It's the little things...

It's the little things...

By Dermot Tynan, Tuesday, October 8, 2019. Tags: flash rebuild, general illumination, hardware, LED lighting, pinball repair, playfield.

So now that the playfield has been stripped bare (on the under-side at least), cleaned, and prepped, we've been focusing our attention on the general illumination. So, a few thoughts on GI...

General illumination started out as a series of 6.3 volt incandescent bulbs mounted underneath the playfield but peeking through the business-side, to light it up. Most often, they appear under playfield plastics, lane guides, and anywhere light can be added where it isn't shining in the player's face.

The bulbs were generally wired in parallel, and powered by either an AC (in the case of electro-mechanical machines) or DC supply, direct from the transformer. While these provide a lot of light on the playfield (and it's wonderful to play a pinball machine in the dark, lit only by the playfield and backbox lighting), the bulbs burn out. We stock packs of ten replacement incandescent bulbs for older machines. A lot of owners have made the switch to LED lighting and it is possible to find direct-match LED lights which look identical to the old #44 bulbs, except they use far less power, and they last almost forever. We don't (currently) stock #44 LED bulbs but it's something we have been asked for, from time to time (Hint: if you'd like to buy LED bulbs from us, drop us a comment down below. Also mention the bulb number you'd like).

On "Flash", we want to replace all of the incandescent bulbs with LEDs but not using the same bayonet socket as the originals. Personally, I have had too many bad experiences with loose or faulty bayonet fittings, where the bulb works just fine until you put the back-glass back in, and all of a sudden, the light stops working! So the plan is to design a small circuit board which will fit over the playfield hole and channel light into the playfield. There are a few decisions to be made, here. First off, if you look at the photograph associated with this posting, you'll see two clear LEDs. The one on the left (with two wires) is a standard white LED and the one on the right is an RGB LED. What you won't see in the above picture is a surface-mount LED. The reason? The printed circuit board will mount to the underside of the playfield, which is around 14mm thick (17/32" for you non-metric types). Putting the light source underneath the playfield will create a "light tube" or spotlight effect so that rather than lighting the actual playfield surrounding the light, it will create a beam of white light pointing upwards.

I did consider something elaborate such as a clear plexiglass rod, which would create a so-called light pipe and diffuse the light, but that is just too involved. So I ruled out surface-mount. The LEDs will be through-hole and will stand proud of the PCB by 14mm. This should distribute the light in a 180 degree pattern around the LED, rather than just straight up. For the purposes of maximum disclosure, I should point out that the PCB is still at the design phase so only time will tell whether this is a better plan than just using a light pipe.

We will actually have two PCB designs. The other one will use the three-colour LEDs (as per the photograph) to light up the inserts. Well, it will in the case of inserts that lend themselves to multi-colour. The other piece of the puzzle, which is unique to Flash, is the flash itself. Those of you familiar with the playfield will know there is a large blue crescent in the middle which flashes a powerful blue at certain key times during game play. In fact, the mechanism for doing this was first developed for "Flash". The designers wanted a powerful strobe effect from the blue crescent, rather than just the usual insert lighting. This is tricky to do for a number of reasons. Firstly, the insert itself acts as an attenuation for the light. Secondly, it is hard to switch on an incandescent bulb in a hurry (no LEDs back then, remember?). The ingenious solution they devised, involved powering the lights with a very low amount of current, which would warm the filament but would not show through the insert. When they hit the lights with excessive power, they would immediately light up.

I won't have this particular issue. However, I do want a solid "kick" from the insert. I'd like it to be even stronger than the original, in fact. I know some purists will take issue with this, but the way I look at it, if Steve Ritchie had access to high power, surface-mount, white LEDs back then, he'd have used them. So I'll do that for him. The third PCB design will be unique to this particular Flash. It will drive three or four 2W surface-mount LEDs on a custom PCB, and that should produce the desired flash effect. One question might come to mind, straight away. If the flash on the playfield uses a blue insert, why use a white LED? Why not a blue LED? This is based on the idea that a playfield insert is actually a colour filter. A blue insert is opaque to red and green (well, most of the colours on the spectrum except blue). So by putting a white LED under the filter, I'm wasting all that red, yellow, green, orange (etc) light power. However, there are two reasons for choosing white LEDs. Firstly, high powered white LEDs are very plentiful. Much more so than blue. But also, I would need to exactly match the blue frequency of the LED with the filter frequency of the insert. Off by a few nano-metres, and your high powered blue LED won't register that much. By choosing white, I'm brute-forcing the filter. I am aiming for a solid-line distribution of colour, which means I'll maximise the throughput of the insert.

If time permits, I will see if I can make the board dual-purpose so those people who have existing "Flash" hardware can replace their incandescent setup with this new PCB. However, this will end up being a nice side-effect and I don't intend spending a lot of time modifying the design for this purpose.

In the case of the other two boards, however, I fully expect that they will be useful to other people who are rebuilding or reconditioning a playfield, so they'll be offered on the Tynan Pinball store once they're done.

The other thing which has been occupying our time here is that little piece of tinned brass in the photograph. It's called a terminal rivet, and it is part of our coil bobbin. We spent a lot of time trying to source these little doohickeys. Small and all as they are, they've caused a lot of trouble and strife. So, we've spent the last few weeks working on small stuff. Oh, and we did get a big shipment of coil bobbins in, so it'll soon be time to fire up the wiring monster. But more on that, later...

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