| Electronics > Beginners |
| Voltage reference not working properly #SOLVED# |
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| FotatoPotato:
So when I disconnect the 431 from the -2.5v the 431 actually does output -2.5v and when I probe the -2.5v rail with the 431 disconnected there is 4.096v on that rail... And once I re-connect the 431 the -2.5v rail goes to 0.99v It doesn't change rapidly, just linearly as I change the pot. |
| StillTrying:
"The output of the 431 is 0.99v now" LOL. There should be only 3 things connected to the -2.5V line, the LM341, the 1.3k supply resistor, and one end of VR29 10k. So, either VR29's wiper is wrong, or there's something else connected to the -2.5V. |
| FotatoPotato:
Well, it must be R29, cause that's the only thing connected to -2.5v I'll replace it and see what happens |
| iMo:
There is something wrongly connected which is able to pull -2.5V up to +0.99V, something like 800ohm - 1kohm from +5V. EDIT: +4.6mA pulls it up to 0.99V |
| FotatoPotato:
So I just replaced the old pot with a brand new one and now the voltage on the -2.5v rail is 0.77v, so something still isn't right. The resistance between pin 1 and 3 on R29 is 10.3k and here is a screenshot of the -2.5v trace on the board. This is the only spot where -2.5v is present. If you want the Altium files I'd be happy to send them over I have a wire soldered to the center pin of U4 and that goes to a breadboard with the LM431 and R1 |
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