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Registered Member #119
Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114
I have a VWR 150HT (Heated Crest 575 (575HTA)) ultrasonic cleaner that I've had for about 4 years. I usually don't use the heater function but did so recently and, despite that tank was full (ie safe operating conditions), it somehow induced an electrical failure. I opened it up and a resistor and capacitor had exploded. I would like to try to repair it instead of buying a new unit. I have some best guesses for repair values but wanted to run it by people and see if there was any feedback.
I contacted Crest about getting a replacement PCB and there is one available but it would be somewhat pricey. Its less than a new cleaner but I'd like to attempt the repair first.
I asked Crest for a schematic today but haven't heard back yet. I couldn't find any schematics online and made a partial schematic to help diagnose: http://siliconpr0n.org/uv/crest/575hta/crest_usound.ps The burned out capacitor and resistor are noted. Anyone have one of these by chance that could tell me the correct component values?
The resistor fragments total about 430 ohm so I'm thinking its possibly a 470 ohm resistor. The outside shield has carbonized which also throws off the readings some. There is a similar Dale CW-2B 3W resistor and this is a littler smaller than it meaning this is probably 2.5W. I've ordered a 470 ohm 3W resistor to replace it.
Similar capacitors on the board are "CDM 470 +/- 5%" and "CDM 200 +/- 5%". These appear to be CDE Cornell Dubilier CD15 or similar (500V mica). I also can see mica in the blown capacitor so this also matches up. I'm thinking of trying to replace it with a 1000V 200 pF.
I can imagine that if the mica capacitor failed it might blow out the resistor if capacitor coupling was supposed to act as a dc block and limit most of the power. Perhaps it overvoltaged? I'm thinking of replacing the capacitor with a 1000V version in hopes it would prevent another failure.
Also worth nothing the board doesn't draw excess power in its current state. The PCB got heated up a little but I don't see anything that should be problematic.
Do my component choices sound reasonable? Anything I should probe/check first? Does my root failure sound reasonable? (don't want the resistor/capacitor to just burn out again)
Registered Member #119
Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114
Someone also suggested I should check the transistors as if a snubber failed they might be damaged.
Conundrum: I'll check but I don't see any evidence of damage nor do I have reason to believe shorted element would cause this failure based on schematic. Re: repairfaq, I don't understand specifically what you were suggesting.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
According to Sam G, the element can fail due to old age as well as running with sharp objects in the tank (point heating!) the simple check is to look for any areas which are blackened or signs of distress, sometimes it is possible to "mask out" the bad area and lose a bit of ultrasonic power but the unit will still sometimes work.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Conundrum wrote ...
According to Sam G, the element can fail due to old age as well as running with sharp objects in the tank (point heating!) the simple check is to look for any areas which are blackened or signs of distress, sometimes it is possible to "mask out" the bad area and lose a bit of ultrasonic power but the unit will still sometimes work.
I believe it is the heater element, not the ultrasonic, which has failed.
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Crest ultrasonic repair
