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#3
April 29th 06, 07:45 AM
posted to rec.radio.amateur.homebrew
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Thermistors! Ah!!
Michael A. Terrell wrote: wrote: Do thermistors go bad or what? I'd like this thing to come on at a lower temp anyway. Does anybody know of a replacement which would do that? I have zero data on the factory thermistor...I don't have a temp probe to check it myself either. -Scott. Yes they go bad. Ask any old TV repairman how many hundred thermistors they replaced in the degaussing circuits. Michael A. Terrell Central Florida Mm, yes - TV set PTC's do go crook, but thats because they get full mains voltage at many amps across them. And it takes a few years to do it. And its usually the heat generated dry joints on the main board anyway that winds the set up in the shop. Easy method - repalce the thermistor, in the meantime stick a fan at the back of the radio so it doesnt melt down. Or wire the fan hard on always....(Hint - put your hand on the heatsink/case, if its too hot to touch, its too hot.) If you want to get technical, then its time for logical fault finding. There are 3 things that can go wrong. _ the fan, the thermistor, the switching cct. You have replaced the fan. The thermistor DOES switch when it gets heaps of heat. Leads me to think the switching cct is faulty. BUT to prove - disconnect the thermistor from cct, stick your ohmeter across it, apply heat. Should be fairly rapid change in dc resistance - and use a hairdryer, not your soldering iron. If the change is only a few ohms, then its faulty - replace. Otherwise, on to next step - check out switching circuit of controller. This is a "bread and butter" fault, shouldnt be too hard to fix..... Andrew VK3BFA. |
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