If you haven't done it already: at first I would replace the electrolytic capacitors involved in the audio circuitry at the aux board.

Check for the presence of the 20V, 16V and 13.6V -> voltages required for the D/A and audio amp circuitry. Check R11 (100 Ohm) if the 13.6V is missing and also the 2 6V8 zenerdiodes. If these are ok, you can check the LM380 Amplifier by making you finger a bit wet and touching its pins. If you hear a loud hum, it is probably ok.

After this focus around the D/A converter Atari created with the 741 OpAmp. They are mixing 2 4bit Digital signals into an audio signal via R/2R ladder dividers.

Both 4 bit signals are buffered by non inverting 7407 buffers and are passing R/2R resistor dividers. At one side the R/2R dividers are switched by a 4016 CMOS bilateral switch.

Without an oscilloscope it is hard to troubleshoot here. If you have a Logic probe you can check the signals at the 7407 buffers. When just shotgunning components I would start with the 741 if voltages and the LM380 are okay. And be sure the signals form the latches are present ($1084 bit 0-3).

Hi Max, among a few other issues, I'm having the same faint sound issue with the Space Riders I just picked up. Very faint sound. Pot adjustment does nothing but quiet the sound all together. Did you resolve your issue yet? I will try and follow the instructions from Maralb but I only have a multimeter. Perhaps you can share what you did and I can try the same...thanks kindly!

Fixed so far: Missing segments from the third player plasma display. Replaced two transistors a q12 and q14 and now I have 8888888's across the board very thrilled by this! Replacing 3 of 4 UNL2003 ICs in row A at J1. Some Zero readings on a few legs. Game goes into attract mode, credits up and plays.

Issues: 1. Faint sound as mentioned above.
2. Some end of ball bonus lamps glow brighter then they should when not in use or triggered. I realize Atari set up their circuit board so that all lamps have some power and stay warm but these are glowing at about 30% when not supposed to be active. The glow should be very faint and not visible thru the inserts.
3. No power to the Y in CITY (right outlane) bulb is fine, new socket, fresh solder. All letters are lit at game start but this one never comes on. Multimeter shows no power at lamp base. I've looked at schematic but I'm not a genius.
Any assistance you or anyone can render would be fantastic! Thank you in advance!

I just solved my low Volume problem on the Atari space Riders. I didn't realize but if you look on the auxiliary board on the side of the cabinet there is a small blue potentiometer/trimmer that is the master Volume control. As soon as I turned it, a lot of crunchiness came out of the speaker! Obviously the pot is dirty so if you spin it back and forth a few dozen times you should be able to get enough of the crud off so that you have volume again. I'm not sure if you checked this before but my volume came on immediately, full blast. Dirty volume pot.

The lm380 chip that is to the left of the pot is the amplifer, check pins for any cold solder joints

Hi,

Have you sold this machine? If not, I may be interested.

Thanks,