hifonics amplifier melting RCA cords

[anwaypasible]

i had this amp hooked up in the car and the amp would play audio at a low level but when i turned the gain up the subwoofer would start flapping in and out.

i forgot that the amplifier was doing that and i remember i had some audio but ground noise in the car.. so i grabbed a spare power supply from an old dell XPS desktop and decided to hook up the amplifier in the house with my home theater receiver for some boost below 40hz

well i got the power supply turned on and had six positive and six negative cables screwed into the power terminals and the amp powered up fine.
excellent, i started to get excited.
i hooked up the rca wires to the receiver and played a low sine wave from trueRTA.

while i was hooking everything up i turned the gain down all the way on the amp.
so i began slowly turning the gain up and the subwoofer let out a noise and the pc powersupply shut off.
thinking little of it i unplugged the rca cords from the amp to protect my receiver and reset the powersupply.
the amp came back on fine.
i hooked the rca wires back up and left the gain all the way down.
i dont remember what i did exactly thereafter.. i know i tried to turn up the receiver to compensate for the amplifier gain being low.
i know i tried to turn up the gain within the trueRTA program to compensate for the amplifier's low gain.
while i was messing around i thought i smelled something but it wasnt a typical electrical smell and it was faint.
i paused for a second and waited for things to get worse, nothing happened.
so i proceeded on the computer trying to get some audio from the amp.
nothing worked and i started to scratch my head as i was taking the setup down.

well once i got to unplugging the rca cords, i realized that they MELTED and there was nothing left but copper for more than one foot in length.
the subwoofer pre-out on the receiver still works because i hooked up a computer 2.1 system up to the subwoofer output and i have normal functionality.
the little subwoofer is tuned at about 34/36hz and bottoms out sometimes with the wide range of music i listen to.
so i want to use my 12 inch woofer in its sealed box to play from 10hz through 40hz

can somebody walk me through the process of diagnosing my amp to determine what is wrong?

someone on this forum already mentioned "perhaps a ground trace has melted,or the ground(s) on the RCA jacks are open."

i've looked at the inside of the amp before and nothing was burnt badly enough to catch my eye. (didnt look for golden / browned resisters though)

i dont have any money to have an electronics engineer work on this amp.
and rather than waiting the many months until i will have an extra lump of money, i thought i would see if anybody was willing to work with me.

[mike49504]

What's the model of the amp Hifonics what? Also do you have a digital camera?

[1moreamp]

Well the fact your RCAs melted I would say the RCA ground is intact and doing its job very well. As it sounds like you sunk a power rail inside the amp to the RCA/internal ground.
This might be plausible since the RCA ground is also the center tap of the secondary supply, and if you managed to let the smoke out of a channel its possible that it shorted to the internal ground, which also headed out to the nearest high current ground like your signal source.
Most car amps have a current limiting resistor inside that connects the RCA ground to the 12 volt supply ground. Now if this was opened up by burn out then yes you could melt your RCAs by sending DC voltage back out the amp along the RCA ground shield. Seen this a few dozen times in my life.

As to what caused it and how badly damaged it is well that will take some teching to figure out. By chance do you have any electronic skills what so ever?
Like maybe how to use a volt/ohm meter. If so I would power the amp back up on a current limited supply with absolutely nothing hooked up but power and turn on. And I would use a 10 amp fuse inline if you lack a controllable power supply such as you PC power supply is.
Then I would measure the RCA DC voltage with respect to the DC supply ground, measuring both the shield and the tip one at a time. If you have more the 500MVDC or 0.500 volts DC you might have the above issue of a shorted channel or internal power supply issues.

By the way could you shed some more light on which model Hifonics amp were talking about ? They had many different types and styles built for them through out the years and not knowing which one could be misleading to you real issues at hand...thx...

[Perry Babin]

The transformer is probably shorted. This is why Pioneer head units use fuses in the shield grounds on their head units. It prevents electrical fires.

With no RCAs plugged into the amp, measure the resistance from the RCA shield on the amplifier to the B+ terminals on the amp. What's the resistance?

