Good morning,
my first post here and found you guys via google searching for a winecooler-repair. I'm Michael (German )and living near Sap Paulo (Brazil) right now.

My girlfriend got a winecooler from friends for free, and they told us, it stops working after some time. I tried and yepp, stops working.
I have some basic knowledge regarding analog electronics, I have a cheap dig. Oszi (china) and some Uni-T instruments, to measure current, temperature, etc.

Fault:
When I plug in the cooler, it starts beeping (maybe 5Hz) and the Leds are flashing with the same frequency. Sometimes after 10s. beeping, sometimes after 1min, sometimes never, it will start running, so no beeping anymore, Leds on, fans on, the peltier is cooling.
When I unplug the Peltier-Element, everything else works right away. Pluggin the Peltier in again -> faulty behaviour.

So for me it looks like, the power supply is not able to supply the drive current for the Peltier. Too weak or some buffer elcos are gone.

Additional observation:
- During that beeping, a very light ticking noise from the PCB can be heard. Sounds like a relay switching but way softer.
- One of the Transistors get really hot

Trouble Shooting done:
1. The PCB shows some signs of corrosion, so I cleaned it and added some copper lines, because I thought there might be a increased resistance resulting in a voltage drop under load -> no help
2. I replaced the "famous" C8 Cap -> no help
3. I replaced all caps -> no help
4. I replaced C8 a second time -> no help
5. I noticed during this beep-cycling, that there is a soft clicking noise, like a relay switching, but softer. So I took a little mic and went over the PCB at it seems, it comes from the left of those big NPN-Transistors. AND, it is getting really hot, something like 80°C, whereas the other power components go as far as 45°C. -> I removed both from the PCB, checked with a Multimeter (seems to be fine) and switched them and reinstalled -> no help and still the left Transistor is getting hot.
6. I measured the Shottky-diode on the huge heat sink and the values are ok.
7. Oh yeah, and I checked the whole board for blown up components -> nada

I'm running out of ideas now. My feeling tells me, it has something to do with the left transistor, and the fault stayed with the left one, even aber switching it. So I guess, something is wrong with the driving circuit -> ?
But I can't read out of the schematic, what's the job of this T6 and how it is driven. I would guess, it is part of a "push-pull"circuit, but in that case, both transistors should share the same load -> same heat.
C14 in the drive circuit had been replaced.

Any ideas ?

Thanks a lot

Michael

 

With the TEC (thermoelectric cooler) disconnected, what is the voltage output from the power supply?
What is the voltage with the TEC connected?

 

The transistors are pulsing the transformer via C16 , which sits at half supply, . What happens if you swap TR 6/7 round , check caps C13, C14 , C17 .

 

SOLVED

With the TEC (thermoelectric cooler) disconnected, what is the voltage output from the power supply?
What is the voltage with the TEC connected?

Hi,

without TEC it is 10.9 V
In case the PCB is able to supply power (when the beeping stops), it,s 10.8V at 4A.

When beeping, I can see on the oscilloscope, that the voltage rises to about 5V and then drops again. In a short intervall, same as the beeping frequency.

I did as well:
- Checked D11, D15, C13, C14, R34, R37, R32, R36, R33, C17, C16, removed/tested T4, T5, D9, D, ...
- swapped T6 with T7 : No help.

BUT, when I was testing R34 in circuit with the Osci, it stoped beeping. So clearly a reaction and R34 works within the T7 circuit. But also, the test-head of the Osci has a internal capacitor, means, the resistance of the test header unlike a Multimeter) drops with a high input frequency. So that doesn't have to mean, that something is faulty here.

I checked the diods D12 and D10 removed: both ok, and then I checked them in circuit again, and somehow, the measurements were not the same.
The D12 Circuit (lower) had different values (and showed in circuit the forward voltage of D12 as well), where as the D10 circuit in both ways had a very low resistance.
Acc to the diagram, that can't be, because the circuits are totally the same.

Solution: On the back side of the PCB, somehow the D10-circuit was shorted. I can't tell you, when or why that happened. Because I already replaced the D10, that might was a fault by me, that D10 was gone, replaced, and then I "installed" a fault again. So I cleaned the back side and made sure, there are now unwanted connections.
-> connected the PCB again and worked right away.

Thanks a lot guys
(repaired for 1.50USD, maybe the caps where ok, so the diode is like 2cents)

PS: funny thing, if you will. I had a similar case with a power source for some loudspeaker. Those had a little PCB with a power source for the stby-operation, so the big Trafo didn't need to be powered all the time.
In this PCB, it blew a few components, I replaced everything I saw damaged, but then, same behaviour. The Source couldn't provide power under load. And at the end, I was almost giving up, I replaced one of those supercheap little diods (which seemed to be ok acc. Multimeter) and, tada, it worked again.