[R-390] Advice on Replacing Components

[2002tii]

Jerry wrote:

>When you have a suspected leaky mica or ceramic cap or an out of spec
>resistor - do you always remove it or do you clip one end and test it?  To
>remove all suspected components seems like a major time consuming task.  I
>have heard many clip one end to test especially in tight places. My question
>focuses on the techniques used to resolder If the component turns out OK.
>Do you juxtaposition the cut ends and just put a glob of solder?  Most
>passive components don't have sufficient extra leads so I am very interested
>in learning from the wisdom of the group.

The first thing to do is learn to really troubleshoot problems so you 
have a darn good idea of what is bad before you start chopping.

Particularly with tube equipment (where you don't have to worry about 
semiconductor junctions screwing up your resistance measurements), 
you should be able relatively easily to figure the nominal 
point-to-point resistances and voltages.  The hardest thing to get 
people to learn as troubleshooters is to use all of the information 
they collect -- they measure all sorts of things, then quickly tire 
of the deductive reasoning that is required to understand what the 
measurements mean and instead resort to random replacing or snipping.

Don't be that guy (or gal).  Figure out what you need to know, then 
figure out how to deduce it from measurements that you can make 
without removing components (except tubes, which are easy to 
remove).  Very often, an experienced troubleshooter can narrow a 
problem to one or two components using information that a less 
experienced troubleshooter has already collected but had not fully 
processed mentally.

If everything is nominal, the equipment works.  Find out what is not 
nominal, then figure out what it means.  (Where is the current 
going?  Why is that voltage too high/low?  Why is there no/too much AC there?)

Also, note that many circuits operate fine with component values very 
far away from their design values.  Don't confuse yourself by chasing 
what are essentially "blueprinting" tasks (resistor values off by 
+100/-50%, for example) when you're troubleshooting.  You're looking 
for what is making the equipment not work.  Fix that, THEN blueprint 
if you want.

Best regards,

Don