Kikusui PAK20-18A - Page 1
Forum section: electronics / repair

author: rvalente
author_rank: Frequent Contributor
timestamp: June 29, 2019, 08:09:54 pm
content: Hello Friends,I've this great piece of equipment, the Kikusui PAK20-18A. 20V x 18A powersupply in a very very small brick.This power supply has some weird history, toke me 15 years to get this. The seller was a old stubborn guy and only sold at a decent price when the shop was closing.Few months ago the PS was working just fine, suddenly the output went of by no reason. A touch of a button and was on again. This started to gets worse and now the output does not come on.The LIMIT and O.V.P works and the display show the set voltage and current. There is no sign of anything burnt (smell or stain).I've no service manual (called and emailed Kikusui and they did not bother to reply me). The circuitry looks very complex (around 7 boards in a tiny package).

author: coromonadalix
author_rank: Super Contributor
timestamp: June 30, 2019, 02:31:27 am
content: Try to get some infos at KikusuiUnder an signed non disclosure agreement you may be able to get schematics ... i did it for my PAD psu, they answered and gave me all the schematics of the PAD series

author: duak
author_rank: Super Contributor
timestamp: July 01, 2019, 12:52:37 am
content: I have an older Kikusui PAR-80 power supply that would sometimes go off as well. Later, the output voltage would suddenly rise for no reason when it was loaded. An oscilloscope showed a large sawtooth waveform. I found that if I put a 220 uF capacitor across the output terminals it would work fine. I took the unit apart and found that the capacitor across the terminals inside the unit was bad. I replaced it and it now works fine.I suggest connecting a 220 uF to 1000 uF capacitor across the output to see if it helps.

author: rvalente
author_rank: Frequent Contributor
timestamp: July 01, 2019, 12:28:30 pm
content: Great, I will contact (again) them and ask for more details with the NDA.

author: rvalente
author_rank: Frequent Contributor
timestamp: July 01, 2019, 12:30:35 pm
content: Hello,tried connecting a 1000uF on the output, unfortunately, nothing happened.

author: fzabkar
author_rank: Super Contributor
timestamp: July 02, 2019, 11:11:13 pm
content: Service manual, but no circuit diagram:https://elektrotanya.com/kikusui_pak_6-60-120--60-6--18-a-m_high-rel_regulated_psus_1989_instr_sm.pdf/download.html

author: bitseeker
author_rank: Super Contributor
timestamp: July 03, 2019, 04:53:02 am
content: This looks like a switch mode power supply. If it's shutting down on its own or not starting reliably, that's often a sign that either the output has a problem, the feedback isn't working properly, or the supply's switch mode controller can't power itself reliably.Check for short circuits on the output, like the bad output caps that duak experienced.Check the electrolytic cap (startup cap) that powers the switch mode controller. The cap and controller are often nearby the power switching transistor(s). The big heatsink in the bottom-middle of the supply and the cluster of four capacitors with transformer looks like the general area of interest or the boards that wires from there go to.If the controller doesn't receive proper feedback from the output, via opto-isolator or isolation transformer, it will shut down. Dead opto-isolators are a common failure point.It's also possible that the switching transistor (or its support components) has a problem resulting in lack of control of the output.Oh, since this power supply supports remote control, make sure that a configuration switch, jumper, wire, etc. didn't get altered, loose, fall off, etc., such that it's getting a signal to turn off.