Just to throw a monkey wrench into the issue. Not a good practice to place NTC's in parallel, they current hog. Just pointing out a bad design from the manufacturer.
Yes, very bad. As soon as one starts to get warm, its resistance falls, causing it to carry more of the current, and so on. I put a soft start in my system about 6 months ago and the datasheet warned against it. I seem to remember them warning against handling them with fingers too. The oil penetrates the casing if I remember right and can cause premature failure. They do work. My lights don't flicker anymore when the amp kicks on.
Those inrush limiters are likely NOT the issue of fuses blowing.
You've got something else downstream going on.
Get the service manual and do some proper troubleshooting, before the thread winds up going into next year.
You've got something else downstream going on.
Get the service manual and do some proper troubleshooting, before the thread winds up going into next year.
Thanks.
Looking at that schematic, Parasound must have changed things a bit on mine: That schema shows the 15amp fuse after the ICL. On my unit, the fuse is where the switch is located and vice versa.
Service manuals ALL are known for having changes or addendums during manufacture.
In a series circuit, no side-paths, order does not matter.
I think I made some headway on this - not sure what it means but here goes:
I did as you suggested and I wired a 300 watt incandescent bulb in place of the thermistor board. Upon power up, the bulb lighted up but quickly faded. I left the power applied and no fuse was blown and I verified that power is passing through the light bulb and reaching the power switch and terminal block beyond.
I turned it off and on several times. No blown fuses but the light bulb never lighted up again on any successive power up and current was still passing through the bulb and reaching the power switch and terminal block after the light bulb. I verified I am getting 110-120v after the light bulb despite the bulb no longer lighting up.
I heard no odd sounds or noises or smoking components like I got from the thermistor board.
I attached a simple flow diagram below.
What should I try next? Does this indicate the problem was with the thermistor board somehow?
Edit: I should also add that I am using a brand new power switch.
Thanks.
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The bulb means the fuse should never be able to blow, instead you would see the bulb light if an overload occurred. So at this point what you are seeing is normal, the brief flash is normal at power on as the transformer draws a high initial current.
If you are happy all seems well at this point then I think you have to try new thermistors and then retest without the bulb. Ideally the thermistors should probably all be replaced with identical types because any slight differences in one could mean either that one or the others depending which way the difference was in terms of resistance vs temperature could hog the current. I think they were in parallel pairs as I remember.
If you are happy all seems well at this point then I think you have to try new thermistors and then retest without the bulb. Ideally the thermistors should probably all be replaced with identical types because any slight differences in one could mean either that one or the others depending which way the difference was in terms of resistance vs temperature could hog the current. I think they were in parallel pairs as I remember.
Also make sure the mains fuse is a time delay type.
Ceramic fuses are available in both fast acting and time delay, and the same goes for glass fuses.
The type is usually specified by the the manufacturers series numbers stamped on the metal contacts, which you may have to look up to determine if it's fast or time delay.
Ceramic fuses are available in both fast acting and time delay, and the same goes for glass fuses.
The type is usually specified by the the manufacturers series numbers stamped on the metal contacts, which you may have to look up to determine if it's fast or time delay.
I finally got the amp to where it no longer blows a fuse upon powering up. The problem was with the feedback resistors on the input board. Swapped resistors and now it works as before.
However, I think I may have a new issue: I am getting a fairly significant hum from the toroidal transformer that I do not think was present before and I am wondering if my replacement of the thermistors may be causing it. I used the exact same voltage, amps and resistance - the only difference is the physical size (the new ones are smaller diameter 15mm VS 20mm). Note that the hum is not in the speakers but is hum from inside the unit.
Wondering if some type of special thermistor needs to be used here to eliminate hum.
Thanks.
However, I think I may have a new issue: I am getting a fairly significant hum from the toroidal transformer that I do not think was present before and I am wondering if my replacement of the thermistors may be causing it. I used the exact same voltage, amps and resistance - the only difference is the physical size (the new ones are smaller diameter 15mm VS 20mm). Note that the hum is not in the speakers but is hum from inside the unit.
Wondering if some type of special thermistor needs to be used here to eliminate hum.
Thanks.
Transformers can have more physical hum when they are heavily loaded. Have you taken any line current measurements to see what the amp draws at idle compared to what it should, based on the specs?
Nothing like that...
Toroidals are notorious for doing this:
or are you just super alert now to everything going on? The noise often varies with time of day and how pure (how close to a perfect sine) the mains is.
This is for info, I don't think it will apply 🙂
If a transformer is run right up to and beyond its voltage limit- meaning that for example a 120 vac primary is fed with a slightly higher voltage such as 125 or 130 volt- then that can push the core into magnetic saturation and cause it to buzz. That is a bit unlikely on a high quality part.
If the original thermistor dropped a little voltage across it in normal operation then that might reduce the buzz as the transformer is happier with a slightly lower voltage applied to it. If the new thermistor has a lower resistance than the original when running at normal temperature then it would put a higher voltage across the primary and that might increase the buzz on a mediocre transformer run at its limits.
When I checked the original thermistors, they were around 7 ohms but the spec on them was 5. The new ones that I put in are 5 ohms.
I am going to try it on my power conditioner that is on a dedicated 20 amp circuit to see if it still hums - just gotta move the 60 pound beast to get it to that room.
I also have another of these amps and I am pretty sure it doesn't hum - will isolate and listen to it up close when I get a chance.
I often wondered why Parasound enclosed their toroid transformers in their later model amps and this must be the reason.
The 2200II doesn't have any sort of a cover for its 2 stacked toroids. Most likely a cover would eliminate the hum that I am hearing.