Cleaning the dropdown - part 1

On the Star Trip pinball table, one of the dropdown targetswill not drop. When the ball hits it, it will usually not drop at all, sometimes it will slowly sink halfway or if I push it it will go down where it is supposed to. The other two work just fine so it was definitely a problem with the one unit.

I thought it might be a bad spring, not strong enough to pull it down and since the others were working this seemed a perfect project as I could compare the good ones with the bad one.

So I set about pulling the mechanism off the table and finding out what was wrong:

At first check, all looked ok. Nothing was obviously broken or bent out of shape.

After unsoldering the connections, I took it apart:

 

It wasn't until I had it all apart and moved things around that I found what I think was the problem. The spring seemed ok and was about the same tension as the other springs, but the whole mechanism was incredibly dirty!

This is the plunger that supposedly slides easily through the solenoid coil, it should be a shiny smooth polished rod:

My polishing tumbler is still on order, so I sprayed everything with engine degreaser and wiped it all down, then reassembled it.

It seemed to work smoother and I eagerly put it back on the table, soldered the leads back on and fired up the table....

Only to have the fuse blow out immediately!

I checked the solder connections, everything looks good....but now it doesn't work...sigh

(more to come)

A few problems with the Harlem Globetrotters

I have done an initial check of the Harlem Globetrotters. It is in pretty poor shape:

The box itself looks to have typical old-wood problem, corners are splintering - but at least it seem solid

The electronics don't work at all. When it is turned on a few lights come on and thats it, no sound, no movement, no nothing.

The playfield is also in pretty poor shape - in addition to the missing graphics in heavy-wear areas there are some more serious issues:

This shows a representative piece of the playfield, much of the paint/graphics are cracked on the wood.

The plastic isn't much better:

The edges are scalloped, cracks around the mounting bolts and even warped sagging pieces - did it sit in the sun or under a heat lamp?


Other problems are around the bumpers, missing and bent ones are in several places:

This one is a bit tough to see but the support pin in the center is bent inward and pushing on the plastic

Also, almost every single slot/hole in the table has a worn out spot where the ball went - this table has seen a LOT of use!


On the positive side, the backglass is in great shape!

it is virtually perfect with only the beginning of paint coming off in the corners around the scoring boxes.

So this one is going to be a lot of work.....

Success (at last)

Success at last!

After finally (2 months in!) discovering that there was another fuse - cleverly hidden by the Game Plan designers under the playfield rather than where all the other fuses were:

Only to discover it blows immediately when powered on.

Then spending all night carefully unsoldering each and every coil (and diode) and testing them all good.

Finally turning it back on (with all of the coils still unconnected) and the fuse blowing AGAIN!

I posted my results and Viperrwk calmly pointed out that there was one more coil.

Down in the cabinet, underneath the ball that rolls back and forth to prevent tipping the cabinet, there is a coil that fires when the match happens - that big "knock on wood" sound you hear when you are lucky enough to get a free play.

I located the coil and unsoldered it. It does not test as good as the others (2.8 ohm instead of 5.5 or 8)

With ALL the coils now disconnected, I put a new fuse in....crossed my fingers...and turned it on.

The fuse did NOT blow!

woohoo, real progress at last.

Of course it could be that it isn't blowing because there was now nothing at all on the circuit. So I connected three coils, crossed my fingers and tried again.

the fuse did not blow!

and, the coils worked. In diagnostic mode they fire one after another and each one I had reconnected worked just fine.

It appears I have real success. I may be able to put it back together and start playing it!

A green world

I just went to see Mad Max in the theaters yesterday. It was quite the action-packed movie!

One thing that really struck me as I walked my dog at the park was how green and beautiful everything is - the movie really showed how difficult and horrible the world would be if it is destroyed by ignorance and greed.

I am quite sure that was not the reaction the writers, producers and directors were anticipating, but it sure made me stop and appreciate just how beautiful our green world really is.

Tiny progress

A quick post to report a tiny amount of progress. I finally discovered that mounted to the underside of the playing table on the star trip pinball is another fuse!

And there was no fuse in the holder. Putting a fuse in, it blew immediately but this is a much different problem then thinking I had a logic problem on the driver board. So a tiny amount of progress!

Star Trip Main Processing Board testing (pics)

While I wait for answers about my questions on the AC leakage from the power supply capacitor. I thought I would turn my attention to the main processing board. I just got a new testing tool, an Atlas DCA55 which says it is easy to use. Just connect it and it figures everything out.

I tried checking the diodes but it is unable to test them while in the board. I'm not ready to unsolder every component and check it yet, so I turned my attention to the transistors.

I checked the first one, and it shows "transistor" and that all is good!

The second one says it is not a transistor but is in fact a diode network...hmmm

with the third one we are back to a transistor again and it is ok.

It thinks the last one is a LED or diode...bizarre

According to the schematic and parts list the bottom 3 are supposed to be the same transistor and the top one is a slightly different transistor. So I guess I will have to unsolder #2 and #4 from the board and check them isolated, it is possible the board connections are messing up the reading.

edit: the manual specifically says it cannot check transistors while in circuit....before i start pulling things off the board at random i think i will look around some more.

While checking the transistors, I noticed the board has a lot of corrosion:

Apparently this is pretty common as the battery they used to store the high scores leaked acid vapors over the years.

After looking around some more it is apparent this board has already been repaired once:

the battery has been removed and the area around it looks to have been sanded down (presumably to remove the corrosion) and even a wire was soldered in where a board trace had failed. So hopefully all of those fixes are still good!

Power supply woes continue

after reading some more about the Star Trip power supply, one of the suggestions was to check the large 11,000 mfd capacitor for AC leakage. According to the article there shouldn't be more than 0.2 volts AC.

After connecting up the multimeter, mine reads 30 volts!

 

So either I am doing it completely wrong (very possible!) or that capacitor is completely destroyed (very possible!)

Off to post more questions...at least I am learning about electronics

A new table - harlem globetrotters

Through the generosity of a friend, I was able to purchase a 1987 Harlem Globetrotters pinball table. The table glass is in excellent shape, the table surface in medium shape with some graphics worn off. The electronics currently do not work, when I power it on a few lights come on and thats it. No sound, no movement, no bumpers.

Another project!

Testing the power supply

After purchasing new probe tips for my multimeter I tested the power supply at the connector to the solenoid driver.

I am getting power where it is supposed to be but the voltages are not right:

when I check pins 4 and 1,2 ... I get 12v which matches the circuit diagram
pins 4 and 12 give 33vac instead of 24
pins 4 and 13 give 27v instead of 24
pins 4 and 15 give 5v. Matching circuit diagram

So its off to the forums to ask if this is the problem or no big deal and it is within tolerances

Power Supply Voltages

After tearing out the power supply (P/S) and discovering that it was mounted on a piece of plywood I did some more asking around.

It turns out that the very first generation of these cocktail machines used a handmade P/S, so there isn't anything inherently wrong with my unit.

I was able to get a circuit diagram and parts layout that showed what the fuse sizes were and the expected voltages across them. So I put the P/S back into the unit and checked power.

4th from the bottom was supposed to be 12V, the meter confirmed it was.

3rd from the bottom was supposed to be 7V, my meter shows 3.5V instead.

 2nd from the bottom was supposed to be 28V. I've got the meter on 25V range and it is showing only 14V.

So I have something actually wrong with the power supply circuitry, not too surprising considering it is almost 40 years old, but it complicates things quite a bit. Perhaps this is the only problem with the table though and once this is fixed everything else will work!