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ProDave

Anyone repaired a Studer Inverter / charger?

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ProDave

I have one to repair, but getting it apart has stumped me.

 

It has one large PCB that slides into grooves in the case, which is basically a large extruded tube.

 

I have removed the couple of screws that seem to locate the pcb, and undone and what appear to be clamp screws on the bottom to clamp some tab power transistors to the bottom ov the case as a heatsink.  There is nothing visible holding the PCB in place.

 

There is not much to pull on to extract the pcb, so I have drilled a small hole on the one vacant bare patch of board to get a hook in and something to pull on, but pull as hard as I can it will not budge, not even a tiny amount.

 

What a stupid design, but there must be a way to get the board out. Any ideas?

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Geoff1946

Have you prised the semiconductor tabs off the heatsink? Some of the compounds used can stick ferociously.

Be careful drilling the board' - it could be multi layer!

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ProDave

Thanks

 

Yes I did get it apart. It was the transistors "stuck" to the extruded case/ heatsink. An engineers steel rule slid down the narrow gap between the case and the board and a gentle tap on each freed it.

 

This is the second time I have had this in.  The first time I sat it on test for 2 weeks and it worked perfectly so went back to it's owner where it worked perfectly again for another 2 months. This time it showed the fault (alarm chirping and battery low voltage flashing) when I got it, but now it is in bits it works perfectly, so I am having fun re soldering lots of poor looking soldered joints in the hope I hit the right one and fix it.

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Geoff1946

Could be a valuable clue in the low voltage warning. Pay special attention to all connections on the high current input circuit.

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ProDave

I don't think it's a busbar connection problem. The low voltage warning came up with no load on the output so input current was tiny.  The fault went away after dismantling, just as it did last time simply by bringing the thing to me. That's why I am concentrating on looking for dry joints. The general standard of soldering is pretty poor, but I am not sure I want to re solder everything just yet.

 

A circuit diagram might help narrow it down a bit.

Edited by ProDave

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Geoff1946

Have you got freezer spray? I've found that invaluable for locating dry joints.

 

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