Two very good cheap pieces of kit, there is plenty of good informative information on using these devices available on the internet. Here are a few good sites to visit:
If you are too tight to part with the relatively small amount of cash
required for these items, it is possible to build your own logic probe (well its a
little different, its a video probe).
Anyway, the logic probe is useful to check what is going on (electrically) on
the inputs and outputs of each IC on the board. Normal logic chips use only two states for operation, on and
off/ 0 and 1/ high and low. These of course are all the same thing and
relate to either a logical high which is +5volts or a logical low which is
active ground/ 0volts. It is therefore possible with the pinouts from a
site such as The Chip Directory
to see if each chip is operating correctly. For example, on 74LS logic
chips you will be able to see if the two inputs which make up an AND logic gate have
the correct resulting output, sometimes the output will be 'floating'
meaning that its neither +5 or ground, which is quite obviously then
faulty. Care should be taken here to not bin parts which aren't faulty as
not all inputs and outputs are connected on every IC and unconnected lines tend
to be floating rather than just off.
Before in that statement I said,
"normal logic chips" referring to the TLL type, there are also the
CMOS type which rather than have a digital output they have analogue outputs and
can work at a much higher voltage. Logic probes can be bought which have a
TLL/CMOS switch to test both types.
The logic pulser is used to inject a high/low pulse into the circuit, this is useful to change the active state of an input or output. Of course, you can use a patch wire connected to ground to make a high into a low (useful for testing reset circuits) and vice versa a patch on +5v for turning a low into a high (for bringing a processor out of a HALT state springs to mind). The logic pulser is a useful tool, one of the best uses I have found for it is to be able to test speakers and amps. This is covered in greater detail in the repair pages later on.