Xenon 1200.1 Fault - Can anyone help?

[Big Valven]

I have a Phoenix Gold Xenon 1200.1 amplifier. I was using it at low volume (no, really, just background listening) at 4 ohms when it suddenly blew the fuse I was using (80A, underrated, but I was in the middle of upgrades.) It very badly overloaded the whole electrical system of the car when it happened, voltage drop down to around 8 volts with the car at cruising RPM!

Back on the test bench, no physical damage is obvious. On my bench supply it will fire up, with a relay initially powering up, and as a second relay clicks to output to the speaker, the current shoots through the roof. The amplifier does not shut /protect though, and did not when it initially faulted.
Funnily enough though, all power supply and output transistors measure OK at a glance, and when it fires up despite the severe overload, on my current-limited bench supply, I can still measure ± 110 volts DC on the main rails. This part confuses me, I'm not sure where to head with suspicions because of it!

I am not too keen to jump into blanket replacements because they either cost me the earth, or take a long time to get to Australia. Any help in diagnosing the fault would be greatly appreciated!

(PS yes I do intend to post a build log of my car, once I have working amplifiers to put in it. )

[cj10488]

If the current is shooting up my guess would be a dead short somewhere... PG made a change a while back to the amp that placed a piece of brown cardboard type tape to the top have of the case. Is this there? Also how do the caps look. Any of them look like they are swollen on the tops?


James

[Big Valven]

I would have guessed a dead short as well, but running from a current-limited 12V supply, the power supply still has +/- 110 volt main rails, which couldn't be the case if there was a short.

Re another person's question on another forum, resistance at the speaker terminals is 30K and rising, settling on 91Kohms after about 30 seconds.

The amplifier appears to have been repaired before including track repairs down in the protection circuitry... now I'm wondering if Xe.load and the protection circuits were even functioning correctly?

[Big Valven]

In reply to questions here and elsewhere, here is some more info on this fault.
There IS an insulating sheet on the underside of the amplifier's lid, rubbing is evident on the uppermost output filter inductor.

I've hooked up the scope and the results I get are as follows.
This is all prior to the speaker relay engaging, and seem to be identical on both high-side and low-side of the output stage.

At the inductor (or transistor outputs, same of course) I get 210mV p-p pulses at about 20KHz (period is 25uS.) The pulses however are virtually zero duty cycle, zooming in they are only a couple of microseconds wide.

Strangely though, the gate signal seems to be the same, 210mV with the same period.

Once the speaker relay engages it all turns to noise approximately 400mV p-p, but there still seems to be remnants of the 20KHz pulses there.

[ttocs]

you say it spikes when the relay clicks on, could it be as simple as a bad relay that is sticking somehow?

[Big Valven]

It's a slight possibility. But as the relay engages, by "spike", I mean a very rapid (50mS) ramp up to, well, however much current you give it, and it stays there until you power off.

[Big Valven]

Bumptacular...

Can anyone give me some insights? I am considering going for some new output transistors at this stage.

[valeks1]

Check resistance on each output FET outside pins and let me know.

[Big Valven]

49Kohms between outer pins on all eight devices.

[valeks1]

49k its good. OK now disconnect both output inductors(just one side)Power up amplifier and if it stays on (power LED stay ON)then one of the inductors shorted inside.

[Big Valven]

Disconnected the inductors, but the problem remains as is.

Note that there is no protection circuit cutting in whatsoever. It just powers up, the relay clicks in, and it overloads my power supply...

[Big Valven]

Bumpskies, Still desperately trying to fix this amplifier. It sounds too damn good!

[Big Valven]

No one's got any ideas? I'm sure it's not the only failed 1200.1 around here...

[Bfowler]

you might have to pm valeks1, he is only occasionally on the forum

[Big Valven]

Hey guys, this amplifier is still dead and I'm lost for ideas. Does anyone have any more ideas?

[Jacampb2]

I don't do any work on the xenons, but it seems that your +/-110Vdc rail voltage is exceptionally high for an amp of this size... IDK, but it seems unreasonable, it doesn't need anywhere near that rail voltage to make it's rated power.

Good Luck,
Jason

[Big Valven]

Thanks for that.

I am in a serious amount of bother with this amplifier, I can't afford to scrap it, no one in Australia will repair it, and no one in the world seems to know much about repairing it?

[Jacampb2]

If you are absolutely certain that the output fets are good, then I would guess it is something in the Class D drive circuitry and it is allowing the outputs to shoot through. You should however be able to measure voltage on the gate showing this to be the case. Maybe pull the output mosfets anyhow and see if the high current draw remains, also measure the gate signal with them out of circuit. It would also be wise to check the mosfets out of circuit anyhow. I have had instances where multiple parallel mosfets still tested ok (not great mind you), but there was a shorted one in the bank. Other than that, I don't have any ideas for you.

Good Luck,
Jason

[rolandk]

Not much help here but the X1200.1 can be and is usually a very difficult amp to repair. The 110V rail is correct. You could try removing all of the output FET's and power the amp up on your current-limited supply. If it powers up and seems to be OK it could be the output FET's and/or damaged IC's on the vertical PCB in the output section.

[Big Valven]

Hey guys, thanks for sticking with me on this one. It has been a while since I have worked on the amplifier.

Tonight, I lifted the gate resistors on the output stage as it was easier as a prelim measure than removing all the fets, the problem remained as described earlier in the thread - current overload on my bench supply with full rail voltage, and no protection circuitry cutting in. The output chokes have already been lifted out of circuit.

Then I removed the output fets altogether, same issue. I followed it with the output relay (yes I know, the chokes are lifted.)

Finally in desparation, I lifted the four jumpers needed to totally isolate the output stage from the power supply. There is a current spike as it powers up, but then it shuts down the power supply and flashes the protection LED - so parts of the protection circuit at least are working correctly.

From that at the moment I can roughly conclude that the power supply and some of the protection circuitry is working, as it fires up it can possibly tell that the output stage is not powering up as usual, and isolating the power supply...

Without the output transistors in place however I am at a loss as to why the output stage still over-currents, there doesn't seem to be anything in there that can carry that much current apart from the output transistors?

[davewaibel]

send it to valek, he has a flate rate on xenon repairs- he has worked on thousands of them- unless you speak russian, or ukranian, good luck on talking to him about specifics, very quiet individual-otherwise- your going to be chasing your tail for some time- or you can just buy mine for 200.00 plus shipping

[Big Valven]

That's not a bad deal but if you notice, I'm in Australia, so postage is likely to double the cost - ironically that's how much this one owes me at the moment as well so I'm not keen to scrap it. Car audio costs a lot in Australia!

Likewise, sending it overseas for repair is likely to land me in a similar predicament.

[davewaibel]

give me an address- ups, and fedx are ridiculous, but usps is actually not real bad

[Big Valven]

To be blunt, I can't think of anything worse than having ANOTHER of these amplifiers to blow up. Sorry. As soon as this is working it's getting the hell off my workbench and hopefully it can get me some funds for new substage amplifiers.

[ttocs]

sorry to hear that man. I would not put it on your bench for any legnth of time if it pulled your voltage down like that.... Sooner or later the magic smoke will come out of it or teh supply.