Stripping and cleaning
I will be doing a complete renovation of this playfield, including stripping all the parts above the playfield, cleaning, touch up painting, clearcoating, polishing all the parts, applying NOS target decals, and restoring the parts.  Finally a new rubber kit will be installed.  This kit was included with the purchase of the machine.

In the original condition, the playfield was rather dirty, and had lots of ball swirls.  These cleaned up well with the Magic Eraser and alcohol.  Then came the touchups.  These were in some small areas.  For example, the area in front of the left sling had some paint missing.  I mixed some acrylics and obtained  a good match.  The touchups were applied with the end of a toothpick for the large areas, and a sewing needle for the really fine work.  For example, the "20" insert was touched up, but I think it looks very original.

In the initial set of games that we played, we noticed that the ball would rumble audibly across the playfield.  We compared this to the Space Shuttle, which I had also clearcoated, where you cannot hear the ball at all.  On that machine, the ball seems to float over the playfield.  It became apparent to me that I had to clearcoat the Flash playfield also.  Another problem was that some inserts had bowed downwards over the years.  When the ball rolls slowly, it could sometimes get stuck in one.  One common way to repair this is to fill them in with water-thin super glue, but I decided to use clearcoat instead.

For this project, I decided to try brushing on the clear instead of spraying it.  I went to the local Lowe's and found that they sold Varathane in one gallon containers only ($46).  They also had another product that was similar to Varathane.  It is the Olympic Polyurethane in half pint cans ($6).  This product has the following in common with Varathane:

1. Available in gloss finish.
2. Water based.
3. Does not yellow over time.
4. In liquid form, the product is milky white.
5. Alcohol disolves this product.
   

The procedure I found worked the best was:

1. Use a cool area to slow down the drying as much as possible.  This allows the clear more time to flow.
2. Plug all the holes in the playfield with foam plugs.  Make sure they do not stick up above the playfield.  If they do, small amounts will be dispersed when you use sandpaper.
   
3. Use a new foam brush for each layer of clear.
4. Brush a large portion of the playfield with quick strokes to wet the area.
5. Pour the clearcoat on the wet area to form a thick film, use the brush to push the clear around.  Try and achieve a consistent amount of milky whiteness over the playfield to have a consistent layer of clear.  You only have a few minutes to do this.  After that, the clear will start to solidfy, so do not touch at that point.
   
6. After several hours drying, and a film has formed, a fan can be used to increase air circulation to speed up drying (I did).
7. Once completely dry, use 400 grit paper between clearcoat layers to smooth out imperfections.  It will take about 24 hours to dry.
   
8. When done, buff with an random orbit buffer and rubbing compound, then finish with Novus 2 and carnauba wax.
   

Although the finish does look nice, and enhances the contrast of the colors (black is blacker, colors are brighter), the result is not as flat as the Space Shuttle's finish.  Spraying directs material at the playfield in a large diffuse pattern, which prevents local high spots.  Locations where the clear is not thick enough can be reapplied with a quick burst of spray.  In the case of brushing, one can only pour a small local mound of clear on places that need more. 

So in the end, I thought it was a worthwhile experiment, but I will probably spray the next time.

One area that was especially challenging were the rollover insert switches.  I decided to remove the star-shaped portion, tape over the hole, and then clearcoat them by hand using a small brush.  After a few coats, I cleaned the star with alcohol and a toothbrush and reinserted it into the playfield.

Reassembly

Back to the Electronics
Although the CPU and associated electronics were working, there were still reliability problems.  After about half an hour of play or use, the CPU would lock up.  To get it to work again, I simply had to press down on the ROMs in their sockets.  Clay recommends upgrading from System 4 to System 6 ROMs.  This required the replacement of the flipper ROMs (U17 and U20 also).  Since a different socket is used for the main code, I did not have to use  the problematic sockets.  After installation of the new ROMs, there were no resets after several hours of game play and letting the machine run in attract mode.

Sealing and touching up the backglass
Close inspection of the back of the glass shows that the missing paint was mainly due to the scraping of the score glasses.  Thus the paint was not flaking due to age.  This meant I could safely clean the back with a paper towel dampened with alcohol.  I took off lots of dirt, but no detectable paint.  Afterwards, I masked the score windows with Vaseline Petroleum Jelly, and sealed the backglass with Krylon's Triple Thick, per Clay's site.  I started with thin coats initially, and then heavier coats later as I was afraid the solvent in the Triple Thick would affect the backglass.  After it was dry, I cleaned up the score window, and was pleased with the results.

The next step was to touch up the backglass with acrylic paints.  Mixing this paint can be difficult, and after several hours, settled on the color.  The dark blue could have been matched better, but the light blue was very good match.

To prevent future damage of this type, I covered the sharp corners of the score glass with a few layers of black electrical tape.  I then removed a few lamps behind the backglass to reduce the overall temperature for less thermal stress on the backglass. 

Note that the above touchup method with acrylics will only work for the opaque areas of the backglass.  Acrylic paint is too thick to be translucent.  I realized that a thinner and darker (more saturated) ink was needed.  I decided to experiment with thinning out the acrylic with water, and achieved good results.  The basic process is to find the darkest and brightest version of the color that you can obtain.  Then thin the acrylic with five parts water.  Apply first to some transparent plastic to get the feel for the thickness needed.  Beware that the paint will be very watery and runny.  After it dries, hold it up to the lit backglass to see how much light transmits through.  Reduce the puddle of paint if it is too dark.  By doing this, I was also able to touchup the translucent areas.  Since the paint is so dark, it reflects the right amount of light when the machine is off.  When the lights are on, the paint is thin enough to pass about the right amount of light and color.