Thermo electric pcb power supply

[kaboom]

Re: Thermo electric pcb power supply

As a first time user of this forum i must say i am very impressed.
I would like to thank all of you for responding and helping me.

You're welcome.

One question i do have right off the batt is, if the caps on this boards need replacing what type of cap do you recomend?

They all need to go. Not "if," or "when," but all.

Nichicon PW, HE, PM, PJ, PA. Panasonic FC, FR.

For the two line rectifier/doubler caps, you'll need leaded, not snap-in. The holes in the board are too small, and the traces too narrow to drill out, for snap-in types. Try Nichicon CS or CY, or Panasonic EE for those.

[Behemot]

Re: Thermo electric pcb power supply

For most kinds of PSU I use low-ESR (but not ultra low). One of these mainly: Samxon (GK, RS, GT), Nichicon (HD, HE), Nippon Chemi-Con (KZY, KY, LXJ, LXZ), Rubycon (ZL, YXG, YXH), Sanyo (WX, WA), Panasonic (FM, FC, FK).

Generally, the bigger/filtrating ones could be slightly more capacitance-wise with no problem, small usually are good to keep mostly the same parameters (even ESR/impedance), it's good to consult datasheet of the original ones before swapping them.

[JOELDJOHNSON]

Re: Thermo electric pcb power supply

As a first time user of this forum i must say i am very impressed.
I would like to thank all of you for responding and helping me.
As i start to repair and replace components i may have some more additional questions so please help me out if you can .
One question i do have right off the batt is, if the caps on this boards need replacing what type of cap do you recomend?

Thanks again to all of you.
Joel

[kaboom]

Re: Thermo electric pcb power supply

Three secondary rectifiers.

One on the heatsink for the fans and Peltier.

Maybe a 2A FR diode for the temp control opamp and LED inside the box. This could be subbed with an FR4004.

And another FR4004/7 for the '494, just like a computer power supply.

[lti]

Re: Thermo electric pcb power supply

It looks like that board is drilled for TO-220 and TO-247 secondary rectifiers and either a TO-220 rectifier is being used or they jammed the rectifier into the TO-220 holes.

[kaboom]

Re: Thermo electric pcb power supply

Thats what I though, but man, how's that possible?

Maybe a missing screw in the tab hole. Powmax did this on some LP6100s' aux supply. The equivalent of a tabbed topswitch was merely 'held' to the primary heatsink by tension in its leads, thermal compound (amazingly), and some of that wonderful conductive glue. All it would take is severe overheating. They must've forgot the spring clip that week.




The overheating would be "planned for" by using caps that eventually go bad and ultimately leak. As in leak on the board. Ironically, this TEC PS also has what look like saturn caps. Come to think of it, the ones I worked on did as well.

And here's a de' ja vu moment- when I first rebuilt one of these "Haier supplies," I swore they were made in the same factory where Deers are born. Same saturn caps, sometimes ceramics across the line/GND, Ruilian fans, and a combination of two 1A and two 2A AC line rectifiers.

It all makes sense now.



These things have abominable soldering as well- there's no way I'd risk a callback w/o soldering the whole board before returning the unit. Makes CTC175s look pristine.

[Behemot]

Re: Thermo electric pcb power supply

Your secondary rectifier desoldered itself, or you took it out to test.

Thats what I though, but man, how's that possible?

[kaboom]

Re: Thermo electric pcb power supply

As far as your particular unit, here's what I think.

At least one primary switcher has blown, taking out its base resistor. The two small caps go bad and the transistors are no longer biased/driven properly.

Your secondary rectifier desoldered itself, or you took it out to test.

The screws for the 13005s are discolored, one more than the other. They were running hot, possibly unbalanced as well. The small caps mentioned above contributed to this. If you lost half of the secondary rectifier, that would also be a problem.

Replace everything in the base drive ckts, for both transistors. You can sub 13003s for low-load testing- some CFLs use them. They can be scrounged when the CFL dies. It's mostly the bigger ones that use them. "Lights of America" 26W ones do.

Check the 2sc945s or 1845s between the '494 and the driver transformer (smaller of the two).

I only marked the values of the resistors that I was certain of. The lighting could be better...

[kaboom]

Re: Thermo electric pcb power supply

I work(ed) on those.

Usually, the caps (all of them) start to leak over the board. Caught early, you end up either having to clean under the caps when you replace them or wash the whole board. Once they make a mess and short traces out while under power, things fry.

The caps also deform over time. For example, one of these units had been plugged in and running for about two years. Power to it was lost during a holiday and no one knew. Several days later, power had been restored. The unit didn't come back up- it only stuttered/chirped and the fans also twitched.

