I'm trying to repair the generator board on a Sonix IV ultrasound cleaner. I need to find a replacement for a transistor (in a TO-3 package), but the manufacturer uses an in-house part id, so I'm trying to figure out what kind of transistor this is.

This guy has a similar problem, but a slightly different generator board: Replacing a transistor when I can't find any info on it. I suspect it is the same transistor though. Like him, the manufacturer is unwilling to give information about the part.

I have tracked the part-placement and wiring on the board, and created a schematic. Can anybody use this to suggest a suitable replacement part?

Schematic: schematic



Top layer PCB: Top Layer

Bottom layer PCB: Bottom Layer



  • 1
    \$\begingroup\$ +1, good job on extracting the schematic. Repair questions like these are great. \$\endgroup\$
    – zebonaut
    Aug 12, 2012 at 19:43
  • \$\begingroup\$ Some transistors to try in this thread: forum.allaboutcircuits.com/showthread.php?t=63669 \$\endgroup\$
    – markrages
    Dec 6, 2013 at 23:14
  • \$\begingroup\$ I recently acquired an ultrasonic cleaner made by the same company. Have you had any success with this repair? I am also trying to figure out the board. \$\endgroup\$
    – user148298
    Jun 9, 2020 at 2:36

4 Answers 4


I am a former employee. It is an NPN High Speed switching transistor (similar to a BUV48A in a TO3 case). Any high speed switching NPN transistor with a rating of at least 600v, 15 amps, with a low hfe should work. You will also need to check the diode closest to the transistor, because it ran hot and failed in this board version. Use an ultrafast 2 amp. Change the 1 ohm resistor (R2) to a 24 ohm 3 watt, and change the 56K resistor closest to the 1uf 400v Capacitor (R4) to a 100K 3 watt. You may need to change the turns on the feedback (toroid) transformers, depending on the output waveform. One full cycle of the output on the oscilloscope should be approx. 16.4usec (~60khz). Measured from the Emitter to the Collector. The "on" and "off" should be as close to symmetrical as possible ( 8.2usec: 8.2usec). Approx 350vpp. The turns on the toroid should be 10T and 4T in general. I suggest using a 2amp GMA pigtail fuse instead of a 1 ohm fuseable resistor.


From having a look at the various links and previous question, my guess is it's a high voltage NPN designed for line switching. Something like the 500V, 20A NTE98. This is assuming the input to the connector marked "PWR" in the schematic is a rectified line voltage (can you tell us anything about the input voltage?)

I think your schematic is not quite correct, the schematic in this link seems more likely (I know it's not the same model) as it has the base feedback from the coil tap.
I'd check the traces carefully, particularly the toroidal feedback coil, I think it should connect to the base junction.


Hard to say.. My guess is they made an online regulator for driver / 60KHz *1 clock/ and a fast TRIAC switch.

*1 or whatever resonant frequency of piezo device is.. which you can measure.

That's why it's proprietary.

That's also how they can transfer a lot of power in a small transformer and have a shielded driver with CM rejection on the other side of transformer.

I might call it a high power chopper design for resonant switching with 60Hz AM. ( no need to make it smooth modulation.)

What is not clear on your schematic is if the piezo resonant element is a powered port with its own driver @50Khz or so, and thus all you need is a switch (Triac) or if it is passive and it needs an integral switch & driver (chopper) . Judging by the lack of Line filters for Chopper, I would guess the piezo port is AC powered only. Hence Triac only AC switch for TO-3. but transformer looks like only 10W size at 50/60Hz. What is the power rating on ultrasonic output? If higher than 10W, then transformer might handle more power at higher chopper rate, but then where is LISN or line filter?


If I looked at the diagram, I think the builder of that unit has changed the type of the active component (in this picture is the"transistor").
On my experience with a few electronic diagram, it is NOT a transistor , but it is a hybrid switching generator which usually used on the switching regulator (like TOP derivate of switching regulator).
I hope this information is useful for you.


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