424 Mk III repair diary | Colour- coding Schematics | Monitor buss

This is some footage I shot on my bench and using camtasia as I analysed and colour coded the schematic in photoshop during the repair of a Tascam 424 mk III.

The unit was bought cheap as a spares or repair item from ebay. It was received with a missing PSU.

I was able to wire up a compatible PSU with thew help of 3rd island's vidoe on the subject;-
   • Видео  

After inital cleaning and testing I discovered the following flaWS;- one dead mixer channel; the headphones only produced signal in the right speaker in mono mode; the right side of the monitor meter was not responding in L-R mode,; the headphone volume knob passed signal but the signal did not get louder or quieter or louder as the knob was rotated.

The mixer channel was narrowed down to the fader using signal tracing with a home made audio probe and an external amplifier. On removing the fader it transpired the conductive plate and the slider were both faulty, so I wired in an equivalent fader from a scrap XR3, reshaping the plastic shaft with jewellers files.

I started off assuming that the issues with the right side of the monitor buss headphone volume had the same casue, but they did not. The rotary dual gang potentiometer for the headphone level was faulty (requiring me to salvage a compatible part from a spares donor) ) whereas the monitor buss issue was casued by a non-conducting section of track on the printed circuit board between the master fader and the monitor switch (which I resolved with a jump wire).

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