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2 boards (been used for 3 years) suddenly dead. Bad Transformer ?


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I have 2 CTB16kpc boards. They were assembled and working for 3 years. I checked the boards a couple weeks prior, and they were fine. came out today, and both boards were suddenly dead. No status light.  

18 pin header had nothing at the probe points.

D1 & D2 - nothing

Probing around the transformer it seems like the transformer is just dead.


Power into the board is fine, fuses are fine.

Cant find any voltage on pins 7-12 of transformer.


Does anyone know what the proper pin outs / voltage is for the transformer ?


I know a transformer CAN go bad, but it seems awfully strange to blow both at the same time, and there be no others signs of any electrical damage.

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there are 2 voltages that come off the 7812 and 7805 ? (the things that look like a transistor in a heatsink) they go back to a set of rectifier diodes and those go to the transformers pins.


NOTE: the one side of the line (1-8) supplies power to the transformer, SO, if that fuse is blown the unit will appear dead.


I agree that the transformer is a heavy item,


BUT, would check input (line voltages on the card FIRST, then fuse, then 120/220 jumper, then input to transformer itself, THEN output side of the transformer).


If there is voltage (120 AC line) right to the pins on the transformer, BUT nothing (AC 16+ on the low side, then I would assume transformer or internal (non-serviceable IN Transformer) one-time fuse.



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To lose two transformers at the same time on different controllers you would have had to have something like a spike happen... and transformers are pretty forgiving so that would have had to have been a pretty nasty spike..  I don't think you could even damage them from the DC side since you would have to go thru the regulators and the bridge rectifiers to get to the transformers...... Unless.. something happened on the DC side to cause a short... then the transformers could have been loaded down for some time.. like perhaps over night while sitting powered up???  (a stretch for sure)


If you checked right on the xfmr pins and got those voltages that would rule out soldering issues.


Very peculiar indeed.


Just for yucks.. perhaps measure continuity on the secondary and see if you get a short or some low ohm value.  If the transformer secondaries are open you should see a pretty high resistance.  If you see a fairly low value, either the secondaries are not open, or you have a short in the bridge rect.    If the former, then you must have lost the fusible link in the primary side... 


Again, to lose two at once.. you are right..very odd

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I jumpered the connections over to another board with a working transformer, and applied power.

I got the usual flashing red led. so hopefully the rest of the board is ok.


I ordered new transformers from mouser, so I'll get those installed, and then test the rest of the board.

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