Wine Refrigerator Board Repair Help

[Peak2Peak]

I will try to make a long story short.

I am trying to fix the board from a Franklin Chef FCW16T wine refrigerator.

The first fix which was a fuse and one of the large capacitors lasted for few years.

The second attempt was after the power shut off and came back on around four times with in about ten minutes, after which I could hear what I call a zitsing noise the after another cycle of the power, maybe a slight high pitch noise.

There was a bad power switching transistor which was replaced. This was a few years ago and when I tested it after replacing it I cannot remember if the rheostat temperture control was plugged into the board. I know I did not have the fan or the internal thermostat hooked up. I only plugged in the power first to the board first and then plugged the cord in to the outlet. The LED's light up and I thought everything would be fine. I then unplugged the cord, plugged in the peltier unit and then plugged the cord back it. Something blew and the LED's did not come back on and I have put everything aside since then.

The cord has a ground which is screwed to the chassis. The board is screwed into the chassis via some plastic standoffs but as you can see in the picture there is no electrical path connection between the screws and anything on the board. So I imagine it has a floating ground, but am not certain.


I have since tested most of the components that I can with the equipment I have, which is only a cheap DMM. The power switching transistor that was not replaced the first time is bad, but the one that was replaced is still good. I am wondering if the reason the other power transistor blew is because of the fact that I did not have the other connections made as detailed above and I had the board just sitting there breadboard fashion or if that did not have any effect.


All the resistors seem good and they are within tolerance as far as I can tell. The zener diodes are working. The diodes test good. The transistors and schottky barrier diode test good. The voltage regulator works. I have hooked the peltier cooler up to a 12V battery and it heats and cools on opposite sides. I can only assume that it works as I am not sure how else to test the peltier.

I do not have and ESR meter so I cannot measure any of the capacitors. I do not have a ring tester so I cannot check the transformers. I do not have an oscilloscope so I cannot test the PWM IC. Is it possible that too is bad? I am unable to test the inductor.

Since that attempt did not fix the problem I am assuming there is something else wrong beside the power switching transistor, or is it because everything was not attached? So my question is what would be the most likely cause of the problem, how should I fix it and what should be replaced to get this working again?

Needless to say I am no where near the level of the others in these forums.

Therefore, any help, insights or suggestions are greatly appreciated.
Many Thanks

 

[kam1787]

you can still do some in-circuit tests on the transformers and capacitors, which could help.

for the caps - zero resistance would not be a good sign. large value caps should show a charge-up behaviour

for the windings - should show near zero resistance

Do look and smell {!} - any signs of over-heating or burning

 

[Peak2Peak]

Thanks for your suggestions.

By charge up behavior I assume that would exhibit itself by my meter showing rising resistance when the probes are applied. If that is so then all of the electrolytic capacitors show this behavior. The ceramic disk, polyester film and tantalums do not. In checking some others of these types I assume they are not supposed to exhibit that behavior.

When I place the probes on each side of the transformers it shows as though the meter probes are not connected at all, infinite resistance. I assume, as all three do this and another that I tested from another scrap board, that this is how it is supposed to be and means they are good, correct?

There are no visual signs or smells of burning or over heating.

 

[karesz]

Hi Kam,
its all Ok, but we can see that some capacitors are over heated! More better, in these case, for beginn to change all electrolythics for 105 C, good quality types, and than apply measurements_if needed...

 

[kam1787]

great!

i neglected to include for the electrolytic caps - check for any bulges - bulges indicate something is wrong

- - - Updated - - -

great!

i neglected to include for the electrolytic caps - check for any bulges - bulges indicate something is wrong

 

[BradtheRad]

The solder joints and traces look all right. Nevertheless it would pay to examine for hairline fractures, using a magnifying glass.

Two of your capacitors appear to have slight bulges. A large and middle size. (See closeup.) They are prime suspects.

 

[Peak2Peak]

The picture that I posted was before I did any work the first time. The larger capacitor that was pointed out was already replaced, sorry I forgot to mention that. The other one that is by the terminals for the peltier was not replaced. It looks only very slightly bulged. I took it off and it does look like there was some leakage.

I will look at the solder joins. To be safe should I heat up each one to reflow it just to make sure?

Are there any tests that I can do or small circuits I can make out of a box of parts from other electronics so that I can test the capacitors to see if they are actually good for this and future projects, in lieu of an ESR meter?

Is there anything else that you think could be causing this, or are the capacitors the most likely thing to fail and cause problems?

