I got a Nak 660zx from メルカリ. It is equipped with an auto head alignment system. There is no bias fine adjust on the front panel. Instead, it has the record sensitivity adjust for each tape types. This is quite strange since bias tends to vary more and makes bigger difference in sound. Supposedly back in the 70s when this deck was made, tapes tend to have similar bias. Anyway, this deck suffered from orange cap syndrome, which is not hard to fix- just a matter of replacing the pp capacitors. After fixing the ocs, i noticed a bigger problem- there was no sound from one channel (don’t remember which one. For convenience, let’s say it us the left channel). I could only heat music from the right channel. Left channel only had noise. I swapped the wires for the head -left to right snd right to left. And the problem swapped. That means the head coil was broken. There id no way to fix this other than replacing the head. I sold at reduced price.
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