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Solenoid issue on my Black Knight 2000 - can anyone help a newbie?

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ffollim

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Hi all, I'm a relative newbie to the Pinball world although I have some electronics experience in repairing vintage video arcade machines. I bought my first pin - a Black Knight 2000 that I have been busy restoring. It has worked flawlessly until the other day when the ball popper solenoid stopped working.

I have checked a number of things, including continuity on both the switch and the solenoid wires to CPU and Aux Power boards - all OK, voltages on the solenoid both terminals showing 72v, a resistance test on the solenoid shows 4.5 Ohms which seems OK. The switch when actuated registers to the game correctly, so seems to be OK, and it disengages correctly when the ball is not present. All fuses are OK also, although F4 on the Aux Power did blow a few days ago, so I replaced it (5A slow blow), and all seemed fine until the popper stopped working.

Is there an easy way to test the Q2 Transistor and D39 diode to see if either of them are faulty? I saw Joe's Arcade test it by connecting a lead to ground then touching the other end to the tab of the transistor - is that something that you would recommend / work?

Many thanks,
Matt
 
Hello, Matt,

The schematic for the Aux Power board in the manual shows F4 on the Aux Power board as being 2-1/2 Amps rather than 5, I'm wondering how/if that's become over-rated. Earlier in the manual, Fuse Listing on page 35 suggests 5A for fuses 2C, 3 & 4 of Aux Power, but the Power Wiring diagram on Page 92 contradicts this for fuse 4 at least; the input to the 50v rectifier is 4A, with the three outputs being 2A for each sides flipper(s), and 2.5A for 50v solenoids, extended or not. Fwiw, the p/wiring diagram does have the Aux Power board labelled '563' indicating Black Knight 2000

One thing with a solenoid 'extended' like this is that the circuit's used for two loads; 06A is the ball popper, and 06C (driven when the extender relay is On) is listed as 'LPF Flasher'. Lower Playfield, according to the diagram, between the U-loop and the ramp. Does that work? If so, the drive transistor(s) are probably alright.

The old faithful jumper wire to ground shows if a solenoid has power, if its winding is alright, and when used on the metal tab of the transistor shows if the return circuit back to the transistor is okay; it says nothing about the transistor itself. F'r instance, if the solenoid worked when grounded at the coil (make sure to ground the 'return' terminal, though)* but not at the transistor, the return would be broken somewhere between.

Q2 on the Aux Power is a '3rd stage' in the solenoid circuit, to allow a 50v coil to be used. It's operated in turn by a solenoid transistor circuit on the main Cpu/driver board, Q 23, Q 19 and chip U 19. As Asia suggests, if the solenoid works with Q 2's tab grounded, measure the various resistances across the transistor junctions, comparing readings with similar working ones. Manually switching a transistor while powered up is a little risky, especially reaching into a backbox.

* Williams had stopped placing tie-back diodes on most coils by 1989, so go by the wiring; the return will have a unique wire colour.
 
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Jay Walker said:
Hello, Matt,

The schematic for the Aux Power board in the manual shows F4 on the Aux Power board as being 2-1/2 Amps rather than 5, I'm wondering how/if that's become over-rated. Earlier in the manual, Fuse Listing on page 35 suggests 5A for fuses 2C, 3 & 4 of Aux Power, but the Power Wiring diagram on Page 92 contradicts this for fuse 4 at least; the input to the 50v rectifier is 4A, with the three outputs being 2A for each sides flipper(s), and 2.5A for 50v solenoids, extended or not. Fwiw, the p/wiring diagram does have the Aux Power board labelled '563' indicating Black Knight 2000

One thing with a solenoid 'extended' like this is that the circuit's used for two loads; 06A is the ball popper, and 06C (driven when the extender relay is On) is listed as 'LPF Flasher'. Lower Playfield, according to the diagram, between the U-loop and the ramp. Does that work? If so, the drive transistor(s) are probably alright.

