Why a TIP102 is a poor long-term MPS-U45 substitute
The 74LS175 that switches each driver can source only about 400 microamps (800 for a 74175) through a 1k base resistor. The MPS transistors, with a gain of at least 10,000, are driven hard on by that; the TIP102, with a gain about a tenth of that and a higher base and saturation voltage, may only half turn on, giving weak coils or dim lamps and loading the chip. Removing the under-playfield 2N5875 in favour of a TIP102 is mechanically easy but likewise not advised.
Systems
Related tips
- Diode-test the driver board MPS-U45 and MPS-A13 transistors
- Drop bank reset coil dead everywhere: driver ground wire moved to the wrong J4 pin
- One driver board fits every System 80, 80A and 80B game
- First power-up, step 5: add the driver board, then coil power
- Coils lock on and burn because of the Gottlieb ground fault
- What the System 80 ground modifications achieve
- Test the driver transistors while the board is out for the ground mod
- Ground mod step 5: direct ground wire to the driver board
Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part One, Clay Harrell (pinrepair.com)