Hifonics Zeus ZXI6406

[Dr Zeus]

I've got this amp on the bench and it wont turn on properly. When powered up, both the power and protect LEDs are lit. There is no voltage at the rail, and none of the larger transistors appear to be out of tollerance.

TL494 pin volts

Pin 1: 2.770
Pin 2: 4.34
Pin 3: 4.61
Pin 4: 0.019
Pin 5: 1.558
Pin 6: 3.481
Pin 7: 0.004
Pin 8: 13.73
Pin 9: 0.004
Pin 10: 0.004
Pin 11: 13.73
Pin 12: 12.83
Pin 13: 5.02
Pin 14: 5.02
Pin 15: 5.02
Pin 16: 8.96

[Perry Babin]

Pin 16 is shutting it down. What's driving pin 16?

[Dr Zeus]

Its kind of tough to tell. let me study this photo and I'll edit this post in a minute.

Pin 16 of the 494 trace is connecting it to R10. From the top of R10, connection is made between Q4's center, and R7.

I'll have to study this more later this morning. Got a meeting to go to.

[Dr Zeus]

Q4's top right leg is leading to a series of diodes in the middle of the audio section. From here, these diodes are leading to 4 x 2690 transistors. Pictured, these Q109, Q209, Q309 & Q409 . All the diodes and transistors check out OK.



The top-left leg of Q4 leads to the Power and Protection LEDs, and also up through the external board (w/ the RCAs) but only over to the remote port. I'm guessing thats the LEDs for a remote control.

-More to come-

[Perry Babin]

Lift the top 2 legs of Q4. Does it still go into protect?

If not, do all channels produce clean audio with no significant DC offset?

Be careful. If the circuit is connected as it appears, this will disable the overcurrent protection.

If it draws excessive current, power it up through a current limiting resistor (all transistors clamped down) and measure the DC voltage across each of the emitter resistors to see which channel is causing the excessive current draw. If you can't get to the terminals of the emitter resistors measure between the emitters of the transistors in each individual channel.

[Dr Zeus]

With Q4 top legs lifted the amp powers off a 5A supply with ~0.025vDC on terminals.

All 4 channels play with a test speaker.

There doesnt seem to be any excessive current draw atm.

[Perry Babin]

Re connect Q 4 and remove the 4 transistors you listed, one at a time to see which one is causing it to go into protection.

[Dr Zeus]

Q4 is back in and conencted. I mis-read the previous transsitors; Q109, Q209, Q309 & Q409. These are actually not hooked into the center diodes. Instead, its Q116, Q216, Q316, & Q416 which are 3189 transisfors. Connection is from the diodes through a 10K to the center legs of 3198s.

I'll pull them one at a time and check everything shortly.

[Dr Zeus]

Pulling Q116, Q216, Q316, & Q416 didnt help. The amp still powers on in protection mode.

I missed something on from Q4's top left lead. Correct; its going to the LEDs, but first through C4 capacitor just behind the power control board. I'll map this out shortly and edit this post.

[Perry Babin]

The transistors that you're looking for likely have their emitter connected to one leg of the emitter resistor. The base likely connects to the other side of the emitter resistor via a resistor. The collectors of these transistors should be connected together via diodes and possibly resistors. The diodes would go to a transistor (like Q4) that would shut the amp down when an overcurrent fault is detected. Are these the transistors Qx16? If not, look for transistors connected as described.

You may want to read the 'Protection Circuit Troubleshooting page' if you haven't done so already.