Fixing a laboratory waterbath

[vrasp]

Originally Posted by sam_sam_sam

“ I dont know if there is a controller but there might be. Is it a chip? How do I find it?”
You just have to Google the part numbers to find what each part number

I know that but what do you call the controller? Is the transformer the controller?

[vrasp]

Originally Posted by eccerr0r

I think he does, https://www.badcaps.net/forum/attach...4&d=1626717671 but M4 is too big (should be M3 or #4), and the plastic shoulder washers for #6 screws seems rare.

Again something really wrong is here that's not being described. In the off state, according to the PCB, gate is shunted to MT1 through the diode/isolation transformer and therefore should be off. Unless MT2 reaches above the isolation voltage limit it won't heat up until it's forced to turn on. So therefore unless there's a wiring mistake somewhere, this makes no sense and not worth investigating further. Based on history, wiring mistakes are abound and has been extremely annoying to work through.

Could be a wiring mistake but then I think it would be on the control board. I double checked and the TRIAC was wired correctly. The last time the waterbath worked was when I used a NTE5671 TRIAC (800v 16A https://www.farnell.com/datasheets/198577.pdf). It does not have a metal plate. I dont know the material but I had installed it without a mica and it worked so it isn't conductive. The original TRIAC (so before the NTE5671) was a IT715 (800v 15A). IT715 seems to be equivalent to NTE56010.

I have not wired anything differently since then. The only difference is the TRIAC which is a NTE56010 (800v 15A https://www.farnell.com/datasheets/202004.pdf).

Below is the schematic in the manual of the waterbath. I posted it earlier too. It's a general schematic for 220v and doesn't go into the details.

[sam_sam_sam]

The description of the device will tell if it is a micro controller or not

Now it could be done with ic chip like a LM339 or something similar where you have a reference value and compare to the input value

V1 is controlled by something the question is what this is controlled by this is where you are going to have to trace where these connections go to it has to go to some type of ic chip to control the triac unless it to some type of resistance pot which I doubt very seriously that it was done this way

One note when you use a device that mount to a heat sink and the heat sink is mounted to the circuit board and has soldering joints that are connected to something else you need to make sure that the tab does NOT have connection to the heat sink so you need use an ohm meter to check this

There is a difference between the two devices one has the metal mounting tab and the other one dose not and if you did not mount the device correctly this might explain why the new device failure happened

Now there are devices that have the metal tab that has no connection to the device but you must check them to be sure that this is the case the data sheet should tell you this information

The one thing that this data sheet does not tell you if the metal tab has a connection to the device so have to go with the assumption that it has a connection unless you have tested this with an ohm meter

[vrasp]

Originally Posted by sam_sam_sam

The description of the device will tell if it is a micro controller or not

Now it could be done with ic chip like a LM339 or something similar where you have a reference value and compare to the input value

V1 is controlled by something the question is what this is controlled by this is where you are going to have to trace where these connections go to it has to go to some type of ic chip to control the triac unless it to some type of resistance pot which I doubt very seriously that it was done this way

One note when you use a device that mount to a heat sink and the heat sink is mounted to the circuit board and has soldering joints that are connected to something else you need to make sure that the tab does have connection to the heat sink so you need use an ohm meter to check this

There is a difference between the two devices one has the metal mounting tab and the other one dose not and if you did not mount the device correctly this might explain why the new device failure happened

Now there are devices that have the metal tab that has no connection to the device but you must check them to be sure that this is the case the data sheet should tell you this information

The one thing that this data sheet does not tell you if the metal tab has a connection to the device so have to go with the assumption that it has a connection unless you have tested this with an ohm meter

There is an LM324 on the control board.

[sam_sam_sam]

Originally Posted by vrasp

There is an LM324 on the control board.

If this is the case I would buy a new one and see if it behaves differently or not
But make sure that you have the triac mount correctly as well

[vrasp]

Ok so this is my new plan:

1) Remove the transformer.
2) Connect a 0.1A fuse on GATE and 15A fuse on MT1.
3) Connect a 100w bulb instead of the heating element.
4) Turn on the waterbath. Without the transformer, the TRIAC should be OFF. If a fuse of GATE or MT1 blows, the TRIAC must be getting shorted on the heatsink.
5) Short MT1 and MT2 to light up the bulb. GATE should not be getting any current from MT1 so if the GATE fuse blows there is something wrong there. (is that a relevant test to do?)

