GMC 4000 Series Service Manual page 435

Sec. 6Y
Page 424
A/C GENERATING SYSTEM
T R A N S IST O R
R4 EMITTER
BASE R ESISTO R
O UTPUT BASE
R5 R ESISTO R
No 6
O U TPU T
FIELD DISCHARGE
T R A N S IST O R
(M OUNTED ON REVERSE SIDE)
2. Lift up on regulator terminal latch and in­
sert wiring harness connector over regulator term ­
inals.
IMPORTANT: Make sure connector is fully
engaged over terminals and locked in position.
Check by attempting to pull connector apart.
3. Connect battery cable to battery terminal.
REGULATOR REPAIR
To check the regulator for defective compon­
ents proceed as follows:
1. Remove four screw s which attach cover to
base plate and remove the cover.
Figure 2 4 — C h eck in g Regulator Circuits
G M C S E R V I C E M A N U A L
R3 V O LTA G E DIVIDER
R ESISTO R
R2 POTENTIOM ETER
No. 3 C A P A C IT O R
AD JU STIN G ARM
HEATING PO IN T
No. 1 TH ERM ISTO R
R1 VO LTAG E DIVIDER
R ESISTO R
No. 7 BACK BIAS DIODE
No. 5
DIODE
Figure 2 3 — Com ponent Parts of Panel Board Assem bly
REGULATOR
2. Referring to figure 21, remove leads from
term inals 1, 2, and 3, then remove screw s 4 and
5 which attach relay to base and remove relay.
3. Remove screws (6 and 7, fig. 21) then lift
circuit board, heat sink and terminal assembly
from the regulator base.
4. Note the insulation between the output tran­
sistor and heat sink, and the insulators separating
the heat sink from the panel board (fig. 22).
5. Remove screws which attach transistor to
panel board and separate the transistor and heat
sink and insulators from the panel board.
6. Visually inspect all copper traces on the
panel board for opens and for shorts or grounds
which could be caused by solder runs.
An ohmmeter having a 1^-volt cell, which is
the type usually found in service stations, is rec­
ommended for checking transistors and parts of
the panel board. The low range scale on the ohm­
meter should be used.
If a component part on the panel board is found
to be faulty, it should be replaced before proceed­
ing with the remaining checks. A 25-watt soldering
gun is recommended, and a 60% tin 40% lead solder
should be used when re-soldering. Avoid excessive
heat which may damage panel board traces. Com­
ponent parts are identified in figures 22 and 23.
In all of the following checks, connect the ohm­
meter as shown, then reverse ohmmeter leads to
obtain a second reading.
NOTE: Refer to figures 22 and 23 for identi­
fication and location of following connections:
7. To check component parts of the panel
board, it is necessary to carefully unsolder the
specific connections at points shown in figure 24.