Watchdog error 2008 Optima

[Cativo]

Hello everyone,   

I see this is not a first time occurrence for this issue, but mine may have a slight twist, so I am looking for some direction. 

I lifted the lid last week and saw the Watchdog dashes across the LCD panel.  I knew what this was because it occurred back in January and I was able to get pasted this issue by warming up the motherboard (MB) area until the unit kicked back on.  Then I ramped the temperature back up to 90. 

Well, last week the temps around here dropped down to the mid to low 30's, so I am guessing one of the components on the MB is not liking the cold weather.  Yesterday I ohmed out the temp and Hi-Limit sensors, and both are within a normal range of resistance.  I went ahead and grabbed my heat gun and warmed up the MB for a few minutes. Then, I powered up the tub and saw an error pop up something like "Freeze" as the circulation pump turned on, but quickly turned off and went back into Watchdog mode.  I am guessing I need a new motherboard.  I see they are about $300 to $500.  Does that sound right?  Or am I missing something?? 

Thoughts?

Thanks for your help in advance!

[clover]

"Freeze" is a code that appears when your water is more than 20° colder than the requested temperature.  It only tells you you're in trouble, as determined by the water temperature, and what it is set for.

The Watchdog signal, "----" that will appear when the temp sensor in the filter bay, and the hi-limit sensor in the heater, are not in agreement to be within range limits.  They should be within 8° to 12° of each other  for normal operation.  When they have a wider range of difference, a watchdog symbol will appear. 

Then again it could be the circuit board and the service man would have a test plug to determine that.  I seriously doubt you have a circuit board problem in a 5 year old Sundance, and it is most likely a temp sensor that is "lying" to the circuit board.  Get a new temp sensor and plug it into the sensor loom with the sensor end hanging over the side of the spa in the water to determine the elimination of the watchdog signal, then install it correctly.  There are a few tricks to employ to make this simple.  Call for service or ask for advice.

[Cativo]

Great info, thanks. 

I will order a temp sensor and give it a shot.  My  old hang up is why the system goes past this watchdog error when I warm up the MB.  That makes be lean towards a IC that is problematic.  .

[clover]

Rarely do we see a problem with the circuit board, but then, we don't live in a perfect world.  Both temperature sensors are thermistors and they are variable resistors to the circuit board, and as such are able to communicate temp data to the circuit board.

When you "warm up the MB" you are changing the factual conditions monitored by the MB. 

Please indicate the ohms that you read on each sensor, and how you are able to determine they are in the normal range.

[Cativo]

Clover, first off thanks for helping me think through this.

As for the Thermistor reading.  The temp sensor ohmed out to 52k ohms, which seems to tie to the temp of the water after being off for a week. My IR temp sensor showed about 52F, and the Hi-Limit sensor ohmed out at around 50K ohms.  This makes me think the sensors may be OK.  I would think if they were bad, they would read very low resistance or be open.

Plus, heating the board should really only changing the condition of the local electronics on that board, and not what is being reported back by the sensors.  Right?  I'm just trying to think this one through, so maybe I just hit the jackpot on the first shot.  I guess $50 is a cheap investment in troubleshooting the issue. 

 

[Dr. Spa™ Ret.]

A 10k ohm thermistor at 52f should be at 18.9k ohms
A 3k ohm thermistor at 52f should be at 5.7k ohms

FYI, the lower the resistance, the higher the temp.

[Cativo]

Hi Dr. Spa,

This is the way the sensor is on the Sundance models too?  I know there are two types of Thermistors, and they work opposite, but not sure which is used here. 

If what you are saying is correct, then both my sensors are reading closely, but way off.  I guess I am a confused tuber.   

The link below is what I found online.  This seems to jive with what I was seeing on my meter.

http://www.spaandpoolsource.com/sundancespastemperaturesensordiagnostic.aspx

[Cativo]

This is an update for anyone who may be interested.  I have access to some variable resistors at work, so I made myself a couple for troubleshooting this issue.  I set one at 30k ohms, and the other roughly at 31k ohms, and powered up the tub.  I still had the watchdog error present on the LCD.  Since the tub was empty, I took this one step further.  I grabbed a heat gun (A hair dryer would suffice too), and slowly heated the temp sensor up, while my meter was connected to the end of the sensor.  The temperature changed on the meter, as the temp sensor got hotter.  Makes sense.  So, this tells me this is working fine.  I actually, had an IR temperature gun too, so I could make sure the readings were at least close to what they were supposed to be. 

Next, I wanted to check the Hi-Temp sensor, but after seeing where that went, I chalked it down to good.  But, I decided to put my meter on the output wires of this sensor and heat up the outside of the housing where this sensor lies.  The temperature gradually moved up as the surrounding area got warmer.  So, to me this is working fine too.  Again, since I faked these out initially I had a good sense it was fine too.  I went ahead and plugged everything back in.

I went ahead and filled the tub at this point. 

After flipping the breaker I still had the Watchdog error. Since I hadn't really changed anything I guess I shouldn't be surprised.  At this point I went back to what worked earlier in the year.  I gradually started to heat up the Mother Board (MB) with my heat gun.  With my IR gun I brought the board temp (upper region of the board - around the Eprom and Processor) up from 54 degrees to about 75.  Here is where I started to see changes.  The display came on for about 5 seconds with the Temp and OH blinking, but nothing else.  I then brought the board temp up to about 85 degrees and that was the trick.  The temperature was now displayed, along with the OH and COOL flashing on the screen.  I let it set and the OH went away and the cool remained until the temperature met my setpoint (Makes sense). 

I went ahead and brought the temperature up to 95 degrees and will leave it there, so hopefully the heat from the tub will dissipate outwards enough to keep that board warmer.  I think leaving the tub at 80 was too low when our temps dropped down to the low 30's.  Doesn't make a whole lot of sense, but there may be something on this mother board that is cooling off and causing a bad solder joint or connection.  Who knows, but for now I hope it keeps plugging away, as I don't want to spend the $500 on a updated MB. 

Fingers crossed.....