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2005 Jacuzzi Hot Tub Help Needed - Detailed

2005 Jacuzzi Hot Tub Help Needed - Detailed


Old 11-26-17, 09:16 PM
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Exclamation 2005 Jacuzzi Hot Tub Help Needed - Detailed


I am looking for some specific help with a 2005 Jacuzzi J-385 hot tub. The information below may be useful in helping to troubleshoot the problem.

Symptom: 3 dashes (---) on display or also known as the "Watchdog Error"

1. Used a phone to capture startup prior to the 3 dashes which revealed:
Assumption 1: Bad temperature sensor as Sensor #3 may be the culprit.
Repair Action 1: Purchased and installed new temperature sensor as willed by the Internet and various online sources; also seems to be one of the first culprits for hot tubs.
Solution did not work, hot tub powers up and immediately enters the Watchdog Error mode.

After stealing patience from other projects, it was time to dive into the issue.
The following list details and conditions of the senors/voltages:

- Water temperature: 63º F
- Heater pipe temperature where Hi Limit sensor is strapped: 73º F
- Temperature sensor resistance: 42.8 Ω
- Hi Limit sensor resistance: 33.33 Ω
- Flow sensor resistance: Open
- Incoming voltages on each leg: 120 - 124 volts on each leg. Together ~240v
- Transformer output voltage: Blue pair: 10.73 volts AC - Yellow pair: 15.43 volts AC
- All fuses appeared to be normal...for now.

2. With the sensor plug (all sensor input) removed, a capture of the reading before watch dog reveals:
ILOC: Interlock error (expected)
SN3: Sensor error

Assumption 2: It appears that all sensors and voltages appear to be within specification. May be a Flow sensor issue or lack of circulation driving the Hi Limit temperature to 106º F as indicated above.
A recheck of all the fuses led me to the hidden mini-fuses F1 and F5. Both appear to be 4A/125 volt fuses however, F1 was blown.
Repair Action 2: Replace 4A/125 volt (F1) fuse.

The plot thickens...

The hot tub was energized, waterfall is running by itself. I played with the other pumps and found that they worked. However, there were the following error codes:

I noticed by looking through the Flow sensor that it was not "wavering" as I would expect with the flow of water. Also, there was a small pocket of air trapped inside that seemed to sit there motionless.

After approximately 2 minutes of operation the F1 fuse (4A/125 volt) blows again. All shuts down with the the dreaded Watchdog Error mocking me for getting this far.

!. What would cause F1 to blow, besides "a bad controller board?" Could a "locked" pump cause this? As I believe F1 to be an output from the transformer, I am further assuming that it controls switching, is this correct?
2. Would the lack of movement viewed through the Flow sensor indicate trapped air, plugged line, or bad circulation motor? Does the circulation motor also run the waterfall?
3. Could there be an issue with the heater. With that being said, I did notice that after the fuse blew and everything shut down, the heater pipe was warm to the touch.
4. Does anyone know where I can find an illustrated parts breakdown of the circuit board with correct troubleshooting guidance to provide voltage levels at various points?

Controller information:
Controller 850 LCD
PWA: 850 NT

P/N: 6600-101 REV C
Date: 05 29

Things to try:
1. Disconnecting the circulation pump and heater, powering back up, and checking the indications on the panel and waiting for the indications of another fuse to blow.

2. Taking a resistance reading of the heater coil.

3. Attempt to bench check the circulation pump. This will be a bit tricky as I would have to test within the hot tub using ~220 Volts; hate to tie this directly to input power and flip the circuit breaker...might be bad.

I would appreciate input from anyone knowledgeable with these symptoms or those who have further detailed troubleshooting guidance.

Thank you in advance!
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Old 11-27-17, 12:58 AM
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Temperature sensor resistance: 42.8 Ω
I'm guessing that should be 42.8kΩ which is around 65 degrees.

The two small fuses protect the two transformer windings. There are two DC supplies on the board. Feel the heatsinks near the fuses..... if either one is hot then that supply has the problem.

There are no service manuals or schematics available. These are proprietary boards.
Old 11-27-17, 09:22 PM
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Thanks Pete.

After performing the final tests mentioned in the thread, I'll probably need to pull the board out and give it a visual inspection. Who knows maybe I'll get lucky and find some minor parts; it does take a few minutes for the overload condition to burn through the fuse.

Worst case I'm looking at a possible circulation pump, flow sensor, and circuit board; still cheaper than buying a new hot tub!

Thanks again for the reply.
Old 12-02-17, 10:27 PM
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The fuse stopped blowing once I disconnected the small pump for moving the heated water.
Replacing this thing does not look simple. It appears that I will also need to get some pex and a pex spreader.
I also discovered that one of the small 3/8 warm water connection into one of the large pumps was leaking slightly. After touching it it snapped off.

I suppose a 2005 hot tub is going to have issues.
Old 12-11-17, 05:21 PM
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12/10/2017 Update

Installed new circulation pump
Replaced 3/8 plastic barbs on 2 of the main pumps with stainless steel barbs.
Replaced a number of crufty looking hoses.
Replaced O rings on found leaky pump.
Removed primary pump from circuit leaving heater and circulation pump only - powered on.
COOL condition reported (63 degrees F), the heater element worked along with the new circ pump.
Turned off and reconnected primary pump, powered back up.
Circulation pump running, heater working, primary pump pushing water through waterfall (automatically?).

