Johnson A419 - no power output

My faithful Johnson A419 seems to have a problem. I think I've a good grasp on the issue but wanted some input from people who might know better.

Just about everything works... it's getting a full 120V input, the temperature probe is operating fine, and all of the settings work. But the problem is there's no output power. The indicator light turns on showing that it is TRYING to power the female plug. There's no longer any audible "click" when the indicator light turns on, so I'm assuming this means there's an issue with the output relay. Is it possible this could be fixed at home if someone is handy working with electrical components?

I had this exact same problem happen to me a year or so ago. I posted on here but did not get much of a response at the time. If anyone has ideas, I too would love to be able to fix this at home.

I just ended up purchasing a new one, but it would be nice to recuperate the old one and have two up and running.

JG

Not having one to look at makes it hard to assist. If you take the cover off of the unit (unplugged of course) and post a photo of the components, it may be easier to help you diagnose the issue. It does sound like the output relay, but what kind it is, or how it will need to be replaced is a different story.

I actually found replacement relays on line. It's a pretty general purpose relay from Tyco Electronics that sells for about $5-6. It's soldered on, but it should be a pretty easy fix assuming that IS the problem. I'll put an update here when I give a replacement relay a try with some pics, for people to reference in the future. Here's hoping it works!

Good luck, post up pics when you are through either way.

yes, if you get it to work, definitely let us (at least me) know - I would love to get mine working for $5-6 (I guess I would need to buy a soldering iron too, but still less than the cost of another temp controller).

My experience with relays, ( autos, aircraft), for a quick troubleshoot, tap on it first, with a screwdriver handle, when it should be in the selected position,and it will sometimes free them up.

Just a troubleshooting tip, prior to replacing it.

Actually, now that I've got more in there with a multimeter and played around some, I'm not convinced the relay is the actual problem.

For reference, this is the wiring diagram of the relay that's in my unit (and thanks to my Dad for labeling it so well!)


The "120VAC" pin should ALWAYS have 120VAC to it in a functioning relay, and the "120VAC until picks" pin should have 120VAC to it when output of the controller is off (not powering anything, LED light is not on). Both of these are true in my case. However, when I set the controller so that the output should be on, the "120VAC when picks" pin is not getting power, which is what should be happening. So the relay is getting power in general, but it's not triggering to output. I checked the 24VDC pins and lo and behold it's only getting 10VDC when the output is "on". So the issue is, I think, that there's not enough power to trigger the relay when it should be. So the problem could actually be the transformer which is beside the relay. I tested it, and it is getting a 120VAC input, but doesn't seem to be outputting at 24VDC. But I'm not positive, because I'm not sure which pin is which yet. It's also getting much hotter than it should.

I'm going to look up its' wiring diagram later to know for sure which pin is which, troubleshoot some more, and update back here when I have something new.

I am not sure about the electrical measurements, but my unit also became hotter than it should once it stopped working.

Keep up the sleuthing - I hope you figure out the problem. It seems to me like this should not be a terribly hard fix, but I might be completely underestimating it.

I have been contemplating buying an STC-1000 pre-made unit, but if I could get my A419 working, I could use that money for something else!

Good luck

.

Popping in for a small update. So, as suspected, the relay is 100% fine and working and the transformer is the likely problem. My dad borrowed a 24VDC power supply from someone at work and we put the power directly onto the coil in the relay and it works completely fine and triggered power output from the controller. So looks like a new transformer is in need to get it working.

Good to hear that you identified the problem. Any idea how big of a deal it would be to replace the transformer? That sounds like a bigger deal to me than the relay, but I am not very knowledgeable about these things.

JG

It's not any more difficult that the relay, really. Just needs soldered into the board.

So, now for the most anti-climactic update of all time. Out of nowhere the entire controller seems to be working perfectly fine today. It's even reading 24VDC in all the correct places, and the relay is triggering right when it should. I've just about no idea why it's suddenly working, and I haven't tried it 'live' yet (with a batch of beer) so it may end up not working again after a while.

The only thing I didn't mention is, while testing it with the 24VDC power supply yesterday we did accidentally fry something for a second on or near the transformer (touched the wrong pins without thinking about it). Was going to replace the transformer anyway so no big deal I thought. I can't imagine that that somehow made it start working again, but it's truly the only thing that we 'did'.

I almost wish it didn't randomly start working so I'd have a better answer on how others might be able to fix it. I'm going to use it soon with a batch of beer to really give it a 'live test' and we'll see if it's truly working again. Hopefully, at the least, this will all be useful information for people looking to troubleshoot their own controllers. I'll report back after a full fermentation run to see how thing are looking.