Hollis Prism 2 electronics in head. Photos!

[telemonster]

I have a used Hollis Prism 2 and I was getting an issue with the 3rd cell dropping out. It was intermittent. If it happens, it usually comes back by the next day. When it happens it ramps down to .00. So I pinged Shearwater and Hollis. I cleaned the already great condition harness between the 3 cells and the bulkhead into the electronics compartment in the head. I could test the failed channel and nothing in the user side would make a difference, so it was like the cabling to the controller inside the head was at fault.

My unit isn't under any kind of warranty, and I like to know what I have. Hollis was quick to respond to any emails sent to them but they aren't going to recommend a customer open the forbidden closet.

I opened it. And took pics. I couldn't find any information anywhere online about what exists inside. There was one security screw with anti-tamper stuff in it so they know when it's been opened. The rest are nice cap head screws.

There is a Hollis "OBOE" board which from what I can tell serves as a backplane PCB to all connections, and has a STM32 chip that is reading the o2 cells for the Shearwater handset (in my case it's over DiveCAN, which is a pretty common highly accessible bus found on a gazillion microcontrollers.)

I *believe* the analog signal from the Cells also feed a sub board, that is the Shearwater PCB that in my case drives the HUD. I'm not sure if the HUD bit itself is responsible for driving the LEDs or how that works when a NERD2 is plugged in.

The OBOE board has 4 connectors that are "CanBUS", which which I think are read only and two that are write.

Not sure what fires the Solenoid, didn't care so much about it.

Anyways, for those that might be curious...

Everything was bone dry, in great condition. The parts are of good quality, the pins look like they're gold plates for real. I gently wiped the pins with DeOxit and put it back together. Good stuff.

*** NOTE - This is not intended to be encouragement to open yours up or attempt to perform any type of service on yours.

 

[abnfrog]

jm marine kevin could help the man is a miracle maker

 

[vitaly]

OBOE board drives the monitor side (HUD, Nerd2 or additional Petrel2). SOLO board drives the controller side. Which one loses the cell reading: Petrel, HUD or both?
PS: Be very gentle with board connectors. It's very easy to broke wires there. Ask me how I know

 

[Narcosis Mike]

I'm having the exact same problem with my unit right now - sensor 3 dead on both the controller and hud. What was the root cause and solution for yours?

 

[vitaly]

I'm having the exact same problem with my unit right now - sensor 3 dead on both the controller and hud. What was the root cause and solution for yours?

I'm pretty much sure it's the harness. Replace it.

 

[telemonster]

Hello, in my case I narrowed out the o2 sensor by swapping them around. I figured it shouldn't be my harness because it was just 6 wires and 4 connectors. And mine was very clean!

It's been a while, but I did take and put deoxit on a qtip and carefully clean some of the contacts. But if I recall the issue apparently was just the connections on the PCBs in the head. I used a light amount of dexoit in there to clean the contacts.

Note, that Deoxit stuff is pretty nasty stuff. I use it for working on pinball machines, arcade machines, old computers, music equipment and synthesizers and stuff. You don't want it in a closed breathing loop. You don't want to be around it without really good ventilation. So be super careful about using that stuff anywhere near the actual breathing loop. I only used it in the sealed electronics compartment as I recall and let it air out a good amount before ever closing it up.

The easy thing to check is the cable that is in the breathing loop first. The one that plugs into each o2 sensor and then goes to a 2x6 .100 connector that passes through into the electronics department. Are the cables in good condition? Have then been exposed to salt water or salty air? Any corrosion?

 

[wetb4igetinthewater]

I find the wiring harness quite fragile. I'll probably have Marty Watson do some upgrades in that regard as that frustrates me as I've been skunked two straight weekends.

 

[telemonster]

Ah! Well if it's the wiring harness on the scrubber side, I believe that is replaced as part of the "annual" service kit.

Not vouching for this vendor at all, but I can see the cable in the pic:

Hollis Prism 2 - Annual Service Kit (220-9010) Revision 5

Hollis Prism 2 (P2) Rebreather Spare Part - Annual Service Kit (220.9010) Revision 5

www.rebreathersuk.com

 

[Narcosis Mike]

Sent my unit into the Hollis factory and for my issue they found it to be a problem with the bulkhead to PCB connector. Unit was fixed up pretty quickly and is en-route to me now. Will test next weekend. Was glad it wasn't the actual PCB as that would have been a nasty expensive fix.