed any paralleled capacitors recommended by other forums. It's better now, drift-wise, but not perfect.

Did you recalibrate the meter after replacing the LM385 with the 8069?

Why would removing paralleled capacitors help at all; wouldn't that actually have made things worse?

Would replacing the SMD capacitors with name-brand low-ESR capacitors be a worth-while adventure, especially for the power rails? 

[coromonadalix]

in the end    more problems than solutions for a mere 40$ ish meter ....  is it or not worth it ??

[iMo]

It initially drifted a lot. I replaced the LM385 with an ICL8069A and it got worse. Replaced the LM385, cleaned the PCB, removed any paralleled capacitors recommended by other forums. It's better now, drift-wise, but not perfect.

Did you recalibrate the meter after replacing the LM385 with the 8069?

Why would removing paralleled capacitors help at all; wouldn't that actually have made things worse?

Would replacing the SMD capacitors with name-brand low-ESR capacitors be a worth-while adventure, especially for the power rails?

Every voltage reference has got some recommended in/out capacitors (because of stability). Some require large caps, some low caps.
The smd capacitors - provided they are ceramic MLCC ones - are the lowest ESR already..

The cheapo 20000/30000/40000 meters are basically with the "older" chips usually used as 4 digits ones (with the last 5th digit used as a "guard digit" and not showing it on the display). That allows to show stable readings and small none-linearity. Two my 30-40y old meters work that way, the last digit is not shown while the chips itself can do one digit more..

[geb]

Did you recalibrate the meter after replacing the LM385 with the 8069?

Why would removing paralleled capacitors help at all; wouldn't that actually have made things worse?

Would replacing the SMD capacitors with name-brand low-ESR capacitors be a worth-while adventure, especially for the power rails? 

Yes, I've recalibrated this thing a LOT. Basically after every time I mess with it.

RE caps: I was following someone else's posted recommendation at the time. I think that one cap near the ADC wasn't on a supply rail and its removal probably made the most improvement. According to the original poster, low-ESR caps made a difference for him.

I did a quick test of my HP-770D yesterday. In the morning, it read the 2.5V output of my AD584JH as 2.4984. At bedtime, it read as 2.4991. (The real answer is 2.49878-2.49882.) I gave the DMM a chance to "warm up" each time, and the room temperature varied by about 2°C between the two readings.

[LooseJunkHater]

The cheapo 20000/30000/40000 meters are basically with the "older" chips usually used as 4 digits ones (with the last 5th digit used as a "guard digit" and not showing it on the display). That allows to show stable readings and small none-linearity. Two my 30-40y old meters work that way, the last digit is not shown while the chips itself can do one digit more..

I never actually thought/knew about this before. Should I then essentially just ignore the last digit of my multimeter if I'm going for more-precise measurements?

I did a quick test of my HP-770D yesterday. In the morning, it read the 2.5V output of my AD584JH as 2.4984. At bedtime, it read as 2.4991. (The real answer is 2.49878-2.49882.) I gave the DMM a chance to "warm up" each time, and the room temperature varied by about 2°C between the two readings.

I never thought/knew about this before, so thank you!

RE caps: I was following someone else's posted recommendation at the time. I think that one cap near the ADC wasn't on a supply rail and its removal probably made the most improvement. According to the original poster, low-ESR caps made a difference for him.

Do you have a source for this post/information, so that I could follow it?

[geb]

The thread over at Kazus discussing HP-770D capacitors... This has the capacitor replacement and also the EEPROM tweak for 55000 counts.
https://kazus.ru/forums/showthread.php?t=120510

I never actually thought/knew about this before. Should I then essentially just ignore the last digit of my multimeter if I'm going for more-precise measurements?

I've seen people suggest that we should ignore the last digit. On some cheap meters, this is a safe strategy. But it isn't automatically true.

Many of the lowest-cost meters were made with Hycon HY12P65. That chip is rated for 5000 counts but its ADC is 19-bit (2 ^ 19 = 524288). It's found in 2000, 4000, 6000, and 9999 count meters. HY12P65 is even used in Zotek ZT-209 and ZT-303* with firmware extending it to 19999 counts. My ZT-303 meter is quite accurate after mods and calibration, so I think kindly of the HY12P65.

With a rating of 50000 counts, HP-770D's HY3131 ADC is better than HY12P65. But my sample of HP-770D is not impressing me.

