The upper circuit board is a component which the lower, main circuit utilizes to carry out some of the functions to operate the marker. Smart Parts prefers to keep their electronics as integrated as possible (meaning everything possible is attached to a circuit board, instead of being connected using wires and such), so that's why the upper board is used in the Shocker SFT and Nerve design.
Solenoid Connection to Upper Board: 
The relation of the solenoids with the upper board is simple in this regard. The upper board is removable with the newer Humphrey solenoids, but NOT removable with the older Parkers. With the Parker solenoids, the two coil terminals stick up out of the coil housing, and are soldered directly to the board. The board therefore cannot be removed unless it is desoldered from the board. I personally do not recommend doing this for any reason, unless you are absolutely forced to do so. I recommend this soldering task only for advanced technicians, since desoldering the solenoid is a very delicate operation and the coil terminals are extremely fragile.
Functions of the Upper Board: 
The upper board doesn't contain any programming of its own, nor does it direct any operations of the marker. It rather houses a collection of various circuit components which are used to perform those actions, when directed to do so by the lower board. Here's a list of parts:
· Energize the solenoid (uses a FET transistor, clamping diode, and two resistors to stabalize for the FET signal)
· Operate the powerswitch (uses the powerswitch all by itself)
· Operate the Vision system (uses a 1-mm FPC connector and two resistors)
· Activate the board indicator LED (uses a resistor, FET transistor, LED diode, and resistor for the FET signal).
Here are some technical specifications on the upper board itself:
· Wire harness connector is a 10-point, shrouded, side-entry type JST eSH series header, JST part number BM10B-SRSS-TB. Wire harness is 32 AWG wire connected between two protrusion-less housings, JST part number SHR-10V-S-B.
· The powerswitch functions off 9v from the lower board. It doesn't interact with any other part of the board; it's self-contained on the upper board. Powerswitch is a subminiature side-actuated tactile switches, ITT CANNON part number KSS321G (7mmx3.5mmx1.6mm).
· The solenoid functions off regulated 7v from the lower board. A rectifier diode is used to preserve the FET responsible for switching on the solenoid current.
· The LED functions off the same 7v supply as the solenoid, dropped down by a resistor. No rectifier is used.
· Vision system functions off regulated 5v from the lower board. A resistor drops the emitter eye current. Another resistor is provided for a pull-down effect on the detector's signal.
A reverse-engineered circuit schematic of the upper board can be found below, which includes a schematic for the stock lower board as well. Specifications for the lower board can be found on its page (see the Related Links section).
Upper Board Versions:
There are currently several different production versions for the upper circuit board. The main three are viewed in the picture below (oldest to newest). Please note that the names "v1", etc. aren't official (I made them up for the purposes of explaniation).
· Version-1: Original boards that were used in the earlier markers.
· Version-2: Redesigned boards that appeared around September 2004. This board mainly rearranged the components, specifically placing all of them on the top side of the board (to reduce production costs most likely). The only noticeable difference here is the LED was switched to a top-viewed LED instead of a side-viewed one (leftover from the Impulse boards). The vertical LED appears on all subsequent boards and shines brighter than the side-viewed ones.
· Version-3: These appeared soon afterwards, first seen in November 2004. This board again rearranged the components, and moved the two eye system resistors back to the bottom of the board. These boards were shaped slightly differently, and included small depressions to help guard against damage from the top grip panel screws. This is the current version board, and was seen on both Parker and Humphrey solenoids, however all Humphrey solenoids use this one.
Another difference is, when the v3 board first appeared, there was no hole for the manual override. This mistake was remedied soon afterwards though.
The most current boards (on the Humphrey solenoids) are identical except they have a small, male connector on the bottom to allow them to be removable from the solenoid.
Vision System Hardware:
The Vision anti-chop eye system used on the Nerve uses very self-contained parts and is quite easy to use. The Vision eye itself is attached to a FPC (flexible printed circuit, or simply eye ribbon for short), which is secured in place on the left side of the Nerve body using a 2-56 x 1/8" screw. This screw uses a 0.05" allen wrench to remove for disassembly.
To access the Vision eye, remove the left side ball detent (1/8" allen wrench) and insert your 0.05" allen into the small hole in the eye cover. Gently move the allen wrench into the head of the vision eye screw underneath. Please note that the screw is angled 15º upwards so your allen wrench will also be angled upwards.
Unscrew the eye screw and the eye cover will fall off, exposing the head of the eye ribbon against the Nerve body.
Do not overtighten the eye ribbon screw. It is easy to strip out and this will cause a lot of problems in the future. No screw on the marker needs to be tightened as far down as possible.
The Nerve body is internally milled in such a way that the eye ribbon can be directed to the upper board through the inside of the marker, instead of being wrapped around the side like on some other markers.
The eye ribbon wraps around the side of the valve housing so it MUST be removed prior to removal of the housing itself. If you fail to remove the eye ribbon, you will tear it when attempting to remove the piston, and will then need to replace the ribbon.
The eye used on the Nerve will only function if plugged into the connector the correct way. The silver contacts must face toward the board. This is opposite of the Shocker/Impulse.
Vision System Performance:
The eye system used on the Nerve is a type of reflective anti-chop eye, which describes an eye that bounces light off the loaded paintball in order to detect it. This eye type is suited very well for detecting special surface features of the object in mention (paintball). Some would say this eye type has problems detecting dark paintshells, but this isn't entirely true, since many people use any color paint they like without any issues. It is true, though, that the Vision programming on the stock board isn't as advanced as some of the available aftermarket boards, and the dark shell detection isn't as reliable. It is likely more developed than many people believe (those that are unfamiliar with how the programming works), however there is of course room for improvement. Aftermarket boards include much more advanced eye systems which are able to more accurately track the movement of the eye from shot to shot (known as eye validation) as well as a more reliable color detection. Please refer to the lower boards’ page for a list of aftermarket boards.
Grip Screw Damage:
If you purchase aftermarket grips for your marker, you must be sure they will not damage the circuit board by screwing the grip screws in too far. Please refer to the Grip Screw Damage Information link in the Related Links section.
Overview:
· The upper board controls several functions necessary to operate the marker.
· Aftermarket lower boards will increase reliability of the Vision system.
· Aftermarket grips that are more thin than the stock ones can cause damage to the upper board.
Related Links:
· General electroincs troubleshooting
· Vision troubleshooting
· Lower circuit board
· Powerswitch actuator
· Grip screw damage information
· Powerswitch repair