Help reading simple schematic - quick question:

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canonken

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Joined 2020
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I bought this cheap little kit and built it: 6 Bits Digital LED Electronic Clock DIY Kits PCB Soldering Practice Learning Board AT89C2051 FR 4 for Arduino|Integrated Circuits| - AliExpress

Simple question...not working and playing with the multimeter. All parts getting voltage except R3 (top-left) - should this be showing voltage? I do measure it as 10k ohms when I measure it in-place. Note, there are three parts to this and only showing the part of the schematic that is causing me to ask this question.

I do not get voltage at pin 1, but I do on pin 20 and most of the others (2-4 volts) and trying to figure out if that is correct.

Thanks!

i-j36JPzL-XL.jpg
 
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canonken

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Joined 2020
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OK thanks. I'll keep digging. Being what this thing cost, and how horrible the parts quality is (these are NOT the sort of parts you can buy on Mouser!), it is possible something it just stone dead or died in install.

It seems everything that should be getting voltage, is.
 
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hpro

Member
Joined 2012
If you have a Oscilloscope then you would get 12MHz on Pin 4 and 5
C6 & C7 is just to keep overshoots out of the Xtal. and the circuit
Check for bad Soldering and or short soldering..
Remove the IC and measure All Pins Voltage.. Except pin 20 there shouldn't be any voltage on other pins.
 
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Mark Tillotson

Member
Joined 2018
BTW that reset circuit is flawed - at power down it will attempt to power the circuit via the capacitor C5 and the input protection diode on the RST pin. I'd add a Schottky diode to ground from pin 1 (parallel to R3), cathode to ground, which will protect that internal diode from any large current spikes by diverting them.
 
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canonken

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Joined 2020
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hpro said:
If you have a Oscilloscope then you would get 12MHz on Pin 4 and 5
C6 & C7 is just to keep overshoots out of the Xtal. and the circuit
Check for bad Soldering and or short soldering..
Remove the IC and measure All Pins Voltage.. Except pin 20 there shouldn't be any voltage on other pins.
Click to expand...

I'm back!

I removed the IC and half the pins on one side (the ones connected the R4-R10) DO read around 3.6 volts. All of the pins read about 0.1 volts (is that just background noise...as is not enough to do anything?)

If that is a problem...that is a big problem!

MikePP - this is a build kit and there is nothing that needs to be programmed. Doesn't mean they didn't do it...there is no provision to do so (and no idea what tools I would need).

This thing was $3, if it is junk I can throw it in the trash and move on!
 
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