hi folks, really appreciate finding this forum and look forward to learning more from you all!
i have an oldish (probably 2011) dehydrator that is digitally controlled, so without the control panel nothing works. worked fine for years, then suddenly turning it on does nothing: no lights on the control panel. not even a hum, which i associate with power transformers, so i assumed it was a switch issue -- and indeed there may have been. but having worked with the switch, it is now correctly providing 120V to the power transformer. in turn, the transformer is providing about 11.5 VAC off the secondary wiring... which is higher than the nominal 9V printed on the power PCB (kind of blocked in images below).
however, only ~0.5VDC is getting to the control panel (and this seems to fluctuate from 0.3 to 0.6V). i have a question in to the service department for Tribest whether that is nominal, but i'm fairly sure it should be a normal 5V based on the fact it uses two HC574 ICs (datasheet here i think: https://www.alldatasheet.com/view.jsp?Searchword=HC574&sField=3).
this would explain why the control panel shows nothing. there are no fuses or thermal cutoffs that i have found yet, which seems strange... unless the reed switch is supposed to function as one. (why is there a reed switch on the control panel? anyway, shorting the reed switch does not result in powering the control panel.)
so my presumption is that something in bridge rectifier or caps from the 9VAC is fried?
there are a sequence of 9 diodes coming out from the 9VAC (i would expect 4 or 5) -- almost as if they ran them in parallel, which seems like a no-no? or perhaps it's two separate rectifiers at different voltages?
there's nothing obviously wrong with the components. but the coloring of the PCB on the back of this area is faintly yellow/brown, which adds to my suspicion.
but i'm not really sure how to test for what's blown? not even entirely sure where to probe to test for voltages. any help at this point very helpful.
can't find schematics online, and the service department "doesn't have them available" -- not sure how helpful that department will be, they told me they'd have to call me back (who knows?) to tell me whether 0.5V is too low for the control panel.
thanks!
(i obviously wish this wasn't a digital control panel, but just had basic components you could easily test and fix, such as thermostats and thermal fuses, etc. if this troubleshooting doesn't work, i may want to figure out a way to sidestep the control panel and put in analog controls of such a sort into the machine... anyone have experience with something like this? it seems the heaters take line voltage, but i think the fans take something else, but i can't trace the PCB clearly... suggestions how to figure that out?)
i have an oldish (probably 2011) dehydrator that is digitally controlled, so without the control panel nothing works. worked fine for years, then suddenly turning it on does nothing: no lights on the control panel. not even a hum, which i associate with power transformers, so i assumed it was a switch issue -- and indeed there may have been. but having worked with the switch, it is now correctly providing 120V to the power transformer. in turn, the transformer is providing about 11.5 VAC off the secondary wiring... which is higher than the nominal 9V printed on the power PCB (kind of blocked in images below).
however, only ~0.5VDC is getting to the control panel (and this seems to fluctuate from 0.3 to 0.6V). i have a question in to the service department for Tribest whether that is nominal, but i'm fairly sure it should be a normal 5V based on the fact it uses two HC574 ICs (datasheet here i think: https://www.alldatasheet.com/view.jsp?Searchword=HC574&sField=3).
this would explain why the control panel shows nothing. there are no fuses or thermal cutoffs that i have found yet, which seems strange... unless the reed switch is supposed to function as one. (why is there a reed switch on the control panel? anyway, shorting the reed switch does not result in powering the control panel.)
so my presumption is that something in bridge rectifier or caps from the 9VAC is fried?
there are a sequence of 9 diodes coming out from the 9VAC (i would expect 4 or 5) -- almost as if they ran them in parallel, which seems like a no-no? or perhaps it's two separate rectifiers at different voltages?
there's nothing obviously wrong with the components. but the coloring of the PCB on the back of this area is faintly yellow/brown, which adds to my suspicion.
but i'm not really sure how to test for what's blown? not even entirely sure where to probe to test for voltages. any help at this point very helpful.
can't find schematics online, and the service department "doesn't have them available" -- not sure how helpful that department will be, they told me they'd have to call me back (who knows?) to tell me whether 0.5V is too low for the control panel.
thanks!
(i obviously wish this wasn't a digital control panel, but just had basic components you could easily test and fix, such as thermostats and thermal fuses, etc. if this troubleshooting doesn't work, i may want to figure out a way to sidestep the control panel and put in analog controls of such a sort into the machine... anyone have experience with something like this? it seems the heaters take line voltage, but i think the fans take something else, but i can't trace the PCB clearly... suggestions how to figure that out?)