My modded ZT-303 (paralleled caps and ICL8069A voltage ref), and minimally modded ZT-102 (EEPROM 9999 limit based on AN8008), and even my newly arrived ZT-702S are pretty reliable on their last digit.

If I had time, I would continue to study my HP-770D and try to figure out what's making it read so differently at one power-up versus another. I'd also like to know if other HP-770D owners have the same issue.

* - The PCB's silk screen says it's an HY12P65, but who knows for sure?

[iMo]

The cheapo 20000/30000/40000 meters are basically with the "older" chips usually used as 4 digits ones (with the last 5th digit used as a "guard digit" and not showing it on the display). That allows to show stable readings and small none-linearity. Two my 30-40y old meters work that way, the last digit is not shown while the chips itself can do one digit more..

I never actually thought/knew about this before. Should I then essentially just ignore the last digit of my multimeter if I'm going for more-precise measurements?

For example the HY3131 is a "24bit sigma delta ADC" according to the DS. That is theoretically ~16million resolution (8.5 digits). You will not get such resolution in reality because of noise, drift, pcb design, etc. etc. (many other params are involved).

The actual parameters (ie number of significant digits) are therefore mostly given by the external factors to the ADC. The cheaper parts and poorer design, the less digits you actually get. Therefore the cheap DMM vendors rather show less digits, as to have let the last digits jump all over the place. If you had access to the firmware of the MCU (which reads the ADC's values) you could introduce some averaging/smoothing to get a better output.

[iMo]

..It calibrates by using basically the same method as ZT-102, AN8002, and other cheap meters using a Hycon MCU. Close the jumper, turn on the unit and switch its dial quickly to ohms. Wait for its self-calibration to finish; it'll beep in mid-calibration and again at the end. Use HOLD and RANGE to decrease and increase, and SEL to advance. One word of warning: If you are displaying 40000 and you increase, the calibration routine will fail and you'll need to reload the EEPROM from a backup..

Could you point us on a detailed guide how to adjust the meter, plz?

[LooseJunkHater]

The thread over at Kazus discussing HP-770D capacitors... This has the capacitor replacement and also the EEPROM tweak for 55000 counts.
https://kazus.ru/forums/showthread.php?t=120510

I translated much of that thread and the associated thread. https://kazus.ru/forums/showthread.php?t=120130&page=3


Translated from Russian to English:
"
I replaced all the stock ceramics 1206/0805 (X5R - 10/4.7uf) in the power supply connections of both chips with decent branded lowesr 100uF polymers and 47uF ceramics. The total capacitance for the +3V supply was about 250 µF instead of 40 µF.
I am quite pleased with the result of the modification, the glitches have disappeared, and it works a little faster than the new one. The reference voltage measurements have not changed. Measurements of resistors <0.3 Ohm have become more adequate, for example, instead of 0.1 Ohm it was 0 Ohm, now it seems stable 0.07-0.08 Ohm.
"
Associated image: https://kazus.ru/forums/attachment.php?attachmentid=160835&d=1614161531

_________________________________________________________________________

From this thread: https://kazus.ru/forums/showthread.php?t=120510

"
What was done:
first I replaced the stock capacitors, 1206 turned out to suck Y5V, and 0805/0603 - X5R/X7R https://kazus.ru/forums/showthread.php?t=120130&page=3#
using 3V power supply I replaced the ME6208 LDO with a low noise LP2985-3.0
"

Ohm's was calibrated simply by using "closed probes" (I guess a near-zero ohm resistance connection?)

"the diode measurement remains (it cannot be successfully calibrated), the direct voltage drop differs from brands like Appa607.71 by 1-2%."

"For power supply, I replaced all the stock capacitor junk (all 0.1 uF were Y5V); LDO HE233 was replaced with low noise LP5907-3.3V; 4.7uf was added to the Icl8069 ion."

"
Replaced it according to the diagram, without recalibration:
C1, C3, C17, C21, C23, C11, C13
The next step was to increase the capacitance (add it in parallel) to the reference pins of the chips; recalibration was required, but the effect was noticeable - the device began to measure electrolytes 2-3 times faster.
Add. Photos can be viewed here http://ixbt.photo/?id=album:66908
"
[I'm unsure what they mean by "diagram" (schematic), and I also don't see what values they changed for C1, C3, C17, C21, C23, C11, C13]

There was also some other content about modifying the firmware values to increase the counts, but it's not very useful due to the poor translation.

