Portastudio 464 - low level on channel 1


New Member
Apr 22, 2024
Gear owned
Portastudio 424 MkII, 464

I finally found the time to clean and setup a broken 464. I replaced the Gear C, cleaned the entire machine, and assembled it back together.

Now I noticed, when I play my test tape, that channel 1 is showing a very low signal in the display (1 bar or none), while channels 2 to 4 are more or less fine. Then I tried to adjust the trim pot for channel one on the board (PB Level) and noticed a slight change in volume by hearing - but no considerable change on the meter. I tested the rec input (unbalanced) with a test signal, same thing: the level is lower then the others, although I can hear just a little difference in the headphones. Tried to adjust the rec trimpot on the board, no noticeable change. Is this a faulty meter? I can not say if this behavior existed before my cleaning efford, due to the fact, that it didn't work at all cause gear C was broken. Does anyone know where to look further to troubleshoot this?

I looked into the board for faulty capacitors or any signs of failure, checked the inside connection wires and connectors, demagnetized and cleaned the playback/record head, dbx and sync is turned off - nothing that seems to cause this behavior.

Any help appreciated, thx

I investigated a little bit further and found out that even the monitor meter shows incorrect values, either in the L/R, CUE, 7/8, 9/10, 11/12 or 2TR input singal chain. The left channel is always as half as high as the right one - even when I reverse L and R jacks. Same on playback: channel one low to almost nothing, monitor L half the level of the right channel. I tested the subjective hearing: I can't hear the difference shown by the meters; channel one is as loud as the other ones. Conclusion: think there is something wrong with the meter. Maybe it's getting wrong information. Anyone ever expierienced that?

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