SERVICE
PROCEDURE
Should for any reason a failure occur in service it is very helpful if the
conditions at the time of failure are reported to the company. Items such as ambient
temperature, line voltage, output voltage and current, mode of operation, and over-
load conditions, if present, will be helpful in making an accurate diagnosis and .
prompt repair of the unit . Other symptoms such as excessive voltage, no voltage,
excessive ripple are of great use in determining the nature of the defect.
TROUBLE SHOOTING
Malfunction of the power supply will in most cases manifest itself as
excessive voltage, no voltage, or widely varying voltage. .In any case the first step
is to examine the printed circuit board for loose transistors, broken copper, burned
spots or heavy dust on the transistor and SCR heat sink. The second step is to make
an insulation test between the minus output terminal and the chassis, Be sure to dis-
connect any leads connected to the rear terminal strips. The test procedure is to
connect a 1 meg-resistor hi series-with.a 1000 volt power supply and the minus output
terminal. Then measure the voltage drop in the resistor or the voltage applied to the
supply with a meter rated at 100,000 ohms/volt or higher. A VTVM is not satisfactory
unless battery powered and an input impedance of 100 megohms. See Figure 6A. The
voltage rise should not exceed 50 volts except in extremely humid environments when
the power supply under test is disconnected from the test circuit. Any fluctuations
may be sporadic arcing between the SCR's or the tee. If for any reason the SCR's or
the power transistors are disturbed the high voltage insulation test is a must. If the
Insulation test is satisfactory then follow the testing section under Preliminary Check-
out. If the unit operates normally then the failure was due to the opening of a sensing
lead, load lead, programming lead originated in the equipment being powered, or is
of anintermittent nature. If the unit operates normally but there is a desire to assure
its operation in detail then start at step #9. in the alignment procedure. If the unit
operates abnormally then proceed to Table I if servicing is to be done by the customer. |
ACEC
