In my previous post, I cleaned up the button contacts on a seemingly water-damaged Game Boy Color. Everything seemed to be working except for the fact that there was no audio from the built-in speaker. Well, today I figured that out.
Does the audio work at all?
I have had other Game Boys where the onboard speaker does not output sound, but headphones work, so that’s what I tried first. I plugged some speakers into the headphone port on the bottom of the GBC, and the sound worked! That was a huge relief. I knew that the headphone port has a switch inside it that is normally
on. When headphones are plugged in, it changes the switch to the
off position. So there was most likely something wrong with that switch.
Cleaning the Switch
I wasn’t sure where exactly the switch was located inside the headphone port, so I did some digging and found this excellent post on Sam’s Asylum that showed exactly where to clean. Luckily, the designers of this headphone jack left a little window in the case to allow me to clean the switch without desoldering it from the board.
I inserted a headphone cable to open the switch and make the contacts accessible. Using a set of precision tweezers, I gently scraped off the oxidation from both sides of the switch. When I was done, I used some canned air to blow out any oxidation dust and put the GBC back together enough to test it. Aaaaand the speaker still didn’t output any sound.
Ok, how does this circuit even work?
At this point, I knew I had to start poking around with my multimeter. I found this extremely detailed schematic for the GBC from Console5 and dove in.
I’ve cropped the schematic to focus on the headphone jack, which is marked as
P5 on the right side of the image above. The red arrow points to pin 5, which is is the side of the switch that connects to pin 6 (
SW) of the sound amplifier
U3) on the left side of the image. Pin 4 of
P5 is connected to ground. When there are no headphones connected, the switch is closed, connecting pins 4 and 5 of
P5 together, which connects the
SW pin of
U3 to ground.
You may have noticed that I’m ignoring
EM4 (part number BLM11B102S), which is in-between pin 5 of
P5 and the
SW pin of
U3. This is just a ferrite bead, and is most likely there to filter out noise. It’s good to have, but not absolutely necessary.
I set my multimeter into continuity mode and found the
SW test point on the Game Boy’s PCB. I touched one probe of the multimeter to that, and the other probe to pin 5 of the headphone jack (the red arrow in the image below). Unfortunately, I did not get a tone, so there was a break somewhere in the trace (the yellow line in the image below).
Fortunately, I quickly found the break. I probed both sides of EM4, which showed continuity, so I tested both sides of the circuit from EM4. However, there wasn’t continuity on either side! I wondered if the oxidation got under the pads on the PCB and lifted them up, so I scraped off some of the coating to reveal the traces on either side of EM4. I tested the continuity from one side to
SW, and there was continuity. Likewise with the other side and pin 5 of the headphone jack. I knew my suspicions were correct.
Fixing the Problem
I tried to reflow the solder of
EM4, but the component was so light that it lifted off the board as soon as I touched it with the iron. I tried to bridge the trace and the pad with solder, but I wasn’t able to do it. In the end, I decided to bypass
EM4 entirely with a piece of very thin (bodge) wire connected between the
SW test point and pin 5 of the headphone jack. I was careful to route it around the button pads, cartridge connector, and screw holes.
And… it worked! The audio comes out of the onboard speaker with no issues, and switches off when headphones are plugged in. I normally don’t like to bypass filters like that, but I’ll address that if the audio quality is a problem in the future. In the meantime, my wife’s coworker can show this off to her daughter!