circuitmangler
Computer
- Jul 5, 2003
- 28
Hi,
I have a used Elenco Digital/Analog trainer, and on board there is an adjustable 0-20 VDC power supply. However, ever since I've had it it's only been able to adjust from 0 to 10 V. I've just gotten around to looking at it, and figured out the following:
- It seems like a standard LM317 setup - there's a 120R resistor between the adj. and output pins and a 1.8K pot between adj and gnd. (The pot is probably meant to be a 2K pot, but it only measured 1.8K full scale.)
- The 120R measured 120 ohms (measured in-circuit)
- The input voltage measured about 24 V.
- There is a protection diode from gnd to out as well as a filter cap on the output.
I replaced the 120R with a 51R, and now it's adjustable to 20 V, but I'm wondering if the real problem is with the 317 itself or some of the other components in the circuit. After all, 120R is the correct value to use with a 2K pot to achieve 0 - 20 V.
Any ideas?
I have a used Elenco Digital/Analog trainer, and on board there is an adjustable 0-20 VDC power supply. However, ever since I've had it it's only been able to adjust from 0 to 10 V. I've just gotten around to looking at it, and figured out the following:
- It seems like a standard LM317 setup - there's a 120R resistor between the adj. and output pins and a 1.8K pot between adj and gnd. (The pot is probably meant to be a 2K pot, but it only measured 1.8K full scale.)
- The 120R measured 120 ohms (measured in-circuit)
- The input voltage measured about 24 V.
- There is a protection diode from gnd to out as well as a filter cap on the output.
I replaced the 120R with a 51R, and now it's adjustable to 20 V, but I'm wondering if the real problem is with the 317 itself or some of the other components in the circuit. After all, 120R is the correct value to use with a 2K pot to achieve 0 - 20 V.
Any ideas?