Referring to the instructional video from YouTube, I decided to try working on my GBS 8200. I address this short instruction to those less proficient in using the English language or unable to watch video instructions due to reasons such as browsing the Internet through a classic Amiga :)
Many of us have probably complained about the significant amount of interference, which is a side effect of the cheap, Chinese 'gadget' from the GBS series. My experiences have shown that they cannot be completely eliminated, although we can reduce them a bit. I am not writing this as a hundred percent professional, so any suggestions/comments will be appreciated. I would like to share primarily what helped me.
The first component to be replaced was the 470uF 16V capacitor (marked as C1), located next to the power socket. I decided to replace it with a LowESR capacitor of the same capacity. It wasn't easy as it is soldered to the PCB on both sides (there are actually 4 solder pads) and reaching the solder from the other side is very difficult. The task is not made easier by the fact that the equipment is factory-soldered with lead-free solder. By the way, it never crossed my mind that I would be cursing in every possible language (including Silesian) while performing this task.
The thin tip, hot-air soldering iron, and flux turned out to be helpful - in my case, AG-5 worked well. Of course, solder wick and a desoldering pump are standard. I think that replacing this capacitor with a good quality SMD one would be a better idea, although in the village of Poznań, I could only get a LowESR capacitor for through-hole mounting. So I decided to 'lift' it a bit from the PCB, in case I wanted to remove it in the future and do it more neatly.
Then I tackled the long paths that are on the other side of the board. Here (besides patience, as I ran out of swear words at the capacitor) a bit of copper tape and a regular multimeter with a buzzer function came in handy. I applied the tape to the path locations and pressed it with a gentle cloth soaked in IPA to avoid messing up the whole thing with glue. Here, one must be very careful, as no solder joint should be covered with tape. Different board revisions differ from each other (I compared) and one can make a mistake due to carelessness. If it's too tight somewhere (e.g. when you need to fit a narrow strip of tape between two solder joints), it's better to skip the taping. I checked the whole thing with a multimeter.
When it was all over, the screen had to be grounded. This can be done in two ways, more or less invasively. The more aggressive way involves scraping the paint off the PCB (near the tape), 'digging down to the copper,' and checking with a multimeter what you are dealing with. All you need is a multimeter with a buzzer. Attach one end to the spot where you were just scratching, and the other end to the VGA socket housing, for example. If there is continuity, it means that the particular spot can be connected with solder and a piece of tape. And so on with each strip.
If we don't want to take risks and scratch the device, we can simply take a piece of thin wire, solder one end to the tape, and the other end to the VGA socket housing. To make things easier, you can use the VGA Input socket, which is not commonly used. Of course, you have to be careful not to burn the traces located under the tape.
Once I had some copper tape, I used it to make an additional screen on the RGB cable leading to the Amiga. Although I didn't notice a significant improvement after this procedure, who will stop the rich? :) If we have a spare 5V fan (because I power my GBS with this voltage), it's worth using it here. The main chip on the GBS (the one with the attached radiator) can heat up quite a bit, and an additional fan will definitely come in handy. It can be connected to the two-pin socket, which is right next to the power socket. A cable with such a plug was usually included in the set, so there shouldn't be a problem.
After turning on the equipment, it is much better. The number of famous 'white dots' has decreased significantly. However, there are still disturbances in the form of regular white, horizontal stripes wandering across the screen, but as far as I know, there is no way to fix it. Supposedly, this is related to the nature of the operation (refresh rate?) of the cheap device made in China (similar to the case of the 'floating' Workbench cursor).
