DRESSTA TD-25M EXTRA, Service Manual

Page: 306 / 595

SECTION 8
ELECTRICAL
Page 30
TD-25M EXTRA DRESSTA
ALTERNATOR
To check the diode trio, remove it from the end frame assembly by detaching the nuts and
attaching screw.
NOTE: The insulating washer on the screw is assembled over the top of the diode trio connector.
Connect an ohmmeter having a 1
1
/
2
-Volt cell to the single connector and to one of the three
connectors, (Fig. 8.8). Using the lowest range scale, observe the reading. Then reverse the
ohmmeter leads to the same two connectors. If both readings are the same, replace the diode trio.
A good diode trio will give one high and one low reading. Repeat this same test between the single
connector and each of the other two connectors.
c. Rectifier Bridge Check
4
5
6
1
3 2
Fig. 8.9. Checking Components
1. Ohmmeter
2. Ohmmeter 3. Ohmmeter
4. Ohmmeter 5. Ohmmeter
6. Ohmmeter
Omit for overcharged battery. To check the rectifier bridge, connect the ohmmeter to a heat sink
and one of the three terminals (Step 1, Fig. 8.9). Then reverse the lead connections to the same
heat sink and same terminal. If both readings are the same, replace the rectifier bridge
by detaching the necessary screws and nuts. A good rectifier bridge will give one high and one low
reading. Repeat this same test between the same heat sink and the other two terminals, and
between the other heat sink and each of the three terminals. This makes a total of six checks, with
two readings taken for each check.
d. Field Coil Checks
To check for grounds, connect an ohmmeter to one field coil lead and to the end frame
as illustrated in (Step 2, Fig. 8.9). If ohmmeter reading is low, the field coil is grounded.
To check for opens, connect an ohmmeter to the two field coil leads as shown in (Step 3, Fig. 8.9).
If ohmmeter reading is high (infinite), the field coil is open.