
Check the IC Ground Pins
Connect the negative lead of the DMM connected to pin 2 of J1 and begin checking the
ground pins of each IC with the positive lead. You should read zero ohms on your DMM
for each pin, or very, very close to it.
Ref Des
Device
Ground Pin
U1 LM358 Pin
4
U2 CD40106 Pin
7
U3 CD4071 Pin
7
U4 CD4093 Pin
7
U5 CD4013 Pin
7
U6 CD4034
Pin
12
U7 CD4034
Pin
12
U8 LM358 Pin
4
U9 CD4053 Pin
8
U10 CD40106 Pin
7
U11 CD40106 Pin
7
U12 CD4093 Pin
7
U13 CD4093 Pin
7
U14 LM324 Pin
11
U15 LM324 Pin
11
Table 8-2: Digital Board IC Ground Pins
That concludes the cursory Digital Board checks. If there are any undiscovered build
problems, you’ll know soon enough…..
Inspecting the Digital Board
Next up for scrutiny is the Analogue Board. It’s the same drill:
•
Visually inspect the solder joints.
•
Visually inspect the socketed ICs.
•
Visually inspect the orientation of polarized parts (transistors, all those polarized
caps, all of those diodes.
Check for Power Supply Shorts
The Analogue Board not only has two power rails to check, but also two ground systems
as well. On top of that, it’s probably a good idea to make sure that it is going to toss the
power signals the Digital Board so craves.
The four pin header J10 is the power entry connector of the Analogue Board. Connect
the positive pin of your ohmmeter to pin 1. Connect the negative lead of the DMM to pin
2 of J10 (Analog Ground). It should read much greater than 0 Ohms. Give it at least a
couple hundred Ohms before you feel good about it.
Now connect the negative lead of the ohmmeter to pin 3 of J10 (Digital Ground). Again,
you should read at least a couple of hundred ohms at minimum.
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