[anwaypasible]

i have a digital camera (2 megapixel webcam)
then i have an analog multimeter.. a soldering gun.. some core resin solder from radio shack.. and a desolder wick.

i grew up in an arcade room and there was electronic engineers that would work on the video games.
i seen about a dozen arcade games disassembled and the pcb boards always excited me like legos.
then i seen the monitors being switched out, and i thought that was very crafty for someone to do that in a 'shop' themselves as a quality to mankind.
i watched them solder some things maybe 4-5 times and basically grabbed the knowledge that the solder gun is how the legos get glued into place.

i am quite a kindergardener when it comes to components.. but my imagination and creativity brings me to conclusive questions that only aspiring college graduates can answer (this really annoys some people).

i remember one time i read an article that explained what the different color codes on a resistor mean.
i have read various articles from this website: Basic Car Audio Electronics

i grow questions so technical that the chemistry behind what makes up such components often come to light.
for example.. the goop that makes resistors, what it is made of and thus the characteristics of those properties result to a functional component to be soldered onto a pcb board or integrated into a circuit.

i'm really clueless yet interested about how circuits work.. i cant write sentences with electrical components (or paragraphs for that matter)
but i have always been a science geek.. and i have participated in a lot of controlled electronic experiments in school.

i started to grow far from electricity when i came across the question of how the inside of an alkaline battery worked.. i didnt get an explanation that served me well, so i gave up and hoped that in the future more people would be knowledgable about the 'zoomed in' basics (fundamentals)

i had a 200 in 1 circuit board science project thingy that you used to be able to buy at radio shack.. i remember building a siren that would rise and fall with a switch.
i also remember putting the wires from one component to the next, i had no idea why i was connecting the components.. so it seems the 'sentence' i was writing with the wires was utterly encoded.

i am the type that would like to start from a power source and then 'drive' or 'steer' the electricity until it reaches its final intent.
even if the electricity has to be viewed as water, with sandbags and uphill risers and downhill channels.
nobody ever explained to me, and i never read anything put into proper perspective.
except for this one time when i read about step-up transformers that can take power and step it up or down to a new voltage (way cool).

i would like to know enough about electronics to be able to modify consumer 'junk' and turn it into something of quality worth using and comparing to other higher priced items.

i'm an audio fanatic so i figure the amount of times that i could modify amplifiers to produce more power or significantly cleaner sound would come somewhat often (and i could do these mods for people i come across)
sometimes i hate throwing out a piece of electronics just because a lego on the pcb board died (and i know that the thing could be diagnosed and repaired if i had the knowledge)
BUT these situations dont come often enough that i would like to make a daily career out of the knowledge.. just a hobby for mods and repairs.

i'm looking to go into school for game and simulation programming and then taking that 3d world of mine and doing many things with it.
interior/exterior design
building houses
audio optimization for listening rooms
maybe store layout optimizations
possibly some plastic designs for consumer products
computer artwork

to name a few..
i came up with a list of about 46 different things i could do with my own 3d world built from scratch.
i would then like to be able to modify some electronic toys, just to save some money and compete with higher priced offerings on the market.
i really think the electronics thing is just to keep my toys in good working order so i have them when i need to relax.

the idea of an amplifier based around some capacitors, and then being able to change those capacitors to higher quality capacitors with a remarkable change in sound quality (or power output) is appealing to me.
its like knowing how to cook meat and living alone.. as long as i know how to cook the meat, i dont have to burn it to make sure its done (and thus ruining the flavor)

while i dont know much about how circuits work, because reading a schematic doesnt appear itself to me as a 'sentence' or 'paragraph' with a detailed start to finish.. i cannot possibly understand that a section of the circuit is ruined by checking the resistance at some given point. (i wouldnt know what resistance value is acceptable and what value is obsurd)
but i can play along and put my red multimeter wire on this and my black multimeter wire on that to discover some results to report.
although, my analog multimeter doesnt show small amounts very well.
finding something like 0.05 volts would be hard to tell if i had to compare it to 0.40 volts.
if the needle flinches.. 0.05 volts would be a good assumption.
if the needle moves a great deal, something OTHER than 0.05 volts is taking place.


anyways.. yeah i would really like to get this amp functional.
i bought it used off ebay and this was like 3-4 years ago.
i have yet to use the amp other than discovering what i thought was a severe ground issue with the car. (which now turns out to be the actual amplifier at fault)

the amplifier is a HIFONICS XX CHAOS
and its rated at 800watts rms @ 4ohm bridged
900watts rms @ 3ohm bridged
1000watts rms @ 2ohm bridged

my 12w7 is 3ohm and the sub is inside an enclosure built especially to specifications as detailed by the jl audio datasheet (with an internal spider brace that is shaped like a + sign with a circle cut out of the middle of the + sign so the magnet can be inserted)
..supposed to help with standing waves..

the last time i was inside of an amplifier i was opening and closing transistors and i got a kick out of that (manually opening and closing them was cute to me).
and i started to think that those transistors take the voltage and chop it up as needed to produce more than one sound (although i really have no idea why they are used)

i'm a real infant that can go far if what i am dealing with is described in such a way that can serve me well.
often times a metaphor or analogy is needed so my grasp on what is going on is that much more tighter.


