J
James
I received a No Fear machine and the flasher circuit wasn’t working correctly, I noticed this first off when the end of game went through it’s T2 style flasher sequence and there was no joy. Notably there was no movement on the flashers throughout – so it wasn’t a case of just one of the flashers blown.
Theory of Flash Lamp Circuit
Flahslamp Circuit on WIlliams No Fear
The flash lamp circuit receives power onto the board from J102 pins 1/2 and 3/4 across a fuse F111 into a Bridge Rectifier and into a 15,000mf capacitor outputting at J106 or J107 into the lamps via a red and white wire. The return is driven by a black and corresponding colour as noted below the game has a total of 15 Flash Lamps, all powered from J106 pin 5 or J107pin 5. The return element of the circuit that controls whether it is on or off is handled by a TIP102 transistor and 2N5401 transistor, all logic coming from the 74LS374. Given that the symptom was the power side of the board.
Testing the Theory
Incoming AC Voltage
The easiest thing to test on a pinball machine is the fuse, so in this case the F111 which sure enough was blown, after retesting with another fuse, it blew again. With this type of repair, given that the draw to blow the fuse could be coming from the playfield or on the board, by removing all wiring to the playfield, it is possible to test if it is an on-board or on playfield issue. Pulling the required connectors and reseating a fuse, pop, fuse gone again. This demonstrated it was an “on-board” issue.
The incoming AC Voltage was within specification, so the issue must be within the board – namely the bridge rectifier and the capacitor. As these components are noted to fail within machines, it makes sense on such a simple circuit to replace both components and be done with it.
Pulling the Boards
After pulling the boards the issue had become clear. The capacitor on the top left soldering was barely making contact with the board and he four pins below on the bridge rectifier were also corroded and poorly finished with flux still left on the board, which should have been cleaned.
After reinstalling the components the new components a trace was required to be added to make the correct connections between the pins, the boards used in this era printed traces on both sides of the board, over heating when removing components can pull the pads and break the traces on causing the circuit to fail, which judging by the initial install is what happened. An easy way to check larger components and their traces is to hold the board up to a light, you can physically see the trace and “buzz” the circuit out, which simply means setting the meter to continuity test and ensuring continuity exists between points. As this trace had been broken a “jumper wire” was installed to complete the circuit.
The board was reinstalled, and hey presto, flash lamps operational once more. A good job well done.
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