On Feb 4, 7:36 pm, "DaveM" wrote:
"Haaky" wrote in message
ups.com...
On Feb 4, 2:06 pm, Bob wrote:
Haaky wrote:
I need some advice guys.
I have an American Audio GX-300 Power Amp i use in my studio. Bought
it used off of EBay. Been working like a charm for almost a year. One
day while tunning up a guitar the amp shut off. Found it blew a fuse.
I replaced the fuse switched it back on and it blew again.
Finially had to take it in . I was told that an Output had gone. Cost
me 140 bucks Canadian to replare it.
I get it back a week later. Take it home, plug it in. And bang the
fuse blows again right away. I return the amp to the repair shop. 2
weeks later i get it back. They told me the Output the guy replaced
was fautly and get this he wanted more money to fix what was suppose
to be fixed properly in the first place.
Any i get the amp back, worked fine for a week. Then 1 day i turn it
on and it pops the fuse again. I replaced the fuse and it worked fine.
A week later turn it on again and it popped the fuse again.
I'm not taking it back the the these guys again. I'de rather try and
diagnose the problem myself and fix it.
Any ideas to where and what i should be looking for and were to start
looking for the problem?
I've been doing alot of research and am comfortable with electronics
to try and narrow down the fault and fix it.
Any help would be greatly appreciated. If you need any more ifo i can
provide it. I also have the schematics for the amp aswell. That was a
bonus courtasy of American Audio Inc.
Let me suggest that perhaps the idling current is set too high. Then
the output transistors start to warm up and after a while there is
thermal runaway and the fuse pops.
Check the idling current and adjust it if needed. Another possibility
is that the temperature sensor, usually a transistor or diode or
thermistor, is not properly attached to the heat sink and thus doesn't
react to warming output transistors.
Bob
Would that be the cause of the fuse blowing at Power On though? That
seems to be the problem as of now. As soon as the unit recievies that
first initial
surge of power the fuse pops.
I'm keeping track of all the suggestions if i would have had this info
at the start i would have by-passed the repair shop and did this on my
own.
I'm a newbie at this but i want to learn as much as i can. I find it
really facinating. And if i can learn to fix stuff like this on my own
even better
In one of the earlier posts, you stated "On the back of the unit it says the
fuse type is 250v T 7A. The fuse that was in it was a 250v don't know if it was
a "T" or not 6.3A."
If the original fuse was rated for 7A, and it's being replaced by a 6.3A fuse,
that could be your problem. I suggest that you try the correct fuse before
replacing any more components. If no more fuse blowing, then you might be good
to go. If the correct fuse blows, I would suggest that you replace all of the
output transistors at the same time. They are all available from MCM
Electronics.
http://www.mcminone.com/product.asp?...roducts&produc...
andhttp://www.mcminone.com/product.asp?catalog%5Fname=MCMProducts&produc...
If you can scan the schematic and post it on abse, we can probably come up with
some pretty good suggestions for you to go with. Does the schematic that you
have give the instructions for setting bias for the output stages?
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)
Some days you're the dog, some days the hydrant.
I was affraid to put in a 7A fuse even though that what is on the back
of the unit. Ever since i've owned the amp it has had a 6.3 fuse it.
I might try a 7 if it keeps popping. Thanks for the link to the
websites. I might order me some just to have as spares
I'll post the schematics of the amp