STTNG firing two balls - SOLVED!

[AskJacob]

Not 100% sure, but is there a switch in the shooter lane (just before the plunger)? Is it working OK?

Cheers
Jacob

[Strangeways]

Not 100% sure, but is there a switch in the shooter lane (just before the plunger)? Is it working OK?

Cheers
Jacob

do you mean the switch mounted just under the catapult ?

[robm]

Yep, there is a switch under the catapult - it also works fine in the switch edges test

[silverball]

have you tested the 2 switches that store the balls under the playfield? Make sure any switches that you test are triggered by a pinball and not your finger.

[Strangeways]

In addition to checking the optos in the subway, check the opto board under the playfield. The IDC connectors sometimes have wires that have dislodged from the connector.

[robm]

I have checked the connectors and they all have continuity

I found that opto receiver switch no 32 (under left gun sw 2) only had a voltage of 40 mV, whereas all the other opto recievers have about 200mV.  This opto does not register in the switch edges test.

The transmitter glows fine when viewed through a digital camera - so i assume it is fine.

There is continuity to the connectors, so i am wondering if one of the LM339's on the 16 opto PCB might be gone??? If so, i don't know how to determine which one....Do you think i'm on the right track or wandering up the garden path???

[MartyJ]

have you tested the 2 switches that store the balls under the playfield? Make sure any switches that you test are triggered by a pinball and not your finger.

+1

I've made this mistake before!

[Strangeways]

As a general "rule of thumb" on ST TNG - The cannons (guns) needs the wires changed. I usually do this by cutting about 10cm from the connector (wire loom) and then solder in new wires - including insulation - right up to the optos, coil and lamp. Tedious - but it needs to be done on all ST TNGs. I was reading somwhere that you can buy a replacement loom - inc connector.

If those cannons are playing up at all - change the looms on BOTH !

[robm]

Its amazing how good it is to leave something and come back with a fresh mind....

As said above, i found the voltage of the opto collector for Sw32 had no (or minimal) voltage.  I then determined that it was the red/orange wire that was the problem, (as the other grey wire had power when tested in conjunction with another switch beside it).

There was continuity to the connector on the 16 opto PCB.

This trace then went to a resistor.....and.....it read WAY higher than all the others, there was also a mark down the length of it.

Looking at the circuit diagram, it was a 2k resistor, i found a 2.2k one in the shed, put it in and everything worked sweet .

Thanks to all who helped, particularly those who suggested checking all switches that store balls under the playfield.

Only other question is will it be an issue with a slightly larger resistor?  I assume not as the others all seem to have a bit of variation.

[ajlaird]

The slightly over-spec resistor shouldn't be a problem, usually there is some leeway for these sorts of things.

[silverball]

 $#$good job

[Strangeways]

Its amazing how good it is to leave something and come back with a fresh mind....

As said above, i found the voltage of the opto collector for Sw32 had no (or minimal) voltage.  I then determined that it was the red/orange wire that was the problem, (as the other grey wire had power when tested in conjunction with another switch beside it).

There was continuity to the connector on the 16 opto PCB.

This trace then went to a resistor.....and.....it read WAY higher than all the others, there was also a mark down the length of it.

Looking at the circuit diagram, it was a 2k resistor, i found a 2.2k one in the shed, put it in and everything worked sweet .

Thanks to all who helped, particularly those who suggested checking all switches that store balls under the playfield.

Only other question is will it be an issue with a slightly larger resistor?  I assume not as the others all seem to have a bit of variation.

Well Done 

2.2K Resistor is fine.