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L&R T-14 Ultra Sonic cleaner.

Thread starter #1
I am trying to repair an "L&R T-14 Ultra Sonic cleaner" this is the plain old "T-14" model there is no suffix after it.

This thing has been sitting for years and was just recently put back into service around a month ago, the fluid being used in it is "Ozzy Juice SW-4" which has been working fine and getting things really clean.

Then about four days ago first thing in the morning after only running for about 10 minutes it let out a very loud POP and then it quit working, the fuse is not blown and the neon light it still on but it no longer buzzes like it did, one other person in the shop did not seem to be very impressed with how it was working but it seemed to work well enough for me so I just kept running it.

I am an experienced electronic tech and am not really looking for any help troubleshooting it, nothing is obviously fried or burnt and it has no strange smells, I'm just looking for a schematic diagram for it and so far haven't found one yet, I did find the other posting on the "T-14B" here but it is not the same circuit, this one just has one transistor the "2N6308" which appears to be the original Motorola transistor from 1973.
 
Thread starter #2
Well... what I have figured out so far is that the 2N6308 transistor is fine although the mica isolator under it was cracked in half sideways across the two pin holes, even though it was cracked it was not shorting through, it was replaced anyway and had new goop put on it.

Elsewhere on the circuit board there is a little four pin chip "MDA 922-7" with a 1973 date code on it that I had initially suspected might be the problem as the side of it looked a little burnt, I stuck my finger nail into the edge and just pulled a little bit and the entire top of it came off, but so far I'm not able to find it via Google search but I'm pretty positive that its a bridge rectifier probably 1 or 2 amps.

Later on...

I found some other models of the MDA 922-X series and based on what I found this is probably a 1000v 1.8 amp rectifier although this unit would probably run fine with just a 200 volt rectifier, which I ended up finding on an electronic surplus site...

https://www.electronicsurplus.com/motorola-inc-mda922-4-diode-fwb-1-8amp-200v

But a standard off the shelf 200 volt 2 amp little round bridge rectifier would probably work just as well.

More later after I get past this point.
 

gophert

Well-Known Member
Most Helpful Member
#4
Well... what I have figured out so far is that the 2N6308 transistor is fine although the mica isolator under it was cracked in half sideways across the two pin holes, even though it was cracked it was not shorting through, it was replaced anyway and had new goop put on it.

Elsewhere on the circuit board there is a little four pin chip "MDA 922-7" with a 1973 date code on it that I had initially suspected might be the problem as the side of it looked a little burnt, I stuck my finger nail into the edge and just pulled a little bit and the entire top of it came off, but so far I'm not able to find it via Google search but I'm pretty positive that its a bridge rectifier probably 1 or 2 amps.

Later on...

I found some other models of the MDA 922-X series and based on what I found this is probably a 1000v 1.8 amp rectifier although this unit would probably run fine with just a 200 volt rectifier, which I ended up finding on an electronic surplus site...

https://www.electronicsurplus.com/motorola-inc-mda922-4-diode-fwb-1-8amp-200v

But a standard off the shelf 200 volt 2 amp little round bridge rectifier would probably work just as well.

More later after I get past this point.

Let me know if you have some odd desire for an original substitute, but I recommend going with something newer than 1980 date code.

42330360-8A22-4FEC-9986-4F22C3338A0C.jpeg
 
Thread starter #6
Thank you for the offers but a local surplus store had some NTE-167's in stock for $2 which will work as a replacement, and will probably run cooler also as they will have air all the way around them.

I tried testing the capacitors "in circuit" with my capacitor tester but I'm getting really really wrong readings and I'm making something (probably the ultrasonic transformer) oscillate and can hear a high pitched noise coming from something, so I'll have to pull those to test them.

More later...
 

gophert

Well-Known Member
Most Helpful Member
#7
It is common for transformers to make noise. Even your iPhone charger likely makes noise. The more amperage drawn by the circuit, the more noise the transformer makes. See magnetostriction.

As for capacitors, you need to disconnect one leg of the cap before measuring with your meter. Otherwise, the cap is trying to discharge it as your meter is trying to feed it a constant current to charge it.
 
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