For leaked SMD caps I know no safer method. Boiling leaked electrolyte with a soldering iron is not good for the PCB either, and melting oxidized solder is very hard to impossible.

I have drilled a hole from top to help to remove the resin block from the inside. Then I've put a LED in that hole

Q500 is not a transistor, but a voltage regulator. If it has 12V on the input, proper GND, and nothing on the output, then something shorts its output to ground. Sound Hardware seems to be recognized correctly - value of 3 indicates, both Yamaha and DMA are present, so the problem is likely in the a...

For FDD most lines there are open collector with pull-ups, so adding capacitance parallel to the ground creates a nice low pass filter.

HigashiJun wrote: ↑Mon Mar 01, 2021 1:34 pm Even if the rivet is overlapping the track, it does not go under the PCB coating - but is just laying on it - and is then perfectly insulated from the copper layer.

I'm not suggesting shorts, but measure the capacitance. You're basically adding a few dozen pF between GND and each line.

It looks nice, but I'm afraid, these areas may cause problems:

Terms "battery" and "cell" are often used interchangeably, however the cell is a single unit, which voltage is denominated by chemistry used inside. While a battery may be build from one or more cells (to be technically precise from two or more cells), and its voltage is a multip...

Atari SM/SC monitors use H/V sync, same is for VGA monitors, but some 3rd party RGB monitors and SCART equipped TVs require a composite sync. Also Chinese upscalers like GBS8200 and SCART-HDMI converters need it.

On the STf it seems that you have to solder in some components if you want to have composite out. I'm afraid this will produce only the composite sync signal (required for SCART RGB), not the composite video. Yet RGB SCART requires composites sync, not composite video (which may be used for this pu...

If you have an oscilloscope, try to observe address lines and Din/Dout lines of DRAM chips while rebooting the system. Look for lines that are always high or always low, or never reach the right voltage levels.If a chip is faulty it may short Din/out (D/Q), or its address lines to GND or Vcc, and th...