Update
We did some more testing / troubleshooting yesterday with the repaired CIM and the focus shifted swiftly to the A5 Board as the initial problems were still present.
The A5 has the operational Brain on it. It's a 8 bit Microchip PIC 17C44 40 PIN Plastic Dip with 8K memory and several A/D Converters and UART as well as I/O Micro Controller.
The relays for fuel pumps, starter, excitation, Network Failure Indicator and all Status LED's on Backplane are controlled by this PIC (we just call them PIC's). He also scans the Start / Stop / Run Switch, Main Contactor Switch, Fault Reset Switch etc.
Since the Device has only so many PIN's, CMOS Multiplexers are usually used. Those are the plastic DIP's with 74HCxxx
One of those who drives the relais / relais drivers is shorted.
The problem in detail:
When the Master Control Switch is set to On:
1. The Network Indicator Light comes on immediately (Before CIM even starts to boot)
2. The Fuel Pumps come on immediately
3. Other Relays come on as well (we didn't further investigate, as the problem is one of the 74HCxxx chips)
4. The CMOS Battery LED comes on immediately
CIM Boots normal and does not display any errors (except overspeed / undervoltage error from previous run which is stored now)
When Fault Clear Switch is activated either after Boot or with S2 in RUN / Prime Position it will clear any error codes on CIM but the Network Failure Indicator will not turn off
The PIC communicates with the CIM and an additional PC (if hooked up) via RS232 - both CIM and PC are slaves to PIC
All A/D D/A conversions are done by PIC and then sent to CIM / PC for display
All sequencing for operation is done by PIC according to S2 switch settings. All Analog Signals from sensors are fed to PIC except MPU which goes straight to Governor Control Board
I will post more details when I get A5 Board here for repair
Note: the software for the PIC was written in Assembler
