cadence

[Hexhclass]

XA 1200d model


Amp plays good audio.With gain and bass boss fully clockwise amp will go into protect before reaching full power.Work had been done on this amp before.Three of the rail caps don't look original.Any ideas?

 

[Perry Babin]

If you drive a 60Hz sine wave into it with the bass boost fully clockwise and then again with it fully counterclockwise, does it go into protect at precisely the same output voltage?

Are you sure that it's over-current protection that's engaging?

 

[Hexhclass]

I don't no if it is over current protection that is engaging.How can i determine that?

I will drive the signal to it and see how it react

 

[Hexhclass]

Went back to this amp today.With the bass boost fully counterclockwise or even 3/4 it does not go into protect.

This amp is almost like the clones but with no driverboard.It has the same q124/5 that heats up fast.Rail voltage is acting strange in this amp.At idle the negative rail is -65.6v.The positive is 60.1v.When i start driving this amp hard the positive rail goes up to about 91.4v while the negative rail is going down to about 40.1v.This happen just before it goes in protect.Rail caps is only 80v.

 

[Perry Babin]

It's probably a driver problem. Likely for the high-side FETs.

 

[Hexhclass]

What is the way of knowing which is the high side?
Am guessing the A42s might be the drivers .They get so hot i cant keep my finger on them for 5 seconds.

 

[Perry Babin]

The high-side has the center leg of the FETs connected to the positive rail (for an amp using all N-channel FETs, like this one).

 

[Hexhclass]

I change all the drivers and the other three rail caps no change.The 4.72k test ok.
Also replace the KIA IC just in case.

 

[Perry Babin]

Did you do that before or after post #7?

 

[Hexhclass]

after

 

[Perry Babin]

Does the secondary center tap voltage change when the rail voltage shifts up?

 

[Hexhclass]

With the black probe on the secondary center tap and red on either side voltage does not go up.I see 104v ac,with another meter i see 78v.

 

[Perry Babin]

Black on primary ground and red on secondary CT.

 

[Hexhclass]

Black on primary ground and red on secondary CT no high voltage.I see Mv that does not reach a volt.

 

[Hexhclass]

I forgot to mention I also notice the transformer is playing audio.

 

[Perry Babin]

Does the voltage shift up when driving the amp into a load?

 

[Hexhclass]

Not sure if the mili- volt matter but is goes form 0.024mv to 0.232mv

 

[Perry Babin]

I should have been more clear. Does the rail voltage shift up when driving the amp into a load.

 

[Hexhclass]

yes

If there is no load i t will not go in protect.

 

[Perry Babin]

When you replaced the drivers, did you use exact replacements in all locations?