Hifonics Zeus zrx600.4

[Bills amps]

This amp came in in protect. Found one channel with shorted outputs. I removed them and checked to see if it would power up. Sure. But found that it had negative rail voltage on the emitters of both B688 and D718. Not sure why. Any pointers?

 

[Perry Babin]

You cannot use the voltage on the various components to troubleshoot when the servo/feedback loop is open (as it is with the outputs out of the circuit).

 

[Bills amps]

Im sorry the voltage is on the base. -22.9vdc.

 

[Perry Babin]

Install the output transistors, power up through a current limiter and see if there are any problems with the channel.

 

[Bills amps]

i get the same voltage at the speaker terminals. and if i hook up a speaker it will go into protect after a few seconds.

 

[Perry Babin]

Is that with the outputs installed?

 

[Bills amps]

yes

 

[Perry Babin]

Remove and check the two driver transistors for that channel. Is either leaky or shorted?

While they're out, is the DC gone from the speaker terminals?

 

[Bills amps]

removed the drivers. both checked ok. no leaking. no voltage on the speaker terminals.

 

[Perry Babin]

The problem is likely farther back in the circuit. Do a quick, in-circuit check to see if you can find a defective transistor.

 

[Bills amps]

i have ran all the transistors in the circuit and none seem to be bad.

 

[Bills amps]

this is the whole circuit.

 

[Perry Babin]

You may have a leaky or open transistor. Pull the drivers from the adjacent channel and (from the top of the board), compare the readings of the corresponding transistors of the two channels.