6) If the bulb lights up and all the fuses are fine, connect the transformer back onto the PCB and turn on the waterbath. If the GATE fuse blows, there is a fault on the input side of the transformer, so that's coming from the control board. If everything is fine... well then everything should be fine.

[sam_sam_sam]

Vwrasp

WHY are trying to be dangerous in what you are talking about doing ( steps 4 and 5 and 6 )

All you need to do is put one led of volt meter to the heat sink and and check for resistance on the three pins on the highest setting if you have any kind of resistance you have an issue you which you need to fix

Then if this part is correct then undo the heater element wires and hook an incandescent light bulb and see if you are getting the signal to the transformer to turn ON the triac if not then you need figure out why this is not working correctly

[vrasp]

Originally Posted by sam_sam_sam

Vwrasp

WHY are trying to be dangerous in what you are talking about doing ( steps 4 and 5 and 6 )

All you need to do is put one led of volt meter to the heat sink and and check for resistance on the three pins on the highest setting if you have any kind of resistance you have an issue you which you need to fix

Then if this part is correct then undo the heater element wires and hook an incandescent light bulb and see if you are getting the signal to the transformer to turn ON the triac if not then you need figure out why this is not working correctly

Alright then. That's the new plan haha

I had checked for continuity between the pins and the heatsink and there was none. However, I did not try with the voltmeter on the max Ohm setting. I ll do that this time and also have a fuse just in case. I ve gone through enough TRIACs.

[sam_sam_sam]

Originally Posted by vrasp

Alright then. That's the new plan haha

I had checked for continuity between the pins and the heatsink and there was none. However, I did not try with the voltmeter on the max Ohm setting. I ll do that this time and also have a fuse just in case. I ve gone through enough TRIACs.

You do not have to use a fuse to check it on ohms scale now if you are going to use the incandescent light bulb instead of the heater element yes I would agree with you to use a fuse before the triac input this would be advisable but use a 10 amp fuse not a 15 amp one

[vrasp]

Originally Posted by sam_sam_sam

You do not have to use a fuse to check it on ohms scale now if you are going to use the incandescent light bulb instead of the heater element yes I would agree with you to use a fuse before the triac input this would be advisable but use a 10 amp fuse not a 15 amp one

I meant to have a fuse there for when I turn it on. Sounds good I ll do that. What do I risk using the 15A fuses? I already bought those.

[sam_sam_sam]

Originally Posted by vrasp

I meant to have a fuse there for when I turn it on. Sounds good I ll do that. What do I risk using the 15A fuses? I already bought those.

Nothing until you try to test it with the heater element

[eccerr0r]

what i'd like to see is how the wires connect from the PCB to the TRIAC... the wire colors don't seem to make sense from the limited photos of the wires in the existing pictures, alas it looks like a lot of splices are in place so things may not be as they seem.

[vrasp]

This is an old picture but the best one I have. It s the first TRIAC.

Blue: GATE
Black: MT2
Orange: MT1


. I wired the subsequent ones similarly.

[vrasp]

I have installed the new TRIAC. A NTE56010. Same as before.

I added 15A fuses on MT1 and MT2 and a 0.1A fuse on GATE. I did not solder the fuses. I did a quick job. The wire is just twisted in the fuse holder's holes. This will be done properly after it's fixed.

I replaced the wires from the PCB to the TRIAC so there is no splice or colour changes. It's now easier to follow.

I plugged the waterbath in series with a 100w bulb and made the following measurements. First, the bulb in series drops the voltage to 77v between live and neutral. I don't know if this is normal.

I also removed the heating element live wire and put a 100w bulb instead.

Resistance is max between any TRIAC pins and ground with my multimeter at the max Ohm setting. Putting both multimeter leads on the heatsink also gives me a max resistance. It should give me continuity or at least some resistance. It is connected to ground. There is no continuity between heatsink and ground either. The heatsink must have a very high resistance. Why is this the case? It makes me doubt that the TRIAC is not shorted. My multimeter works fine and the leads are clean, so are the surfaces I m measurement on.