This thread appears to have the stock firmware (in case you modify the firmware and mess it up; I of course can't verify the legitimacy of the firmware): https://kazus.ru/forums/showthread.php?t=116225

Direct link to firmware download: https://kazus.ru/forums/attachment.php?attachmentid=125109&d=1518199910

[geb]

iMo, I've been asked to create a detailed guide for HY12P65 and derivatives. It's a fair bit of work to document it with all the side-topics and variations, and it might have to cover topics like "But I just want to calibrate this one favorite mode and be done with it -- what can I skip?" If my work deadlines would ease up, I could consider it. In the meantime, I don't think I have one favorite guide that you could apply to HP-770D.

A translated DTM0660 datasheet might be worth reading as a starting point. Section 12 covers calibration. But change all of the 5's to 2 or 3 or 4. For example, in the first step while the selector is still pointing to the ohms scale, whereas the datasheet calls for 500mV and 50K sources, your first known-good reference sources for HP-770D could be 400mV and 20K, or 300mV and 40mA, and so on. Press SEL to skip ahead, HOLD to decrease, and RANGE to increase. And never hit RANGE when the count is above 39999!)

LooseJunkHater, I've attached the screenshot from the same Kazus thread about the increase in counts. It requires editing the data EEPROM's contents, which means attaching to the EEPROM and reading/writing it. Change the bytes outlined in orange to the values in the picture. But please note that "firmware" in this case is merely the contents of the data EEPROM. It would be wonderful to get a copy of the firmware (I mean the program code), and/or a guide to the contents of the data EEPROM.

[BillyO]

....  and seeing the fuses .......  not

It's a hobbyist meter.  It cost less than a set of fuses for a Fluke.  If you are going to use this meter to check power entry switchgear in a NASA facility, you should have your head examined.  If you are going to use it to measure the supply voltage your sending to the servos on your latest attempt at an Iron Man helmet, then it is a perfect choice.

Not everyone needs a Fluke 289.  Some people need to buy snow tires or pay the mortgage or buy medication for their ailing parents instead of dropping $1000 on a DMM where a $40 DMM will be overkill for their needs.  TEE (Test Equipment Elitism) is a worse disease than TEA, because it only serves to belittle people.

BTW, I'm just as guilty as the next guy, so take the above with a grain of salt.

[bdunham7]

Not everyone needs a Fluke 289.  Some people need to buy snow tires or pay the mortgage or buy medication for their ailing parents instead of dropping $1000 on a DMM where a $40 DMM will be overkill for their needs.  TEE (Test Equipment Elitism) is a worse disease than TEA, because it only serves to belittle people.

But you can get a perfectly decent real meter with real fuses for $40. 

https://www.lowes.com/pd/Klein-Tools-Non-contact-Lcd-Receptacle-Multimeter-10-Amp-600-Volt/5014355425

Or if that is too basic or you want something more suitable for electronics, <$50.

https://www.amazon.com/Multimeter-Auto-Ranging-Klein-Tools-MM400/dp/B018EXZO8M?th=1

[BillyO]

But you can get a perfectly decent real meter with real fuses for $40. 

What makes "IT" real?

https://www.lowes.com/pd/Klein-Tools-Non-contact-Lcd-Receptacle-Multimeter-10-Amp-600-Volt/5014355425

Interesting for sure.  Lots of neat toys added in to boot.  One could argue about the lack of counts and the manual ranging, but neither are of terrible importance(?).  Do you have a link to the teardown showing the $50 fuses?  Not that it matters much for hobbyist use.  But for $40, why not?  It's just that the other choice is just as good in real hobbyist use, maybe even better for the added resolution and auto ranging, which we all really know is just a newbie feature.

[BillyO]

Or if that is too basic or you want something more suitable for electronics, <$50.

https://www.amazon.com/Multimeter-Auto-Ranging-Klein-Tools-MM400/dp/B018EXZO8M?th=1

Nice!

I like the "Temp 600V"  and of course it is "Orange".  That's not yellow but it is orange.

I have a full set of Klein electrician's tools.  It's a nice kit.  But I got this set of tools in 1992.  They are awesome and still perfectly functional even after all these years.  However, one of the screwdrivers would cost more to replace than either of those meters, so forgive me if I don't think that Kline have not sold out.

Anyway, I guess that's not what we are talking about.  So let me cut to the chase, what about either of these would be a compelling sell for the guy measuring the voltage going to his servos?  Does he even have to spend $50, or will a nearly indestructible $19 Kaiweets KM-100 do just fine?

