Tascam 424 mkii input switch gain/crackle issue

[jojsrecords]

I've had my 424 for a few years now, a while back I began having a problem where that little input switch at the top started to affect the input gain. Will usually be like whatever I have on the input will be static-y, crackly, with a very faint sound of the input playing among static. Usually to resolve this I'll spend a while fiddling with the switch as with some fiddling the sound will come in and out and a combination of things like blasting the gain knobs and cycling through inputs. Haven't had it out in a while but if I remember it happens on inputs 1-4, stereos are fine. Anybody know what might be causing this or where to start in terms of diagnosing and fixing the problem? I miss when my porta was hanging free and easy

 

[sweetbeats]

Hey welcome.

So I’m *pretty* sure you are just dealing with switches that need to be exercised. The switches, and pots too, have contacts inside that can oxidize and dirt/dust can get inside. Typically with regular use this is less of an issue. It also depends on the environment in which the unit is typically used or stored. Dry is better. Exercising a switch simply means rapidly switching it back and forth...like, 100 times. Try it and see if that helps. You can do the same thing with a pot by removing the knob, and wrapping a shoelace around the shaft and then pulling the ends back and forth to rapidly rotate the shaft lock to lock a bunch of times. Ideally you would couple this with application of some contact cleaner (like DeoxIT D5 or similar for switches), or fader lube (like DeoxIT F5 for carbon element pots like in the 424 mkII). But it is verily a pain to get to the switches and pots in order to apply the chemicals on units like the 424. So try starting with exercising. If the unit is stored in a damp non-climate-controlled environment, get it into a warm dry space and keep it there. Worst case scenario you have aged coupling capacitors that need replaced, but that is not where I’d place my bet. Try exercising the source select switch and input trim knob on one channel and compare to the others to see if that helps. It won’t make the problem go away, but it may greatly improve the symptoms. Bottom line this is all pretty normal stuff one has to deal with on an older analog audio unit.