Portastudio Weak Signal | Read Schematics & Replace Capacitors | Tascam 488

Here is some footage I shot while i was refurbishing a Tascam 488.

Having carried out basic refurbishment taks such as deep cleaning, lubrication, replacement of rubber belts etc, on attempting to calibrate the playback amplifiers I found I could not get track 8 of my test tape as loud as the others.

In my experience weak, distorted or dead signals in one or more tracks of a portastudio or other ' multitrack cassette recorder are often resolved by replacing the coupling capacitors surrounding the operational amplifiers which provide amplification in these circuits.

So in this video I show how I interpreted the schematic, colour coding in photoshop to identify the audio path, power rails, and major components through which the audio signal passes from the input to the output of the audio circuit and which might therefore account for weak signal, or bad impedance matching between gain stages resulting in gain issues:

I then go on to make a list of these parts' reference designators(c101, r202, are reference designators, sometimes I just call them "parts numbers" but sometimes that gets mixed up with serial numbers, which is somethingdifferent...I digress....), identify them on the board using sharpie then absent-mindedly replace them while I watch TV (sic).

I find that at least 4 times out of 5 this works, and it did this time. Even where further diagnostics are required, I figure touching up sodler and replacing capacitors which are 20-40 years old is good due-diligence/future-proofing anyway? You mileage may vary....

Her eis another video about colour coding schematics

And this one shows my approach to soldering in more detail

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