RESET for driver board
Remove unwanted activation of the coils and the
unpleasant noise ("Schlank") when starting the pinball machine.
For Gottlieb SYSTEM 80, 80A et 80B.
This article describes an assembly that we install on all driver boards of our Gottlieb SYSTEM 80/80A/80B pinball machines. Unlike other achievements presented on this site, we are not the authors and it is not really no more new. We simply explain here, in detail, the principle of operation and one of the possibities of realization.
Origin and problem of the "Schlank"
The problem exists on all SYSTEM 80/80A/80B series pinball machines because there is a design error on the driver board. According to the pinball machines, the phenomenon is more or less marked and is more noticeable on complex models.
The "SCHLANK" is the noise made by the coils when they are activated when the pinball is started. It's unpleasant, but most importantly, this is abnormal behavior, as there is no reason to activate these coils when turning on the pinball machine. In addition to the unpleasant noise, the duration of activation is excessive (well above the normal duration used during the game).
The origin of the problem goes back to the fact that, to overcome the shortage of the number of outputs that can control coils (9 maximum on the CPU board), the designers used "lamp" outputs.
From the beginning, this lack of exits was felt, since three small relays are systematically used on the outputs lamps 0, 1 and 2 (Q relay of "Game Over", relay T of "Tilt" and the lock of the slots of coiners).
Subsequently, other lamp outputs (usually L12 to L19) were used for more powerful coils (ejector, ramps, diverters). The problem then became more obvious, because what was tolerable for the three small relays (hidden under the tray and can work permanently), was no longer at all for elements mounted on the playfield.
Default and solution
The inadvertent activation of the outputs of the driver board at startup, comes from the fact that it uses 74175 flip-flop circuits. By definition, the original state of a flip-flop is undefined. This is the case of the 74175 and to compensate for this unstable state, a CLEAR entry (CL) is available to reset the flip-flop.
Unfortunately, this entry is not used on driver cards because it was simply connected to +.
To control lamps, it is not very important. Indeed, the CPU board regularly scans all 74175 circuits and sends them commands to enable or disable the outputs. So once the CPU board is started, the status of the lamps or solenoids returns to normal operation.
On the other hand, when solenoids are connected to these outputs, they are in an unstable state until the CPU board is fully started. And since this start is not instantaneous, this latency is sufficient to trigger the coils.
Technically, the solution is simple: just install a RESET circuit on 74175.
If you want to be purist, you should install this circuit for all 74175 board. But in practice, we can limit ourselves to three circuits, because the coils are always installed on the groups L0..L3 and L12..L19. A glance at the diagram shows that only circuits Z1, Z4 and Z5 are concerned.
The implementation will be greatly facilitated by the use of "ECONO RESET" circuits, of the DALLAS DS1233 or MICROCHIP MCP100 type. These circuits are easily found in conventional packages (TO-92). We can not be simpler with only three wires: two for the power supply and one for the RESET signal.
Any version of the DS1233 (-5, -10 or -15) or the MCP100 can be used.
Special case of Z3:
On the first SYSTEM80, the L8 and L9 lamps were also used to drive coils. For those, the modification will also have to be done for the Z3 circuit. This is particularly the case for pinballs:
- Pink Panther
- Black Hole
Although this modification is not essential for the other models, we advise to do it systematically.
Start by locating circuits Z1, Z4 and Z5 on the driver board.
Identify pin 1, where the RESET must be connected.
In the same way, locate the circuits Z1, Z4 and Z4 on the track side.
Identify pin 1 on the track side. This time, it is on the other side since the board is returned. Nothing difficult, because it is indicated on the printed circuit board.
For the wiring we will use very fine wire, like "wrapping". The only component to add will be the ECONORESET.
Here we will use a MCP100 TO-92 package. Pin 1 is the RESET output, Pin 2 receives the + power supply, and 3 is the ground.
Phase 1 : isolation of pins 1
Warning: The tricky part starts here, because you have to cut some tracks. The cleanest way is to do it with a mini drill (DREMEL) equipped with a cutting disc. Being cautious and going slowly, it goes easy.
Start by cutting the track to isolate pin 1 from Z5.
This is the simplest because there is room and the cut is straight.
If you want to change also Z3, it's easy because the circuit is right next to Z5.
The cut to be made is straight, similar to that of Z5.
Continue with Z4. Here it's a little more complicated, because there is an oblique cut and the other is close to another track. Note that these cuts also isolate the pin 16 power circuit. It will therefore be necessary to think of restoring it afterwards.
We then go to Z1, with a straight cut at the big track. Again, we isolate a line of + that we will have to restore after.
We end the isolation of pin 1 of Z1, making a cut, but this time, on the components side. It is a little tricky to do, but once finished we can put away the mini drill.
Phase 2: Restoring power supplies +
Since some circuits have been cut off, it must now be restored by soldering a few wires. Start by scraping the end of the wide track near Z1, to remove the protective varnish and have a nice weld spot there.
Solder one, or better, two wires to the nearby + line.
Do the same for the Z4 power line that was cut. Here, only one thread will be enough.
Phase 3: Connecting pins 1 to the MCP100 RESET
It is now necessary to connect by a wire, all the pins 1 circuits Z1, Z4, Z5. We can start by connecting Z4 and Z5. Then pull a wire to Z1.
In the case where one has treated Z3, it is the same, one will pass the wire by the pin 1 of this circuit.
We weld on pin 1 of Z1, and we prepare a wire to connect the MCP100. Fold the legs of the latter with forceps, to weld directly near Z1. We now have a RESET wire connecting all the pins 1 of Z1, Z4 and Z5.
We finish by welding the RESET wire on the leg 1 of the MCP100. The leg 2 will be welded on the + and the leg 3 on the mass.
That's it, it's over. We can fix the wires and protect the MCP100 by a few points of hot glue.
And do the same, if we connected Z3.