Do the flipper coils have voltage?

What voltage is on the pop coils?

Pull ball out

Prop up playfield.

Meter on DCV 200V

Turn on machine, start a game.

One lead to ground (like the metal rails, or the braided grounding straps), one lead to a coil tab.

Be careful, don't short anything out, or touch more than one tab at a time.

1. DC voltage. It is usually in the upper left hand area of a dial meter. It has a symbol of a letter V with a dash after it and three dots under the dash.

2. Machine turned on.

3. Black lead to a ground. Ground braid is good, it is the flat, uninsulated, silver-colored wire that you should see in the bottom or sides of the cabinet. Red lead to either outside lug of a coil (make sure the coin door is shut). You may have to scratch some of the corrosion off the coil lugs to get a good reading.

Do you have a manual for your Flash? Here's a link to it: http://mirror2.ipdb.org/files/871/Williams_1979_Flash_Manual.pdf

Here is a good repair site: http://www.pinwiki.com/wiki/index.php?title=Williams_System_3_-_7

Your voltage is fine. You may have a weak ground.

Remove connectorsJ3 and J4 from the power supply board. That's the smaller board on the right. Always remove connectors by holding the plastic connector itself, never by the wires. Inspect the connectors and wires: are any burnt or discolored? Any wires loose or not attached? Plug these back in and remove them three or four times. This may help remove corrosion that could be causing a weak ground.

Do the same thing, inspect, then off and on, off and on, etc. on connectors J9, J10, J11 & J12 on the driver board. That's the lower of the two boards that are attached in the middle.

Do the flippers fire weakly or not at all?

One other thing. There should be a ground braid that comes up through the hole under the head, and is attached to the metal plate on the back of the head with a wingnut.. Is this braid there, and is the nut tight?

Here's another site that should help you: http://pinball.flippers.info/system6resources.asp

Was it ever fully working?

Is it possible its all seized up and rusted/gunky?.

Can you manually move flippers with almost no effort and do they fall back into place?

Its almost impossible for it not to be mechanical if your measuring voltage correctly- how confident are you that the rest of the game is poor if flippers are dead? Its pretty damn hard to tell if flippers are gone- just sayin there are any number of reasons the flippers could be weak or dead and 75% is pretty close to 100% for the rest of the game for someone who admits to being new at this- I would be fairly hard pressed to tell you if a game was really fully powered vs 80% or 90% etc without having played it previously if I came to it and the flippers were basically dead.

I vote at least check mechanical and corrosion on all switches and gaps on EOS.

Fix flippers- if you can its not got anything to do with anything but mechanical.
If you cannot fix them- with help here- then its something electrical your missing. Could be that- even might be- but i would want to know answers to above before casting my vote.

Tough to say exactly whats going on, but if you getting good voltage and the components are not corroded/tough to move, and if its both flippers (which have an end of stroke switch that could cause this) AND pop bumpers or slings (which do NOT - ruling out that possibility or at least its not explaining everything)- then I am unsure- and will defer to people who may be able to offer true insight- I have one kinda stupid idea thats a little risky, so I will not mention it here- other than to ask others-

Could it be that somehow he has a poor connection or even transformer thats somehow limiting current flow- and could he find that by loading it and looking for a hot spot? Or is it too risky?

Flash isn't a high action game. It's got all of those crappy Williams EM mechs - especially the flippers.

There's a chance you just aren't used to older games and think it's exceptionally weak. Could just be a normal flash.

They can play well but really need to be dialed in - totally shopped out, rebuilt flippers, etc.

There could well be a problem but hard to say without actually playing your game. Maybe you can shoot some video for us. "75%" sounds about right if you are comparing it to even a System 11 game.

Disagree. Flash should have great snap to it.

Seems like you may have a short somewhere. Or leaky caps.
Can you post any pictures, clearly taken and well lit of the boards? I recommend look up Vids guide to bulletproofing system 3-7. Also, I am convinced re-pinning and crimping new molex truifurcon connectors on everything.