Ultrasonic cleaner: transistor identification help please

[VujeDe]

I inherited an old, dead, Ultrasonic Cleaner. Inside was a loose live wire which seems to have likely shorted to ground and damaged some caps, diodes and two transistors, as well as popping the inline fuses.

Attached are images of the power board, a close-up of one of the good transistors, and the results when I put the latter in one of those transisitor-tester things (I've never used the latter for this type of component before so I don't know how accurate it is).

As you can see there are no markings on the chip at all (other than a faint smiley face, so I don't get it mixed up with the duff one). Could anybody who's more experienced at this sort of thing have a quick look, and maybe offer some advice for a suitable replacement? Or point me in the right direction?

Many thanks for your time.

Edit: Added an image

[eccerr0r]

Re: Ultrasonic cleaner: transistor identification help please

Acceptable Replacement Guess #1

http://www.mouser.com/ProductDetail/...onics/BUF420AW

[stj]

Re: Ultrasonic cleaner: transistor identification help please

there is a good chance that the rough surface is screen-printed paint, and the part number is under it.

[VujeDe]

Re: Ultrasonic cleaner: transistor identification help please

Acceptable Replacement Guess #1

http://www.mouser.com/ProductDetail/...onics/BUF420AW

Thanks eccerr0r, I'll put that on the list of possibles!

there is a good chance that the rough surface is screen-printed paint, and the part number is under it.

This gave me a little hope! I tried cellulose and 2k thinner, a knife blade, then various grades of sandpaper, but unfortunately it really is just a rough surface.

If I did go for BUF420AW as a replacement, should I replace all 4 transistors, despite 2 of the "old" ones being good?

And what should I be looking for in a replacement if I wanted to compare the old, to the BUF420AW and others? How do you learn that?

Thanks again!

[stj]

Re: Ultrasonic cleaner: transistor identification help please

i would desolder all 4, and meter the resistance between the pads on the board to see if all 4 positions are the same.
incase something else is wrong.

[eccerr0r]

Re: Ultrasonic cleaner: transistor identification help please

Since I can't tell what the characteristics of the transformer is, I'm also assuming that you were at 220VAC range since your profile implies you're in .uk, hence the 400V transistor selection. If my assumption was wrong, perhaps you can go lower in voltage, but a lot of those power transistors are somewhat similar in characteristics...

[VujeDe]

Re: Ultrasonic cleaner: transistor identification help please

@stj I'm yet to go through the board thoroughly but there are definitely more damaged components. Fortunately all part numbers for those are ID-able.

@eccerr0r Your assumptions are correct Many thanks again.

[redwire]

Re: Ultrasonic cleaner: transistor identification help please

That looks like an insulated Isowatt218FDX or TO-3PF package that ST makes. The middle leg plastic is for high voltage.
BUF420AW does not have insulated (tab) body, so big hassle getting HV insulators and mounting hardware?

I would look at BU508AF, ST1510FX or MD2310FX 1.5kV 7A 62W hFE 6-28.

[stj]

Re: Ultrasonic cleaner: transistor identification help please

bu508af wont be fast enough, it would need to be bu2508af

[eccerr0r]

Re: Ultrasonic cleaner: transistor identification help please

these things likely won't run more than 50KHz.
Looks mostly like a typical CFL inverter which also runs about the same frequency.

[stj]

Re: Ultrasonic cleaner: transistor identification help please

bu508 was the sucessor to the bu208, both are intended as horizontal drive on tv's
so 15Khz.
bu2508 was an upgrade for 100Hz tv's and pc monitors.
so atleast 32Khz - maybe a lot more.

[eccerr0r]

Re: Ultrasonic cleaner: transistor identification help please

The other thing is that this will likely be running somewhat sinusoidal so no need to worry about harmonics that need to be accurately amplified. Seems most ultrasonic cleaners run around 40KHz.

It's also weird that they don't post gain bandwidth product/transition frequency limits for these power transistors, but they do specify rise/fall times for inductive loads which might make more sense as likely they will be switching inductive loads for power supplies. Oddly enough the bu2508af appears to be somewhat slower than the bu508af due to their switching times, but both seem to be able to switch just fine at 100KHz and beyond, so it should work unless the operating frequency is known to be higher than probably ~175KHz for the bu2508af.

Seems most of these power transistors listed start having problems at 400KHz though. Which is sort of expected, a 2N3055 rev 2 Ft is only 2.5MHz which is within an order of magnitude (then again it sure won't oscillate at Ft, so you can't oscillate a 2N3055 that fast, gain not high enough.)

[redwire]

Re: Ultrasonic cleaner: transistor identification help please

Those HV transistors are all for colour TV horizontal deflection (HOT), switching use.
Datasheets 1998, 2007. But still used and available today.

OP's circuit is basically full bridge so 500V parts should be sufficient?

[VujeDe]

Re: Ultrasonic cleaner: transistor identification help please

Sorry for the delay in replying. I'm more than a little out of my depth here but I think I am managing to follow bits and pieces of the discussion.

I dug the cleaner out from the shed today, and snapped a picture of the label (attached). There are 6 transducers inside, and if the label is to be believed these run at 30khz.

@redwire You're right. It completely slipped my mind to mention it, but the middle legs are insulated.

And @eccerr0r thank you for the schematic!

Am off to check out some datasheets