Ultrasonic Cleaner Driver Board

[hasbihal]

Hi,

I've got a problem with an ultrasonic cleaner and have difficulties identifiying the parts / the problem.
I've replaced the big bridge rectifier. The transistors are working fine, so does the low voltage part (after the small bridge rectifier). I've replaced the IC aswell (I bareley could read the 4046 on the chip even tho it is sanded). It looks like someone already replaced the transistor on the upper right side of the pcb. I dont get any voltage reading from any transistors whatsoever. How likely is it that all of them died?
The foil capacitors seem to be fine aswell. (correct capacitances reading from multimeter).

Also, the whole PCB is kind of swamped with a red-brownish substance, hard but sticky.


According to a video I've found, the output to the piezoelectric transducers should have ~154V AC.

Does anyone know what else to look for? And where I can get the transistors replaced or what alternatives I could buy?

Thanks in advance.

Edit:
The two relays on the upper side are there to adjust the power. I am aware that the yellow cable on the right connector is broken but it should be at 100% power then regardles of what I set. Even if I unplug both relays, the system should run at 100%. So disregard that.

[t1d]

Also, the whole PCB is kind of swamped with a red-brownish substance, hard but sticky.

Determining the source of the substance may lead to a failed part. Even though it is on the entire surface of the PCB, it can easily have sprayed out of a failed electrolytic capacitor. So, chase that down. Additionally, that type of substance sounds like the old type of glue that was used to secure big components to the board and is known to become conductive and caustic, over time. That stuff will shut down an entire device and eat your traces. You might try testing it with a milliohm meter. At any rate, I would get every bit of that substance off of the board and use a new proper glue to re-secure everything. HTH.

[hasbihal]

Thank you. I don't have a milliohmmeter so I tested with my multimeter. The readings were all ok from the traces. I desoldered the transformers and cleaned the mess up.

I desoldered half of the board and when I measure the resistance of the transformers, I get a really low reading like a few ohms. Is that an indicator of them being dead/shorted?

[fmashockie]

Thank you. I don't have a milliohmmeter so I tested with my multimeter. The readings were all ok from the traces. I desoldered the transformers and cleaned the mess up.

I desoldered half of the board and when I measure the resistance of the transformers, I get a really low reading like a few ohms. Is that an indicator of them being dead/shorted?

Transformers are just coils of wire wrapped around a ferrite core.  The primary and secondary side windings will have low resistance normally.  It will vary depending on the size/type of transformer.  If you have low resistance across different windings, then that would indicate a possible issue such as internal breakdown of the transformer.

With all due respect, I wouldn't recommend this method of troubleshooting.  Desoldering everything from the PCB has its risks.  Test for voltages first.  Start with mains and follow the circuit from the high voltage side to the low side.  Use datasheets for the ICs on the PCB (like the 4046) to your advantage.  The datasheet for the 4046 provides waveforms that you should see for each pin that you can verify with an oscilloscope.