Last time I turned it on, I didn’t get the usual boot-up sound of ‘Seeeeegaaaaa’.
There’s a little chip next to the earphone plug. I haven’t checked yet, but I suspect it’s some kind of amplifier. So I’ll warm up my good old TEKTRONIX 314 scope and go hunting for some sound waves, hoping the sound chip itself is still ok… The undressed Game Gear looks like this:
The 2 Sega chips to the right may be the brains. The top right PCB contains the volume control and a dual amplifier for the headphones and the internal speaker. I suspect there is something wrong with it. The TDA2822M gets 2V supply voltage from the main PCB and signals of about +-100mV. According to the datasheet the minimum supply voltage is 1.8V, pretty close to the edge I think.
The sound amplifier board basically contains a potentiometer for volume control and the amplifier chip. The 2 fat caps are for supply voltage decoupling. The little SMD resistors and caps are hooked to the 2 outputs of the chips and seem to be a crude low-pass filter, just like in the datasheet. The 2pin connector goes to the internal speaker. What the inductor-ish black thing is good for remains a miracle at the moment. I haven’t reverse engineered the schematic yet, I just checked if the signals get to the chip. Maybe some caps are gone.
These 2 SMD parts look a bit strange. Maybe it is just flux, maybe something boiled.
The AC part of the audio signals look like this:
Scope settings: x: 0.5ms/div — y: 5mv/div (AC coupling, effective 50mV, 10:1 probe). There is a significant DC offset on the signals.
Before I can go on I’ll have to find out what the raw audio signal should look like in terms of voltage levels. Maybe I’ll set up an amplifier myself and try to pick up the audio from the main PCB and hear if that’s anything resembling music. I found a source for a detailed Game Gear repair for replacing a bad capacitor. I’ll need to check them. Here’s the test circuit for the chip.
It made it to the Game Gear almost without changes as far as I can tell so far. People seem to have had problems with the caps at the output of the chip. Others have had problems with caps on the main PCB giving bad video output. I won’t touch these.