Cell failure on handset

[jfe]

I need advice please. since service I've done 3 dives on my unit, shallow dives to 15m for a total dive time of 229 minutes. Incerted new cells with a total time of 136 min.
This weekend on my 2nd dive at the safety stop my handset suddenly showed cell 1 FAIL, however the hud kept on displaying PO2 value, did not show cell failure. Once home I've 1st changed the cells around but got the same error message. I've replaced the wiring with brand new ones and still got the same.
So from the two variables I know neither worked, I have not tried to recalibrate the unit, would that be my next step in fault finding? I've also send Hollis an email but I'm reaching out to the community as well. New to this and need to learn.
What buggs me as well is the other two cells are showing .35 in normal air, was never this high and used to mainatin .21. Could it be because of the new cells. They were left out for 48 hours before they were placed in the unit and calibrated. Dived another 12 hours after that.
It is a Hollis Prism 2 unit, please I'm looking for constructive help.

 

[JohnnyC]

Most likely a bad cable. You could try to recalibrate with O2 to see if they return to normal in air just to see what they say. That being said, if you've swapped cells around and are still showing the error, and swapped the cell-side cable (this is a thing in the Hollis?), chances are it's either the hardwired cable or the computer itself.

 

[doctormike]

Not sure about 0.35 in air, that sounds like a calibration thing. But are you saying that you switched the cells around and still got a failure on cell position one on the handset? And at the same time, all three cells are reading normally in the HUD? If so, then it might be a Shearwater issue (controller) and not a rebreather issue. Not how the Prism works, but on the JJ there are separate boards for the HUD and the controller. Maybe if the handset itself is OK, it's the controller board?

 

[vitaly]

I've been there. In my case it was a bad wire harness. I would double check it with a multimeter before checking anything else.

 

[a878bob]

Just my 2 cents.

1.If you run the checklist, you calibrate everytime you set up your rig. Both handset and hud.

2. If a cell is more than .1 out, it will be voted out and fail. But that’s not saying the other 2 cells aren’t the bad ones. What po2 did cell 1 give you on the hud?

3. What are the cell millivolts when you get this error. They should be 8.5 - 14 in air.

So to help run down the error, I would check the mv in air then calibrate.

If you report back the numbers, it may be easier to pinpoint the issue. And be a good exercise for the rest of when it happens on our rig.

 

[vitaly]

2. If a cell is more than .1 out, it will be voted out and fail. But that’s not saying the other 2 cells aren’t the bad ones. What po2 did cell 1 give you on the hud?

Voted out != Fail. Petrel still shows PO2 for all cells even there are way off. Fail = no signal.

 

[rjack321]

Since the HUD didnt experience this... I'm going with cable issue or internal wiring in the shearwater failing.

 

[vitaly]

Call Shearwater. They are more knowledgeable than Hollis support.

 

[jfe]

Thank you so much for the feedback. I actually did check against all systems but as a new rebreather noob paranoia rules over logic in some cases.
I checked everything - cells with multi meter, new cables, flood the system with O2 the whole 9 yards - except for pushing the calibration button on the handset, stupid isn’t it, as my brain said look nothing changed.
So I reassemble it again and repeat everything while making a video and actually did press the calibrate button this time and eureka problem solved. All the cells are displayed, and reading correct. Valuable lesson learned, don't assume follow through.

So what caused this to happen, as I said it happened at the 6m stop on the final dive of the day and only the handset not the HUD. Am I correct to say if the handset still give you the cell's mV, and it's within the values, it is due to a spike or drop in the cell output during the dive that has caused this to happen and system / hanset needs a recalibration? Since the system used two iduvidual boards for the primary (hub) and secondary (handset) systems how come one indicate this and not the other?

I will also still ask for info from both Hollis and Shearwater as I need to understand this for future reference.

 

[rjack321]

The flash memory in the handset lost it's calibration data. It happens.

If it happens again send it in, probably needs a new board. If not, just move on