The old faithful jumper wire to ground shows if a solenoid has power, if its winding is alright, and when used on the metal tab of the transistor shows if the return circuit back to the transistor is okay; it says nothing about the transistor itself. F'r instance, if the solenoid worked when grounded at the coil (make sure to ground the 'return' terminal, though)* but not at the transistor, the return would be broken somewhere between.

Q6 on the Aux Power is a '3rd stage' in the solenoid circuit, to allow a 50v coil to be used. It's operated in turn by a solenoid transistor circuit on the main Cpu/driver board, Q 23, Q 19 and chip U 19. As Asia suggests, if the solenoid works with Q 2's tab grounded, measure the various resistances across the transistor junctions, comparing readings with similar working ones. Manually switching a transistor while powered up is a little risky, especially reaching into a backbox.

* Williams had stopped placing tie-back diodes on most coils by 1989, so go by the wiring; the return will have a unique wire colour.
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Hello Jay, thanks for such a comprehensive and detailed reply.

I will have checked the manual and I can see what you mean about the contradictory documentation - it would be interesting to know what was fitted at factory. The fuse that I replaced was a 5A and looked original, but that might not be the case.

For the benefit of my head, you are saying:
So looking at the schematics for the Aux Power board, 06A is on circuit A and the LPF flasher 06C is on circuit C - both are switched via the relay which is fused by F4, and fed 50v via the BR2 rectifier. So what you are saying is that if I run the test on the LPF flasher at 06C and it works, then the transistor at Q2 should be OK. If it doesn't work then it is likely that transistor Q2 is to blame?

Re the Jumper wire test, the transistors used are TIP36C which I read do not work with the grounding test - is that correct, and if so is there an alternative i.e. grounding the corresponding transistors on the CPU board instead?

Many thanks,
Matt
 
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The extender relay selects which of the two loads is connected to the drive transistor, on the supply side. With the relay Off, its 'A' side contacts are closed, supplying either 25 or 50 volt power to the 'A' side circuits. With the relay On, the 'C' side is powered, but only with 25V, as flashbulbs don't use 50V. Each pair of circuits, eg. 6A & 6C, meet again at the group of large diodes near the relay, in this case D 39 & 40, to connect to Q2. Having the C-side load work but not the A-side could be a case of the A-side return being broken, such as a faulty coil winding (though it seems not this time) or a poor connection in 6A's return circuit, which passes through the Backbox Interconnect, or D 39 being open-circuit.

06C not working either leaves things much as before; Q2 may be open-circuit, or not being switched from the Cpu board. In turn, Q23 there may be bad, or not being switched (by Q 19).

To be frank, I hadn't thought if the grounding test worked with the TiP 36 transistors. They have the emitter connected to the return circuit, rather than the collector, as with the TiP 122 used on the Cpu/Driver. It depends which of them is also the metal tab for the TiP 36 - if it's the collector, which is already grounded, nothing would happen. Jumpering is more a check of the circuit back to the device, though. It's not really different from measuring for solenoid voltage along the return circuit.

The Tip 36 is the opposite polarity to the 122, with the circuit showing a resistor between emitter and base. That would pull the base up towards the level of the emitter, so I think grounding the Cpu transistor, and thus the base of Q2, ought to switch Q2. After all, the Cpu doesn't differentiate between solenoids with an extra stage and those without. And the transistor guide Asia's linked above reminds me that a PnP transistor, such as a TiP 36, is switched by a 'low' input on the base.
 
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Jay Walker said:
The extender relay selects which of the two loads is connected to the drive transistor, on the supply side. With the relay Off, its 'A' side contacts are closed, supplying either 25 or 50 volt power to the 'A' side circuits. With the relay On, the 'C' side is powered, but only with 25V, as flashbulbs don't use 50V. Each pair of circuits, eg. 6A & 6C, meet again at the group of large diodes near the relay, in this case D 39 & 40, to connect to Q2. Having the C-side load work but not the A-side could be a case of the A-side return being broken, such as a faulty coil winding (though it seems not this time) or a poor connection in 6A's return circuit, which passes through the Backbox Interconnect, or D 39 being open-circuit.

