Repairing the Gremlin Trapshoot Wall Game
By, William Stephens
(clicking any picture in this article will bring up an enlarged version)
The procedures outlined in this article are very dangerous for the clumsy and inept among us. If you think this applies to you then read but don't do, you might kill yourself.
Picked this one up at an auction for a couple bucks. This game had been canibalized a bit but had good artwork and most of the parts. It was severly nicotine stained and cruddy but seems to be worth resurrection.
First things first, let's take some inventory. It had an original owners manual and being made back in 1976, it is very detailed, even to the point of it having descriptions, diagrams and operating theory on the individual chips on the circuit boards. It also has clear and easy to read schematics, theory of operations and troubleshooting information.
The game was missing the 27mhz transmitter and receiver, the fan? a line cord and that's about it for missing stuff. It didn't seem to have any broken parts with the exception of one of the draw latches that close the front window of the game.
I disassembled the front frame and removed the artwork panel, foam lightbezel panel and rear panel which I set aside so I could manhandle the main frame without scratching, cracking or breaking these irreplaceable parts. I lifted the game up onto my bench and began a detailed examination of the circuits and systems.
First thing was to hook up some AC power and see what we have. Upon power-up some of the plafield lights came on and there was some whistles and a continuous drone of the crowd noise... that's it, the coin input did not do anything and of course the play button did not work because the transmitter/receiver was missing.
Next, I removed the logic and p/s boards and ESR'ed the electrolytic capacitors which have never been replaced and as I thought, most of the lower value caps were toast! This would explain why the crowd noise just droned on. In the operation descriptions the crowd noise is normally ON and is shut off by a charge built up on an electrolytic capacitor. If the caps were dead, there was nothing to prevent the sound from playing on and on. Obviously re-capping the game is the first order of business.
In examining the logic board I noticed that several IC's had been either replaced or removed and re-inserted: U71, U51, U52, U53 and U28. There was circuit pad damage and even missing pads but the circuits seem to be rigged up correctly although quite sloppy. These chips all deal with the game counter circuit and receiver input, most of which are 7474 latches (flip-flops). I have found these chips to be a bit touchy in the past so I bet there is still a fatal problem in this circuit somewhere. I will delve into this after I have good caps all around.
Basically the cap kit I derived physically from the circuit boards does not exactly match with the parts lists so I will believe the physical boards over the possibly out of date documentation.
Gremlin - Trapshoot Logic Board
Model 5001A-DLC Trapshoot
1- 1uf 25V
1- 2.2uf 25V
1- 4.7uf 16V
3- 10uf 50V
3- 22uf 16V
1- 47uf 16V
2- 100uf 16V
Gremlin - Trapshoot P/S Board
ASSY NO.: 802-0003A
5- 1uf 35V
1- 2.2uf 25V
1- 4.7uf 16V
2- 10uf 25V
4- 100uf 16V
There are some larger capacitors in the system but these caps usually last many decades bacause of their size or mass. They all check out within specs so they will not be replaced and this will keep the repair costs down as well.
**** A WORK IN PROGRESS ... ****