ultrasonic cleaner MH-060S, replacing transistors [fixed > broken again]

[elektryk]

2SC3320  also has V_CEO=400V

From my experience MJE13009 are enough to drive 2 transducers 60W each.

[htm]

i've got an update and wondering what to do next;
transistors
i ordered a few SC3320 from aliexpress.com(€3.08 for 5 ), ordered a few BUV48A(€4,24 for 1) from tme.eu and i salvaged 1 good transistor from the main board.
Then i used my new component tester . Turns out the AliExpress ones are all seen as a Diode!? (see attached picture)
How can that be? i mean, how wrong must the component be for the component tester to think it's a diode?

transducers
I measured the resistante between the two leads going to each set of 3 ultrasonic transducers. They show open loop.
But when in 'voltage meter DC' setting and connect the black lead to the black probe, and tap the red wire with the read probe, then the measured voltage increases with approx 10mv per tap, until it reaches 400mV and it resets. That happens for both sets of transducers. Not sure what that says though

what next?
Should i just replace the broken components (transistors, fuse and diodes) and give it a go 🙈(after filling up the tank)
or is it better to first check if the transformers/inductors are still Ok. i'm not sure how to go about it though..
i have a simple function generator and a basic analog 10Mhz scope. Could i do something with that?

[fzabkar]

Perhaps the Ali parts have a C-E damper diode? I would perform a B-C and B-E diode test with your DMM.

[htm]

@fzabkar
Afaik, the C3320 has pin layout: 1(B) 2(C) 3(E)
The diode tests show:

BC
black on 1, red on 2 = OL
red on 1, black on 2= OL

CE
red on 2, black on 3 = OL
black on 2, red on 3 = 0.488V

BE
red on 1, black on 3 = OL
black on 1, red on 3 = OL

[fzabkar]

Those Ali parts are fakes.

[wraper]

@fzabkar
Afaik, the C3320 has pin layout: 1(B) 2(C) 3(E)
The diode tests show:

BC
black on 1, red on 2 = OL
red on 1, black on 2= OL

CE
red on 2, black on 3 = OL
black on 2, red on 3 = 0.488V

BE
red on 1, black on 3 = OL
black on 1, red on 3 = OL

It's an N-channel MOSFET, what you're measuring between pins 2 and 3 is an intrinsic body diode. Tester detects is as a diode probably due to high gate-source threshold voltage.

[htm]

@wraper
I tested it. Indeed!
The MOSFET is changing from Off to On from 4.1V to 5V.

But why didn't the Component tester see it as a MOSFET? aren't most mosfets switching in that area

[wraper]

@wraper
I tested it. Indeed!
The MOSFET is changing from Off to On from 4.1V to 5V.

But why didn't the Component tester see it as a MOSFET? aren't most mosfets switching in that area

Most modern ones have lower V_GS(TH). Your tester probably cannot supply enough voltage or measure above some value below it. Or maybe its firmware has some quirks. I wouldn't outright trust what such testers automatically detect.

[htm]

Today i finished replacing the defective diodes and the 4 transistors.
On both boards 1 transistor seemed ok, but i replaced those as well, just in case. I rather have them all be the beefy BUV48A

Did a testrun of a minute, and..   

Thanks for all advice!

[htm]

  .. he used it about 3 times, and then it quit on him again.

i'll take another look at it, to see if the same thing happened again.

[floobydust]

Check your model is likely the same as a Vevor, for repair and safety issues as well. I also mentioned it here:
https://www.eevblog.com/forum/repair/vevor-30l-ultrasonic-cleaner-went-up-in-smoke-take-tranducer-out-of-series/msg5605060/#new

[wraper]

As this has single layer PCBs I suggest thoroughly inspecting with magnification if there isn't some cracked solder joint. Sometimes it may be even not a crack as such but component lead not properly wetted by solder and moving within the joint that may look fine on a first glance.

[fzabkar]

As this has single layer PCBs I suggest thoroughly inspecting with magnification if there isn't some cracked solder joint. Sometimes it may be even not a crack as such but component lead not properly wetted by solder and moving within the joint that may look fine on a first glance.

This is the reason that I was taught to always reflow the solder at inductors and transformers.

[wraper]

As this has single layer PCBs I suggest thoroughly inspecting with magnification if there isn't some cracked solder joint. Sometimes it may be even not a crack as such but component lead not properly wetted by solder and moving within the joint that may look fine on a first glance.

This is the reason that I was taught to always reflow the solder at inductors and transformers.

FBT solder joints were basically guaranteed to crack sooner or later in CRT TVs/monitors if manufacturer did not add rivets in the holes. It also amazes me how often I see single layer boards used in high vibration environment, it's just plain stupid  .