Thanks again for the assistance.

 

[Ickme]

I commend you on taking photos of the board and cropping them so they are easier to see.

If you have not done so, I would suggest replacing the large capacitors. Also, check the solder joints for what is called cold joint. Sometimes reflowing the existing solder as you were asking about can be helpful. Sometimes old adhesive can become conductive as it ages. Look for any adhesive contacting a component's lead.

I also found another website with the same type of wine cooler and similar symptoms you have had with this board that has some useful information in addition to what you have here.

 

[Peak2Peak]

I finally got enough time to spend some time to fix this.

I replaced all the electrolytic capacitors with ones that I scavenged off other items in my scrape pile. I also replaced the fast recovery and glass passivated diodes for the transistor driver circuit and transistors and the bad power transistor with new. The two main filter caps are brand new. All that I replaced are outlined in the attached photo.


The good news is that it did not blow up and is now fixed, sort of. The one issue that has arisen is that when I unplug the power the larger transformer on the left in the photo makes the noise in here: **broken link removed**

I don't know how to describe it as I have searched for similar descriptions in hope of finding a cause that may be for transformers in general. I would call it a croaking sound. It happens both when if the peltier unit is hooked up and when it is not when the cord is pulled.

I did have the transformer out to test the primary winding for a short as mentioned above. I had them in an ESD bag and moved them around a few times. Nothing that I would think would damage the windings or break the lacquer, but I wouldn't know how fragile it was to begin with.

I do not know if it is being induced by another bad part, harmonics in the windings now evident due to cracked lacquer insulation, or something I re soldered poorly due to the bad quality board traces not adhering well, or an bad electrolytic capacitor discharging and sending an odd frequency through the transformer causing the noise.

Any thoughts as to what this noise from the transformer is and what might be causing it is appreciated and hopefully how to fix it.

Again thanks for the assistance

 

[BradtheRad]

Your wav sound is a rapid clicking. It sounds like arcing.

My oscilloscope once started making a similar continual sound, and it turned out to be arcing inside the main power transformer. It was caused by high voltage, coming from the beam generator circuit. The winding's insulation had lost its effectiveness.

Does your unit have high voltage anywhere inside? A coil that has its current flow suddenly cut off?

 

[Peak2Peak]

Does your unit have high voltage anywhere inside? A coil that has its current flow suddenly cut off?

I do not know what the voltages are on this board so I cannot say if there are high voltages, nor have I yes to figure out what is the hot side ground so that I could measure some things.

What would be considered high voltages?

If by coil you mean inductor, yes there is one. The issue only arises when I remove the power.

I have heard this type of noise before on a tv/dvd combo power board also when the power was removed, though to a lesser extent. Because it only happens when the power is removed and seeing as it would be plugged in all the time would it therefore not cause any damage while in operation and be safe to use without incurring further damage?

Thanks

 

[BradtheRad]

What would be considered high voltages?

My scope has 1000 volts. The arcing made the scope unusable. I solved it by installing a separate small transformer for the heater in the 1000V tube. The problem returned after I stored the scope in a high humidity basement.

If by coil you mean inductor, yes there is one. The issue only arises when I remove the power.

There is a chance the clicking is not serious.

You must listen closely to find out where the clicking occurs. It could be inside an inductor/ transformer.

 

[Peak2Peak]

I do not think there is any voltage that high in this little power supply. The power transformers are rated to 700 volts but I can't even see them coming anywhere near to that.

I did listen closely with an automotive stethoscope and it most certainly is coming from the transformer i mentioned, but only when the power is removed.

 

[BradtheRad]

It is probably arcing then.

Since it happens only at shutoff, the unit can last for a while as is.

However each time the arcing occurs, it burns away a tiny amount of wire. Eventually a gap will widen. Then you're looking at two outcomes. Either:

(a) the gap will grow too large for arcing to occur, ending the problem and allowing the unit to function normally,

or,

(b) the wire will get burned away, a bit at a time, until internal continuity is broken, and the unit stops working.

Congratulations on your success as a fixit man.

To get arcing, you need for the insulation to perforate between two wires, and you need voltage differential greater than 400 or 500 or 600 V, depending on how close the wires are to each other.

Carbon deposits in the vicinity will conduct electricity. The carbon may vaporize, creating an environment for arcing.

All of this creates a lot of unknowns for a troubleshooter.

There is a chance the arcing can be stopped by installing some component somewhere, such as a bleeder resistor, or capacitor, or snubbing network, etc.