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

--- Quote from: geb on September 19, 2023, 02:18:31 am ---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.

--- End quote ---

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:

--- Quote from: LooseJunkHater on September 19, 2023, 02:58:25 am ---
--- Quote from: geb on September 19, 2023, 02:18:31 am ---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.

--- End quote ---

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?

--- End quote ---

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:

--- Quote ---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? 
--- End quote ---
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:

--- Quote from: iMo on September 19, 2023, 10:11:50 am ---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..

--- End quote ---

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?


--- Quote from: geb on September 19, 2023, 02:34:34 pm ---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.

--- End quote ---

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


--- Quote from: geb on September 19, 2023, 02:34:34 pm ---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.

--- End quote ---

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