I've never seen an AC powered fan with internal temperature control in all my years in service and seeing literally hundreds of different fans. But this by no account means they don't exist.
Meat Plow schrieb:
^^^
Of course the the ac voltage is rectified by D15 and, additionally, filtered by an electrolytic capacitor ...
Sorry for my obviously misleading formulation.
Ciao
Reinhard
N_Cook schrieb:
...
IMHO the LT3011 LED/LDR is part of a separate control loop which limits/reduces the PA's input voltage as a function of the output signal.
The FETs IMHO are part of a second control loop which limits/reduces the PA's input voltage as a function of the temperature at PTC R84 (page 1). Maybe that's your "blob" ...
HTH
Reinhard
monitoring
Agreed that is the intended function of the blob but it should be nearer a heatsink , rather than the fan. The whole air handling system is in a duct so it could be anywhere for monitoring internal air temperature , but directly over the fan is not where it should be. If the fan stops then cool air would be convected in there, falsely telling the control that the amp is now cooler, and would accelerate the already hot amp to quick destruction.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Experience shows that those amps rarely if ever fail through overheating, so either, the device does it`s job, isn't really necessary, or isn't carrying out the function you suspect.
In all the cases of destroyed output devices I`ve come across, the fault has been almost certainly shorted speaker cables - I dont recall a sub amp failing. I have replaced sub speakers on a couple of occasions which would suggest that the amps are tougher than the speakers when overdriven. IIRC the sub amp is a pair of identical amps running in bridged mode, yes?
The other 'common' faults (IME) are failed mains transformers, smoothing capacitors breaking loose and broken volume controls
There`s a mod btw for the output transistors, which involves a different output pair and the addition of a couple of 1N7004 - I have the details somewhere if you need them.
Ron
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