Thermo Scientific 3403 Manual page 54

Section 8
Appendices
8-22 Midi 40 CO2 Incubator
J4 – Input from Key Switch
For reference, wiring diagram 3403-70-1 provides a schematic depiction of
the key switch and J4. Pin 1 is toward the top of the board, away from
"J4" label.
Pin 1 – "+5V" Output to key switch
Pin 2 – no label Enables battery charging circuit. When key is in position
2 ( | ), +5 VDC will be present. Approximately +4.3 VDC (diode drop
from +5) will be present on this pin when the key switch is in position 3.
Pin 3 – "ALARM-EN" Signal to CPU that the key switch is in position 3
(X). Also enables battery charging circuit via a diode to Pin 2. +5 VDC
will be present on this pin when active.
Pin 4 – "PS15" Primary DC voltage supplied to key switch. Typically,
this will measure ~11.7 VDC. During normal operation, as long as line
voltage is supplied to the unit, this should always be present. See
additional information below.
Pin 5 & 6 – "PS15R" This is the signal that initiates a power up. When
the key is in position 2 or 3 ( | or X), the DC voltage measured at pin 1
should be present here. See additional information below. The PS15
signal passes from the power board through the CPU and Interface board
to its final destination – the key switch. Likewise, PS15R travels back
through these boards to trigger a power up. Thus, there are several points
available to check these signals and troubleshoot a power up problem
through the process of elimination.
The following is a summary of key points to check.
• If the display is blank, the PS15/PS15R circuit can actually be working
correctly. If a unit appears not to be working, the first thing to check is
for activity on the power board. With the key in position 2, wait for a
few seconds and check for illuminated LED's on the power board. If
LED's are illuminated, serial communications to the display should
become suspect. Begin troubleshooting the CPU J10 to Interface J5
connectivity. Check the CPU J10 connection first & wire tie if neces-
sary. If LED's do not illuminate, begin troubleshooting PS15 & PS15R.
• To confirm that a break in the PS15(R) circuit has occurred, with power
to the unit & the key switch on, check for PS15R at J4 pin 9 on the
power board (302268H02). If present, troubleshoot elsewhere, i.e. check
for 5 VDC on the CPU. If not, check for the presence of PS15 at J4 pin
8. If PS15 is not present, check the fuses and power coming in.
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