punch 200ix excessive current draw

[vincegironda]

I have a Punch 200ix which was pulling over 32 amps when remote applied, I checked the power supply fets which tested all good.
Next I tested the output fets and a few where out of tolerance so I pulled the lot off the board and powers up the amp, result was the amp powered up fine.

So I replaced all the irf540''s and commenced to power up the amp, unfortunately it almost immediately began drawing excessive current.

Any thoughts would be appreciated??
thanks in advance

 

[vincegironda]

When I power it up with a 12v bulb inline in place of a fuse the amp plays clear audio on both channels at medium volume, any higher and it begins to clip

 

[jkrokenberger]

Check the output drivers. Also look for solder bridges. Is there any voltage across the source resistors?

 

[Osvaldo de Banfield]

If the thing has over 5 or 6 years, I would change all electrolytic caps, the input and output filters (Bigger units). They may be leaked and or devaluated.

 

[Perry Babin]

My opinion but I wouldn't blindly replace the capacitors unless you have a reason to do so. I've checked caps that were about 30 years old and they were fine. I've seen some that failed in just 10 years.

Did you set the bias?

Does it draw excessive current with the bias pots set to the fully counter-clockwise position?

 

[Osvaldo de Banfield]

Bad caps are responsible of near 90% of the faults of electronic devices. I work repairing electronic inductial devices (Frequency converters, SMPS, CPU's, displays, touch screen, motor drivers, etc.), and the first thing we do is to replace all electrolytic units, including SMD elements. They usually fault in several ways (loose the C value, increase ESR, shortcircuit or open circuit), but clearly the worst mode of fail is when they leak the electrolyte over the PCB. Vias, tracks, resistor and including complex IC pins are corroded by the liquid conductive.

In the least symptom of doubt, replace them.

 

[Perry Babin]

Again, my opinion but in 30+ years of repairing car amps, that is what I've found to be true.

In some electronic equipment, like the flat-screen TVs of a few years back, some of the caps would fail in about a year. The HD and DSM amps had a problem with the 10uF@16 v SMD caps. Some other amps (PG, Zapco, some of the ZED amps) had problems with the primary side caps. Some of the very old Orion amps (made in the late 80's, early 90's) are now having some significant capacitor problems.

There may have been a few other common problems but capacitor problems in car amps isn't a significant problem. I don't like to see people waste time and money for nothing.

 

[vincegironda]

Hi Perry

I turned the bias pots fully counter clockwise and the amp stopped drawing excessive current.

How can I set the correct bias on this amp?

thank you

My opinion but I wouldn't blindly replace the capacitors unless you have a reason to do so. I've checked caps that were about 30 years old and they were fine. I've seen some that failed in just 10 years.

Did you set the bias?

Does it draw excessive current with the bias pots set to the fully counter-clockwise position?

 

[vincegironda]

The amp plays clean audio on both channels and idles without any issues with both bias pots turned down.
I would like to set the bias to the correct setting though so any help here would be great thanks?

 

[barber02]

Everything you ever wanted to know about biasing an amplifier from class A and up. Then you will know that you know that you know.

YouTube

You are basically applying just enough voltage at the base of the transistor so that it is slightly on without generating too much heat.

Hope this helps,

David

 

[Perry Babin]

This is how I set them:
http://www.bcae1.com/temp/ausettingbias.swf