{"id":1424,"date":"2019-11-14T17:01:35","date_gmt":"2019-11-15T01:01:35","guid":{"rendered":"http:\/\/media.davebaar.com\/wordpress\/?p=1424"},"modified":"2019-11-14T17:01:35","modified_gmt":"2019-11-15T01:01:35","slug":"ultrasonic-humidifier-repair-the-unoscillating-nebulizer","status":"publish","type":"post","link":"https:\/\/davebaar.com\/wordpress\/2019\/11\/14\/ultrasonic-humidifier-repair-the-unoscillating-nebulizer\/","title":{"rendered":"Ultrasonic Humidifier Repair – The Unoscillating Nebulizer"},"content":{"rendered":"

One of the items that was brought in by a friend to a recent Repair Caf\u00e9 event in Campbell River was a non-functioning portable humidifier, a Honeywell model HUD-200. I didn’t have time to get to it during the Caf\u00e9 afternoon, but was able to fix it afterward. These devices are based on an ultrasonic “nebulizer”, basically a piezoelectric element in a high frequency oscillator circuit generating ultrasound waves in water, and thereby causing droplets to form and flow out in an airstream from a fan. The symptom was that water was flowing through the device, but no moisture was being created. <\/p>\n

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the nebulous humidifier<\/p><\/div><\/p>\n

Disassembly took a bit of work: about 8 Philips screws under the unit and two on the side on a moisture level potentiometer held the exterior case together. The problematic nebulizer was a bit harder to get at; it was housed inside a snap-together metal shield underneath the ultrasonic transducer at the top and side of the unit. <\/p>\n

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humidifier internals<\/p><\/div>
\nRemoval of the shield and 3 screws holding the board plus transducer to the plastic case made the nebulizer circuit board accessible. \"\"<\/a>\"\"<\/a>
\nI drew a quick circuit diagram. \"\"<\/a> The circuit uses a probe of the resistance through the supply water in the pool for the transducer to turn on the power oscillator when sufficient water is present, a form of safety interlock, so I “fooled” it for a quick dry test by simulating the water with an 18K ohm resistor across the probe. I used an oscilloscope to examine the output voltage at the transducer; the patient turned out to be flatlined; no output ultrasound. However, close inspection of the circuit board revealed a suspicious looking solder joint at capacitor C5 that is in series with the transducer. I resoldered that, tested again, and behold, a strong 1-2MHz signal at the transducer.

\"the<\/a>

Nebulize on!<\/p><\/div> Reassembly and testing with water confirmed that the device is fixed. Nebulize on!<\/p>\n","protected":false},"excerpt":{"rendered":"

One of the items that was brought in by a friend to a recent Repair Caf\u00e9 event in Campbell River was a non-functioning portable humidifier, a Honeywell model HUD-200. I didn’t have time to get to it during the Caf\u00e9 afternoon, but was able to fix it afterward. These devices are based on an ultrasonic […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1424","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/posts\/1424","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/comments?post=1424"}],"version-history":[{"count":0,"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/posts\/1424\/revisions"}],"wp:attachment":[{"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/media?parent=1424"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/categories?post=1424"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/davebaar.com\/wordpress\/wp-json\/wp\/v2\/tags?post=1424"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}