Sos from the past is a Time Cruisers Audio Drama released in 1996.
It's March 12, 3777, at 11:58 pm and 37.5 seconds (thanks to Cranky for this incredibly detailed time!) and the gang is still working in the Lab. A few minutes after midnight (so on March 13) Dr. Cyber finally finishes building his latest invention, the time transcendental receptor machine, a sort of radio that can pick up signals from other time zones which he invented after being unable to locate Cranky's signal during Operation Cybercom. They test it out, and the first thing they hear is a desperate call for help. So, they decide to home in on the signal by traveling to two time zones in order to find the location and time of the signal's origin.
The next morning they take off in the 6493 Flying Time Vessel(called Flybo in story) once again, but decide to take Cranky with them this time. They choose a random time to gather the first half of the information, which turns out to be the year 1602, the Pirates era. They land in the ocean and see the islander Islands as well as the Armada Flagship delivering a prisoner to Imperial Outpost. They decide to stop at Volcano Island as this seemed like a perfect place for the professor to set up his machine. They've heard of the island from history books and, out of curiosity, enter the secret cave where they find a 250 year-old skeleton and a treasure chest full of gold. They leave the treasure and climb up the volcano. There, the professor sets up his machine and homes in on the signal while Tim watches the ocean for pirates. Sure enough, soon a large pirate ship sails straight towards them and starts firing its cannons at them. Tim and his monkey Ali return fire using a catapult and lava rocks. After a while, the pirates surrender and Captain Roger comes onto the island with a rowboat to talk to them. He asks if they were pirates too and what country they were from. They tell him that they are time travelers and that country borders don't exist anymore in the time they're from, although it could be said that they are from Europe. Redbeard doesn't believe them of course and tells them that his ancestors are from Spain. He then accuses them of attempting to steal his treasure. When they tell him that they're not interested in the treasure as it would only be "useless ballast" for them and that it was probably pirated treasure anyway, Redbeard believes them to be gods of the ocean and lets them go. As the Armada Flagship comes to fight the pirates, the gang returns to the Zero-time.
Next, they travel to sometime in the 20th century (a more detailed date is not given unfortunately as the time cruiser already starts landing while Dr. Cyber is still adding and subtracting years to the timer). They find themselves flying over Paradisa, and although it's nice and peaceful, they decide to keep flying as there are too many people there. They find the Gator Landing and believe the hut to be abandoned, so they set up their machine there. But just as Dr. Cyber gathers the last piece of information, a seaplane lands by the hut and the pilot gets out to meet them. It turns out that this was a rendezvous spot for smugglers, and the pilot mistakes them for the people who were supposed to deliver him the goods (the pilot greets them with "Hello friends" but goes on to speak German, so perhaps this is an indication that Paradisa and the rest of the leisure sets are set in the US or another English speaking country). He tells them that his smuggler friends, Frank and Benny, are on their way, too, on different vehicles to put off the police. Dr. Cyber and Tim play along until luckily a police elite commando arrives to arrest the smugglers. In order to avoid getting arrested again, the gang quickly escape in their time cruiser.
Using the information they gathered, the professor is able to determine the origin of the SOS, so they travel to that time and place. They arrive at the Main Street of Legoredo City in the Wild West at night and spot a large shed next to the General Store where they decide to hide their time cruiser. While inside the shed, they hear voices coming through the walls from inside the general store. There are three men holding a young boy and girl captive. Robbie Robot and Ali the monkey make so much noise that the men send the boy, Johnny, out to investigate, who claims that the noise came from rats in the shed and pretends to go drive them away. When he meets Dr. Cyber and Tim, he tells them that his parents own the general store, but they left town to go to a funeral and left the kids to look after the store. Soon after they left, the three men entered the store, took Johnny and his sister Lucy hostage, and started digging a tunnel underground in order to rob the bank next door. He then reveals that he's a young inventor and that he built a radio in order to secretly call for help. The men call him back, and so Dr. Cyber and Tim go to the sheriff and together, they devise a plan to stop the bandits.
The next day, Dr. Cyber and Tim pose as delivery men transporting new money to the bank (which they switched for rocks). When the three bandits, Luke, Jack, and Ken, come in to steal the money, they are surprised to find that the crates are filled with rocks, and Dr.Cyber blasts Jack and Ken with the Zero-time cannon, only leaving Luke. After Ali throws the rocks at him and his weapon has no effect on Cranky, Luke surrenders. The sheriff arrests him and the other two as soon as they reappear a few minutes later, and Johnny's parents return later that day, so it's a happy end. After another brief accidental detour to the Aquazone, the gang returns to their own time. There, they discover that Johnny left his radio inside their time cruiser as a gift for his heroes from the future. They also find that Cranky has fallen asleep due to the exhaustion from their adventure, despite claiming earlier that robots don't need sleep