my friend gave me a new audiobahn amp. its stuck in protect mode. any way to fix it?

 

Get a service manual an oscilloscope and a function generator and trace the signal thru the circuit to see where the bad component (or components) is.

With the high hourly rate charged by bench techs these days the cheapest route to go would be to buy a new amp.

 

Don't always need an oscilloscope (and then don't always need a function generator). Plus.....not everyone has access to a function generator and an oscilloscope......and if he did, chances are he would have no idea how to operate them or what to look for...

What model amp is it? Unless its up there in price...I would just save time and buy a new one. Obviously your friend gave it to you because he knew it wasn't working properly, right?

 

ha no. less of a friend, more of a co-worker. he doesn't know anything about car audio. And I hook people's systems up for money. So he asked if I wanted it and I took it hoping it would be an easier fix. Its like a 4 channel auidobahn flame series. I want to replace the amp in my car with it but I need to get it working first.

 

Probably blown output FET. Check resistance between +/- of each speaker terminal, if around zero - you found failed channel. Very frequently FET will bring together with it a part of driver circuit, gate resistor, etc. What is the model, and can you post a pic of board?

 

whats a normal resistance between them supposed to be? I'll put pics of the board up once I've taken it apart. its an audiobahn A6004T 4 channel amp.

 

Even better, when you open it up, check resistance between pins (all 3) of output FET's (they mounted on heatsink, bigger ones, under blue plates) then check resistance between pins of smaller FET's (PWM power supply, close to toroid transformer on heatsink, under blue plates too). Audiobahn amps are always showing protect light even in case when power supply isn't working. There should be no short's between FET's leads. LMK what you find.
You should have something similar to this, but a little bigger:

 

Could you possibly use paint to put some arrows on the things that I need to test the resistance of. I'd appreciate it a lot. thanks

 

Your power supply is definitely down, you can see discoloration due to overheating on bottom left, around 2 FET's. I pointed blue arrows to 3 leads of one FET, red - 3 of another. Measure resistance between 1-st and second, first and third, second and third leads of each FET. If there is a short - you found blown FET. Then proceed to check the same way all the rest big fets, mounted on heatsink. Post your findings. If you find a blown FET, do not hurry to replace it, there some more checks needs to be done to prevent newly installed FET's from blowing again.

 

okay here is what a found.

Red Arrows: 1 and 2 : around 2.0 ohms
1 and 3 : around 2.0 ohms
2 and 3 : around 2.0 ohms

Blue Arrows: 1 and 2 : around 12.0 ohms
1 and 3: around 13.0 ohms
2 and 3: around 1.0 ohms
(this one looks slighly burnt)

Here is what I found on the set right next the those..

First 3. 1 and 2 : around 19 ohms
1 and 3 : around 20 ohms
2 and 3 : around 1.2 ohms
(the first pin on this one is blown apart from the other 2 but its still showing some resistance (19))

Second 3. 1 and 2: no reading
1 and 3: .9 ohms
2 and 3: no reading

heres a pic with the heatsinks taken off of

 

You found it, good example of blown FET's, please also check first 3 from the left FET's on opposite side of board, which are under heatsink too, these can also be damaged.
Gate resistors seems to be damaged too, judging by it's color, I marked them with arrows on pic. Their resistance should be less or equal then 100 ohm (blown FET's needs to be removed for this), when they overheats resistors can burn wide open or increase their resistance.
Check the same way simular, but bigger transistor, which are also bolted to heatsink (outputs, there 8 of them) for short or very low resistance inside, they rarely fail, but it will gaurantee that newly installed power supply FET's will not blow at first launch.
So, so far you need 3 FET's, fist three from left, fourth is a rectifier (I would replace all 6 including same devices on opposite side of board) which are probably IRFZ44N, can be substituted with 75339P, which are better then originals and also cheaper (search for 75339P on www.digikey.com) . Then definitely at least 3 gate resistors,I can't see color code on them to read value, check it, should be around 100ohm each.
When components will be replaced at first start use a headlight bulb, 1-2 A fuse as a current limiter in series with amp - it will act as a current limiter and protect good parts from being burn instantly.

 

Okay I checked the Gate Resistors that you labelled and they all read about 30 ohms.
Here is what I found for the top 3 Power Supply FETs
FET1 1 and 2 .9 ohms
1 and 3 1.3 ohms
2 and 3 1.2 ohms

FET2 1 and 2 1.2 ohms
1 and 3 1.3 ohms
2 and 3 1.2 ohms

FET3 1 and 2 1.2 ohms
1 and 3 1.1 ohms
2 and 3 .9 ohms
I took the heatsinks off all these and none appeared burned but I dont know what the numbers tell you.

Here are the output numbers starting from the top 4. then the bottom 4.
top1: all were at 1.4ish

top2: 1 and 2 were at 80
1 and 3 were at 80
2 and 3 were at 1.4
top3: no reading from all of them
top4: no reading from all of them

bottom1: no reading from all of them
bottom2: no reading from all of them
bottom3: no reading from all of them
bottom4: no reading from all of them

if I made it too confusing I'll label a picture to make it simpler.

 

If all measurements are correct, then from what you wrote, these are due for replacement:
- all 6 power supply FET's (3 from the left, top and bottom)
- one channel is blown, top 1 and 2 output FET's should be replaced too (read labels on them, search on Mouser, Digikey, etc), please also check all big green resistors - they should read close to 0.1 ohm each. When FET fails, they burn almost every time. Then check smaller resistors, connected to 3-d leg of each big FET (looking at bottom fets on last picture) - they should be around 3 ohm. On failed channel they can be wide open, and newly installed FET will blow in a second.

 

okay I'll post up the results from the big green resistors and the smaller resistors(I dont know exactly which ones) once I check them. Were the gate resistors on the power supply FET's okay? Also, what is FET an acronym for?

List of things to buy so far:
6 of those power supply FET's
2 output FET's
anything else?


thanks

 

Field Effect Transistor

EDIT: Can get a very basic understanding about them here - http://en.wikipedia.org/wiki/Field_effect_transistor