So I have this old Matorro Jagdtiger bought a few years ago for a project with the original 27 Mhz pcbs & no transmitter. I’ve stacks of other builds to get into so I thought OK, let’s stick a new old RX18 into it a bit rapid, so it drives & fires etc. and sell it.
Yeah, great idea, got it sorted then nothing! Basically, the transmitter (new & unused), started playing up then died, no light in fact b***er all

After trying different batteries, (Heng Long recommend Panasonic in 27Mhz, for some reason) & pulling the transmitter apart and prodding around with a multimeter for an hour, it turns out to be the the transmitter LED. I replaced it and away we go
