Kikusui PLZ334W: Broken power button and bleaching question

[hp3310a]

The Kikusui PLZ334W I just received was damaged during shipping (practically no padding) and as a result a foot broke off and the power button snapped. As it turns out, the latter might be a major issue because the button isn't available any longer.

I found a thread (https://www.eevblog.com/forum/repair/kikusui-plz334w-electronic-load-power-switch-issue/msg5046901/#msg5046901) where user @chubbymonk had a similar problem and created (and shared) a replacement PCB with a shaft-compatible button from C&K. I will probably have to do the same unless someone found a source for the original button. I didn't find one. The metal case says PSBS, no other markings except rated voltage. Photos of the damage and button attached.

The second question I have is about bleaching the front plastic bezel using hydrogen peroxide. I've never done this and am concerned that it might affect the already dim labels. Has anyone done this with this specific panel?

[hp3310a]

I'm redoing the switch board for a new power switch as the original is no longer available. C&K series NE18 is compatible with the button-shaft and I'm slightly puzzled by Digikey's offerings. They list 3 different suitable switches:
   
NE18 2A EE 6AMP / https://www.digikey.com/en/products/detail/c-k/NE18-2A-EE-6AMP/2043260
NE18 2A EE SN L 6AMP / https://www.digikey.com/en/products/detail/c-k/NE18-2A-EE-SN-L-6AMP/2043264
NE18 2A EE P 6AMP / https://www.digikey.com/en/products/detail/c-k/NE18-2A-EE-P-6AMP/2043262

The linked datasheet is the same for all and doesn't explain what SN, L or P stand for.

If the datasheet is to be trusted, I want NE1846EE which appears to physically match what I need. But which of the 3 at Digikey's is this?

Help deciphering this would be appreciated.

[fenugrec]

Not the first time I'm disappointed in recent CK datasheets. Sometimes searching for the series name gets you older catalog pages like
https://media.digikey.com/pdf/Data%20Sheets/C&K/NE18%20Series.pdf

Not super clear but it would appear 'SN' for snap-in, 'P' for 'PC pins'

Granted they are not cheap but you could always buy one of each... or look for 3D CAD models on littelfuse or even different distributor sites in case they have better photos.

[hp3310a]

Thanks, that's very helpful.

The given dimensions in that datasheet (pin spacing and overall) are different from the datasheet linked on the Digikey product page, so maybe that part of it can't be trusted. Sounds like I want SN + P, which doesn't exist. I guess I'll order SN L and P and see what I get.

[hp3310a]

If you order 2 out of 3 possible options, you really can't expect to get what you want. Murphy never sleeps.

I would have needed one with snap-in legs and PCB pins.

[hp3310a]

Turns out the switch I wanted is this one:

NE18CTII 2A EE SN P 4AMP  https://uk.rs-online.com/web/p/push-button-switches/1544702

RS managed to put the correct product pictures on its site. The luxury costs dearly, though.

Anyway, I was wondering about something: Which of the buttons are supposed to have backlighting? On my unit the MODE and RANGE buttons don't have LEDs and I found that odd. I can't tell from the picture if the LEDs are ripped out or were never there.



Can someone with such a unit shed some light on this?

[fenugrec]

heh, third time's a charm : )

thanks for sharing correct part#.
Regarding backlight : I don't own one of these (yet), but it seems to be designed that way, comparing other listings:
https://auctions.yahoo.co.jp/jp/auction/d1193826448
https://aucview.aucfan.com/yahoo/r1063181886/

i.e. only 4+6 buttons are lit.

[hp3310a]

Thanks, could have figured that out too, but didn't

Actually the product image at RS is slightly wrong too, the switch you get is a DPST type, so 2-pole off/on with 4 pins, not the pictured 6-pin DPDT version.

[fenugrec]

While you're in there, make sure to get good pics of the PCBs, dump ROMs / eeproms as necessary, etc !

[hp3310a]

Actually it is back together again, I had it completely apart, thoroughly cleaned it and flxed a bent in the frame (evidently it has been dropped). Of course I took tons of pictures. But EPROM, I'm not sure I can spot it, I'm attaching a photo of the two control boards. Everything is soldered on. Firmware seems to be fairly old, judging by the one in the second link you posted.

[fenugrec]

Hm it's hard to read any of the IC markings but if I had to guess, small board near the button cell, some low-power battery-backed SRAM for config/user data, possibly calibration (hopefully not; maybe a soic8 eeprom ?). Nothing strikes me as standalone rom/flash IC. The larger board has a hitachi(renesas) H8/3067 mcu with onboard flash ; smaller board possibly has similar mcu with also onboard firmware.

[hp3310a]

There's a firmware updater(*) available from Kikusui: https://global.kikusui.co.jp/dri-fir-upd/wavy-for-plz4w/

I think I'll try that later today and report back.

(*) Edit: The updater is for PLZ-4WH and PLZ-4WL models (**). Those appear to be newer than the PLZ-4W which I have. Not sure if that is going to work.

(**) Edit 2: Maybe not, seems I misread.

[hp3310a]

Back to the other question, about whether bleaching using peroxide will impair the faint blue alternate lettering, I have an answer: By the time the panel has whitened to an acceptable degree, the blue will have vanished

I put the panel in a seal-able plastic bag with minimal amount of peroxide and put that into direct sunlight.

Original state


After about 4 hours in 3% solution


After another 8 hours in 3% solution


After about 3 hours in 12% solution



Where did all my blue go? Overall impressive, though. Binding post knobs, power button and the encoder knob cleaned up to almost original color. A word of warning: The 12% solution is already in the nasty stuff category, don't get that on skin, it will burn you.

In an effort to make the alternate functions readable again, I traced the lettering under the microscope using a lacquer pen. The pen was too thick (0.8mm) and the end result looks like a 4 year old had their way with it. Usable but not presentable, but I'm still happy overall.

[hp3310a]

I'm redoing the switch board for a new power switch as the original is no longer available.

Turns out the switch I wanted is this one:

NE18CTII 2A EE SN P 4AMP  https://uk.rs-online.com/web/p/push-button-switches/1544702

This is complete now, too. I did receive the PCBs last week and went to solder on the components. This was less relaxed than expected due to the huge thermal mass the traces produce.





The advantage of this new switch is it is 2-pole, so the unit is truly separated from mains when switched off.

What I would do differently is flatten the little ears that provide support for the original switch when the unit was completely dismantled. This needs to be done because the new switch is wider than the original. Doing this with all the boards inside limits the options considerably.


Very happy with my new electronic load.

PS: In case someone wants to do this too, I have additional PCBs left to give away for free for the postage (sent from Austria/EU). No components included, just the PCB.