[Test-Equipment] testing semiconductors

[Brooke Clarke]

Hi b/:

1) Yes.
2) either digital or analog
3) Digital DMM Diode or Ohms analog Ohms
4) diodes and bipolar transistors all appear as diodes.  Others are specialized.
5) Yes.  Older analog meters (prior to the introduction of semiconductors) used 
high voltages on the Ohms range and depending on the range setting might blow 
out transistors and other semiconductors.

But . . . I'd say that capacitor failure is as or more likely.  Electrolytic 
caps can loose their electrolyte causing the capacitance to be much lower 
and/or the Effective Series Resistance to be too high for proper circuit 
operation.  Tantalum caps typically fail as shorts which typically causes a 
nearby component to burn out.  If you find and replace that burned out 
component it will fail again at power up.

Often you can recognize burned out components because they look brown, black or 
physically broken.  But recently I came across some resistors that were blown 
that appeared at first glance to be OK, but upon close examination were white 
and the lettering was burned off.  See:
http://www.prc68.com/I/HaT.shtml#60PP9202
and scroll down to "Note the lower resistor is marked 6".

There are other tips on this page, the key one being that the most probable 
failure is caused by oxidized connections.  See What Goes Wrong:
http://www.prc68.com/I/HaT.shtml#Wgw

Have Fun,

Brooke Clarke
http://www.prc68.com

Rasputin Novgorod wrote:
> While reading thru back messages (perhaps in a discussion 
> about power supplies), someone said that the usual fault is
> blown semiconductors. They suggested to quickly meter across
> all the leads of each semiconductor for shorts or open
> (i.e. obviously blown).
> 
> I'd be grateful if someone elaborate further, is simple language
> about quick semiconductor testing.
> (i.e. think "Dummys guide to electronic Repairing...".
> What is obvious to you pro's, is intimidating to we beginners.
> 
> 1) Can the tests be done in-circuit? 
> 2) Can a digital or analogue VOM be used?
> 3) What are the meter settings?
> 4) All semiconductors? (FETs, Triacs, etc).
> 5) Can small parts be damaged by testing?
> 
> Sincerely
> /b
> 
> 
>       
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