Hi! When dealing with old audio components restoration, I recommend removing the resistors from the circuits and checking their resistance value against the color code. The resistance values varies with time and I've seen a lot of 100ohms resistors become 120 or more ohms and 1K ohms becomes 1.4Kohms or higher.
If you have anti-static mat, use it. If you have anti-static wrist-wrap, always wear it all the time when you are handling the board.
Since it's only a small board, it won't be time consuming to check all resistors. But better yet, why not replacing all the old resistors with all fresh new resistors?
Before removing anything, read the color code for each resistors and calculate the value. The small magnifying glass is handy to read the color. I think there are a couple of resistors (R516B and R511?) that looks burnt on the PCB.
From the size of the resistors, most of them are 1/2 watt metal oxide flame proof type resistors except the smaller ones which are 1/4 watt. There are also a few power type resistors that you can read the numbers and buy from online electronics store like mouser / digi-key / newark.
Before ordering any parts in, I think it's a good idea to swap out the old electrolytic capacitors at the same time so why not read the value and order the electrolytic caps too? Heck, you can also read the part number on the ceramic type disc capacitors and order in the same time.
I know there are lot of parts there but it's cheap enough to replace everything at one time than doing it multiple times and one at a time.
The diodes seems to be like silicon type 1A but I don't know there is any part number on it. Without the manual, it's hard to say what exactly are they. So, just remove one side of the diodes and use Diode Test function in your Digital Multimeter to make sure they are OK too. Don't replace the diodes if they are good. If you find one diode is not working (open circuit / shorted, etc.), just check the other good ones and order in the closest diode with similar forward voltage drop value.
For transistors, remove one at a time and test it with diode test functions between two legs at a time for all 3 legs. If you can afford the new transistors, just order in too.
When you get all the parts in, replace one part at a time. It's a little more time consuming but it'll ensure you replace the old parts with the new parts and will not mix up and screw up. Also, check and double check the resistors to make sure the values match when replacing them. For electrolytic capacitor, check the polarity of the cap and the markings on the PCB to make sure the polarity is the same.
For Diodes, make sure of the polarity too. For transistors, make sure of the orientation and CBE (Collector Base Transmitter) pins accordingly.
When you done with replacing or checking all the components, check the finished PCB against the pictures you attached here and pay attention to the caps, diodes and transistors for their correct orientation. After all done, clean the trace side of the PCB and pray that it'll work fine again when you plugged it in.
If you smell smoke or it's not working yet, there are other things/boards that requires a thorough checking.
Hell, I wrote a short essay but I wish you good luck!
