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Author Topic: Common faults  (Read 10000 times)

woody

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Common faults
« on: March 26, 2016, 08:56:50 pm »
Most common faults with the older detectors such as SD 2000 2100 2200 is the input N channel Fet going noisy , short circuit or open circuit. This component has around 185 volts of clamped back emf from the coil across the drain to source connections, mind you that this part is rated at 200v or some are 240 volts it can still fail by a number of causes.  Removing the coil when the detector is operating can generate high voltage that can blow it up. A bad coil connector pin and socket on the coil connector, or shorting coil wires can cause it to pop.  The device is very old, it have a ohmic loss of 10 ohms and that is bad, newer replacements are only 1 or 2 ohms loss, it makes a big improvement when driving the LM394 differential preamplifier.  It is easy to find, follow the yellow coil wire to the circuit board, using a multimeter find the connection to the black transistor with 3 legs, unsolder and replace with the same part VN10 or get a new input get with instructions from me. The pins are in different positions and needs explaining on how to do this.

Joeboy

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Re: Common faults
« Reply #1 on: October 12, 2016, 11:04:10 pm »
Gday woody i have a sd2200 that fails to turn on, wondering what could be the cuase of this problem. The carboard minelab box was exposed to water with the detector inside, Tho the control box wasn't directly exposed do water there would of been alot of moisture around it over a 2 day peroid.
Its not a standard model, it had the full upgrade done by you some year's back with variable gain mod also. Its my brothers detector and he's not prepared to spend more money on it, so its getting sent to me. Im going to open it up for a look and see if there's any obvious signs of damage. I found my first gold nugget with this 22, so I'm hoping its only a simple part to replace, any suggestions would be greatly appreciated on which component might of failed on start up and what to look for? assuming it did fail when turned on.
Cheers joeboy

woody

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Re: Common faults
« Reply #2 on: October 12, 2016, 11:53:28 pm »
More than likely the small bipolar transistor near the choke in the power supply will be dead, too much load caused by moisture on some sensitive parts can cause this to pop.  other than that the input voltage wires have fallen off or the on off switch is high resistance.  Any of these are the likely problem.

Joeboy

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Re: Common faults
« Reply #3 on: October 13, 2016, 12:19:14 am »
Thanks woody, when i open it I'll check the input voltage wirrs first. Other than that is the bipolar transistor easy enough to replace and is it available to buy from somewhere

woody

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Re: Common faults
« Reply #4 on: October 13, 2016, 12:40:56 am »
It is under a big pile of hot melt glue minelab use on the big capacitors, i will send you the part number later.


Joeboy

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Re: Common faults
« Reply #5 on: October 18, 2016, 08:26:29 pm »
Thanks for your advice woody, pulled the control box apart today and just like you suggested to check... input voltage wire had come away, easy fix cheers.