Hi all,
I purchased HP Keysight E3616A bench PSU 5 days ago from ebay. It was in not working condition and I decided I could fix it.
But it became my nightmare. The problem is that it turns on, outputs voltage but very unstable, voltage is floating and has extremely high noise and peaks. Almost 3 vpp and 400mv floating with random waveform. I've got oscilloscope and good measurement staff so I can check almost anything. I have schematic and repair manuals.
I have checked reference voltages and they have identical noise as the output, but when I drop output voltage to 0 noise is gone in reference voltages. I checked every part in reference circuits and they are ok. Also checked Constant Voltage circuit parts, main mosfets input voltages, diodes caps they are all ok. +5 volts, -12 volts, +10volts they are all ok. I also disconnected other circuits like SCR controls and OVP circuits and Constant Current circuit but noise is still there.
In repair manual there is some check points and there I have huge problem. There is Reference and Bias Circuit Troubleshooting chapter and I cannot pass the check voltage between TP6 and point3 and voltage between TP6 (common of reference voltages) and point5. I am getting -2.5 (should be -5.1) volts with noise and 0.8 volts (should be +5v) also noise. When I disconnect the panel meter from mainboard the voltages are -12 and +8
. But I think panel is making some common connections to make circuits.
So, I found that when I disconnect the panel meter from mainboard, PSU is more stable and there is no noise in the output. Then I checked pannel meter inputs and there is constant 100 ohm resistance between +5v and 0. Panel schematic is draining 300ma current and making about 70mvpp noise.
I need help and some advises. Do you think that panel is causing this problem? And If anyone has the same PSU I will be happiest man in world if will tell me what is the resistance between panel pin 1 and 2 (+5v and 0). These are the panel power pins. Also I forgot to mention, panel is lighting up and showing some +-3 volts difference from output voltage, and current meter displays 1.999, sometimes 1.000 it does not correspond the load.
I will provide schematic and measurement data if anyone is interested. Also if anyone has schematic of panel itself please provide, I could not find anywhere
NOT Noise OSCILLATION