Mill power feed has died; what do I check?

I fixed it. I was testing it before I put it back and it worked. Put it in and it didn't. Took it out again and noticed that it worked intermittently as I moved it around. To get to the point, I noticed it worked when I flexed the circuit board. I discovered a cracked soldering joint in that big ol' heat sink (large, white square component). I added some solder, tested it again and it seems to have solved the problem. I'll let you guess where I soldered.

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That is a power resistor.

That solder still not good.

The resistor can take some heat.

Ckt board maybe not.

You need to get enough heat on the component to melt the solder, looks like it did not flow to the board.

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That's a cold solder joint. Not enough heat to flow properly. Need a bigger iron (more watts) or higher temperature.

However, nice find! Good job finding the problem.
 
Yep that long white part is a 1500 ohm power resistor. They often come loose from vibration and heat
Good sleuthing job! Not so good soldering job LOL
The power device is a BT152 which is a SCR thyristor- looks like it's a simple light-dimmer type of circuit- maybe half-wave
 
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ARC-170 said:
I fixed it. I was testing it before I put it back and it worked. Put it in and it didn't. Took it out again and noticed that it worked intermittently as I moved it around. To get to the point, I noticed it worked when I flexed the circuit board. I discovered a cracked soldering joint in that big ol' heat sink (large, white square component). I added some solder, tested it again and it seems to have solved the problem. I'll let you guess where I soldered.

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If you can borrow or buy a hot air rework station. I have one off amazon that was $50 and has worked really good over the years for things like this. I have used it for through hole components, just watch for the solder to flow and remove the heat. Try not to over heat anything. Also helps get in to doing surface mount boards, which are so much easier to do and cheaper then through hole. A fringe benefit I use the hot air gun to bend and weld plastic. Shrink tube, it has a lot of uses that most people don't see until they have one.
 
Soldering takes some practice, no matter what tool one uses. A good 40 watt iron with a clean tip and rosin core solder (almost) never fails for circuit board repair
Some careful scraping with an x-acto knife often helps make a better joint
 
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Yes, soldering is not one of my stronger skills! I have a really old (I think it was my grandfather's, and he died 20 years ago) 40W soldering iron.

I could not get the solder to melt nicely. It kept leaving a ball instead of flowing. Maybe it wasn't hot enough?
 
Not enough heat.

Many of the old irons have a tip inserted into a hole with a screw holding it.

Loosen screw and clean it up a bit.

After clean put back in and make screw is snug.

Take a small file and make the tip a chisel shape, not critical, just need clean metal.

Plug in and as it heats up touch your solde to the filed spot.

When hot enough it will melt and flow well.

If it a wood burning iron it may not get hot enough.

A 100 watt weller iron also will work but you need more skill.

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A 40w iron should be enough heat for PC board work.
Make sure the tip of the soldering iron is clean and freshly tinned.
Paint the joint with flux (Aka soldering paste) before applying heat.
You can use braided copper desoldering ribbon to remove excess old solder. No need to buy expensive rework tools.
Only use rosin core solder, never use plumbing or acid core solder for electronic or electrical applications.
 
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