Pushed the button to turn on lights...poof...all functions dead...Watchdog error.
Goes back to the hard to find fuse (4A 125v mini) that likes to blow for some reason as previously posted.
Found great troubleshooting guide here:


As the fuse protects the secondary winding on the transformer, the diagram shows that it protects against excessive current draw from the either circuit board or multi-colored light. Will disconnect pesky lights and try again; I can do without the disco lights if I have to.
Old 12-11-17, 11:05 PM
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Excellent link for servicing. Thanks for posting that.
It's so hard to find online services to recommend.
Old 12-12-17, 01:04 AM
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12/11/2017 Final Update 23:49
Problem found...problem solved - No circuit board expense required.

As it turns out, I believed it was the circulation pump blowing the fuse (F1) in my previous post however, the dumb lights were on and I wasn't aware as I didn't actually see light...not thinking.

Removed disco lighting (multi-colored in tub and waterfall) which, when activated, overdrives the circuitry and blows that dratted fuse.

Replaced F1 (4A/125 volt slo-blo mini fuse).

Activated tub; all pumps working and heater doing its thang!

Waited 4 hours and the tub has finally reached a temperature of 90 degrees; one of the main pumps which prevents ice finally shut off...circulation pump continues to hum along nicely.

The issues with this Jacuzzi were two-fold:
A. Failed circulation motor which lead to HOT condition and causing a shutdown.

B. Seemingly shorted lighting system, which placed too much of a load on the circuit board and caused F1 to fail (protecting the transformers secondary winding) with the dreaded Watchdog (---) error.

Lessons learned and a few tips I discovered along the way:

A. If your hot tub will at least power up the display and your getting the three dashes of doom (---), use a phone to record the event while somebody else is applying power to the tub. Play (or edit) the footage so you can see all the errors in slow motion. Otherwise, your specific fault indicator should lead you to the faulty sensor or part (i.e. SN1, SN3, FLO, HOT, etc).

B. You will more-than-likely not have multiple failures as I experienced; patience is a virtue.

C. Most hot tubs operate on the same principle; don't be afraid to look at other posts describing your problem for other makes and models.

D. Use Google. Personally, I will throw a number of symbols around my search terms to get what I want. However, try this site for better results: https://www.google.com/advanced_search

Hint: Most manufacturers and parts suppliers will have your user manual and parts guides to help you solve your mystery; use PDF as a document type in the advanced search. I lucked out and found a 2012 guide for Jacuzzi with extra troubleshooting steps and even a description for 2 of the jumper blocks with extra fun settings; wish I found it sooner. :/

E. If all roads lead to buying a new Circuit Board, you have a few things to consider:

- Many control boards are not published nor will have the information you need such as test points for voltages and sine/data wave analysis.

- Continue to research, read ALL the posts, and ask smart people, like our moderator, questions to help guide you through the troubleshooting process. If I stopped at "Replace Circuit Board" for my specific problem as many posts and manuals led me to believe, I would have a spare ~$450 board as it would not have fixed the fuse issue (shorted lights) or the bad circulation pump.

- CAUTION: I cannot stress this on enough. If you are unsure about your troubleshooting skill sets around high voltage and sensitive ESD circuit boards, opening the panel to reveal the control board may not be your cup of tea. I have a fundamental knowledge about electricity and its safety, too include those tiny components found on a circuit board. If your doing anything beyond a visual inspection with the cover removed at the Control box with power shut off, just know your limits or it could be expensive and/or lead to failure of ones heartbeat in the process. :P

Otherwise, brave on and be sure to don approved gloves and eye protection; I've had large capacitors explode on me which was not pleasant to say the least. Have a good multi-meter capable of measuring resistance, voltage, and amperage. Also, ensure that everyone knows that you are working with potentially high voltage and to leave the circuit breakers alone! Reference: Lock Out Tag Out devices may be found at Home Depot.

Lastly, if your sensors are good, the heating element resistance is fine, and you've found the correct voltages coming, too include the transformer input/output, and still have a stubborn problem like mine, (assuming all fuses test good), there are still a few more things to try. Remove power from all the fancy extras not needed to provide the circulation of hot water; then slowly add components back in. CAUTION: Some types of circuitry require a load, so do your homework prior to attempting this troubleshooting method or go for broke and be prepared to shell out the extra for a new Circuit Board...your call.

I went as far to remove power to everything but the circuit board, topside controllers, sensors, and circulation pump...power on..test. Pump is working fine. Then I slowly added in the main parts of the hot tub starting with the heater...test. Then the large pumps...test. You get the idea. The last item I added were the lights, but everything continued to work! I didn't realize it until my son wanted to see the lights displayed in the waterfall "...because they are cool.." Then all at once everything died again. I did some more research and found an answer in yet another Jacuzzi manual (not my specific model but close) which gave me the answer for what the transformer is actually used for...the circuit board power and, you guessed it, disco lights!

One last hint: If you have a 12 year old tub, it doesn't hurt to take a good look around at all the plastic fittings and hoses. When I purchased the circulating pump, I also added some 3/4 and 3/8 inch tubing, stainless steel barbed nipples, and new clamps to replace as much tubing as I could; I decided now was the best time to get after it with all the covers removed. Additionally, I found a small drip on the outlet of pump #2. So I wrestled with it and replaced both O rings with plans to do the others if they misbehave.

Enough rambling. Good luck with your adventures and be sure to tip your waiter!

Old 12-13-17, 09:43 PM
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Otherwise, brave on and be sure to don approved gloves and eye protection
Good advice.

Thanks for the follow up. It not only adds to my knowledge but it helps others following along.

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