troubleshooting pwr protection, car audio amp

[masterchief]

I have more than one car audio amp that goes into protection mode as soon as powered up. The amps are various brands, but look pretty much alike inside. I can send pics, if needed. I am looking for help to repair this fault.

 

[parsecaudio]

Hi masterchief
This is a frequent problem on this amps.
The first thing are to determinate where is the fault.
Separate the SMPS power suppli and connect a variable laboratory dual power supply and power on :if the power amp work,the fault is in protection circuit.Check them and substitute the fault components.
What is the protection circuit that is on? power supply or power amp?

 

[masterchief]

protection circuit

I think it is the pwr supply that is going into protection, because there are no amps showing on my pwr supply meter. It appears to be a PWM type system with a toriodial transformer, presumably to raise rail voltage. There is a IC that I think tests the pwr to the amp and if there is a fault detected, it bypasses and lights the protection light. I would like to bypass this, but am not sure how. Maybe if I post some pics, someone would recognize the circuit config.

 

[anatech]

Hi masterchief,
Parsecaudio told you how to do this. I use the same method myself. Power up the amp section alone and make sure it works properly, then work on the supply. Never bypass the protection, there is a reason for it.

-Chris

 

[masterchief]

pwr supply

Thanks for the help, guys. I am going to have to try a different approach. The only bi-polar pwr supply I have is 15v. I am thinking of testing the switching mosfets in the pwr supply, and the diodes. masterchief

 

[mrshow4u]

Make sure your power supply has enough "moxie" (Current). Sometimes there is no such thing as "soft-start" and the amp's supply will have steep current requirements to get whizzing. This may make your bench supply' voltage drop. This can start an endless cycle of amp trying to start, power supply current limiting, amp trying to start, etc, etc.

 

[anatech]

Hi mrshow4u,
That's what the car battery I've seen on many benches is for.

Masterchief, try to run your amplifier section on -+ 15 VDC. It may work.

-Chris

 

[mrshow4u]

That's what the car battery I've seen on many benches is for

Yeah, that whigs me out a little bit. Don't car batteries vent hydrogen? Can't they have violent explosions, spraying some acid-dy mixture all around? Yuck.

I'd rather have the electrolytics blow up in my face. I understand the battery. Handy when power testing. I made myself a little spoiled by getting one of those 50A 13.8 V (unregulated) supplies. Awesome because I can use the VariAc with and monitor current. My 3A split supply just couldn't do it. It just kept collapsing when the DC-DC converter started. (....and the amp was fine)

 

[anatech]

Hi mrshow4u,
Hey! I don't use a battery. I have a few supplies. One is good for 25 A and it's regulated (they all are). There is a 5 A and a 10 A somewhere too. I use a 3 A on the bench normally. I also have a 2.5 A bipolar and a 0.5 A bipolar (HP) for checking the amp sections.

Batteries do all kinds of nasty things on a bench. I'm just saying I've seen them.

-Chris

 

[mrshow4u]

Hey! I don't use a battery.

Sorry, I wasn't inferring that you did. There's plenty of other things to go wrong besides them batteries. Hp meter? old grey one's? Harrison?? Love those things.


edit: "They're all regulated". Is that true? I've got this thing from Tripp-Lite and I rember looking inside and just seeing: Big-fat transformer, parallel bridges, and pretty hefty filters. That was pretty much it. When I've VariAc'd the supply, it seems to just ramp smoothly with no apparent regulation voltage. I didn't specifically try to see if the output voltage would limit before the VariAc got to ~130VAC.

 

[anatech]

Hi mrshow4u,
Yep, 6263A although I don't know where it was made. I got it in my late teens or very early twenties. It's probably a good 27 years old now or more. Yikes I'm old!!!

Seems anything HP makes in the way of test equipment is great. Agilent now. I am contemplating a new scope now.

-Chris

 

[masterchief]

Thanks guys. I just remembered I have a high voltage bi polar pwr supply. I salvaged an old Peavey public address system. It had a 80v bipolar, 400w pwr supply. I think that and my variac will get the job done! masterchief