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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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