VFD displays
Bugs and setbacks
When engineers do anything!
Design errors
As described in the article dedicated to VFD technology, four elements must be taken into account for the operation of these displays.
- The grids of each digit
- The segments
- The filament
- The dispersion grid
The development of VFD displays was not without some mistakes on the part of Rockwell-Gottlieb engineers. We can see that from the start, they did not fully master the subject.
Thus, for the very first SYSTEM-1, two models of 6-digit displays were produced!
The first, PB00-D140-001 uses Sprague UDN6118A circuits. The second, PB00-D140-011 uses Dionics DI513 circuits. It is easily recognizable because it needs resistor networks on its inputs and outputs. Very quickly, this model will be abandoned in favor of the one using the classic UDN6118A.
The PB00-D140-001 model will later be reused for the SYSTEM-80 and the "bonus" display of the SYSTEM-80A.
Confusion in diagrams
The layout of the six-digit display, as well as that of the seven-digit display, contains a gross and confusing error. There is indeed mention of "GRID". But this is completely FALSE!
This has nothing to do with the individual grid of each figure because it is actually the "dispersion grid"... which is not the same thing at all!
Note here, that the location shown on the diagram also corresponds to the physical location of the "dispersion grid" claw on the displays. For Futaba 6-JS-01 (6 digits) it is located in the center. For Futaba 7-JS-03Z (7 digits) it is located on the right side.
In both cases, the resistor R1 (10 KΩ 1/2W) has not been forgotten, and connects the "dispersion grid" well to a potential.
But if, concerning the six and seven digit displays, the engineers have taken into account the four elements to be controlled, one wonders then why, it was not the same for the four-digit display!!!
4-digit display bug
On the SYSTEM-1, the four-digit displays PB00-D150 are recognizable because one of the circuits is mounted vertically.
These displays will also be used on the first SYSTEM-80 (from the Panthera to the Pink-Panther) until the beginning of 1981.
From March 1981 and with the arrival of the "Mars God Of War", a new display (E-20927 or MA-115) will be used, this time with the three circuits mounted horizontally.
Futaba's 4-LT-11 tubes are originally intended for use on clocks.
In addition to the four digits, they can display a small star (grouped on the grid of the first digit) and the two separating dots (mounted on a separate grid).
These elements are not used on pinball machines, the pin corresponding to the star is soldered, but not connected to the printed circuit.
For the two separating points, there Gottlieb went further: the pin is squarely cut flush with the tube! It's silly, because there was no justification for cutting this pin like this.
This dirty habit of cutting the pins, will end up playing a bad trick on them, when they use NEC tubes for the seven-digit displays.
But the main problem is not there. There is much worse: if we look at the diagram, we see that the resistor to connect the dispersion grid is missing!
Indeed, this resistor has never been installed, neither on the PB00-D150, nor on the MA-115. The defect is not necessarily noticeable at first glance and it does not prevent the display from operating.
Gottlieb will eventually realize this error very late.
At the end of 1982, they will add the missing resistor, by soldering it to the back of the display.
The first pinball on which this modification was applied is "#675 - Striker".
From this date, all product displays will receive this "patch" and the documentation will be corrected (still with the misleading mention "GRID"!)
This specifies that the resistor is mounted on the rear face of the display. Until the end of production of the SYSTEM-80A, Gottlieb will not manufacture a new printed circuit to integrate this correction. Likewise, they will remain very discreet on the subject and this will not be the subject of any service bulletin.
The "forgotten" resistor bug affects all SYSTEM-1, SYSTEM-80 and a good part of SYSTEM-80A. It can be estimated that it affects around 90% of displays produced.
7-digit display bug
In order to overcome supply problems, Gottlieb also used tubes manufactured by NEC. They are easily recognized, because on the Futaba, the grid bearing the numbers is in the shape of an inclined tapestry, while on the NEC, it is in the shape of a perfectly straight rectangle.
The NEC tubes used carry the reference FIP7B25A and have some differences from the Futaba.
Usually the filament is connected on the pins at the ends of the tube. At Futaba, six-digit tubes use only one pin, while seven-digit tubes use two (always placed at the ends). The printed circuits are therefore provided accordingly and adapted according to the tube model.
The NEC FIP7B25A tubes have the particularity of using not two, but three pins at the ends for the filament. To make it fit without changing the printed circuit, Gottlieb simply cut off the extra pins, and only kept two like on the Futaba.
We can see on the right side, that the resistance R1 provided in principle for the dispersion grid, always arrives on the third pin (from the right). Gottlieb absolutely did not change the circuit board to mount these NEC tubes.
Yes, but... NEC tubes have another major difference compared to Futaba.
On these tubes, the claw of the dispersion grid is not mounted on the right, but in the center!
And there, Gottlieb made very strong, because the central pin of the tube was cut!!!
Not only is the dispersion grid not connected, but there is also a pin connected to resistor R1 that shouldn't be .
Fortunately, this does not affect the operation of the display, but it is still not correct. They really messed up and the worst thing is that it's hard to fix, since the pin was cut.
