My Tascam 48 was not recording on any channel, with in depth troubleshooting I found out the recorder was not erasing tape on any channel either, I had some tape with previous recordings on it, was not erasing. I numbered the channel cards(very important not to mix up the cards) and swapped some of the cards around, still no recording on any channel. Cards were put back in original places and I decided the master Bias oscillator had to be the problem!
I searched Ebay and found a master oscillator board for a Tascam 38, could this work?? After some research I could see that the 38 oscillator has the same connection pins and was the same 150khz freq. Looks like a winner for 25$.
All I had to do now was de solder the 38 oscillator from the board I purchased and de solder the main oscillator from the main board inside my 48 and replaced it with the one from Ebay.
The oscillator was a real pain to get to on the 48, but I did not want to remove the main board, it would be a time consuming chore and I might break one of the plugs. So with the 48 turned upside down I carefully de soldered the old oscillator and replaced it with the purchased one. Fired up the 48 and once again I could record on all 8 channels. Only thing left to do was a good setup and calibration.