Fixing a laboratory waterbath

[vrasp]

Hey all,

I ve narrowed the issue down to the board you see in the picture. The round fuse works, the other components have not been tested(not sure how to). I believe the issue might be from the transformer but can't find anything online about that part. This is a bit over my skill level. I am able to solder new parts if needed.
Here are the things I believe I should do next:

How would I find a similar transformer online? Can I test this transformer with my multimeter?

I also found the manual for this device. http://www.hvg-verwertung.de/ebay/do...da/RMS6_20.pdf
It has a schematic. The board that is on the picture is number 24 and the transformer is number 26. Not sure if this info is of any use.

Any help would be greatly appreciated!

https://ibb.co/DpHccBp

Kindly,

Vrasp

[redwire]

What is the "issue" with the bath heater? We can't read you mind.
Would need a picture of the other side of the PC board to see what the transformer is about. It looks like a power supply board.

[petehall347]

check the ac voltages are coming out of the transformer

[vrasp]

Thanks for the replies.

The waterbath wouldn't turn on. The transformer input read 120v but nothing at the output. Someone from reddit kindly made this diagram of the PCB:



https://imgur.com/a/ZdlGBoU

The line where the black spots are (bottom) was rewired and the system worked. However, wiggling the transformer caused the screen of the device to turn on and off. Unfortunately, I broke the pins of the transformer while trying to remove it to remake the connections.

I now have to get a new transformer. I was not able to find any specs for the old transformer. It states 15v/20v/8v on top. The reddit user who made this diagram said it's either 15v or 20v. Is there anything else I should be looking at aside from the input and ouput voltages when purchasing a transformer? Does it have to have 6 pins on the output? Is it possible that the some of the pins output 15v and others 20v? Is there any test I can make with my multimeter to guess the ouput voltage of the old transformer? I d love to hear your thoughts.

As you can probably guess, I have a very basic knowledge of electronics.

Thank you!

[redwire]

OP fixed it, melted pcb trace. People so lazy when asking for help across the Internet
reddit thread https://www.reddit.com/r/AskElectron...ory_waterbath/

[petehall347]

wont let me go to the end . i see the general gist of it ..was just a blown fuse . lots of stuff missing on this thread like pics for one .

[vrasp]

Read the reddit thread more carefully. I did not fix it. It worked until I touched the transformer and it stopped worling again. The transformer broke while I was trying to remove it to resolder the connections. If you are not willing to help please dont reply anything.
I provided pictures of the front and back, and the manual. If you tell me which pictures you want I ll provide them.

Thank you.

[petehall347]

i dont see any pics in this thread

[vrasp]

The pictures are in the links. The IMG tags are not working for some reason.

Here they are

https://ibb.co/DpHccBp
https://imgur.com/a/ZdlGBoU

Since my last message, I was told the transformer is a multitap, hence why it says 15v/20v/8v. It is very old and there is no info about it online. Do you have an idea as to how I can figure out what transformer to buy without this info? Maybe I can somehow find out the voltages required on each line?

Thanks!

[petehall347]

can you not repair the broken one ? or find the data sheet for it ? or at least fix it enough to see which pins are which .

[vrasp]

Unfortunatly not. The transformer is in some kind of resin case and the pins broke inside the case. I even tried to remove the case with pliers but I can't get to the metal inside the case.

There is no datasheet for it. It was made in 1987 based on the writings on top. Nothing shows up on google.

I m going to email the company but there is a high chance they will blow me off because its over 30 years old. Thing is a new lab waterbath like that one costs thousands of dollars.

[eccerr0r]

So ultimately the problem is a trace got vaporized and you added a link.... and apparently it worked for a while but then stopped.

So it seems like either the solder link is bad or the transformer's pins or internal connection to its pins are not working correctly. Ideally it's welded to the posts internally but sometimes they're soldered and if you dwell on the pin too long you melt the internal pin and all hell breaks loose... Or if you overload the transformer...

Would have to say these transformers are hard to come by these days, specifically line frequency to multiple output.

I also have to mention that the transformer/tracks may have been underspecced Looks like the manufacturer may have tried to make it easy to switch between 120/240V but did not compensate for the fact that it takes 2x more current at 120V...

BTW you may end up having to use multiple transformers... or if you're really crazy you might be able to get a step up transformer and rewire the transformer to 220V and power it that way ... LOL

[vrasp]

How would I search for a similar transformer? I ve been googling "multitap 15v/20v/8v"

Could I just get 3 different transformers that supply 15v, 20v, and 8v separately?

[eccerr0r]

Measure the resistance between the outputs, likely it's not really multitap but have three independent outputs of 8V/15V/20V. And yes if it physically fits, you can use three separate transformers.

Or just one if you're really adventurous and it really is a 120V/240V transformer

[vrasp]

The output of the transformer? I can't even see them. They re covered by all this resin and removing it makes a whole mess I can't even see anything. I ll try but if you have another way plz shoot haha

[vrasp]

Maybe I ll sand the resin until I see something.

[eccerr0r]

Just use an ohmmeter if you have one?

[vrasp]

Maybe I m not understanding. You re saying I should measure the resistance at the output of the transformer right? Thing is the output pins of the transformers are burried into the resin. There are no visible pins because they broke off and the transformer is in the resin. Thats why i thought of sanding the resin so I can get to the metal part on where the pins were attached before I broke them. Unless you re talking about something else

[eccerr0r]

So you damaged the transformer more than it had already been broken? As in you cut the transformer off the board? I guess this would make things a bit more difficult, though you're probably safe with independent transformers instead of getting a single multitap (multitap implies the windings are connected together.)

[vrasp]

Yes. I was trying to remove it with a heat gun while pulling. It wouldnt come off. I eventually pulled hard thinking the pins would rip off the board but they ripped off the transformer instead. I dont mind getting independent transformers. I just need to figure out which lines were 15v , 20v and 8v on the board. I tried following the lines to see what components they are connected to (on another board that is not shown on pics) and see what voltages they are rated at. Is that a good idea? Is there another way I dont know about?