Fixing a laboratory waterbath

[vrasp]

There is continuity between the output of the zener and ground. Now I have to find why that is.

[vrasp]

I fully disconnected the display board and the short is still there.

I noticed that Vcc of LM324 and OP07CP are also on this line and so there are shorted as well.

Now this is the part that I don't understand. It looks as though they are all purposely grounded. If you look at the board on the attachment of this post, I drew a red line over the circuit I m talking about. This line ends up on the bottom right corner where it is grounded (I desoldered the capacitor there so we can see the line). I must be wrong as it wouldn't make sense. But do you see this as well?

[petehall347]

you forgot to solder this ..

[vrasp]

Originally Posted by petehall347

you forgot to solder this ..

I m gonna add some solder on that. Do you see that the Vcc seems to be connected to ground or is it just me?

[vrasp]

Sorry but this is really bugging me. Is this pin circled on the picture a through hole? If it is then Vcc is directly connected to ground.

[petehall347]

this needs looking at .

[vrasp]

Originally Posted by petehall347

this needs looking at .

Thanks. I did check those connections and they are isolated from adjacent ones. I will still redo them.

The waterbath is in the lab so that's where I work on it now when I have time during the week. It's good that it works because if that display issue can't be fixed it can still be used at a set constant temperature which is likely how it would have been used anyways. I just need to put a temperature probe in there and find the right temperature with the potentiometer knob. However, it would still be nicer with a display.

I m thinking of a way I could see if that solder in my previous post is a through-hole or just on the surface. There is a solder pad on the other side of the board on that same spot which I thought meant it's a through-hole. Why would they run that line all the way to that same spot if it's not a through hole? But then if it is a though-hole, it means Vcc it connected to ground... and that wouldnt make sense.

[vrasp]

I redid those solder joints today.

I m still stuck on the same problem. The trace of Vcc of LM324 goes to the metal corner of the board. I cant figure out why.

[vrasp]

Continuing the waterbath saga.

I was able to resolve the issues I had. Everything worked fine until it didn't anymore. The problem is that I replaced the long pins with wires and I think there is a lot of strain on the solder joints. I keep having issues with wires popping off the solder joint and causing shorts as it touches other parts. Especially when I run the waterbath at high temperatures for long periods of time. I might not have the best soldering skills. There is also not much space so the wires end up being bent and twisted when I out everything back together. I m going to add solder to the weakest joints and add hot glue to all of them. If you have suggestions for this plz let me know.

The last time it happened it shorted something on the power supply card and the relay switch is now grounded. That short blew a trace so it probably killed the few components on the line. I think the wire that popped touched ground and a pin from the relay switch at the same time.

I m going to replace the relay switch and the other components around it. My problem is the same as the very first issue I had when starting to fix this waterbath: there is no info on the relay. I dont know what the specs are and so dont know what to replace it with. All I know is that the relay is connected to a 0.68 uF 250v capacitor getting 120v from the wall, and a 800v 15 amps triac. I believe I need a non latching relay since it has to turn off when power is off (for safety).

The relay is on the bottom left of the photo attached.

How can I figure out what relay to buy for this context?

Thank you!

[sam_sam_sam]

Originally Posted by vrasp

Continuing the waterbath saga.

I was able to resolve the issues I had. Everything worked fine until it didn't anymore. The problem is that I replaced the long pins with wires and I think there is a lot of strain on the solder joints. I keep having issues with wires popping off the solder joint and causing shorts as it touches other parts. Especially when I run the waterbath at high temperatures for long periods of time. I might not have the best soldering skills. There is also not much space so the wires end up being bent and twisted when I out everything back together. I m going to add solder to the weakest joints and add hot glue to all of them. If you have suggestions for this plz let me know.

The last time it happened it shorted something on the power supply card and the relay switch is now grounded. That short blew a trace so it probably killed the few components on the line. I think the wire that popped touched ground and a pin from the relay switch at the same time.

