Author Topic: B&G Zeus Boat Plotter with broken NMEA2000/CAN Bus / Burned Resistor Value?  (Read 253 times)

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Offline maxmatteoTopic starter

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Hey there,

i have a b&g zeus 2 board here which works fine, except a complety non functional CAN-BUS/NMEA2000 System.

Bus Diagnose Shows BUS-OFF and 255 TX Errors.

I checked the CAN Transceiver (ON Semi AMIS 30660) and Isolator IC (ISO7221), all look fine but i do not have the proper Supply Voltages.

12V Comes in via a small 3 pin Transistor(?) and then through a standard 7805 regulator.

i see 7805 IN 2.7V and OUT  1.2V. so i assume we have some power issue here.

Close to the 7805 i see a burned Resistor, but cant identify any possible value. 4009? Would be way to much i guess.

Resistor currently measures 15kOhms.

Thanks for any educated guess :)

Max



« Last Edit: November 21, 2024, 10:42:55 am by maxmatteo »
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Offline Jon_S

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12V Comes in via a small 3 pin Transistor(?) and then through a standard 7805 regulator.

I would suspect it is a SOT23 diode from the pinout, and the fact that pin 2 doesn't look to be connected to anything.

Close to the 7805 i see a burned Resistor, but cant identify any possible value. 4009? Would be way to much i guess.

4.99 Ohms is a standard value and would be marked '4R99'. I can't make out the second character enough to be sure it is an 'R', but that seems plausible.
 
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Offline maxmatteoTopic starter

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thanks for the help.

diode confirmed! just saw a voltage drop on one pair of pins!

regarding the resistor:

so its either 4,99 (4R99) Ohms or 49,9 (49R9) Ohms :)

I tried with 50 Ohms and got proper 12V and 5V after the 7805.

anything against using 50 ohms? i guess its just for current limiting?
« Last Edit: November 21, 2024, 05:12:40 pm by maxmatteo »
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Offline Jon_S

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I think what you have labelled as a diode (by the regulator) is actually a Unidirectional TVS. A small-ish series resistance before a TVS is really common for simple surge protection. The resistor just limits the peak current into the TVS, as you are trying to protect your own electronics not clamp the whole vehicle. Also, when when a surge exceeds the TVS power limit they tend to fail short and the resistor pops before the traces do...which is nice!

So, if you don't have an excessive voltage drop over your resistor then everything should be good.
 


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