Product review (2 stars): It the highest selling spare part for the system - a perennial best seller!
PROBLEM MEMBRANE SWITCH WB24X10115 for GE JVB94SH1SS GE vent system:

This system is was always problem - especially the membrane switch.  A customer says he changed 5 switches within 8 years. It the highest selling spare part for the system - a perennial best seller!.  The membrane switch is a shoddy design and breaks easily because membrane switches are inherently finicky.  Temperature, pressure (from finger), grease, cleaning fluids, moisture and repeated use deteriorate the switch fast. There is also a knack to operate this switch: you should hold it down lightly and as the motor engages you must let go off the switch.  If you do not press long enough (1/2 sec) the motor won't start.  If you hold for a long time, the vent snorkel (yes, thats what they call it, snorkel) comes up but the snorkel may slip off the rails which will necessitate a visit from the repairman (it happened to me).

A WORD ABOUT GE REPAIRS and PART PRICES:
There is a $90+ charge for the house call and there is additional charges for parts and additional labor. GE charges about $129+ for the membrane switch (which should cost about $5.)  It appears that there is a potential after sale profit from this poor quality of design and manufacturing -  thus why should GE fix the problem?  The prices for this 3 inch strip range from $45 (Amazon) to $150 (Sears) in the internet - so shop around. So far I have not found a cheaper alternative for the membrane switch.  Some people suggest  a simple mechanical push button, but it may not look pretty.

SHOULD YOU FIX THE PROBLEM YOURSELF?  YES!
All it takes is 15 Minutes + Sharp knife + Phillips Screwdriver + 2 sharp thin needles + Patience
It is really easy (if you know the answer) - even for a novice like me.  But it took a novice a while to diagnose the problem and preparing the vent.  The so called experts' solutions from the internet, while not incorrect, are  incomplete and confusing. You can always contact them and pay them a nominal fee. It should be smaller than GE or other visiting repairman.  Also I think some part sellers, with premium prices, may provide guidance as well.  I do not fault them they need to live too, but I did not use them, you can.

DIAGNOSING THE PROBLEM: Is it  the Switch? Controller? or the Motor?  Your best and optimistic bet is the Switch. If you have been experience a deterioration of the switch function over time before it completely broke down, then it could be definitely a switch issue.  Controller and motor issues require elaborate dis-assembly of the vent enclosure.  But fortunately they break less often than the switch. The switch being the weakest link, it could be the most probable culprit but easiest to fix.  Once the switch is completely separated out you can test its  functionality with a simple continuity check (optional for the electrically inclined geeks).

ANATOMY OF THE MEMBRANE SWITCH: The switch  is a very thin push button membrane assembly  that activates the controller.  It is a 4 inch piece of plastic strip covering two thin wires. A small black clip at one end of the strip snaps into a connector from the controller. The business end, of the wire is a small push button circuit that is  sandwiched between a plastic black/white cover plate (with two triangles) and a metal plate.  You push on this plastic cover plate to turn the switch on.  The metal plate is a self-adhesive and stuck around a square hole on  top of the snorkel trim.

1.  SEPARATE  THE BUSINESS END OF THE SWITCH FROM THE TOP TRIM.
With a small thin sharp knife carefully pry the metal plate of the switch  from the trim by gently prying all around the edges.  Some experts claim the switch becomes useless once plastic cover and/or the metal are meddled with.

2.  MAKE SURE THE SNORKEL  IS UP POSITION.  If it is UP you can skip this section!
I was not that lucky. My snorkel was down.  I do not know if the snorkel can be moved up just by pulling it. In my case, after separating the switch metal plate from the trim I could access the plastic strip with two white metal strips in it.  I wanted to close the circuit by shorting the two metal strips to activate the snorkel. So I inserted two needles one on each metal strips and closed the circuit by having the needles touch each other.  It was not as easy as it sounds.  The plastic strip was very resilient and I pierced the strip in many locations to adequately make an electrical connection.  When the circuit closed motor kicked in and the snorkel came up.  Clearly the switch was the problem in my case.  If the motor does not activate by shorting the white metal strips then the problem could be with the controller or the motor. This requires more elaborate procedure to access the raise/lower motor arm to move the snorkel  manually up. BE SURE TO TURN THE POWER OFF IF YOU PLAN TO GO NEAR THE MOTOR!!

3.  REMOVE THE WIRE COVER.  (Phillips screw and a tab)
Wire cover is a 1 inch wide L-shaped (each leg 9 long) rigid metal strip. It protects the membrane switch strip and the fan controller switch wires from the exhaust grime.  The end of the vertical leg  is connected to the snorkel by a small Phillips screw at the bottom right hand side of the snorkel.  The end of the top horizontal leg of the wire cover has a lip that is engaged to a tab at  the top of the snorkel .  Remove the screw.  (I had to lift and move the range assembly temporarily away to access the screw since my range top was obstructing the access to the screw.  Then gently work the wire cover to disengage from the tab. You may have to try several times.  Once the wire cover is removed you can see the other end of the switch connected to a small controller plug.

4.  DISCONNECT THE SWITCH FROM THE CONTROLLER. Gently pull the switch connection while pressing the small clip. (DO NOT TRY TO SHORT THE CONTROLLER WIRES.  THE SNORKEL WILL GO DOWN!!)

5.  CONNECT THE NEW SWITCH TO THE CONTROLLER.  Make sure the connector at the end of the plastic strip goes through the hole on top of the trim. Test if switch works ok. If it does not check the connections. If connections are ok, check the switch for continuity.  If the switch was fine then we have the problem with the controller or motor. Ouch!

7.  INSTALL THE WIRE COVER back.

8.  ATTACH THE BUSINESS END TO THE TRIM. Clean the grime from the edges of the hole on top of the trim.  Peel away the protective cover  for the adhesive from the metallic side of the new switch. Press the edges of the switch to stick tightly around the inner edges of the trim hole. YOU ARE DONE.