37
Resistance check
Once you have completed a visual inspection of the circuit the next step is to perform a
resistance check of the circuit. This will help to assure that parts have been connected
to the proper terminals and soldered properly before any AC mains voltage is applied
to the circuit.
( ) Turn the volume control all the way down.
( )Attach the negative lead (typically black) of a volt-ohm meter to ground. A good spot
to do so is at terminal 12. Use of a clip lead to connect the black test lead to the
ground will free one hand, making testing much easier.
Using the positive lead (typically red) of the volt-ohm meter, check the resistance of the
following terminals. They should read roughly like this:
Note that the term K denotes x1000, and the term
denotes ohms, so 1K
equals
1000 ohms. 1Meg
equals 1,000,000 ohms. The values signified with a * are going to
vary from ohmmeter to ohmmeter because these terminals are connected to the filter
capacitors, which try to charge themselves off the battery in the meter, causing a
fluctuating reading. If the circuit is connected properly these readings will wander in the
tens or hundreds of Kohms or higher range. What you want to watch out for is a zero
reading at one of these terminals, which would indicate that something is mis-wired.
Terminal
Resistance
1
*
2
*
3
0 ohms
4
*
5
*
6
2.4K ohms
7
2.9K ohms
8
0 ohms
9
2.9K ohms
10
2.4K ohms
12
0 ohms
13
* will climb slowly toward 270K ohms
14
0 ohms
20
0 ohms
22
0 ohms
B3
2.9K ohms
B6
2.9K ohms
RCA jacks:
Ground lug
0 ohms
Center pin
90K ohms
—
100K ohms