Help with pcb issue

[Ashly90]

Hey everyone, I’ve got a electronic pipe freezer ( was given to me by a friend as faulty ) . I’ve got it on but it doesn’t seem to do a lot, if I push the buttons they light up whilst it’s pressed and I get a couple of lines on the screen that’s it. I’ve noticed the resistors look bad to me ( look almost rusty) would changing these out be a possible cure to the problem? Everything is running on the machine I just can’t control it as the buttons/screen won’t stay on. I’ve attached some images. Thanks in advance for the help

 

[Ashly90]

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[hyedenny]

I doubt the resistors are bad. It looks like there are a few electrolytic capacitors missing, unless they're on the other side of the board.
What the heck is an "electronic pipe freezer?!?"

 

[narkeleptk]

Makes a ice clog in the pipes so you can make repairs? Never knew they existed, learn something new everyday.

If nothing much is working it could be the mcu there that is dead. Does not look like it was kept very dry during its service life.

 

[hyedenny]

I don't see how that's "electronic," or why it needs a fancy control board unless it uses Peltier coolers.
Interesting, though -- I always thought freezing a pipe was something to be avoided at the risk of rupturing the pipe!

 

[KeepItSimpleStupid]

Ever heard of pipe bread"?.. e.g. http://168.215.203.131/prod/cat7/dissolvable.php

 

[Ashly90]

Thanks for the replies. Haha yes they exist and to be honest there quite handy for changing a part without having to drain down a whole system. Once the pipes frozen they stay frozen until you ask it to defrost it which is why I wanted to get this working. I have no idea how it works really, it has two radiators with fans which do run and a pump with a coolant tank which is also running. It’s just the lcd and buttons not working correctly. They will light one or two of the 7 bars on the screen when I push them but then go out when I let go. There supposed to stay on and either freeze or defrost whilst showing the temp on the screen. The only reason I thought the resistors is they have brown what looks like rust/corrosion on them but not sure if this would cause that issue.

 

[Ashly90]

Some more pics, this is what happens when I hold the buttons. The buttons should select the pipe size and then the bottom 3 buttons should either freeze or defrost and then start it. As you can see the screen is not showing any temps and only a line when I hold the button
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[hyedenny]

You didn't say anything about the electrolytics. Are they on the other side of the board, or are they missing?

 

[Diver300]

As others have mentioned, the electrolytic capacitors are either missing or on the back of the board. The spaces for them are the white circles surrounding two pins, with the white sector.

I suspect that the electrolytic capacitors have either dried out through age or broken off. The voltage regulator is labelled "7805". The middle pin of that is the ground and is also connected to the screw that holds it down. The pin nearer the 28-pin IC (PIC16F76) should be at 5 V. It's also worth measuring the ac voltage on that pin which should be nearly zero. If it's not, the capacitors have probably failed.

 

[Ashly90]

Sorry I completely forgot to post the image of the back of the board, I’ve attached it below. So I’ve got 5v on the right pin and the ac is 0 on that pin.

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[hyedenny]

It's hard to tell from the picture, but I see at least 1 cracked/dry solder joint. Get a good magnifying glass and check all the solder joints -- especially those around the relays.
The one I saw immediately was right above the first relay on the left -- the first joint to the right of the electrolytic. There's another one right above the 3rd relay on the right -- immediately above it and to the right. It looks like someone with an unsteady hand and a soldering iron was already messing with this, judging from what looks like melted plastic and sloppy flux and solder work.

 

[Ashly90]

Brilliant cheers for that, I’ll have a look. On the side opposite to the relays there’s a couple of joints bridged, I’m guessing this is right? As those are for the 28pin chip which I’ve just noticed gets considerably hot.

 

[hyedenny]

The 28 pin chip is a PIC Microcontroller -- the "computer" that controls everything, and no, it should not get hot AT ALL!

 

[Ashly90]

Thought so, I’m guessing it’s either the chip is gone or it’s shorted somewhere. Could those resistors cause this issue as they don’t look great at all, and they attach to this chip?

 

[hyedenny]

The resistors are mostly for the LED readout, and a few others are pullup/pulldown resistors, and bias resistors for the transistors which switch the relays and the other end of the LED readout. They are the least likely cause of any problem.

 

[hyedenny]

I would pull the transistors, then check all the voltages at the PIC.

 

[Ashly90]

Brilliant cheers, I’ll try and get that done this week and let you know how I get on

 

[narkeleptk]

I do not know PIC at all but generally in my type of repairs dealing with similar situations (mild water damage) and a mcu is at fault its usually from data corruption in the memories which can be fixed by rewriting the programming with proper flashing tool. I assume PIC have similar functions. If yours is getting very hot however then its probably internal hardware failure of the chip and would need to be replaced and then programmed.

I would first call the company who makes the device and see if they sell just that board. Many times companies do and its not that expensive, so its worth a shot.

If not your only hope of replacing a bad mcu and programming it is to know what the programming is that was on it.
First you would need to learn how to read/write the flash for this mcu. Not as hard as it sounds.
Then you need to find another unit with same model number either from a friend, purchase a working unit, or buy another "for parts" unit and hope its not the same issue. Then buy a replacement mcu and write the saved programming to it and install it back to your machine. Once you have two working units your good to sell one and keep the other if you need to recoup costs.

Personally I would just sell it as is on ebay "for parts only" and then if I needed one for my plumbing business I would buy a working unit.

 

[hyedenny]

If not your only hope of replacing a bad mcu and programming it is to know what the programming is that was on it.
First you would need to learn how to read/write the flash for this mcu. Not as hard as it sounds.
Then you need to find another unit with same model number either from a friend, purchase a working unit, or buy another "for parts" unit and hope its not the same issue. Then buy a replacement mcu and write the saved programming to it and install it back to your machine. Once you have two working units your good to sell one and keep the other if you need to recoup costs.

Sorry, but I disagree. The first thing you'd need to do is figure out WHY the pic went bad -- if it's bad at all. Then, if it's just a matter of replacing the pic, and since this is such a simple board, you could probably spend some time and write your own program to make it work the way you want. Borrowing or buying another board in order to port over the programming would probably be a waste of time and money because the programming is most likely code-protected.