Data East Solved Last Action Hero (Data East, 1993) Two Solenoids are not working

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boksholm

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Attack from Mars
Hi!
I have a LAH in which the Drop target-solenoid and the Left scoop-solenoid have stopped working after the F5-fuse was shot. I guess that some damage has been done to transistor Q24 and Q26(??) on the CPU-board(??). Both of the solenoids have the same (brown) colour on one of the cables which is also shared with the deverter (which is working!).
Is it possible that two out of three transistors broke at the same time? What else could cause this problem? I am now changing all weak fuse-holders, but that´s mostly to keep the project alive.


Thanks!!

Link to Schematics:
http://mirror2.ipdb.org/files/1416/Data_East_1993_Last_Action_Hero_Schematics_BW.pdf
Manual:
http://mirror2.ipdb.org/files/1416/Data_East_1993_Last_Action_Hero_Manual.pdf
IPDB:
http://www.ipdb.org/machine.cgi?id=1416
 
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Solution
Coil_Smoke
Those coils are powered by a 'Darlington Pair' of back to front transistors driven by logic level outputs. The 5 volt level logic delivers a voltage to transistors. That voltage represents either one or zero. It is interesting that a draw back of the darlington pair is it needs twice the voltage to turn it full on. That makes it a good choice for switching power on with logical "one" voltage of +3.1 V or so.

You can remove the transistor from circuit and check it proper diode like conductivity with your ohm meter. Or look for those trigger signals. But a DVM is not a good instrument to detect short logic level pulses(it misses them). An oscilloscope is probably best. There are logic probes of all sorts. I imagine a low current LED or...
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That would be some quirky bad luck. loosing two transistors at once? You'd think it would cost 2 fuses to take that ride. It looks like red wires should bring +32Vdc to those three coils. Is that 32V present at those coils? Are the snubber diodes shorted or blown open ? A brown wire with yellow trace leaves the diverter coil heading for the driver (board?). Brown with violet for the scoop. The drop target has brown with green. Check those wires, power off with ohm meter, for continuity and shorts; together and to ground. Grounding those wires or the tabs on their power transistor, should fire it's coil.
There is a "a/c" type relay that increases the number of coils/flash lamps from 21 to 29. Data East is calling it "Left/ Right" relay. It is involved in operating coils 1 thru 8. So... You mentioned nothing about coil/flash lamp test results. How do things fare while the CPU is triggering those circuits?
 
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I forgot to mention- Test the coils for shorts, they should read 5 -35 Ohms. That 50 VDC scale should show + 32 v real good. I can't see the plugs but make sure the leads are in POS+ and COM-. A continuity test from the coil to the Collector Tab of the transistor should read 0 ohms. Grounding the tab bypasses the transistor(and any current limiting resistors, being another possible fail point) to ground.

The brown wires that leave the coils are positive @ +32 volts above circuit ground. The coil's transistor makes the connection to ground when CPU turns it on. So, grounding anything on that side of the coil activates the solenoid.

But, before all that, What are the Coil/Flash Lamp tests revealing ??? Those coil circuits(22-29 0r 1-8?) are added to the flash lamps control and switched back and forth by that relay. Is it possible?> transistor is bad both playfield devices fail. The other device than the coil is most likely a flashlamp and would also not work?
 
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During the Coil-test everything works fine except coil 13 and 15. Nothing happens when I try to trigger those. All flashers works fine.

I forgot my multimeter at home when I went to the machine yesterday. But I tried to get the coil to trigger by putting a cable from the brown cable to the tab of transistor Q24. I guess I did something wrong, nothing happened.

Thank you for your patience. As you can tell I´m quite a newbie. I would be grateful if you could help me by explaining a bit more about how I trigger the coils manually via the transistor!
=)
 
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Those brown wires are connected to the tabs on their driver transistor. Grounding the tab fires the coil. The transistor operates that way too. When the transistor turns on, it grounds the coil.
 
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Aha! God I´m stupid. So I should ground the Q24/Q26 Tab to the ground strap? Anywhere on any ground strap?
 
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It's not stupid...It's just learning how these circuits work. As for the ground. You are looking for a 'circuit' ground. That is the ground used by the board you are working on. It is not the building ground or power line ground. The + v 32 volts is above circuit ground coming from power supply. So look for a good ground connection on the boards. I don't know where exactly that is on your game. I look for an obviously marked test ground or connections that go to the large ground traces that surround the board. The ground wire that returns power from gadgets running all around under the playfield is can be a good choice too(there is a chance that ground is not referenced to the same ground so stick with the board you are working on) . Touching the tab of Q24,26 to the proper ground should fire the coil. This does not turn the transistor on. This test will prove the coil,coil circuit connections are working and power is on in the circuit. I guess you know to be very careful while poking around shorting things to ground. This is a tad crude way to find things. Sensing the +32v above ground, with a meter, is getting to those collector tabs is almost as revealing.
 
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When grounding the transistors the coils fire!!
Does this mean all cables and diodes to the coils are ok?
What now? Change the transistors?

Thanks / Filip =) =)!
 
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Those coils are powered by a 'Darlington Pair' of back to front transistors driven by logic level outputs. The 5 volt level logic delivers a voltage to transistors. That voltage represents either one or zero. It is interesting that a draw back of the darlington pair is it needs twice the voltage to turn it full on. That makes it a good choice for switching power on with logical "one" voltage of +3.1 V or so.

You can remove the transistor from circuit and check it proper diode like conductivity with your ohm meter. Or look for those trigger signals. But a DVM is not a good instrument to detect short logic level pulses(it misses them). An oscilloscope is probably best. There are logic probes of all sorts. I imagine a low current LED or maybe two in series(+resistor) would reveal logic pulses making it to the bases of those coil controlling transistors.
 
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Solution
Problem solved:
The Emitter-legs on the two transistors had no contact to the ground because the "ground-line" on the CPU-card was broken. I soldered them to the next transistors emitter-leg and then it worked. Not a perfect fix but it works for now.
Thanks alot to Coil_smoke. I hope to get your help the next time I´m having trouble! :) :)!
 
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