Sterling STT70, STT40 Troubleshooting, Introduction, Problem, Possible cause, Corrective action

STT40 / STT70

9. Troubleshooting

9.1. Introduction

The utmost in safety precautions should be observed at all times when working on or around the machine and the electrical components. All normal trouble-shooting must be accomplished with the power off, line fuses removed, and with the machine tagged as out of service.

The use of good quality test equipment cannot be over-emphasized when troubleshooting is indicated. Use a good ammeter that can measure at least twice the AC and DC current that can be encountered for the machine. Be sure that the voltmeter has at least minimum impedance of 5,000 OHMS-per-volt on AC and 20,000 OHMS-per-volt on DC scales. Popular combination meters, VOM and VTVM can be selected to provide the necessary functions.

Before making haphazard substitutions and repairs when defective electrical components are malfunctioning, we recommend that you check the associated circuitry and assemblies for other defective devices. It is common to replace the obviously damaged component without actually locating the real cause of the trouble. Such hasty substitutions will only destroy the new component. Refer to wiring diagrams and schematics.

Locating mechanical problems, should they occur, is relatively straightforward. When necessary, refer to the parts catalog section.

Problem	Possible cause	Corrective action
	Dirty filter.	Clean or replace filter.
	Desiccant beds are contaminated	Replace desiccant. See Page 42
	by material or plasticizer leaking
		for more information.
Little or no air coming from	into the system.
the process delivery tube.	Blower overload has tripped.	Fix the problem and reset the
		overload.
	Blower fins filled with dust or	Remove blower side plate,
	contaminants.	clean baffles, replace.
		Stop the dryer.
		If the dryer was connected to
		the drying hopper, check to see
	Phase is reversed on power drop	if the desiccant and process air
Suction in delivery tube,		heater has been contaminated
	coming into the dryer.	with resin.
pressure from the return tube.
	(Note: on STT 70 only)	If so, replace the desiccant and
		remove any resin carry-over.
		Otherwise, change the phase of
		two legs of the three-phase
		power drop.

Troubleshooting 9-1