06C not working either leaves things much as before; Q2 may be open-circuit, or not being switched from the Cpu board. In turn, Q23 there may be bad, or not being switched (by Q 19).

To be frank, I hadn't thought if the grounding test worked with the TiP 36 transistors. They have the emitter connected to the return circuit, rather than the collector, as with the TiP 122 used on the Cpu/Driver. It depends which of them is also the metal tab for the TiP 36 - if it's the collector, which is already grounded, nothing would happen. Jumpering is more a check of the circuit back to the device, though. It's not really different from measuring for solenoid voltage along the return circuit.

The Tip 36 is the opposite polarity to the 122, with the circuit showing a resistor between emitter and base. That would pull the base up towards the level of the emitter, so I think grounding the Cpu transistor, and thus the base of Q2, ought to switch Q2. After all, the Cpu doesn't differentiate between solenoids with an extra stage and those without. And the transistor guide Asia's linked above reminds me that a PnP transistor, such as a TiP 36, is switched by a 'low' input on the base.
Click to expand...

Thank you once again. You are a great educator.

A bit of a development albeit a strange one.. I noticed that when powering up the machine, it would randomly crash / freeze e.g. when going into test mode and moving to the music test, or running the machine for a few minutes. I disconnected the J3 connector from the Aux power board and powered up the machine and the ball popper solenoid burst into life and popped the ball out. I had replaced the connector with a new molex recently and fully tested it and checked the wires were correct (I snipped them and moved them to the new connector one by one to be sure, and keyed the new connector). The old connector was black, but not melted. Continuity on the new connector is 100%.

I then powered off the machine, reconnected the J3 connector to the Aux Power board and ran through the solenoid tests - this time no crashing or freezing. When it got to the ball popper solenoid, it worked for the first few pulses, then made dull thumping noises as if it was trying to fire, but not fully. Every time the 05 06 'C side' test for the ramp flasher worked. I cycled through the tests again, and the second time the pall popper solenoid worked for a bit longer then got the dull thumping noises. The third time I cycled through and got to 05 06 'A side' for the ball popper, the solenoid fired continuously.

A bit of a strange one. I guess it could be a failing diode or transistor potentially? All wired connections seem pretty solid. The pattern seems to be that first time it fails, then with every subsequent cycle of the test, the less it fails and eventually fires the solenoid consistently.

First movie 5311 - working after a few goes
Second movie 5312 - fires once, then faint ‘thunks’ can be heard.

Matt
 

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The connector J3 on Aux Power is the solenoid switching from the Cpu board for what Williams called 'Special' solenoids, No's 17 to 22. I think Black Knight 2000 was the last game to use these as intended, i.e. the jet bumper switches switch the coil transistors almost directly, with the Cpu/program only finding about it from seeing the 'scoring' switch, after the event. Used earlier for slingshots too, this game saw the special switches make a return appearance, but only for the bumpers. The method's great for responsiveness, but was always vulnerable if an operating switch got stuck closed; the related solenoid would remain On, with the risk of overheating, damage to coil, transistor, traces, etc. I mention this due to the existing connector being 'black, but not melted'. A safeguard device, the One Shot Trigger, has been developed, which limits the coil driver pulse even if the switch remains closed.

The jet bumpers use the 25v solenoid power rather than 50v, and so don't have a 3rd stage added on the Aux Power. All the solenoid circuits are routed through though, to connect the tie-back diodes.

I'm not sure how J3 could affect the other solenoids, though. Sensibly, J1 is the switching for solenoids 1 to 8, J2 for No.s 9 to 16, and J3 for No.s 17 to 22.

The ball popper working and then going clunky may simply be it getting stuck, which the device can be prone to. In this case, it's tricky to see if it's dropped back properly, as it's hidden under the upper playfield. Without a proper coil stop, the collar on the plunger hits the coil bracket to serve as a stop, and the two can get worn.
 
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