Diver Daves' Mark-15 Electronics Page

Having exhausted the pneumatics system, we'll move to the last system, the electronics. Here I have removed the electronics pod for inspection. Visible are the attachment clamp, the pod, the main Bendix cable that connects it to the sensors, and the primary display. The two other Bendix connections on the pod connect to the solenoid, and to the switch.

The Primary Display shows the loop PP02 as compared to the setpoint of the rig. For a rig set for 1.4 PP02, the green 'O' is illuminated when the rig is 'at setpoint'. The yellow '1' indications are for slightly high and slightly low. The red alarm 'L' and alarm 'H' indicate a serious deviation from setpoint. The 'A' shows status of the sensors, being illuminated when a sensor is voted out by the digital electronics. Although called the 'Primary' display, this is really just a crosscheck on the computer. The REAL primary display is the analog secondary display, shown below.

This is the analog 'secondary' display, which is really the main way that the diver monitors the PP02 of the system. This is merely a millivoltmeter, reading the raw output from all three sensors. The scale of the face of the meter is calibrated in PP02, and the display is calibrated to the cells when new cells are installed. The rotary switch on the left is used to select cell 1,2, or 3 for viewing, and can also be used to read the battery condition. straight up on the needle is where you want to see it. The display is viewed periodically, and the 3 sensors are compared. If the primary shows one sensor has been voted out, the secondary can be used to confirm the failure. In the event of 2 sensors failing, a loop-flush with diluent is performed, and the remaining good sensor can be identified by knowing what the diluent PP02 should be at the present depth.

The primary is connected to the pod with this Bendix, which drives the display bulbs.

Here is the original switch removed for service. It is connected to the pod by a Bendix as well. If you remember from the top of the page, this can be replaced with a remote switch that may be more conveniently located.

In order to remove the battery and calibration plug, the first step is to remove the bleeder screw. DO NOT forget to reinstall it! There are two types of Mark-15 divers: Those who have ruined a pod by leaving this loose, and those who will ruin a pod one day. I try to eliminate the problem by removing it entirely, rather than simply loosening it. With it removed, I'm a lot less likely to jump in the water with it not tight, but if you just loosen it, it looks the same tight or loose. Be warned!

Now the top of the pod may be unscrewed, revealing the battery. You can see the retention ring, the top, and the bleed-screw on the bench. The battery is a series of 18 AA cells wired to give both 12 and 24 volts. These are usually home-made, and take about 10 minutes to construct. The battery is connected to the pod by a 3-pin Molex connector, which you can see as the white connector.

Even with the battery compartment open, the actual electronics are still not exposed to a flood. There is still one more O-Ring sealed plug between the battery compartment and the electronics. You can again see the care taken to protect the system from failure. In this photo the battery has been removed and we are ready to open the calibration port.

Now, we are finally into the electronics area. The circuit board is down in there someplace, along with the setpoint adjustment and one of two ways to calibrate the system.

Here is the selection switch for changing the setpoint. You can see the small table of settings, and the slotted switch. Just turn to the click-stop to change the setting. The push-button is used to calibrate the unit. The procedure is to purge the loop with pure 02, and then push the button. The primary display will flash three times, and the system is fully calibrated.

Well, that's about as far as it goes! With nothing left in the chassis except the basic pneumatic system, all of the remaining components are easy to view. I've laid the regulators up in the area where the center section is installed, and you can see the entire routing of the pneumatics, and see the solenoid and the accumulator. The only question is, will it all go back together again? The answer is definitely 'Yes', as I tear down the rig to this degree before any major dive. Careful preparation and maintenance is an essential part of diving a system like this, and any owner should be able to do an inspection like this one.

	Having exhausted the pneumatics system, we'll move to the last system, the electronics. Here I have removed the electronics pod for inspection. Visible are the attachment clamp, the pod, the main Bendix cable that connects it to the sensors, and the primary display. The two other Bendix connections on the pod connect to the solenoid, and to the switch.
	The Primary Display shows the loop PP02 as compared to the setpoint of the rig. For a rig set for 1.4 PP02, the green 'O' is illuminated when the rig is 'at setpoint'. The yellow '1' indications are for slightly high and slightly low. The red alarm 'L' and alarm 'H' indicate a serious deviation from setpoint. The 'A' shows status of the sensors, being illuminated when a sensor is voted out by the digital electronics. Although called the 'Primary' display, this is really just a crosscheck on the computer. The REAL primary display is the analog secondary display, shown below.
	This is the analog 'secondary' display, which is really the main way that the diver monitors the PP02 of the system. This is merely a millivoltmeter, reading the raw output from all three sensors. The scale of the face of the meter is calibrated in PP02, and the display is calibrated to the cells when new cells are installed. The rotary switch on the left is used to select cell 1,2, or 3 for viewing, and can also be used to read the battery condition. straight up on the needle is where you want to see it. The display is viewed periodically, and the 3 sensors are compared. If the primary shows one sensor has been voted out, the secondary can be used to confirm the failure. In the event of 2 sensors failing, a loop-flush with diluent is performed, and the remaining good sensor can be identified by knowing what the diluent PP02 should be at the present depth.
	The primary is connected to the pod with this Bendix, which drives the display bulbs.
	Here is the original switch removed for service. It is connected to the pod by a Bendix as well. If you remember from the top of the page, this can be replaced with a remote switch that may be more conveniently located.
	In order to remove the battery and calibration plug, the first step is to remove the bleeder screw. DO NOT forget to reinstall it! There are two types of Mark-15 divers: Those who have ruined a pod by leaving this loose, and those who will ruin a pod one day. I try to eliminate the problem by removing it entirely, rather than simply loosening it. With it removed, I'm a lot less likely to jump in the water with it not tight, but if you just loosen it, it looks the same tight or loose. Be warned!
	Now the top of the pod may be unscrewed, revealing the battery. You can see the retention ring, the top, and the bleed-screw on the bench. The battery is a series of 18 AA cells wired to give both 12 and 24 volts. These are usually home-made, and take about 10 minutes to construct. The battery is connected to the pod by a 3-pin Molex connector, which you can see as the white connector.
	Even with the battery compartment open, the actual electronics are still not exposed to a flood. There is still one more O-Ring sealed plug between the battery compartment and the electronics. You can again see the care taken to protect the system from failure. In this photo the battery has been removed and we are ready to open the calibration port.
	Now, we are finally into the electronics area. The circuit board is down in there someplace, along with the setpoint adjustment and one of two ways to calibrate the system.
	Here is the selection switch for changing the setpoint. You can see the small table of settings, and the slotted switch. Just turn to the click-stop to change the setting. The push-button is used to calibrate the unit. The procedure is to purge the loop with pure 02, and then push the button. The primary display will flash three times, and the system is fully calibrated.
	Well, that's about as far as it goes! With nothing left in the chassis except the basic pneumatic system, all of the remaining components are easy to view. I've laid the regulators up in the area where the center section is installed, and you can see the entire routing of the pneumatics, and see the solenoid and the accumulator. The only question is, will it all go back together again? The answer is definitely 'Yes', as I tear down the rig to this degree before any major dive. Careful preparation and maintenance is an essential part of diving a system like this, and any owner should be able to do an inspection like this one.