I m going to replace the relay switch and the other components around it. My problem is the same as the very first issue I had when starting to fix this waterbath: there is no info on the relay. I dont know what the specs are and so dont know what to replace it with. All I know is that the relay is connected to a 0.68 uF 250v capacitor getting 120v from the wall, and a 800v 15 amps triac. I believe I need a non latching relay since it has to turn off when power is off (for safety).

The relay is on the bottom left of the photo attached.

How can I figure out what relay to buy for this context?

Thank you!

Do you have a temperature controlled soldering station
If you do then turn the heat up until you have it where when you can put iron on the terminal and it melts the solder with in a few second not the trace pad you want to heat this last

Because it sounds like you are not getting the terminal connection hot enough

[vrasp]

I have a hakko soldering station I use at 300°C. I melt enough solder to allow the whole tip of the wire to be fully "submerged" in solder (but not too much either). The solder stays on the pad but sometimes, when i move the board around to put everything back together, a wire will pop off while the solder stays on the pad. I ve been leaving the iron a bit longer and it seems more steady now.

Any idea about the specs of the relay switch?

Thank you!

[sam_sam_sam]

Ok if the pads are ripping off the board then you are putting to much force on the connector wiring which should be avoided if possible even if this means you have to extend the wiring somewhat or solder the connectors when everything is mounted

Or you are not getting the wire connector hot enough like I said earlier heat the connector and touch the solder to the wire connector not on the iron tip or you need to use flux on the wire connector if the solder is not staying on the connector

[sam_sam_sam]

For the relay unless there is a part number on the relay it is going to very difficult to know what will fit on the board or use some type of relay that you can find the relay socket and wire them to the board

[vrasp]

Originally Posted by sam_sam_sam

For the relay unless there is a part number on the relay it is going to very difficult to know what will fit on the board or use some type of relay that you can find the relay socket and wire them to the board

The relay is 24 x21 mm. I think as long as I know what specs I need then I ll try to find something that fits. The part I have trouble with is all the relay specs I dont understand. For example, it s getting 120VAC. Should the relay therefore be rated at 240v minimum? The 120VAC side is connected to the 800v 16A triac. Should the relay be rated at 16A or higher as well? I think both answers to these questions are yes, it should. However I know electronics can be more complicated than that. Same with the coil voltage and other specs. How do I know what to get?

Thank you!

[vrasp]

Or if you cant figure out the specs from the info I provided. What tests can I run to get that information. Should I measure the incoming activating voltage? Or is it the current that matters in this case?

[eccerr0r]

Why are you assuming it's a relay? What evidence do you have?

I'm beginning to think it's not even a relay ... and have no clue what it is...

[sam_sam_sam]

Show a picture of the bottom of this device
I am not sure what this device is it could be several things

[vrasp]

The trace that goes from the 120VAC to the capacitor and relay was shorted and blew up. I m not 100% sure it's the relay, but the short happened where the relay was. Maybe it s the red capacitor next to it, or both. Without being 100% sure I was going to replace both the capacitor and relay. I have the specs for the capacitor but not for the relay.

Also I dont know if this is normal but the relay has continuity on the common end (high current end). The circuit inside the relay, where the triac would be connected, is always closed even without current (it tested it off the PCB). I put it on a breadboard and connected 6v to the low current circuit to see if I can close or open the high current circuit at will but it doesnt change anything. I dont know if this is how a relay is tested.

[vrasp]

Originally Posted by sam_sam_sam

Show a picture of the bottom of this device
I am not sure what this device is it could be several things

Originally Posted by eccerr0r

Why are you assuming it's a relay? What evidence do you have?

I'm beginning to think it's not even a relay ... and have no clue what it is...

I was told it s a relay. It has 4 pins on the bottom. I ll post a picture.

[R_J]

You need to post a clear (in focus) high res, picture of the trace side of the board the relay is mounted on.
Looking at the top suggests the small bridge rectifier and the 470µf capacitor are the supply for the relay, the to220 transistor controls the relay coil, The small glass diode next to the relay will be across the relay coil. I suspect the relay coil is either 12 or 24v based on the voltages marked on the transformer