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-   -   Fixing a laboratory waterbath (https://www.badcaps.net/forum/showthread.php?t=96459)

vrasp 06-07-2021 04:54 PM

Fixing a laboratory waterbath
 
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



https://ibb.co/DpHccBp

redwire 06-08-2021 11:49 AM

Re: Fixing a laboratory waterbath
 
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 06-08-2021 05:20 PM

Re: Fixing a laboratory waterbath
 
check the ac voltages are coming out of the transformer

vrasp 06-09-2021 06:52 AM

Re: Fixing a laboratory waterbath
 
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

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 06-09-2021 03:10 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 03:30 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 03:43 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 03:50 PM

Re: Fixing a laboratory waterbath
 
i dont see any pics in this thread

vrasp 06-09-2021 04:14 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 04:20 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 04:25 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 04:30 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 04:34 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 04:40 PM

Re: Fixing a laboratory waterbath
 
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 :D

vrasp 06-09-2021 04:50 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 04:52 PM

Re: Fixing a laboratory waterbath
 
Maybe I ll sand the resin until I see something.

eccerr0r 06-09-2021 04:57 PM

Re: Fixing a laboratory waterbath
 
Just use an ohmmeter if you have one?

vrasp 06-09-2021 05:03 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 05:19 PM

Re: Fixing a laboratory waterbath
 
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 06-09-2021 05:24 PM

Re: Fixing a laboratory waterbath
 
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?

eccerr0r 06-09-2021 05:43 PM

Re: Fixing a laboratory waterbath
 
At this point you can only make a guess... Hope that they are in adjacent pairs and in the sequence the voltages are listed on the transformer. Likely the 8V winding is connected to the fuse and bridge on board to the 5VDC output (but no guarantees, just likely). Where the other wires go to will determine which one is the 15 and 20V, but likely the center ones are 20, and the other to the side is 15V.

Again this is custom so it's only an educated guess without more information.

I'm still disappointed you damaged the transformer while removing it from the board. It would have been really funny to get it working by using a single 120-240V step-up transformer and using the 240VAC winding on that transformer if it really is... Not the most efficient way but you'd only need one transformer that you could swipe from one of those travel adapters...

vrasp 06-09-2021 05:50 PM

Re: Fixing a laboratory waterbath
 
Thanks for your input! If I were to get three transformers with those voltages. Could I figure out the proper voltages required on each line but wiring them and checking if it works properly? Like if I wire the 8v on the 15v then i ll see it it works and if it doesnt then i try 15v. As long as I dont put a high voltage with a low one I wont fry anything right? What do you think?

eccerr0r 06-09-2021 05:59 PM

Re: Fixing a laboratory waterbath
 
You *may* be able to depending on where the circuit is connected. But putting 20V on the input that wants 8V may required in more snap crackle pop crispies....

Even the 20V on 15V there's no guarantee it will survive, you'll have to trace where it goes. That 5V difference could fry things... Also you may get nondeterministic behavior if the voltage is not quite high enough. Best to look carefully where they go.

vrasp 06-09-2021 06:09 PM

Re: Fixing a laboratory waterbath
 
I see. I guess the easiest way to find out right now is by teying to reach those output pins on the transformer. When I measure the resistance, how do I find out the voltage from that?

petehall347 06-09-2021 06:37 PM

Re: Fixing a laboratory waterbath
 
first check is if they all connect to each other or not . if all in pairs it makes it easier to do a bodge repair . if you can measure resistances you could power it up and see which voltages are which .

eccerr0r 06-09-2021 06:53 PM

Re: Fixing a laboratory waterbath
 
Based on the board layout an educated guess is that they are isolated from each other, but which voltage to what is the trouble. Since the pins on the transformer is damaged it would be hard to collect data at this point.

But you still know where each wire goes... this is still critical information that's lacking by as far as I know, all who's reading these posts...

vrasp 06-09-2021 07:13 PM

Re: Fixing a laboratory waterbath
 
I was able to dig through the resin, found what looked like copper, and shoved some quick braid wire in there to make it easier to measure. The resistance between primary and secondary is infinite and between pins of the secondary is 0. There is continuity between the seconday pins. Is that normal?

What can I do to guess the voltages? Also, there were 6 pins that originally came out of the secondary of the transformer. As you can see I only found 4 "holes". What do you guys think I should do now?
https://ibb.co/HTF08G0

EDIT: Would picture of the board this PCB connects to help?

vrasp 06-09-2021 07:42 PM

Re: Fixing a laboratory waterbath
 
Quote:

Originally Posted by eccerr0r (Post 1051436)
Based on the board layout an educated guess is that they are isolated from each other, but which voltage to what is the trouble. Since the pins on the transformer is damaged it would be hard to collect data at this point.

But you still know where each wire goes... this is still critical information that's lacking by as far as I know, all who's reading these posts...

Here are pictures of the board that this PCB is connected to.

First pic is the PCB. I added it here to make it easier
https://ibb.co/1MGnLvk

This is the board below it. On the right you see 8 holes in which the 8 pins of the above PCB go into.
https://ibb.co/SVxqk04

This is the other side of the board above.
https://ibb.co/n3KXN5h

Hopefully this is clear. Let me know if you need anything else.

Thank you!

eccerr0r 06-09-2021 09:25 PM

Re: Fixing a laboratory waterbath
 
You may have lucked out, if there's nothing else connected to those 8 pins, one set of the 15 or 20V isn't even connected to anything. The other set is rectified and brought through a regulator and thus, to an extent, doesn't matter what voltage it is.