***as to what perry babin said***
i put the positive lead on the battery positive terminal and on the outer terminal of the rca jacks (the needle went past infinity or zero)

i put the negative lead on the battery positive terminal and on the outer terminal of the rca jacks (the needle went past infinity or zero again)

i put the negative lead on the negative battery terminal and on both rca jacks (the needle went past infinity or zero)

i put the positive lead on the negative battery terminal and on both rca jacks (the needled went past infinity or zero)

did the amplifier need to be powered on?
i did the above tests with the amplifier simply sitting on the floor receiving absolutely no power.
(nothing is connected to the amp except the speaker wire coming from the speaker terminals)

i dont have the power supply with me right now because i put it in a box and tossed it into the storage unit (my place is small and i dont like to be cluttered)

my storage unit wont be accessible until some time next month.

[Perry Babin]

If you're using an analog meter, set it to the lowest resistance scale and touch the probes together. What does the meter read?

Check the B+ to RCA shield again leaving the probes in place for at least 5 seconds. How does that compare to the meter reading with the probes touching together?

[anwaypasible]

touching the leads together made the needle swing all the way to the right.

i read the little pamphlet that came with the multimeter and it said how to calibrate it.. obviously it isnt calibrated anymore.

i'll calibrate it and re-do the test.

**edit**
nvm this one has a calibration to set the needle at a certain spot when at rest and the leads arent touching.
i was trying to get the needle to read infinite when touching the leads together and i grew dumbfounded that the ohm adjust dial wasnt doing anything.
(then i played with the calibration screw and realized my error/forgetfulness)


the reading while holding for 5 seconds or longer is...
i did this twice.. once with the ohm adjust dial all the way in one direction.. and then again with the ohm adjust dial fully in the opposite direction.

i cannot place a difference, i was looking for something half a millimeter different and i didnt see any difference.

[anwaypasible]

well i finally got my power supply from the storage unit and hooked the amp up again.

i checked for voltage at the rca inputs and there was nothing.
first i tried with the dial at 50v then again at 10v

a dead AA battery can make the needle move a great deal.. so obviously there is nothing coming out of the RCA inputs.

i am going to take a picture to show that the amplifier is turned on and the protection light isn't on.
(the little fans inside the amp are spinning too)

what should i try next?

**edit**

here is a picture of the amp turned on

[anwaypasible]

i tried measuring for voltage on the rca inputs and speaker outputs with the gain all the way down and then once again with the gain all the way up.. nothing.

i heard a mild buzz when i stuck the multimeter probe really deep (maybe too deep?) into the rca input.
the buzz goes away when i slide out the probe just a bit.
..totally reproduceable.

the amp has been powered on sitting there for roughly 15 minutes without any hiccups or odd smells.

[anwaypasible]

i checked the voltage at the amplifier terminals with this cheap analog GB instruments multimeter (model gmt-12a)
with the dial on 50v the needle said 32volts.

then i read this:
Step 4
If the amplifier goes into protect with the RCAs plugged in (but all speaker wires disconnected), there could be several problems. You first need to check the RCA shields of the head unit. THIS link takes you to a page where it's explained in detail. If the shield ground of the head unit is OK, the amplifier could have one of several problems. You need to power up the amplifier and measure the voltage on the shields (shiny outer metal ring) of the RCA jacks. Touch the black meter probe to the ground terminal of the amp and the red meter probe to each of the RCA shields. If you read 10v or more, the amplifier may have a shorted transformer. If you read something less than 1v, the transformer is likely OK.
(taken from Basic Car Audio Electronics)

so i put the black probe on the ground terminal of the amplifier and then the red probe on the rca shields...
both shields read 32volts.

the paragraph says i MAY have a shorted transformer.. as in, not certainly but possible.

how do i check if the transformer is shorted or good?
and why is the amplifier powered up without any protection mode?
also.. why did i hear output from the amp with the gain set low.. and then oscillation when i turned the gain up?