Sub amp blowing fuses?

[Ericfg]

Driving home from droppin' the youngin' off for a game my sub stops.
I get home and find the 30 amp fuse, that is about a foot, literally,
from the battery has popped. I put in another and it immediately
blows.

The 60 amp fuse in the dedicted subwoofer amplifier itself is OK. PPI
A-600 BTW. This setup has worked 100% for at least 5 years. No
electronic incidents to report of late aside from the constant alt
whine.

I would like some advice on what to do next please.

Thanks in advance, Eric G.

[Christopher \Torroid\ Ott]

"Ericfg" > wrote in message
oups.com...
> Driving home from droppin' the youngin' off for a game my sub stops.
> I get home and find the 30 amp fuse, that is about a foot, literally,
> from the battery has popped. I put in another and it immediately
> blows.
>
> The 60 amp fuse in the dedicted subwoofer amplifier itself is OK. PPI
> A-600 BTW. This setup has worked 100% for at least 5 years. No
> electronic incidents to report of late aside from the constant alt
> whine.
>
> I would like some advice on what to do next please.
>
> Thanks in advance, Eric G.


You need to isolate the short circuit to either the amp or wiring.

Disconnect the power lead at the amplifier and safely secure it so it cannot
short against anything else.

Insert another fuse (the smallest you have available) and verify it does not
blow. If it does, you need to look for a short on the power lead. If it does
not, the short is in the amplifier.

Where to go from there depends on the results, and your comfort level with
electronics.

Chris

[Ericfg]

Thanks Chris for the good advice. I will check this out later this
morning and report back. :)

[Ericfg]

Following the advice above I inserted new fuse with amp unplugged. No
blow.
Plugged amp in and restarted: POP, the fuse blew. And what's weird is
as I restarted the car the second time (with the amp plugged in) I was
watching the amp for signs of....well, anythin, and I swear I saw the
power lead move. WTF?!?!?

[arthur[_5_]]

an attempt at infinite power consumption is more like it.

arthur



On Wed, 19 Sep 2007 11:46:17 -0700, I. Care >
wrote:

>I don't know about your case; but, I have seen power cords move when
>huge amounts of current were going through them. That could be the case
>if your amp is presenting a direct short, huge momentary current draw.

[Christopher \Torroid\ Ott]

"Ericfg" > wrote in message
ups.com...
> Following the advice above I inserted new fuse with amp unplugged. No
> blow.
> Plugged amp in and restarted: POP, the fuse blew. And what's weird is
> as I restarted the car the second time (with the amp plugged in) I was
> watching the amp for signs of....well, anythin, and I swear I saw the
> power lead move. WTF?!?!?


Not much to do at this point. Amp is popping fuses, it needs sent off for
repair.

You can isolate it to the power supply vs. the output stage by unplugging
the speaker leads (so the amp is completely unloaded), placing another fuse
and powering up. If the fuse still pops, it's time to focus on the power
supply - if not, the output stage is the best place to start.

Pretty irrelevant from your standpoint though...

Chris

[arthur[_5_]]

I am not familar with this amp but I assume power FET's or similar.
Fundamentally they are transistors which can be viewed as 2 diodes
back to back. Guess what will happen when a shorted diode is in a
circuit? The other failure method would be an open diode which would
look like a dead circuit.

So, one or more shorted output FET's will blow that fuse instantly ...
load not needed. Unplugging the output speakers will eliminate a
shorted speaker and is, IMO, a last resort test.

arthur



On Wed, 19 Sep 2007 12:31:17 -0700, "Christopher \"Torroid\" Ott"
<spamtrap at ottelectronics dot com> wrote:
>
>Not much to do at this point. Amp is popping fuses, it needs sent off for
>repair.
>
>You can isolate it to the power supply vs. the output stage by unplugging
>the speaker leads (so the amp is completely unloaded), placing another fuse
>and powering up. If the fuse still pops, it's time to focus on the power
>supply - if not, the output stage is the best place to start.
>
>Pretty irrelevant from your standpoint though...
>Chris
>

[Christopher \Torroid\ Ott]

This is completely academic as he's probably not going to be repairing it
himself (anyone qualified to repair their own amp wouldn't need to ask how
to troubleshoot a blown fuse), and I would tend to agree that the output
stage would be an unlikely source of his specific problem.

However, the condition you describe is not really accurate. Both supply rail
transistors would need to be shorted for the output stage to pop the fuse
without the load connected. A single output transistor can short to its
power rail and potentially blow the fuse with the speaker connected (there
would be a terrible thump on powerup), but it will not do so with it
unconnected.

His specific issue is likely:

a.) A shorted safety diode on the load side of the amp fuse. This is used to
pop the fuse if the power leads are wired backwards, and is standard on most
car audio amplifiers.

b.) A shorted power supply FET which powers the transformer/inductor on the
switchers.

c.) A shorted transformer or inductor (depending on the design) in the
switchers.

Popping a 30amp fuse so hard the power cable jumps will require a pretty
substantial short. Time to send it off for repair.

Chris


"arthur" > wrote in message
...
>I am not familar with this amp but I assume power FET's or similar.
> Fundamentally they are transistors which can be viewed as 2 diodes
> back to back. Guess what will happen when a shorted diode is in a
> circuit? The other failure method would be an open diode which would
> look like a dead circuit.
>
> So, one or more shorted output FET's will blow that fuse instantly ...
> load not needed. Unplugging the output speakers will eliminate a
> shorted speaker and is, IMO, a last resort test.
>
> arthur
>
>
>
> On Wed, 19 Sep 2007 12:31:17 -0700, "Christopher \"Torroid\" Ott"
> <spamtrap at ottelectronics dot com> wrote:
>>
>>Not much to do at this point. Amp is popping fuses, it needs sent off for
>>repair.
>>
>>You can isolate it to the power supply vs. the output stage by unplugging
>>the speaker leads (so the amp is completely unloaded), placing another
>>fuse
>>and powering up. If the fuse still pops, it's time to focus on the power
>>supply - if not, the output stage is the best place to start.
>>
>>Pretty irrelevant from your standpoint though...
>>Chris
>>

[Ericfg]

Thank you, gentlemen, for all your advice and insight. I guess it's
time for my amp to go to the Doctor's office. I've had this amp for
about 10 years, and got it used at that. It stopped only once before
and when I sent it back I was told the output transistors were blown
(not that that matters here, now).
The real ****er though is the fact I've been out of work for almost 5
months now and I just don't have dime one for anything other than
food, booze and mortgage payments. :(
At least the other 6 speakers work. :)
Thanks again,
Eric G.