Graco 390 Repair Manual page 11

Problem
Low Output
310824C
What To Check
(If check is OK, go to next check)
1. Worn spray tip.
2. Verify pump does not continue to
stroke when gun trigger is
released.
3. Prime valve leaking.
4. Suction hose connections.
5. Electric supply with volt meter.
Meter must read 100-130 VAC for
110-120 VAC models and
210-255 for 240 VAC models.
Low voltages reduce sprayer per-
formance.
6. Extension cord size and length.
8. Leads from motor to circuit board
for damaged or loose wire con-
nectors. Inspect wiring insulation
and terminals for signs of over-
heating.
9. Worn motor brushes which must
be 1/4 in. (6 mm) minimum.
10. Motor brushes binding in brush
holders.
11. Low stall pressure. Turn pressure
control knob fully clockwise.
12. Motor armature for shorts by
using an armature tester
(growler) or perform spin test,
page 16.
What To Do
(When check is not OK, refer to this column)
Relieve pressure, page 7. Replace tip. Refer to
gun instruction manual, 309639.
Service pump. See page 13, Displacement
Pump Replacement.
Relieve pressure, page 7. Then repair prime
valve. See page 23, Manifold Replacement.
Tighten any loose connections. Check o-rings
on suction hose swivel.
Reset building circuit breaker; replace building
fuse. Repair electrical outlet or try another
outlet.
7. Replace with a correct, grounded extension
cord. See page 6, Grounding and Electric
Requirements.
Be sure male terminal pins are centered and
firmly connected to female terminals. Replace
any loose terminals or damaged wiring.
Securely reconnect terminals.
Replace brushes. See page 18. Motor Brush
Replacement.
Clean brush holders. Remove carbon dust by
using compressed air to blow out brush dust.
Replace pressure control assembly. See page
22, Pressure Control Assembly Replace-
ment.
Replace motor. See page 26, Motor
Replacement.
Troubleshooting
11