Initial Power Up (PC Engine GT)
Start by removing the motherboard with game cartridge board attached. Remove all wires.
The power path from the batteries to the system goes through a bunch of inductors, filters and fuses.
The ground circuit of the PC Engine GT comes in from the battery ground, through the inductor L501 (under epoxy usually) and to the DC jacks ground switch which joins the BAT- to ground through the switch when no DC jack is inserted.
Confirm this is ok by measuring for continuity from the battery negative to TP510 (which is often covered by epoxy).
If you do not want to remove this epoxy measure the top left pin of the X500 filter.
If you have no continuity remove the epoxy and check the L501 inductor, and the DC jack.
One last check is to make sure the battery ground makes it through the X500 filter path and to the system ground.
To do that test continuity to the bottom left pin of X500 and to TP507 which are both system ground.
The first place the BAT+ goes is through the L502 inductor (typically under the epoxy).
Measure for continuity from the BAT+ pin to the fuse on the other side of the console to confirm if the inductor is good.
If there is no continuity just bridge BAT+ to the fuse.
The next check is that you have continuity through the F500 fuse.
If not bridge or replace the fuse.
After this the power to the system enters the power switch. At this point we call this the VSYS rail.
VSYS then goes (when the switch is turned on) to:
- Audio Amp (IC100) through current limit resistors (2x 68R)
- To 5V Circuit (Q502 emitter)
- To backlight circuit (through BLH)
- To contrast circuit (though L500)