[bdunham7]

Do you have a link to the teardown showing the $50 fuses?

There is another thread right now started by someone who accidentally shorted mains voltage with his Klein MM400 multimeter while the leads were in the 10A socket.  He tore it down (unnecessarily) and it had blown the fuse.  It uses 600V ceramic fuses, not the Fluke style, and they can be found for $3-4 from the right places, $12 from Home Depot or Zoro.

https://www.eevblog.com/forum/beginners/i-was-an-idiot-and-may-have-destroyed-my-multimeter-any-way-i-can-test-it/msg5070877/#msg5070877

Anyway, I guess that's not what we are talking about.  So let me cut to the chase, what about either of these would be a compelling sell for the guy measuring the voltage going to his servos?  Does he even have to spend $50, or will a nearly indestructible $19 Kaiweets KM-100 do just fine?

IDK about the mighty Kaiweets, but the discussion in this thread seems to be about a meter with 'bang for buck' that seems to drift and generally not work well, making it's 40,000 counts sort of pointless.  The Klein may have less counts but from what I know will be reasonably accurate, stable and durable.  Now if your hobbyist is so broke from buying his ailing parents their medication and $19 is all he can swing, well I guess the Kaiweets will have to do.  But it would be nice to have something that won't blow up in his face when he's trying to fix his poor parents furnace or something.

[BillyO]

Yes, the meter under discussion may not be an ideal example of a low cost meter for hobbyist use.  And those Klein's you linked to do look nicer.  Probably a better choice just for the quality aspect even though they may lack a few features the hobbyist shouldn't really care about anyway.

I've always been the kind of person (and of course this is strictly my personal perspective) that avoids buying a thing because of its whizz-bang features.  I'd rather the money I spend go into things that make the basic functionality better.  Just like those Kline meters.  However, the fact that they have 600V rated fuses and supposedly can actually be used in a CAT III or CAT IV environment really means very little to me.  I've never used one of my own meters in those circumstances and I'm nearly 100% sure I never will.  I'm 95% a CAT I kind of guy and the other 5% would never go beyond 120V CAT II.

So, why did I buy a Brymen BM786?  Well, not for it's nice fuses or CAT ratings.  I bought it because they have a reputation for quality, accuracy and stability.  But now Dave relates they have higher than expected failure rates with the Brymens.  I guess I just have to hope mine's not one of them.  In the end, the fuses will probably outlast the meter.

That said, back in the late1970's I bought a couple of "cheap Chinese junk" meter's off of Radio Shack (actually both are made in Korea).  A Micronta 22-210 analog and a 22-198A 3.5 digit digital.  They both have their original little 250V glass fuses in them and they both work and operate within their specs.  The Fluke 8020b I picked up in the 1980's on sale (it was still more than twice the price of those Microntas combined) is long dead.  It's little 250V glass fuse survived it.  So much for buying expensive stuff.

[bdunham7]

So much for buying expensive stuff.

Extreme longevity isn't necessarily a good indicator of quality, especially single examples.  Extremely crude and simple things can often survive the longest.  Supposedly after the human race has killed itself off, cockroaches will still be thriving.  I have a Harbor Freight DT830 that has technically outlasted my first Fluke 289, but that is only because I never got around to making any mistakes that would blow the DT830 up.  So I guess the DT830 is the DMM equivalent of a cockroach.

[BillyO]

So I guess the DT830 is the DMM equivalent of a cockroach.

Your DT-830 must one of the original "good" (consume salt now) ones.  The last one of those I saw was without doubt the worst meter I have ever seen.  Brand new out of the box the beeper had fallen off and even when re-attached you could not hear it over a gerbil sleeping 3 rooms away.  The mA ranges did not work as the shunt resistors measured in the K ohms even though they were marked 1 ohm and 9 ohms.  Right on the front it said the mA and lower ranges were fused with a 200mA fuse.  On opening it to see what was rattling around it was discovered there was no fuse at all in it and where it was marked "500mA 250V fuse" (yes 500ma, not 200mA) there was just a trace shorting between the two solder pads.  To top it all of, there was no socket for the transistor checker, just some bent metal clips on the PCB which could not be made to work.

Yes a cockroach indeed.  I ended up fixing everything except the transistor checker "socket", but you are 100% correct.  It will survive due to non-use.