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2005 Jacuzzi Hot Tub Help Needed - Detailed

Christo_Mohito's Avatar

Join Date: Nov 2017
Posts: 3

11-26-17, 09:16 PM   #1 (permalink)  
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: 63 F
- Heater pipe temperature where Hi Limit sensor is strapped: 73 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 106 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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PJmax's Avatar
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11-27-17, 12:58 AM   #2 (permalink)  
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.

~ Pete ~

Christo_Mohito's Avatar

Join Date: Nov 2017
Posts: 3

11-27-17, 09:22 PM   #3 (permalink)  
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.

Christo_Mohito's Avatar

Join Date: Nov 2017
Posts: 3

12-02-17, 10:27 PM   #4 (permalink)  

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.

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