Kikusui PLZ334W Electronic Load power switch issue

[neverendingstudent]

Hello everyone!  I recently got an amazing buy at an auction: a Kikusui PLZ334W Electronic Load for $11, and it works!  They seem to go for ~2K USD new.

Not to worry!  I've made sure to fix that pesky 'working' condition.

The e-load was absolutely filthy from use in an industrial environment, so I took it apart down to the individual board level and cleaned everything, then put it all back together.  Problem is now the power switch won't stay in the depressed/on position for some reason.  It definitely worked before, not sure how I broke it though.  The device will power on and work properly if I hold the switch in manually - it's just an issue of the switch not latching.

I took the switch apart and have attached pictures.  I feel silly saying this but I can't figure out how the switch mechanism is supposed to latch and stay depressed.  The little round red/brown plastic bit that gets held down onto the contactor by a spring did pop out when I took it apart, but I found that and put it back in.  The only thing I can think of is maybe another part of the mechanism flew out that I didn't notice?

If anyone knows of some pictures or a video of how the latch mechanism on these switches works it would be appreciated, maybe if I understand how the latch functions I can fix it.

Another option would be if anyone knows how I would go about sourcing this part.  While I could use a Dremel and replace it with a non-matching switch, I'd prefer not to do that if possible.

It looks like I can only attach a couple pictures per post - I'll have to reply to my own topic to add the rest of the pictures.

Notes for anyone else looking to disassemble one of these: The blue plastic grate on the front shattered for me when I removed it - and I did not use excessive force.  It has upward facing friction-hold hooks and detaches simply by pushing it down after unscrewing the two main load screws.  Maybe for me it was just a matter of whatever it was exposed to over the years (aerosolized oil maybe?) - but anyway, I would advise holding the bottom to provide gentle counter-pressure and sliding it down slowly and gently as possible.

*Edit*: after looking up examples of how latch mechanisms work I realized there must be more there and was able to disassemble the switch further, where I found a broken plastic nub in the mechanism.  If I can get my microscope camera setup working properly I'll add pictures.

[neverendingstudent]

Pictures 2:

[neverendingstudent]

Pictures 3:

[neverendingstudent]

Pictures 4:

[neverendingstudent]

Pictures 5 (last):

[fzabkar]

I think the latch mechanism is under the metal housing. The latch alternates between the two sides of a groove (?) or something similar.

Something like these ...

https://www.iccfl.com/images/PWL-2P2T-SELF.jpg
https://res.cloudinary.com/rsc/image/upload/b_rgb:FFFFFF,c_pad,dpr_1.0,f_auto,q_auto,w_700/c_pad,w_700/R1239059-01
https://sharvielectronics.com/wp-content/uploads/2021/01/Right-Angle-PCB-Latching-Push-Button-Switch-DPDT-6-Pin-self-locking-key-switch-sharvi.jpg

[neverendingstudent]

Yep, I took it further apart and found the latch mechanism, it is indeed under the metal housing.  The plastic plunger can be removed from the metal housing after the square-shaped c-clamp that holds the spring in place is removed, then the mechanism can be accessed.  A small but important plastic nub had snapped off.  Very tiny, but it's the control point to keeping it on the 'on' position.

I'm currently planning on cleaning it out to get rid of all the grease, then I'll try to superglue the nub back in place and see if that works.

Edit (2023-Jul-4): attempted repair of the power switch - cleaned grease out of the switch as best as I could, applied superglue to the surface of the nub and inside the switch where it broke off of, held pressure on it for 5 minutes and left it to harden for another 45min or so.  After reassembly, the mechanism worked briefly, then the glue join failed.  Ah well.  I'll probably just have to replace the switch with a different one and dremel out the opening to mount it.

[coppercone2]

their called e-switches I believe, replace it on digikey for a few dollars. e-switch is the brand name

[neverendingstudent]

Not seeing it - I searched Digikey for all within the E-Switch brand, specifying all options 120VAC and up, 15A and up - got a bit over 200 results.  (The switch shows as rated for 125VAC/15A.)

I've been searching on Amazon as well and found some in (roughly?) the same form factor but not sure if they are rated the same - I'm seeing lots of different sellers showing exactly the same pictures of switches but claiming different amp ratings.

