21
Baker Instrument Company
The Measure of Quality
D
ISPLAY UNREADABLE AND FLASHES
ON
/
OFF
,
DOES NOT INITIATE SELF TEST
1.
A check of the DC supplies and crystal frequency to verify proper conditions, see
Voltage Busline and Crystal Checkout procedures.
2.
A loss or loading of any one or more of the following lines due to faulty components
or connections will cause this occurrence. Since these signal lines are tied to the A/D
board, I/O board, and the Controller card it will be necessary to troubleshoot in the
manner outlined in step 3.
___ ____ __________ _________ _________ _________ ____
RD, Reset, CRT Enable, 103 Enable, 102 Enable, 101 Enable, SAD, RD/WR, ALE,
Reset, DB0 through DB7, AD1 through AD7 and AD8 through AD14.
3.
To determine which printed circuit is defective, unplug the A/D board and the I/O
board with the power off. Turn on the tester and observe the tester response. If the
tester now begins with a Baker logo then the fault is not on the Controller card. The
tester will fail the A/D Memory test due to the A/D card not being inserted into the
Motherboard. Turn off the testers power.
4.
Insert the A/D board into the J1 connector and switch power on. If the display returns
to the original fault condition, then a fault will be on the A/D board. Turn off tester
power.
5.
Insert the I/O card into the J3 connector of the Motherboard and turn on the testers
power. If the display returns to the original fault condition, then the fault will be
located on the I/O board.
6.
After determination as to which card is defective, remove power and the defective
card. Install the faulty card on an extender card and apply power.
7.
With a 10X-scope probe begin monitoring the data, address and signal lines noted in
step 2. It will be helpful to record all lines, which do not have data present. See
Motherboard DST Series schematic for pinout contacts of these signal lines to each
card. Data is defined as a high frequency 0 to 5-volt amplitude logic level changes
determined by the programmed U3 27C256 EEPROM located on the Controller card.
8.
After determination as to which signal lines are stuck low or high, it will be necessary
to trace the defective signal lines to all components that are tied to the same line and
replace one at a time. It may also be necessary to check defective signals lines with a
digital multimeter set to ohms for shorts to GND and to +5 volts DC. Also check
