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Pirate of the Puget Sound
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715 Posts
Discussion Starter #1
One of my 2-year-old ST-200 audio servo driver boards has suddenly crapped out on me without any warning.
No apparent damage, power LED fails to light, no servo response. I tried powering it alternately by battery and wall wart but with no success.

I'm guessing it might have died for some reason, but I want to see if there is anything I can do try to fix it.
Is it possible to resuscitate a dead board? Any known issues with this board?

I tried contacting Carl of Cowlacious, but have yet to hear back from him.

 

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It looks like the three legged chip attached to the heatsink is a voltage regulator.

It should have a number like 7805 or 7806 or something of the sort.

the 78 is the series and 05 is the voltage (5 Volt in this example)

if you take a voltmeter and check the leg on the left side of the chip you will see the input voltage that can be 5 to 24VDC according to the spec on the web site.

and the voltage on the pin to the right of the chip should be the voltage in the part number.

if it doesn't match then the chip is probably bad,.
 

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Pirate of the Puget Sound
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715 Posts
Discussion Starter #5
I will have to get a voltmeter and check out the voltage regulator. (It says it is 5 V.)
Now that you mention it, I think I remember it acting a bit funny whenever something touched the heat sink, which is connected to the voltage regulator.
 

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Pirate of the Puget Sound
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Discussion Starter #7
A closer look at the connections of the voltage regulator shows that one of the legs is in fact disconnected from the board. Must not have been soldered very well. Pushing down on the voltage regulator and tilting it at an angle creates a contact and powers the board although it is intermittent.
Is it worth resoldering the broken leg back to the board, or would it be better to swap it with a new voltage regulator?
 

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just resolder it. Depends on how much current they are passing, I have seen them heat up enough to unsolder themselves.
 

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The solder joint my not have broke but the pad came off the board (copper part that is attached to the fiberglass) if that is the case you have to solder a wire to the lead of the regulator and find the next lead that the trace goes to.
 

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Bête noire
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If the pad actually came off of the board, it must have gotten pretty hot. Same goes for de-soldering.
Haunter, what voltage is the power supply you're using with the ST-200? I know it can run on 5VDC - 24VDC, but 24 volts would be pushing the 7805 a bit. Make sure you have reasonable ventilation for the heat sink if you're using a high voltage supply.
 

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Pirate of the Puget Sound
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Discussion Starter #11
It looks like the voltage regulator leg broke at the soldering point. I can see the exposed copper of the broken leg piece embedded in the board. I don't think the board overheated because I only ran it with a 6VDC power supply. It's more likely the heat sink was impacted when mounted inside the skull, placing stress on the leg.

 
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