That regulator would be interesting to know - what's the part number of the TO-220 (metal+plastic) regulator next to the bridge rectifier in the corner? It's the 3-legged device next to the 4-pin DIP which is the bridge - both of these are in the corner farthest from the display board connector on the blue green board (that has the grounding)?

If it's 7812 or LM340-12 then 15V would do, else if it's 7815/7818 or LM340-15/LM340-18 you will need 20V there.

BTW they need to be isolated and not a multitap.

vrasp 06-09-2021 09:34 PM

Re: Fixing a laboratory waterbath
 
Quote:

Originally Posted by eccerr0r (Post 1051455)
You may have lucked out, if there's nothing else connected to those 8 pins, one set of the 15 or 20V isn't even connected to anything. The other set is rectified and brought through a regulator and thus, to an extent, doesn't matter what voltage it is.

That regulator would be interesting to know - what's the part number of the TO-220 (metal+plastic) regulator next to the bridge rectifier in the corner? It's the 3-legged device next to the 4-pin DIP which is the bridge - both of these are in the corner farthest from the display board connector on the blue green board (that has the grounding)?

If it's 7812 or LM340-12 then 15V would do, else if it's 7815/7818 or LM340-15/LM340-18 you will need 20V there.

BTW they need to be isolated and not a multitap.

It says MC7812. Are you telling me all I need is a 15v transformer and that's it? That would be awesome.

vrasp 06-09-2021 09:36 PM

Re: Fixing a laboratory waterbath
 
This is it. https://ibb.co/TwcgqYm

eccerr0r 06-09-2021 09:42 PM

Re: Fixing a laboratory waterbath
 
6 Attachment(s)
It looks like 15V should do for the "middle" AC output and the 8VAC for the 5VDC circuit Not sure what's up with the other output (the "green" pair on wFziNau.png), just noticed it goes to the display board directly... what it does with it is now the question.

btw all pictures posted so far here...

vrasp 06-09-2021 09:54 PM

Re: Fixing a laboratory waterbath
 
Thanks for putting all the pictures together. Very helpful!

vrasp 06-09-2021 10:37 PM

Re: Fixing a laboratory waterbath
 
Quote:

Originally Posted by eccerr0r (Post 1051459)
It looks like 15V should do for the "middle" AC output and the 8VAC for the 5VDC circuit Not sure what's up with the other output (the "green" pair on wFziNau.png), just noticed it goes to the display board directly... what it does with it is now the question.

btw all pictures posted so far here...

Do you want a picture of the display board as well?

I ve never bought a transformer before. It seems there aren't many 15v or 8v ones. I see lots of 12v and 24v. Do you have a website to recommend? How do I avoid buying a low quality one? Does the amperage matter?

Thank you!

eccerr0r 06-10-2021 06:48 AM

Re: Fixing a laboratory waterbath
 
To confirm that other voltage, yes the other board pictures would be nice.
Ideally you want the voltages to match. Theoretically you can go 'up' a little and it would be fine but it would stress the regulators. If you attach heatsinks to them it may help with the higher voltages.

You should be able to get 16V transformers which would be OK for 15V. A center tapped 16 would get you 8V. 9VAC would be fine for 8V too. But don't use the same 16V transformer for both the 15 and 8V, you need two separate transformers, and then the last 20v winding, still needs investigation.

The thing I'm not sure about is that the display usually requires some current to keep the segments lit, and I've used 7805's before. Using a 7805 with 4 LED 7-seg displays at car voltages, it gets quite toasty with no heatsink and expect similar behavior with similar circuitry.

In any case that original transformer doesn't seem all that large (measure it?) and 1A per winding may be sufficient. I think the 15V winding may be okay to go less than 1A. The remaining winding ... remains to be determined.

What I'm wondering is why did the transformer primary winding blow, still seems kind of odd to me...

vrasp 06-10-2021 07:15 AM

Re: Fixing a laboratory waterbath
 
I see. I d like to help figure it out but this out of my league. I ve emailed the manufacturer and asked if they have the specs of the transformer or some kind of schematic.

This is the display board.

https://ibb.co/5BXFDzg

https://ibb.co/r7qptKM

eccerr0r 06-10-2021 07:17 AM

Re: Fixing a laboratory waterbath
 
btw redwire, again we find crossposting on different sites, do you happen to monitor reddit and see this guy's posts there or did you happen to search and find it?

I don't monitor reddit...

eccerr0r 06-10-2021 07:37 AM

Re: Fixing a laboratory waterbath
 
4 Attachment(s)
Quote:

Originally Posted by vrasp (Post 1051547)
I see. I d like to help figure it out but this out of my league. I ve emailed the manufacturer and asked if they have the specs of the transformer or some kind of schematic.

This is the display board.

https://ibb.co/5BXFDzg

https://ibb.co/r7qptKM

Eeek. Looks like another board layered on top of the board. Probably a 7107 hidden underneath, but what I don't get is why this board needs 20V... hmm...

wasting more of Topcat's hard disk space here... hate it when resources go poof...

vrasp 06-10-2021 07:38 AM

Re: Fixing a laboratory waterbath
 
The display board is made of 2 boards. This is it.

https://ibb.co/yhhkXB9
https://ibb.co/VYw70L4

vrasp 06-10-2021 07:50 AM

Re: Fixing a laboratory waterbath
 
I dont know if this helps, but the green/blue board is also connected to these things on the image.

https://ibb.co/sv7pSH0


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