Gottlieb System 1 (Close Encounters)

Sirius

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Just an update and a question, I replaced all of the connectors on the MPU and driver board. Added ground wires and led's. Replaced 3 transistors which control 3 lights and got 2 out of 3 working. Replaced misc bulbs and made some adjustments to the roto wheel. Replaced the caps on the PS. It still needs some work because it will sometimes seem to lock up and not spin, or perhaps the solenoid is getting weak? The other problem is with the displays. Players 1 and 2 and the credit/ball display will not display the #9. They display the #1 instead.

According to the pin repair guide, and I quote... "There is also a circuit that makes number "1" to be shown with an extra eighth segment in the middle of the digit instead of the usual two right side segments. This is done with chips Z13/Z14/Z15 on the CPU board. Suspect those if there are problems in showing number "1".

So I have to assume that if it displays the #1, the circuit is working correctly? The other statement in the guide says...

"The displays are controlled by CPU spider chip U6 and a few TTL chips. The 7-segment decoders Z16,Z17 (7448) control the digits for the displays. If the displayed numbers look strange then one of these chips is probably bad. Chip Z16 controls player 1/2 displays and the credit/ball display, while Z17 handles player 3/4 displays".

So, would I be correct in assuming that Z16 is the problem? I need to order the TTL's and their a bit pricy, so I'd like to get it right before attacking the board with a soldering iron. Any suggestions would be appreciated. This pin really turned out to be a good buy for $200 and I'm glad I decided to take a look at it. Although I really feel that Gottlieb dropped the ball when is comes to the sound.
 

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Testing TTL's

Thank you for the advice. While the link you provided requires an account, I did google "testing ttl chips" and came up with a few links on doing it. I'll try testing the chip in question and see. I suppose I can at least compare the readings between Z16 and Z17 to see if there's a difference. Thanks much.
 
I tested both z16 and z17 and they both test the same? From what I can make of the test they both seem good. On both chips I have continuity on pins 3 and 5 (which according to the schematics seems correct) and all other pins test .500 or better.
 
In my endeavor to teach myself how to troubleshoot TTL's. I did discover the reason the 3rd bulb wont work as mentioned in my first post...it's a bad 74175 ic. Now if only I had one! Dern it! So this leads me to believe that Z16 is good? Perhaps a bad resistor? I'll start checking those...
 
Ok, so I found what I thought was a bad resistor. It was supposed to read 2.7 ohms. The reading I was getting was about .62, I figured it was bad so I replaced it. Guess what...I got the same exact reading after I soldered in a new 2.7 ohm. I traced the solder traces back to the ttl 7417 (Z11) that works with Z16. I tested the ttl on that pin (#8) and I only get a reading of about .195 on the other 7417 (Z17) that controls players 3/4 I get a reading of about 1.234? Could this be the reason it displays the #1 instead of #9 on the displays? I'm just not sure of how low is low and how high is high for ttl's.
 
Solved!

Problem solved...with the strange reading I was getting from the adjacent resistor and the low reading I was getting on pin 8 of the 7417, I knew that had to be the problem. I soldered in a new 7417 and sure enough, It now displays 9's on both player 1 and player 2 as well as the credit/ball display. I guess my TTL problem solving skills are improving.
 

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