Pin*Bot Pinball Machine




Introduction
This machine was posted for sale on RGP, it was at a low price and it was close enough that I decided to purchase it.  It is one in a series of three machines (Pinbot, Jackbot and Bride of Pinbot).

Repair of the electronics
There were some minor defects with the electronics.  Here is how they were repaired:
  1. Missing 'g' segment on two-digit credit display.  This was repaired by finding a broken trace on the display's board.
  2. Intermittent boot.  Found a crack in resistor pack SR8.  It has several key pull-ups including the SW1 and SW2 self-test circuits. This led to non-boot at times. After some tests with my CPU tester, this problem became apparent.  I also replaced C30 (a 22 uF capacitor in the power-on reset circuit) as it measured around 3uF.
  3. Hum on startup.  The audio would have a hum on startup, and go away after 2-3 minutes.  I tracked this down to a bad C8 on the power supply board (47 uF).  The main bridge rectifier on this board was also bad.  The problems may have also contributed to the intermittent boot ups.  More details here.
With these repairs, Pinbot's electronics were now completely functioning.  The machine is fun to play with its ball-lock visor and wrap around ramp to the bagatelle on the right. 

Repairing a broken plastic
A commonly broken item on this machine is the plastic to the left of the ball visor.  Before restoring the playfield, I decided to see if I could make my own reproduction.


This is the site of the repair.  This plastic is commonly broken.

I had originally thought that this plastic was a small piece.  My plan was to simply replace it entirely.  However, when I disassembled the top of the playfield, I realized that this plastic was very large, and spanned the ball lock.  Since it is not practical for me to build such a large piece, and I did not want to cut the plastic in half, I had little choice but to just replace the small part that was missing.


Color was matched by using a color wheel.  Here you see that the plastic is much
larger than just the long part next to the visor.

I found a scan of this plastic on ballsofsteel.net.  I cleaned up the image by removing blemishes and making the colors solid.  I then printed the first test print on glossy photo paper with a color wheel.  That allowed me to calibrate and color match.  The next important part is to figure out what to print on.  I tried a variety of substrates (waterslide paper, clear transparency plastic, translucent paper, glossy photo paper, etc).  I needed to match the translucence of the original plastic (when backlit), and also how it looks under ambient light (front lit).  In the end I found that, surprisingly, ordinary white paper produced the best look.  Thicker paper blocked too much light, and painting a clear film white produced too many brush strokes or also blocked too much light.


A material was needed that filters the light in the same way as the white paint
layer in the back of the plastic.  Here you see the new piece backlit,
and the match is quite close.

So the color-corrected image was simply printed on plain white paper, and then bonded on some polished cut Lexan plastic.  The glue used was 467MP transfer adhesive (sample courtesy of Bryan Kelly) .  The results were very good.  When backlite (above image), the amount of light blocking matched quite closely with the original plastic.  Also, when lit with ambient light such as from the GI circuits, the match was very close.  Be sure to rub down firmly to remove the tiny air bubbles under the glue.


Same two items front lit.  With the bright flash of the camera, the new piece looks
lighter, but it looks rather close under ambient light.

The original plastic was trimmed back to a black line, and the new piece was mounted with a clear protector underneath.  In addition to preventing ball hits, this protector also serves as a means to line up the original plastic with the new one.


Two views of the restored area.  Note the clear protector to prevent future ball hits.
Gotta touch up that playfield some time.....

Links to other plastic repair and reproduction sites below.

Ramp Repair
Another commonly broken part on this machine is the mounting tab of the ramp.  Since it is exposed, ball hits tend to break this tab off.


Before repair.  Tab is missing.

The tab was repaired by cutting out a small piece of clear Lexan.  The bottom of the existing tab and the new piece were sanded rough.  These were then cleaned with alcohol.  Then the new tab was epoxied under the existing tab.  I then prepared a tape dam all the way around the tab and dripped in more epoxy to replace the missing plastic.  This technique produced a flat square edge, matching the original ramp's appearance.  After it is all cured, the ramp was test fitted into the machine, and the mounting hole marked and drilled while the tab is still transparent.  Finally, the top face of the tab is sanded flat, and painted with acrylic paint.  I found a color among my collection that matches the color of the ramp very closely.  It is "Folk Art # 719 Plaid Blue Ribbon".


Tab repaired and painted.

See also:
Space Shuttle Ramp Repair
Indiana Jones Ruins Repair

Ball lock repair
The two ball locks in the back of the playfield performed poorly mainly due to damage at their entrance.  To begin with, hard shots from the flippers would very often cause frustrating bounce-outs.  In addition, once a ball was locked, the depression in the playfield cause by the wear would sometimes trap a second ball, and you had to nudge the machine to get the ball out.  Finally, the ball eject mechanisms would sometimes get stuck in the 'up' position, and it would not allow the ball to enter the lock.


The ball lock area before repair.  Both locks looked like this.  The wear was
so bad that the ball lock could sometimes hold two balls in each lock.

The repair was done by putting a small strip of duct tape in the opening of the ball trap to form a tape dam.  I then filled the worn area with epoxy.  Once cured, I used a small round file to recreate the bevel at the lip of the ball lock.  I then finished the area by painting it back in.  I was able to obtain a near-perfect paint mix by using the right proportions of pastel green, plaid white, and brown.  The match is indistinguishable by naked eye, but you can see a difference due to the bright flash in the photo below.

The colors used were: Folk Art #619 Poetry Green, Delta Ceramcoat Antique White, Crafter's Edition #72029 Spice Brown.


The repaired ball locks.  The touched up area color is perfect match with the naked eye. 
By the light of the flash, one can see a difference.

In addition to the repaired playfield, I also raised the deflector tab about 1/4" above the playfield.  This extra room, allows the ball more space to drop down into the ball lock.  The result was very impressive.  I can now hit the ball lock with a full force flipper shot, and it did not bounce out in three test games.  Prior to that, I had tried applying some of the same foam used on the IJ and MM on the deflector tab, but that did not work as well.



Links

Log
March 31 - 2007, Purchased machine from Mike Singer for $600.
April 16 - 2007, All of the electronics issues resolved, and Pinbot plays great.
May 19 - 2007, Rebuild plastic.
May 20 - 2007, Fixed ramp tab.
June 1 - 2007, Repaired ball locks.  RGP discussion.
Feb 23 - 2008, Sold machine for $1000.

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(c) 2007 Edward Cheung, all rights reserved.