Fixing a laboratory waterbath

[petehall347]

no idea how much free space is in the connector pass throughs on the board but maybe pinning through with single strands of wire might help .

[vrasp]

Originally Posted by petehall347

no idea how much free space is in the connector pass throughs on the board but maybe pinning through with single strands of wire might help .

I dont have anything that small. It looks like the inside has metal "tweezers" that hold the pin when inside and I dont want to deform them.

I m letting the board sit in 99% isopropanol overnight. Hopefully it s gonna dislodge whatever is in there. I suspect somebody in the lab spilled some sticky solution in there. I was also able to melt some solder where the holes are to make them smaller. The pins dont get in rhat easily but at least there is contact.

Now why did the car lamp start flickering when the LED board was on I dont know. Something grounded? The LED board barely has anything on it. I guess it might make it easier to solve.

[sam_sam_sam]

The pin connection on the right hand side of the green looks like crap it appears to be flux from the picture if so re-solder them or is it just the way the picture was taken

[vrasp]

Originally Posted by sam_sam_sam

The pin connection on the right hand side of the green looks like crap it appears to be flux from the picture if so re-solder them or is it just the way the picture was taken

It s not the way the picture looks. It was actually quite bad. Cleaned it off but havent reappplied solder yet.

Is the car lamp blinking for sure caused by a short to ground in the LED board if it only happens when it is connected?

[eccerr0r]

If that car lamp glows very brightly, interpret it as if you just had to stick in another fuse.

[vrasp]

Originally Posted by eccerr0r

If that car lamp glows very brightly, interpret it as if you just had to stick in another fuse.

It s not very bright. You can just see the filament warm up. And now that I think about it, it could just be blinking because of the constantly changing number on the LED which varies the power drawn.

Could it just be normal that the car light lights up slightly? I dont wanna look for an issue where there is none.

[eccerr0r]

Yes it's fine for it to be dim. Don't worry about it, it's expected.

The sole alert is if that it glows brightly - it saved you from replacing another fuse.

[vrasp]

While I try to figure out how to properly fix the connections between boards, can someone explain to me how the knob system works? In this case, the knob serves to pick a preset temperature.

Is the plastic knob supposed to have a circuit that touches the the metal parts of opposite sides to activate the circuit? I m just guessing here. I need to understand how it works to see hownit can be fixed.

The actual knob (not shown in this picture) goes into the white round thing on the top board of this picture.

[eccerr0r]

That's about it, just selects different resistors...

[vrasp]

Originally Posted by eccerr0r

That's about it, just selects different resistors...

Thank you. I was asking because the knob I have does not have any metal in it. I think I might have broken it while trying to remove it from the board and maybe the metal part got lost.

I think I m going to buy a new rotary switch. The one on the board works by creating a contact between the center golden circle and the outer golden metal. I d like to get a similar one. Is there a specific name for this?

If you have other suggestions to replace this switch let me know! Thank you

[eccerr0r]

if you're inclined to look for the small metal piece lost, it probably looks like a bent leaf.

The unfortunate thing is that getting an exact match will be hard...mainly to fit in the board. Rotary select switch is pretty much is all you can look for, and it appears to be a 5 throw 2 pole (DP5T) rotary (of which it really just needs 1 pole but the original designer appears to have cheesed the switch to make it easier to route PCB tracks?) perhaps if you can't find the leaf it's easier to just hardwire it to the adjustable setting?

[vrasp]

Originally Posted by eccerr0r

if you're inclined to look for the small metal piece lost, it probably looks like a bent leaf.

The unfortunate thing is that getting an exact match will be hard...mainly to fit in the board. Rotary select switch is pretty much is all you can look for, and it appears to be a 5 throw 2 pole (DP5T) rotary (of which it really just needs 1 pole but the original designer appears to have cheesed the switch to make it easier to route PCB tracks?) perhaps if you can't find the leaf it's easier to just hardwire it to the adjustable setting?

I didnt think of that! That would save me the trouble of looking for a proper rotary switch. I m gonna see if I can do that right now.

[vrasp]

Originally Posted by eccerr0r

if you're inclined to look for the small metal piece lost, it probably looks like a bent leaf.

The unfortunate thing is that getting an exact match will be hard...mainly to fit in the board. Rotary select switch is pretty much is all you can look for, and it appears to be a 5 throw 2 pole (DP5T) rotary (of which it really just needs 1 pole but the original designer appears to have cheesed the switch to make it easier to route PCB tracks?) perhaps if you can't find the leaf it's easier to just hardwire it to the adjustable setting?

How do I hardwire it? I thought I just had to wire the fifth outer pin (that corresponds to the manual temperature selection) to the inner pin (golden metal ring). Things started getting smoky and I turned it off immediately. The smoke came from one of the capacitors or the resistance next to it. I think I reacted quickly enough. If I have to replace it it's no big deal. However, I don't understand what pins to wire.

Basically, I did this:

[vrasp]

The capacitor is fine. It is the resistance that blew.



Are you able to see the lines? I can't tell what ohm this is.

[petehall347]

go through your pictures to find a good close up of the resistor .

[vrasp]

Originally Posted by petehall347

go through your pictures to find a good close up of the resistor .

I did, it s really difficult to see.

The bands look like Red brown something (grey?) brown red. Of course the blown resistor had to be the one that is the least visible in the pictures.

Is there a trick to figure out the resistance of a blwon resistor before it blew?

[petehall347]

tell us what it connects to ?

[eccerr0r]

appears to be a kind of jumper... which could explain the need for 20V as there'll be a drop across this resistor to reduce heating of the regulator...

[vrasp]

Originally Posted by petehall347

tell us what it connects to ?

It's getting 20v AC from the transformer and on the output it goes to the bridge rectifier which goes to the voltage regulator.

Originally Posted by eccerr0r

appears to be a kind of jumper... which could explain the need for 20V as there'll be a drop across this resistor to reduce heating of the regulator...

The voltage regulator is a 7812. If I am able to find out more or less how much current is in this circuit I can calculate the resistance needed to lower the voltage from the 18v of my toroidal transformer to about 13-15v. Is that a good approach? I could connect my multimeter in series to measure the current where the resistor was, and calculate a resistance that would drop the voltage by, let's say, 5v.

[eccerr0r]

The resistor may still be good. Measure it.
I don't understand why it smoked, sure you didn't short something else by mistake?