put it in switch test , if it works in test , disable the claw and start a game.

Had same problem my claw will work the first time .Then it dosent move back then to the left it moves over to pick the ball up again and thats it.If you take the glass off get the ball put it back in the game it will not start another game.Everything works perfect in test mode including start button.I have the claw disabled and it works fine.Im going to try to figure it out this weekend.

The start button is part of the switch matrix. If there's a board problem then an entire row, or column, in the switch matrix would be out. First thing I would do is check the other switches in the same row and column as the start button. The switch matrix diagram in the manual will help you identify the switches.

I happen to have a Dredd manual next to the computer here. Let's see. In the same row (white/orange) is:

Ticket Dispenser (probably not installed), Left Rollover, Outside Right Return, Captive Ball 2, Left Ramp to Lock (opto), Left Popper (opto), Trough 3.

In the same column (green/brown) is:

Left Fire Button, Right Fire Button, Plumb Bob Tilt, Left Shooter Lane, Left Outlane, Left Return Lane, and 3-Bank Targets

If all these work in test, but the Start Button doesn't, make sure you have all the plugs plugged in on your MPU board. Also, make sure no wires have pulled loose from them.

Actually, that's row3 and on u18. Cols are controlled by the more-often-failing u20. You tested this row via jumper wire method from pinwiki?

Actually, this is one of the easiest tests there is.

Pull all the switch plugs off the bottom of the cpu after putting the game in switch edges test mode.

Now take a jumper wire, connect to column 1, and touch to all 8 rows.

Now take same jumper wire, connect to row 1, and touch all 8 columns.

The correct switch should show closed for each test.

If it shows good, you have a broken wire under the playfield.

This is really easy.

Look at the bottom of your cpu.

Three sets of pin headers, left center, and right.

The left-hand headers are for your cabinet "direct" switches (the coin door buttons, and coin switches) and the other "in cabinet" switches, namely the start button, tilt bob, and slam tilt.

The center headers are wired the same ... all are the column drives.

The right headers are also all wired the same ... all are the row returns.

The way the switch matrix works is, the game sets each column drive, one after the other, column 1 through 8, from "high" to "low" ... or +12 to ground.

The row returns (and indeed, any other switch input including flipper buttons and direct switches) are simply sitting there looking for the input to be connected to ground.

The "matrix" is simply an arrangement of switches, with diodes, such that each column "activates" a set of 8 switches, and any closed switch, the ground signal from the column goes through the switch (and its diode), back into the row return input. The game then reads the signal, and knows the swtitch state for that column's switches.

Then it activates the next column, then the next column, lather rinse/repeat in an endless loop.

So ... for this test, you want to use the coin door buttons to put the game into "switch edges" test mode.

Then unplug all the plugs from the bottom of the cpu -- this ensures nothing is connected to any switch inputs.

Now touch a jumper wire to pin 1 on the center set of headers, the switch columns.

Touch the other end to pin 1 on the right-side set of headers, the row inputs.

You should see the appropriate switch (11) show on the display.

Now move to pin 2 of the right-side set of headers, all the way to the last pin.

Then do the same procedure, but go from pin 1 on the right side headers, to each pin on the center headers.

In this manner, you are testing each and every possibility of row/column.

This would eliminate the CPU as the issue, if it passes.

Jumper is just a wire to connect the pins of the CPU together. You can use an alligator clip lead it's it allows you to lock the jumper in place as you move the other end of the wire.

Marc

It's pretty hard to get an alligator clip on those small .100 pins though.

Literally, take a short piece of wire, strip 1/2 inch or so of the insulation on each end.

Touch one end to one pin, touch the other end to the other pin, look at display, see if switch shows as closed.

Use a wire, paper clip, whatever. This is all on pinwiki

No, you're not touching anything on the direct switches inputs at all.

going by your picture, using ONE jumper, pin 1 of J206, then touch to pins 1 through 9 of J208.

the pin 2 of J206 to pins 1 through 9 of J208. Repeat for 3 through 9.

Then pin 1 of J208 to pins 1 through 9 of J206. Repeat for pins 2 through 9.

U20 is the col chip. U18 handles rows.

Well, let's see what the test shows, then go from there.

Let me jump in here and ask, did you check the MPU for battery corrosion? I had a FT that would not start either, it turned out to be the battery had leaked acid on a chip below the pack.

Before you replace U18, check the resistors and diodes associated with the Row 3 input.

There's also a LM339 prior to U18.

This is where you need to be able to read a schematic of the circuit.

I have a very similar problem with my Demo Man. My start button works, but 50% of the time my launch and right thumb button won't work. What's even stranger, is that sometimes when this happens, the right trigger button will launch the ball when pulled. In the switch test, the launch and right thumb switches show as closed on the diagram and do nothing when pushed. If I let the machine sit in switch test for a while, sometimes while I am staring at the diagram they will randomly go open, though I am touching nothing. I assume I should be doing similar jumper testing.