NAK BX-125 no output L.channel

[mdr2973]

Hello,there is no audio output from one channel of my nakamichi bx-125 cassette deck.prior to losing output there was intermittent dropout using the variable output control.now there's none.same via the headphone out jack.opening up the case then removing the front panel revealed the location of the pot that controls the output levels to be innaccessible without a service manual diagram. any ideas?i'm assumimg it's the output pot.....

 

[anwaypasible]

well for starters.. i wouldnt short the pot to try and regain audio because the pot might have resistance when the knob is set to allow full output.
shorting the pot would cause zero resistance and might destroy something else.

i am assuming you have seperate pots for each channel.
since a variable resistor isnt usually stereo unless there are two seperate potentiometers with one knob.
to select which potentiometer, the knob would be pushed in or pulled out.

if there is another pot for output control (one for left one for right)
grab the resistance from the working pot to be used for the broken pot.

but there might be a very odd design choice that makes one pot a different value than the other pot.
and i would check the impedance of the wires that connect to the pot to look for differences in impedance readings.
if those lines are the same, it should be safe to replace the pot with a replica of the other pot.
but there might be something down the road after the wires that connect to the pot that really dictates a need to have seperate pot resistance.
that would probably be the actual amplification circuit.
while the amplification circuit might be designed to have the same impedance at the wires that go to the pot.. the actual functionality of the amplifier might be different.
thus leading to a different resistance needed at the pot so that the different amplifier works at the same level as the other channel.

a service manual would tell you what the pot values need to be.
but i would check to see if the other working pot is within the specifications of the service manual.
because maybe the pots were replaced with slightly different values as an upgrade.

cant do anything without learning the amplifiers.
you could try to determine if the amplifiers are identical.. but you need measuring equipment to get real values.

if you do get a service manual.. maybe you have the chance to upgrade the output power of the amplifiers by changing the values slightly.
but maybe that will break it 🙁

without the service manual.. you gotta learn each component of the amplifier and ensure that both channels are the same.
by learning the amplifier, you should be able to calculate what resistance range is needed for the amplifier to be within its safety limits.
however, the amplifier might be working far below its safety limits to benefit from higher sound quality.
the only way to know that is to try.

i think you either need to hunt down a service manual or find an electronics technician who is willing to take the extra step needed to learn the amplifiers.

i dont know if you can take the potentiometer apart enough to repair it.
they say a potentiometer is a 'resistive strip' with a 'wiper' that goes up and down the strip.
maybe the 'wiper' is broken or has become crooked.
or maybe there is some decay on the resistive strip.
maybe the 'wiper' and the strip arent touching anymore because the wiper is worn.

you might be able to have a look at it and see what caused the pot to stop working in the first place.
then decide if there is any way to bring functionality back.
maybe you can tilt the wiper so it is straight again.
or maybe you can clean the resistive strip.
or maybe you can add some electrical grease to the resistive strip to help the wiper touch again.

maybe you can set the volume to a fixed point where you usually have it and focus on getting the wiper to touch the resistive strip at that specific spot.

maybe you can take the whole thing apart and gather impedance values for the wiper and resistive strip and terminals.

when you say that the pot doesnt work anymore when you spin the knob.. obviously one of two things has happened:
-the wiper isnt making contact
-the resistive strip is ruined.

i'd say.. if you do take the pot apart to gather information, start at the low volume and listen to the amplifier to determine if it is too loud.. which would indicate that the resistance is way off.

you could also check the impedance of the pot and see if the pot is still working and if its the amplifier that is broken.

 

[mdr2973]

Best answer selected by mdr2973.