Thermo Scientific 3403 Manual page 55

Thermo Scientific
• The next step would be to check for the presence of the PS15 & PS15R
signal at the CPU board. Easiest point to check these will be J12 pin 8
(PS15) and J12 pin 9 (PS15R). If PS15 is not present, check the har-
ness assembly between the power and CPU board. If PS15 is present
while PS15R is missing, proceed to the interface board.
• Jumper J4 pin 4 to J4 pin 5 on the interface board. If the unit powers
up, the key switch assembly is the probable cause. If not, troubleshoot
the connectivity between CPU J7 and Interface J2. Another verification
that there is a breakdown in connectivity here is to short J12 pin 8 & 9
on the CPU. If the CPU J7 or Interface J2 connection is the issue, the
unit should power up.
J5 - Serial Communications In from CPU
None of the signals at J5 or J6 can be accurately measured with a typical
DMM. Some activity maybe discerned with a DMM but an oscilloscope
is really required to capture these signals. Plus, measuring points on the
305172H01 are essentially inaccessible. Troubleshooting is basically
limited to swapping harnesses or assemblies. A strong indicator of a serial
communication problem with the display is when there is LED activity on
the power board yet the display is blank. On other occasions, a unit may
have been running and then the information on the display becomes static.
It is also common for erroneous dots to be illuminated on the display in
this scenario. This is indicative of a successful communication link being
broken. Reseat J10 on the CPU as well as J5 on the interface board. A
wire tie around the J10 connection is recommended.
Pin 1 – Serial Data
Pin 2 – Latch
Pin 3 – Blank
Pin 4 – Ground
Pin 5 – Serial Clock Pin 6 - Ground
J6 – Serial Communications Out to VFD Display
Pins 1, 3, 5, 7, 9, 11, 13, 17, 25 – No Connect
Pins 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 - Ground
Pin 15 – Serial Data
Pin 19 – Blank
Pin 21 – Serial Clock
Pin 23 – Latch Pin 26 - +5V
J7 - Ground and 5 VDC Out to VFD Display
Section 8
Appendices
Midi 40 CO2 Incubator 8-23