Quoted from ravve:How about the resistor R3, do you have any idea why it is "mandatory" to replace it? I can confirm that it is measuring (and looking) fine. Maybe it is necessary due to that cr7 and R10 are to be replaced for other values than the original?
For the same reason. It's a very cheap component that is prone to failure and separating this board from the heat-sink plate is a royal pain in the ass. Replace what you can when you have the chance.
Quoted from ravve:Also, I can only find resistors of 0.25W or 1W, pinwiki says 0.5W. Which one should I go for, 0.25W? Or maybe 1W is a better option?
Wattage rating is the MAXIMUM power the resistor can handle. When in doubt, go UP... never go down. If you need ½-watt then ½-watt is the MINIMUM you should use.
Quoted from ravve:And the most important question: The trim pot, I read that it should be replaced by 500ohm 1W, but I can only find 500ohm 0.5W, would that work??
Where is it saying to use 1-watt? The circuit shows this pot in series with ¼-watt resistors R7 and R14, so if ¼-watt resistors can handle the branch current, then so will a ¼-watt potentiometer. Otherwise, the original R7 and R14 resistors would have burned up decades ago.
Screen Shot 2023-03-23 at 11.46.39 AM (resized).png
I replaced mine with this ¼-watt pot 2 years ago - no issues.
https://a.co/d/9v6dh7h
For this pot, 0-500 ohms is the range you need. If you can only find 0-750 ohms, that would work too. You can go up a little on the pot's resistance within reason. Example, if you use a 0-1,000 ohm, then only the first half of the number of screw-turns will be 0-500 ohms. If you use a 0-10,000 ohm, then the 0-500 ohms will be so low within the number of turns, adjusting it will be very difficult. Try to get something as close to 500 ohms as possible without going too far over. The closer you get to 500, the easier adjusting it will be.
Finally, the number of potentiometer turns. If you get a higher number of screw turns, then adjusting it for precise voltage will be much easier. More turns to achieve the same amount of change.