planet audio vx2200d

[bdgf2004]

got this the other day and found one of the power supply fets was shorted. all 4 gate resistors measured at 97 ohms so i replaced all 4 fets in that bank. now the amp will come on but will go in and out of protection. it will produce audio but i can't tell if it's clean or not because it doesn't stay on long enough. does anyone know where i should look next?

thank you

 

[Deadly Sones]

did you only replace the one shorted ps fet or did you replace them all? Are you sure none of the others are damaged?

 

[bdgf2004]

only 1 was shorted but i replaced a total of 4 because they were in parallel. i did notice though that as long as a have a load on the output it appears to not go into protection. almost as soon as i disconnect the load (2 ohm subwoofer) it will go in an out of protection. it is not producing clean audio though. with a sine wave it sounds fairly clean but with music it is definitely distorted. with the scope i can see the sine wave is not completely clean and smooth.

 

[Deadly Sones]

hmmmmm... honestly I don't wanna lead you astray, so I'll see what others say. Just wanted to make sure you did in fact replace all 4 transistors. This stuff is a constant learning curve for most of us. Hope you get r fixed.

 

[Perry Babin]

Post a scope image of a 100Hz sine wave with a load on the amp.

 

[bdgf2004]

100hz sine wave with 2 ohm load

 

[Perry Babin]

Try replacing Q124 and Q125 on the driver board. Install the new ones so that they're within about 1/16" if the fan blades.

 

[bdgf2004]

q124 &q125 are mpsa42. is it ok if i replace them with mpsw42?

 

[Perry Babin]

W42 is what I'd use.

 

[bdgf2004]

appears to work perfectly now! it's been playing about 5 minutes or so with no problem. i'll let it play for a while and call it a day.

thank you so much mr. babin

 

[Perry Babin]

Make sure that the fan is working properly and turns freely. When it's running at top speed, make sure that it's not vibrating. If it is, it will need to be lubricated.

 

[bdgf2004]

It does vibrate a bit. I have 1 replacement fan on hand if necessary from a previous repair (bb2400 i think) thanks to you.

 

[Perry Babin]

If you're going to work on amps with fans, you need to learn to clean and lubricate them. Virtually every amp that uses fans uses fans with sleeve bearings and the lubricants that they use dries up.

 

[bdgf2004]

i have cleaned and lubricated them before. i think i had 1 that was broken or seized up or something. i bought an extra a while back just so i would have it handy.

thanks again