An older wireless remote for a large overhead crane came across my bench in need of repair. The issue being that the receiver no longer responded to commands issued by the remote.
One clear issue was the rechargeable battery pack had been replaced with non-rechargeable alkaline AA’s and there was seriously bad corrosion on the battery terminals. I ended up replacing those with Lithium AA style batteries and cleaning it all up, but there was still no measurable signal being transmitted from the remote itself
I spent some time reverse engineering the schematic for the RF PCB which is shown below. This remote operates in the region of 433Mhz and is mostly beyond the limits of my test equipment so I started pulling transistors and checking them with a transistor tester/LCR meter. Q1 read an especially low gain compared to its counterpart Q2 making it my main suspect. The transistors are marked with V0P which seemed to be PBR941 NPN RF transistors with a transition frequency of 8GHz. Despite this remote being 30 or so years old this transistor is still being produced, and after ordering and replacing Q1 and Q2 the remote started operating normally once again.
Manual download: