HELP , Fix Kenwood KAC-7295 600 wt Car Amp

I have a Kac-7295 amp I need to fix. I had a small speaker on it to test it and it played. Once I ran my subs on it the resistor fried. I'm not sure what needs to be replaced please help. I own a multimeter also to test anything with some help. Would really appreciate it as I can't afford a new amp right now. I fix my car and test stuff in there and did my own fuel pump ect but this has me stumped. I will add pics

Questions ask please direct me with this. Again it powered up fine and worked on a 4 inch speaker but my 10 in made the resistor fry but it has been sitting for a long time before this. Thanks
 
Was the sub cooked or wired incorrectly in the box? Although rare, it's possible for spade lugs to come off the terminal post or the connector at the box and short both both wires together. Depending on actual amplifier (not familiar with yours), it can then either pop a fuse, go into a stand-by, or take out a bunch of internal parts like outputs, etc.

For all you know, the resistor was already at the point of failure, your test speaker worked, then once in the car and a stronger signal went into it and gave the ghost.

If the color marking on the resistor is still colored, look at other resistors in the amplifier and try and find an identical "twin". Resistors are commonly paired, and/or used more than once. Lift a leg of a twin to remove it from the circuit (no point trying to probe them in-circuit as it'll skew the value from other connected pieces) then probe it.

If there are other "twins", consider probing those as well as it can either help average the values of your dead one, or can help show if/how far they are out of spec. There are color-coded charts online that can help you find the exact value + the tolerance of the resistor, but in my limited experience it can be a RPITA trying to distinguish some colors i.e red or orange? gold or yellow? etc. since every factory uses their own paint batches.

Really cheap resistors might have a 15% tolerance, which means the rated value of the resistor can be +/- 15% of the value the colors are saying it should be. If there are other, identical colored resistors, consider replacing them in one go (talking the larger resistors near outputs for example) and getting 2-5% tolerance so the new ones are very similar to each other, AND hopefully you'll avoid continued failures. I'd consider a more durable resistor with the higher wattage rating if possible. If you can't determine the material it was made from, try posting a pic of it out of circuit. If burnt really bad, try posting a pic of the twin if possible. You definitely want the replacement to be as strong or stronger and able to tolerate the same amount of heat. If you are REALLY lucky. it didn't blow any outputs.

Parstsconnexxion has resistors as does digikey
 
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Thanks for the reply. I am trying to upload pics now that I can see my thread but it asks for URL ? Is there a mobile version to add pics easily ? I will add many pics to show you , I also contacted Kenwood for a Schematic of the amp but no reply. I think it's a 10 ohm resistor that fried. There are 4 in a area together then 2 transistors then another 4 resistors and that's where they fried or one did I think but took out others around it. The row of them next to it are the same resistors I think as if there are 2 sets of 4 next to the row of transistors. Could be 4 transistors then 2 diods bit they look the same but have a dioide marking on them. I will keep trying to add pics as itss hard to explain. Really appreciate the help tho man, if I get it solved I can send you a few bucks on your PayPal for your time and help. I also believe I switched it to mono when I used the big woofer after it was on stereo while testing the small speaker idk if that caused an issue but I can't see how.
 
here are some pics i can take more
 

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here are some pics i can take more

The burnt section appears to mirror the other section you took a pick of. You have matching resistors, then the diode, then 2 more resistors, and all the resistors appear to be same colors as their mirrored counterpart though some are harder to discern what color they are from pic.


I'd lift the leg of the good resistor and check it's value. Then try and get 2 replacements in the same range.


What you can also do is probe to get the value, write the colors down, use an online color chart, than see if you deciphered the colors correctly by comparing their supposed value to your meter. It should, if done correctly be within 5-15% depending on quality of resistor they used. Being that small, it's probably a 1/4w or similar. as long as it's not intended to be some safety feature i.e. burns out to save other components (I don't know enough about this to be honest) from destruction, I imagine you can increase it's wattage rating, especially if this was a design oversight they fixed in a later revision. (when it costs $0.05 between "it'll work and next better part, X 150k units, that 0.05 adds up quickly)



I'd replace both to be safe, and see if amplifier works or not before dumping more money into it.

Also, next time you have some spare change, consider buying a used amp as a back up ;)
 
Save your money for stuff you need. I'm by no means a pro.

Resistors are color coded with color bands. Zener diodes are the little ones with the almost clear casing and a diode marking on them denoting current direction. Basically they take less forward current to work than typical black diodes with silver or white markings. They also can't tolerate issues as well as the larger ones can, so you might need to inspect the one next to the burnt resistor.

I wouldn't worry about trying to troubleshoot other areas yet. Just try replacing the resistor (might get lucky and be able to find one at Radio Shack as they sill sell them in assortment packs back in their drawer section) and cross your fingers that's all that failed.

Bridging an amplifier uses both channels, essentially making it a mono amplifier with the combined L/R channel wattages, if only bridged connections are used. In tri-way, you get stereo L/R, + the bridged mono (assuming amp can tolerate this; most newer amplifiers can). Amplifier will still share the wattages across the speakers, but the mono channel will still be louder unless you run 8 ohm on bridged. So say you have a small pick up and want to run stereo + a small sub, but only use one amplifier, you could do that, but you really need to add a passive crossover or at minimum a voice choke for woofer and run higher freq. at doors/dash
 
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BTW, here's a little thing on diodes. If you scroll down on the left, it has pics of various styles: How A Diode Works

If you multi meter has a diode setting (might say diode or have drawing of the anode/cathode) you set it to that, lift a leg of the diode to remove it from the circuit, then use the meter, observing the direction of the solid triangle on the line to connect correct probes to correct diode ends.

When doing this with a meter, it supplies a small forward voltage to operate the diode. It'll tell you if your Zener diode next to the cooked resistor is good or not.

Problem is they are small they don't really offer much info. If your shows as open/blown you can probe the mirrored Zener diode for the reference.

GL and update if it gets working again.
 

Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
This is likely a 729S, not a 7295.

The resistor is in the pulldown circuit for the power supply FETs. The FETs (at least one) have almost certainly failed. R208 is a 10 ohm resistor. The diode is a standard switching diode (not a zener).

You need to pull the two PS FETs that are being driven by this part of the drive circuit and check them.
 
This is likely a 729S, not a 7295.

The resistor is in the pulldown circuit for the power supply FETs. The FETs (at least one) have almost certainly failed. R208 is a 10 ohm resistor. The diode is a standard switching diode (not a zener).

You need to pull the two PS FETs that are being driven by this part of the drive circuit and check them.

Sorry about Zener error. Do you happen to know which are the FETS so he knows? And can he still get legit replacements? If so, who sells those?