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C800H Technical

 I have a problem with my C800H, there is a short circuit somewhere on the PCB.  I have been trying to trace this fault but have hit difficulty in that the schematic given in the User Manual is different from the PCB.  For example the PCB has 2 transistors on it, while the schematic only shows 1.  The circuit symbols bear little relationship to any standard i have come across in my servicing work over the past 60 years, I am an electronics engineer and spend my days servicing, to component level, many more complicated devices than the C800.  Please can anyone supply me with the correct schematic of the electrics/electronics of my tractor?

Whats the issue with your machine ?

Sorry we cannot give out the schematic to our boards.

Please advise what your issue is ?

Thank you Darryl for the reply, I did expect this, but no matter I am in the process of back engineering the PCB so will have a schematic shortly.

The problem started when I took the unit out for the first time this year, I jumped on pressed the brake pedal turned the key, the ignition led did not light and very quickly a whisper of smoke and a smell of burning.  This could only have come from behind the dashboard so I removed the PCB and unplugged it.  Inspection in the workshop quickly revealed that 2 of the PCB tracks had overheated and one was open circuit.  Ah ha I thought we have a short circuit somewhere.  I quickly found a short circuit diode, a 1N4002 and as this is connected to a transistor I decided to remove this and put it on my transistor tester - it tested up as 2 diodes back-to-back, certainly not a transistor so this I also replaced.  Both items came out of my extensive stock of spare parts and were tested before fitting to the PCB.  It was then only necessary to carry out a repair to the PCB track, easily done.

I suspect that one or other seat/brake interlock switches are not operational and will be my next check.  The only reason for asking for a schematic is to save me time, I don't want to have to back engineer the board as this does take valuable time.  I am a reliable and trustworthy electronics engineer and have access to many very complex schematics from many very large companies, such as Fender Music and Yamaha and I have never, and never would reveal these to anyone else, I take this trust more than responsibly.

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