I've recently bought a used TPS 4000 linear PSU (Model 4303) for 1.200.000VND(around 52 USD).
I tried testing the load regulation using a simple CC load(LM358 driving a MOSFET), PSU set to 15V, current limit pot turned to max sweep from 0-3A, measure voltage at binding post. Channel 1 works perfectly, fluctuating within a few mV of 15V. But Channel 2 acts really weird. At 0A, output measure 15V, as I increase the load current, the voltage jumps to more than 30V. When I increase load current pass about 1A, output voltage starts to lower, close to the set 15V as load current is increased to 3A, and during all this, a hissing sound is heard, which disappears when I remove the load from Channel 2.
So I tried connecting a 3R9 power resistor to Channel 2, set to 5V, current limit turned to max:
-No R: 5.057V
-With R: 4.552
-Delta V: 0.505V(9.92% of 5V)
This is way worse than Channel 1, which holds 5V perfectly when the same test is done.
So I try following the troubleshooting section of the manual:http://www.dudleylab.com/Power%20Supply%20TPS-4000.pdf
Everything was right till the Voltage Control Circuit test, step B, in that step, I measure:
-Channel 1: +1.57V
-Channel 2: -3.57V
Channel 1 is close to the +2V +-20% while Channel 2 is way off.
So what should I do now?