As far as how the power to the TECs is controlled with respect to setpoint, we find that these power supplies rely on an old 'trick.'

For example:

The inside and outside fans, as well as the TEC, get power from the "main" output, that is, after the main secondary rectifier, output inductor, and large secondary cap. The duty cycle controls the output voltage.

The LED inside the box, the OPAMP for the temp control, and the '494 are fed from rectifiers before the output inductor. One rectifier and cap for the '494, another rectifier and bigger cap for the LED and temp control.

Since the rectifiers before the inductor see the full amplitude pulse when energy is transferred, the loads served by them get practically the same voltage regardless of what the duty cycle is. This means that the '494 and temp control still have power to work even after the box is down to setpoint and the PWM duty cycle has backed down.

That's basically how these units can deal with "having some things on with others off."


Needless to say, replace all the caps. Even the two in the line rectifier/doubler. They make a mess over the board.

Secondary main rectifier should be an SBL3040, TO-3P or TO-247. Only because the heatsink is small. That big part can easily handle the ~6A load of the TEC at the higher temps achieved with the smallish heatsink.

Notice that the two switchers are not insulated from their heatsinks- you'll get a shock if you touch them.

Make sure snubber R's and C's are connected. Better yet, resolder everything.

Line rectifiers should be upgraded to 2A devices to better deal with rapid cycling of the AC line.

Don't go bigger than 220uf for the two line voltage caps. AC power goes through a switch mounted on the back of the "Temperature" pot inside the box- this is to take it easy on those contacts.

You may also have to change the "hot side" fans to ones more powerful.

I think the TECs these use are borderline, perhaps undersized. I've found these things take a while to get to temp, especially after the urethane insulation ages after a few years. TEC upgrades are possible.


One last thing. When the box is hot, they run full voltage, 12V to the fans and TEC. As it nears setpoint, the duty cycle drops just a little- you'll have 8-10 volts at this point and hear the fans slow. Once satisfied, the fans will stop and voltage should be close to nothing.


By all means try to fix it. $20 for a new one, but with "new" bad caps.

-Paul

[budm]

Re: Thermo electric pcb power supply

This may be close to what you have based on what I can see from your pictures.

[budm]

Re: Thermo electric pcb power supply

The 22 Ohms resistors for the Gate/Base drive is burnt up, yes it is half bridge drive setup. He needs to take out both transistor and check for shorts, also the Gate/Base drive diode that is in series with the 22 Ohm resistor.
There are many wires and connectors attached to this board, can I see the whole setup to see where all these wires go to?

[Behemot]

Re: Thermo electric pcb power supply

I had a feeling that stuff on resistors is just carbonized and broken heatshrink, the pictures are not so good on my 1920x1440 px display As for transistors, just use diode tester on them first and see, it may be just some damage on the plastic package without influence on function.

But really, I think there is rectifier on the third heatsink. You see how the solder is practically not in contact with the two legs?

[tom66]

Re: Thermo electric pcb power supply

This isn't a schematic of your power supply but it is a representation of how the two transistors are wired up (from one of th3_un1qu3's posts):
https://www.badcaps.net/forum/attach...8&d=1345579998

[JOELDJOHNSON]

Re: Thermo electric pcb power supply

visually i would say that this is where the problems are , the two xistors that have burned out / up and a few odd resitors.

i sure wish i could find a schematic

[tom66]

Re: Thermo electric pcb power supply

I have a feeling this is a half-bridge switching power supply. Th3_un1qu3 would know, but I think this is the type that self-starts based on transformer characteristics. There's little to go wrong apart from those transistors, so swap 'em out and see if it works. That one transistor definitely has a hole in it.

[rogfanther]

Re: Thermo electric pcb power supply

Seems the board has two hole patterns, maybe for bigger parts. But in the last photo isn´t there a resistor with burnt marks ?


And in the 3rd photo is there a hole in that transistor ?

[Behemot]

Re: Thermo electric pcb power supply

Thers something strange going on! Can you get image of the third heatsink, there is something like rectifier mounted in there? From the lower side photo it seems that thing got totally unsoldered or what?!

[JOELDJOHNSON]

Re: Thermo electric pcb power supply









here are some photos i took last night

thoughts?

[budm]

Re: Thermo electric pcb power supply

Is this a wallwart switching power supply type? If you crack it open then we may be able to see and guide you.

[JOELDJOHNSON]

Does anybody have or know where i can get a schematic for part # rf-5210-11 power supply?
This is for a sears thermoelectric refridgerator.
I know to replace it would be around 20 bucks , but where is the fun in that!
I called the haeir company ( they use the same pwr supply ) but they would not give me the schematic.

Please help me if you can