An exact or close-enough-to-work form factor would be great, but it's looking like I'm not going to find that with the same rating of 15A at 125VAC.  Or at least I haven't so far.

[coppercone2]

not sure then, my kikusui had a e switch, but its different

question though, do you need 15 amps for a load, its not a supply.

[coppercone2]

it says the power consumption is 90 VAmax. That is like 1 amp to run fans

I would say a 10 amp would be fine. The inrush is 45 amps it says but the switch should be able to handle that, its pretty standard for mains appliances I think, even 10A.

A switch manufacturer expects like 4-8 times nominal current for inrush, so the 10A would probobly be rated for 40-80 amps inrush. Probobly 100 I bet with a decent manufacturer lol, 4 is really low balling it

[neverendingstudent]

question though, do you need 15 amps for a load, its not a supply.

I was wondering about that, since you're right, it's not a PSU.  I suppose I could put the Kill-a-Watt in line with it to check, it may just be the power switch was over-spec'd on general engineering principles.

[coppercone2]

its in the manual it says 90VA with 45 amp inrush, I doubt you need to check a japanese companies work. Kill a watt probobly sucks at inrush.

Personally I would feel comfortable with most switches rated at least 5 amps to handle the inrush and the steady state current. it has extra safety too since its a plunger.

A e-load basically consumes no power other then the transistor trigger circuit, if its a mosfet then its just a tiny mosfet drive PWM maybe if it has that option, and the computer board and the fans. Many linear e-load circuits do not use a supply at all!

A mains switch will be picked for
1) asthetics
2) cost
3) rating

They do not care bout over rating them at all unless it increases cost. The design team will pick the one that looks the nicest since it sells products, and the one that is most available IMO. The easiest thing for a design review team to nail you on is ugly things the customer sees. I would expect that there are alot of under-rated switches in use because the proper one did not look to the image of the industrial designer lol

[coppercone2]

and I am surprised that design does not have a PTC inrush limiter or something. Seems a little high for the inrush spec

[coromonadalix]

sometimes the latch is under the round spring, you sometimes see a small rod ..........

[chubbymonk]

My PLZ334W had the exact same issue, same tiny piece of broken plastic which rendered the latching mechanism unfixable. The original switch is, I believe, manufactured by Sagami Shoko Elec, complete unobtainium.
I couldn't find a replacement switch which would fit into the existing footprint nicely so I ended up remaking the switch board with a switch from C&K, their NE-18 series. The length and height work perfectly with a new set of standoffs.
Regarding the power rating, the higher wattage and 0V input model PLZ664WA model is rated for 1500VA in the datasheet, explaining the 15A rating. It seems like the -A models have an unusually high rated power consumption for some reason. It'd be interesting to see how they implemented the 0V input in the -A models to require so much extra wattage.

[neverendingstudent]

Thanks for adding to this thread chubbymonk.  Could you upload or link to pictures of the remade switch board?  I haven't done anything with my 334W yet to complete it as I was waiting on a 3D printer to print a replacement blue air intake filter faceplate.

I had bought some generic switches and was going to dremel out the housing, but if you have an option that can fit right and lets us use the same power button that would be aesthetically superior.  I would like it to look nice.

[chubbymonk]

I uploaded some images of the board here: https://imgur.com/a/R0yOXYT
My unit had a missing power button so I can't confirm if the same power button can be used, however comparing the dimensions at the button end of the switch, the C&K is identical to the original switch so I don't see why the original button wouldn't fit. Both measure 3.25x3.25mm and have the same pattern of grooves.
I've also attached the original Altium .pcbdoc and gerbers for the switch board, the board does have a mistake in that one of the holes for the standoffs is in the wrong position, I goofed the measurements for that one. Still works as you have the other standoff, but you might want to fix that if you plan on ordering boards.

[neverendingstudent]

That looks excellent!  Did you use PCBWay or some similar service to make the board?

[chubbymonk]

I used JLCPCB. In my experience JLC is always much cheaper than PCBWay and gives decent quality boards. I would offer to throw one in a letter and post it but I'm pretty sure shipping from AUS would be more expensive than getting it direct from JLC .

[neverendingstudent]

This is excellent.  Thank you very much.  This is of even more use to me than when I originally posted this thread as since then I've picked up several more of the same model E-Load from the same local industrial auction house.

My plan now is to clean / test / refurbish them, then sell the extras on eBay.