Klark Teknik DN22 EQ

drrats

Member
2016-05-30 10:33 am
Hi everyone, I'm a little new here but getting into repairing my own gear. Before I take this to a repairman i'd like to have a go at doing it myself and learn something in the process perhaps. I have a multimeter, soldering iron etc

It is a stereo unit . . . induction based :) However the right channel has clicks and pops at a very low level, it's sound like an old dusty badly taken care of record. The noise only appears when an xlr is plugged into the right hand side xlr output but it is always there no matter what switches I flick or what pots I move. However both channels volume (level) pots are very scratchy and make a lot noise when I move them.

Could the thing just need a really good clean? Can anyone point me in the right direction for troubleshooting it? I can supply photos and a schematic if that helps?

Thanks
 

turk 182

Member
2012-10-26 3:03 pm
wow an old dn22 cool
a unit of that age is going to require some parts replacement to get the "popcorn" out of the signal chain particularly the balanced input as most are driven hard or into oscillation from improper connection.
cleaning the controls is a good place to start along with a visual inspection of solder joints on all the faders and input output pots while your in there check all the xlr connections as well.
you mentioned having basic stuff like a soldering iron and multimeter any chance you have a scope or signal tracer?
be careful if your monitoring operation of noisy controls as the transients can cause problems down steam (don't know what your test setup is) so be careful not to hurt other components in your rig (as is popping a horn driver or tweeter or putting an amp into oscillation from bad grounding or funky connections)
 
Crystalizd looking joints or one where the wire is exposed without much solder puddle are suspect. I'd just reheat the solder joints on the noisy channel, perhaps adding a little solder. Pops are quite frequently bad solder joints.
Loose wiper on input pots can also cause pops and sudden volume changes. sometimes these can be sprayed out, but I've replaced a lot of old pots with too many hours or adjustments on them.
You could use a sound probe to determine if the pops happen before or only after the first transistor or thereafter . A sound probe is an amp speaker combination with the input protected from DC by a .047 uf cap, and a line to line parallel led after that to clamp input below 1.2 VAC.
Early transistors can also have bad welds inside them which cause pops. There also can be bad solder joints on resistor and caps in the sound path.
Spraying with circuit cool compound can more quickly determine the source of pops sometimes. Also pushing wires and components around with a plastic or wood stick while you listen to music through the device.
 
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turk 182

Member
2012-10-26 3:03 pm
hey Indy thanks for joining in!
drrats if you simply google "visual examples of bad solder joints" you come across a gallery that gives several photo's of things to look for which should help in that respect.
a good magnifying glass is almost a must(or maybe that's me and my bad old eyes).

the signal tracer would allow you to "listen in" at various points along the signal path (if you find a point along the signal path that no pops or crackles are heard then you've eliminated a good many components as a potential source of fault) without having to use other system components to monitor your "repair/fault finding".
i guess that as a service tools/technique signal tracing is an intuitive "go to" for me that others may not be familiar with or commonly use.
 
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