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DMcMahon · 5th Apr 2020, 7:51 pm

I do not know this model but by looking at the schematic.

The bias frequency adjustment is C221 (150 - 750pF) and the bias amplitude (adjusted for current by measuring voltage across a resistor in the procedure) adjustments are (if 4 track) C1 and C2 (10 - 60pF).

The pre-amp board layout drawing shows C221 fitted on the board, as far as I can see C1 and C2 are not fitted to the board, so assume that the trimmers you reference by the heads must be C1 and C2, would possibly expect these capacitive trimmers to be physically smaller than C221, because they have smaller capacitance value.

Have you tried scope connection without its earth lead connected ?

5th Apr 2020, 7:51 pm	#2
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Tandberg model 15 bias adjustment I do not know this model but by looking at the schematic. The bias frequency adjustment is C221 (150 - 750pF) and the bias amplitude (adjusted for current by measuring voltage across a resistor in the procedure) adjustments are (if 4 track) C1 and C2 (10 - 60pF). The pre-amp board layout drawing shows C221 fitted on the board, as far as I can see C1 and C2 are not fitted to the board, so assume that the trimmers you reference by the heads must be C1 and C2, would possibly expect these capacitive trimmers to be physically smaller than C221, because they have smaller capacitance value. Have you tried scope connection without its earth lead connected ?