There are the measurements:

GATE - MT1 : 30 Ohms
GATE - MT2 : 47 Ohms
MT1 - MT2 : 17 Ohms
GATE - Neutral : 35 Ohms
Bulb (so MT2-Neutral): 12.1 Ohms

Of course these measurements were done when the waterbath is off so the TRIAC is not activated.

I then turned on the waterbath with the bulb in series and measured this:

GATE - MT2: 77v
GATE - MT1: 0.1v
GATE - Neutral: 77v
MT1 - MT2: 77.1v
Bulb (so MT2 - Neutral): 0v

At this point I haven't tried plugging the water bath staight into the wall. I think the TRIAC is OFF because it's at the same potential then live and neutral, hence why the bulb in place of the heating element does not turn on.

I believe this could also be due to the fact that only 77v is supplied to the waterbath. This might not be enough to power the whole thing and turn on the TRIAC. I m not sure. I m not confident enough at this point to plug it into the wall. I have fuses on each TRIAC wire but they are 15A and 0.1A so I think the TRIAC could still blow.

This is where I need your help figuring out what to do now. Anything else I can do before plugging it into the wall?

Thank you!

[eccerr0r]

Proverb: "The fast acting transistor always blows first to protect the fuse." -- unknown

[vrasp]

The reason I said it could still blow is that the max GATE current is below 0.1A so I m worried about that. Or thats what I understood from the datasheet. Also maybe I should get a 10A fuse instead. I dont know how fast a fuse blows but what if a current just over 15A has time to blow the TRIAC before the fuse blows. I have no idea if this is possible. Do you think there is a risk?

I ve gone through enough TRIACs already.

[sam_sam_sam]

I could be wrong but I would concern that it seems like you do not have a control signal to the transformer but the question is why

Because if your light is not lighting up this not making any cents to how it blowing up the triac

[vrasp]

Originally Posted by sam_sam_sam

I could be wrong but I would concern that it seems like you do not have a control signal to the transformer but the question is why

Because if your light is not lighting up this not making any cents to how it blowing up the triac

I dont think there is a control signal like you said, but it could be because the waterbath is only getting 77v instead of 120v. I guess I ll have to just plug it into the wall to find out.

If there is 77v on the primary of the toroidal transformer (for the control PCB and display) then the secondary voltages must be much lower than supposed to be. That could be insufficient. The display LCD does works though.

I wonder why a 100w bulb drops the voltage by that much. Its resistance must be high but why...

[vrasp]

Originally Posted by eccerr0r

And that's why I'd suspect that the TRIAC should be fine as is controlling a shorted heating element, even... and it should end up throwing a breaker before it "instantly fries the TRIAC". With the past history of this thread, I'd highly consider the possibility of the miswiring of the TRIAC when soldering it, causing it to blow. Again connecting the gate terminal and MT1 (the diode drop) across mains voltage will instantly fry the TRIAC. Other miswirings would just cause issues in it turning on or it being always turned on.

Seems as typical for all these three terminal devices that aren't high powered RF devices, when facing the TO-220/TO-247 the left pin is the high impedance input (gate for TRIAC, base for BJT, gate for MOSFET), center pin (and thus metal tab) is the "output" (MT2 for TRIAC, collector for BJT, drain for MOSFET) and the right pin the low impedance common input (MT1 for TRIAC, emitter for BJT, source for MOSFET).

Oddly enough SCRs seems to not follow this pattern - more like diodes ... and again RF transistors where the center pin is typically emitter/source...

I was rereading all the answers to make sure I hadn't forgotten anything. Just realized you said left pin is GATE, middle is MT2 and right is MT1. Are you sure about this? The datasheet (attached below) seems to indicate the GATE is right, MT2 middle and MT1 left. The diagram in the datasheet is showing the TRIAC from the front correct? If it's actually from the back I ve been wiring it wrong this whole time...Could you check my photos with the wiring above and tell me if it's correct?

It goes
Purple - GATE
Black - MT2
White - MT1

Thank you!

[eccerr0r]

Well you're right it is MT1 MT2 Gate, but sorry, no additional clues why it's frying. You're on your own.