Splish Splash! Help me Understand Bathtub Control Units
 

I know we have some electronics gurus on here, and for some reason I've completely failed to find answers to my problems in other corners of the Internet.

I have a jetted bathtub in my 1990-era bathroom; nothing fancy: a pump driven by a 3/4 hp 110V motor circulates the water through jets in the tub. No extra frippery, and the system is driven directly from a 110V wall switch (used to be a wall timer, but the principle remains the same), which feeds current into a control box (labelled a "delay switch"). 110V then goes directly to the pump motor. There is a ribbon connector that goes from the control box into somewhere on the tub. As far as I know, it connects only to a power LED, but limited access prevents me from confirming that.

On to the problem: since I've owned the house, it takes up to a dozen attempts to get the pump started. Flipping the wall switch results in the power LED momentary flashing on, sometimes accompanied by the pump running for a second or two. Once the pump finally catches, it'll usually run no problem for as long as I want it to. The pump/motor shaft turns nice and freely by hand. No evidence of leaks or wetness anywhere.

I started to attempt to troubleshoot the electronics, but haven't been able to find any info on how this system is supposed to run. It seems to me that I could run 110V directly from the wall switch to the motor, bypassing the electronic control unit altogether. This is probably a bad idea, but I don't know why.

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AC In from the switch and AC Out to the pump are at the top right, labelled TS1. The in/out grounds and neutral are each bridged directly together. The brown that you see appears to be flux or something from manufacturing. Nothing looks burned or loose to my untrained eye. The live goes through the relay/contacter D4. When I apply AC power, the contacter coil doesn't get its 12V DC. I get power up to transistor Q5, but it doesn't seem to switch, and I have no idea what logic is used to make it switch, if any. If I bypass the transistor, the contacter clicks on. Keep in mind that I'm an electronics dunce, and needed help to even get this far in my troubleshooting.

Does anyone know how this thing is supposed to work, and why there's so much song and dance just to activate a single phase 110 AC motor? Is there some kind of water level sensor or something that I haven't yet found? Given that we're talking water and electricity, I don't want to bypass something that's going to compromise safety. These jetted tubs came with lots of options - heaters, air pumps, lights - which I don't have, so I don't know how much of this control board is actually used in my application. I just want to safely run the pump.

Thoughts, advice, or links to reference material are appreciated.

Does it have a flow switch?

Sounds like when the flow switch on my hot tub is sticking.

No flow switch that I'm aware of. As I understand it, those are usually meant to protect the heater, aren't they? My system has no heater.

That sounds really complex.

The house i just moved out of had a bath with jets.

The system literally consisted of a pump connected to a power socket (standard wall one like what you plug your tv into) installed inside the cavity behind the bath, with the on switch wires going to the button on the side of the bath.


No fancy electronics.
No sensors, you just know to not run it with the bath empty.

Or protect a mechanical sealed pump from running dry...

This could make sense, although I can't find any reference to bathtubs having a flow switch. I'll have to see if I can find a way to follow my ribbon connector to see if it plugs into anything but the power LED. The challenge is that the tub is framed and tiled in and the only access point is a 12" x 12" panel in the wall from the next room.

Was there a sticker on that Motorola mc68705p3s chip?

No, no additional markings.

Failing start capacitor on the pump motor?

So that motorola is from back in the day - you would actually expose the chip to a bit of UV light and it would erase all the stored bits on the substrate - hence where the term "flashing" comes from. But I would've expected a sticker to be placed over it to prevent it from forgetting whatever program it was.

microcontroller is.. 112 bytes of ram, 1804 bytes of eeprom.. old af. I'm gonna guess the chip labellled VR1 is a 7805?

As for what it does.. no clue. It could be something as simple as adding a 30 second delay to give you time to disrobe and get into the tub before powering the jets.

I’ll bet that thing is either doing PWM, or has an optional switch panel for different speeds or pulse patterns..

https://cimg8.ibsrv.net/gimg/www.mia...97dcd4fa17.jpg
This is a rock concert, not the bleedin' splish splash show. Goodnight Springton! There will be no encore.

Sorry, I have nothing to offer in the way of actual help.

Good luck.

Alright, just to identify some more components..

db1 db2 - bridge rectifiers
74hc14 - hex schmidt trigger
opto1 - gonna guess that's an optoisolator for the relay flyback
vr1 - 7805(?) 5v voltage regulator for the mcu

what does this all mean? well, not a whole damn lot. I see a few passives for the transistors, the 74hc14 could be used as a timing crystal (astable multivibrator - not real sure why, but I'm also not well versed in microcontrollers this old). Either way, with a the center of that mcu exposed I wouldn't be inclined to believe the program is intact on it anymore. Nothing really jumps out and says "this was used for X" - it's got some inputs and outputs and controls a relay. But you knew that already.

That was my first thought before I began troubleshooting, too; the motor is difficult to start and runs fine once started, so it would make sense.

The trouble is that the controller doesn't even trigger the relay which sends AC power to the motor, so at least one of my problems seems to lie upstream of the motor entirely. The other problem with the theory is that I have yet to locate a start capacitor, even though it does have a momentum switch on the end of the shaft. Is it possible that the capacitor is internal to the motor housing? I have yet to succeed in disconnecting the plumbing in order to remove the motor for further inspection, but at this point I think I have other problems to solve anyway.

Coming back to this, I made a makeshift selfie-stick out of an old iPhone and some rolled plastic I had lying around and did my best to follow my ribbon connector in an attempt to find any sensors it may be attached to. I can't say it with complete confidence, but there don't seem to be any sensors or switches along the jets' or intake's plumbing path.

My thought was also a start cap, and the PWB is entirely a red herring, not part of the problem or the solution.

Some motors have a switch assembly on the end (which I assume cuts the start cap in and out), and these can stick. Think points from a 1960's era car.

That's about the sum of my knowledge of electrical wizardry.

Is it a split phase motor? Those don't have start capacitors. Do we know the motor voltage? If 110v wire it to an extension cord whip and plug it in. See how it acts.
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Could well be. Until you mentioned it, I never heard of one, but it would explain why I don't see a capacitor, but do see a centrifugal switch. Thanks for the tip.

My next step will be to hook up the motor straight to my switched 110V. I was looking for a reason why it wouldn't be a good idea, but I haven't found one. Motor is 110 and my switch is a regular light switch, rated to 15 amps. Pump is rated at 11 amps. I think I'll grab an inductive ammeter and see what it actually draws when running.

Came in here expecting a discussion about NC steering wheels :dunno:

So I removed the control box from the circuit and wired my switch directly to the motor. As expected, it starts and runs beautifully. I'll probably still put an ammeter to it just to confirm that I'm not drawing more current than expected, but I think this will be a permanent repair. Still curious as to what that control box did. If it was a delay switch, as labelled, it really didn't delay very long; the pause between hitting the switch and hearing the motor run is the same to my ear now as when the control box was in place.