How to identify transformer specs to find a replacement for control board

[clsmith6]

How can I identify the specs of the transformer on the garage door control board in these pictures, so that I can purchase a replacement?
**broken link removed**

The transformer is labelled "PCX-1635-AUN W2107", roughly 33x41x25mm (d,w,h) and has 7 solder joints on the board.

As a result of sustained overvoltage throughout my house (I measured 150VAC, caused by disconnected neutral due to damaged main line from road), quite a few appliances and electronics were fried. After power company fixed the main line, I fixed the dishwasher board (blown MOV and trace), and next on my list is to fix my garage door openers (Linear LS050). As you can see in the pictures from the charred area, an MOV (labelled RV1) between nuetral and hot blew (I removed it). I plugged the board back in and I see the 120VAC on the primary side of the transformer, but get nothing on the secondaries, so I assume the transformer blew too. The resistor R23 which feeds the transformer looks discolored and the area on the board around it looks like it got really hot, so thinking I should replace it too, though I measured it at 40 ohms. I'm hoping replacing the transformer will fix the board, but I guess something downstream may have already been fried also -- wish I had an idea of what the odds were, but willing to try if there is a chance (to satisfy my DIYer urge and feel like my Electrical Engineering degree isn't going to waste).

 

[carmusic]

ive seen that there is 12v relay, is there only 2 terminals at transfromer secondary or is it center tapped. how many diodes make the rectifier (2 or 4). Is there some volatge regulator (7812) on board also.
those are often 20 or 24vct 5-6VA transformer or 10-12v no ct transformer.

 

[clsmith6]

Thanks for the reply. Yes, the relays are 12v. There are three terminals at the transformer primary (120VAC, one that measures 160 ohms from the 120VAC though there are no traces to it, then neutral). There are only two terminals at the transformer secondary, and they have continuity. Four diodes make-up the rectifier. I don't see a voltage regulator on the board.

 

[MikeMl]

Trace the three terminals near the transformer primary. Does one go to L1 (Black input wire, maybe thru a fuse), another go to Neutral (White input wire), and the third go to Ground (Green input wire)? If so, the one that goes to Green is a shield and will not have continuity to any other terminal on the transformer, except maybe the frame. It sounds to me that your transformer survived...

 

[carmusic]

If you get reading on both transformer coil it is probably ok.

 

[OldTechie]

Have you measured the continuity of the transformer's primary? If it's open, you might be able to resurrect it. Quite frequently, the transformer mfr will insert an overheat fuse inside on the priimary side. This might have opened when the overvoltage heated the transformer. Carefully remove the wrapping from the primary winding and see if there is a small cylindrical component (usually metal-cased, two connecting wires) in series with the primary wire. Check its continuitl. Should be very low resistance. If it's open, there's your problem. You can either choose to connect the primary wires together and continue without the overheat protection, or try to find a replacement fuse.
If you want a replacement, you can estimate the VA rating of the xfmr by the core size and weight. Since your board doesn't have a regulator, you can assume that the output of the power supply will be 12VDC (since the relays are rated at 12V coild). That means that the secondary voltage should be in the neighborhood of 9 VAC. Go to https://www.signaltransformer.com/content/low-power–miniature and look at 9VAC transformers having size and weight close to your xfmr. Most suppliers, such as Mouser (www.mouser.com), Digikey (www.digikey.com), and others, carry these transformers in stock.
You might check out the board for other problems if you have a bench supply that you can plug into the board (after the rectifiers). This should get the board back into operation while you see if it works correctly. If it doesn't, then all bets are off. You're probably better off by buying a new opener.
Won't your homeowner's insurance cover the damaged appliances?

Cheers,
Dave M

 

[clsmith6]

That was it! I was confused by the fact there were three terminals on the primary side (line, neutral, and a mysterious third -- which was not ground). I had continuity between line and the mystery terminal, but no continuity to the neutral terminal from the other two. A thermal fuse in the transformer (which I can not see) between the mystery terminal and neutral which had blown would explain what I'm seeing. So, I shorted the mystery terminal and neutral (on the back of the board) and the board is working again!

Btw, afterwards, I measured the voltage across the secondary terminals and it was 17.8VAC. (I didn't want to have to take apart the opener on our main garage door which I had already replaced the entire unit for, but I did to make sure that voltage was correct... I measured its secondary voltage and also got 17.8VAC... phew!)

I should probably be responsible and replace the short with a new thermal fuse and replace the blown MOV (if I can find correct values), but if I don't, am I introducing any additional danger other than frying the board?

Btw, the plumber's insurance covered the damaged appliances since the line was damaged exactly where he dug to run the water. I still wanted to fix the things I could for fun.

Thanks for the help! I will soon have our second garage door running again and a spare opener!