Nakamichi 481

calman46

Journeyman
Joined
May 9, 2012
Messages
115
Location
MA
#1
I'm working on nak 481 . New belts and tire and recapped (e-caps and orange film). The deck plays fine but is not recording correctly . I did record with it before the recap but I didn't playback the recorded tape , I just went by the meters and didn't use all 3 tape types . So I'm not sure if the problem was there before the recap . The problem is the deck will record in ZX but not in SX or EX . The recorded ZX is attenuated I think as the deck's meters on playback are no where near their level when recording . SX is severely muted I barely hear playback and EX is dead quite . I did notice that the green side polarity markings for C401 ,C402 are reversed, the component side (matches schematic) is right (the way I have it). The voltages are a little low so I was looking for a problem . PIN # 5 on IC 101 & IC 201 is 17.4 Vdc and 18Vdc and should be 21.5Vdc .The voltages are a little low all back to the PS. I have clean the switches a couple of times . I did a test record while switching between ZX, SX, EX . Listening with headphones to the recorded tape ,ZX seems to play louder than what meters are displaying ,SX mutes way down and EX is silence . Any ideas ? the low voltage or switches ? thanks
 

calman46

Journeyman
Joined
May 9, 2012
Messages
115
Location
MA
#4
The 68 ohm resistor looks good . I'll lift a leg to be sure . I did replace the bias and record level trimmers on EX only . Replacing the bias trimmer didn't fix the problem , replacing the record level trimmers return the volume level back but the sound is still distorted . The recorded music sounds kind like a radio out of tune . The new trimmers are at their mid point (25k) . I 'm going to turn the bias down and hear what happens.
 
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