Phoenix Gold xs4600 repair help

[johnzenobia]

So i bought this Phoenix Gold xs4600 off ebay. Description said pristine condition, well it was fair condition to say the least. Got it hooked up and getting a squealing sound coming out of the speakers. Opened it up to see the main power supply caps were bulged and leaking. Ordered 10,000 uf at 25 volts and installed properly and also found two shorted transistors in the outputs too. Any advice would be greatly appreciated. Also does anyone have the wiring diagram for the lpl to make one up. Thanks

[trickyricky]

Best bet is to replace all the diodes and transistors as well as the two main outptut mosfets in that channel. You'll spend about 5-6 bucks in all the components needed in one channel and will pretty much guarantee a successful repair.

Here's a link to the LPL44 info.http://download.phoenixphorum.com/TechS ... L_Info.pdf

[johnzenobia]

Ok thanks for the quick reply and the information. Do you think anything could be wrong in the preamp section of the board? The squealing noise seems to be slightly affected by pushing the crossover button in and out.

[trickyricky]

There could be an issue with the xover-preamp board, is the squealing noise coming from one channel (bad channel?) or all channels? Does the noise increase if xover is bypassed?

Also what channel is shorted/bad?

[johnzenobia]

I didn't check if both channels are affected but after re-check on the outputs the transistor I thought was bad was a diode so I think the outputs are fine. Need to do some more work on it this week when I get home from work.

[johnzenobia]

Yes the noise is stopped if the x-over is bypassed.

[trickyricky]

Okay that's a clear indicator that there is an issue in the xover circuit, next is to see if the noise is there only in the LP or HP or both. There are several components (op amps and resistors) that make up the xover filters, having a bench scope will help find what component is causing the squeal.

[johnzenobia]

Both channels thumb when selecting the 24 db crossover and when pushing the hp/lp button the squeal starts and stops. thanks

[johnzenobia]

Update. Seeing 28 volts on half of the power supply caps

[trickyricky]

28v on the primary or secondary caps? If measuring the rails (secondary) voltage then I go right to the center pin of the rectifiers. You should have same positive and negative voltage on the rails when using secondary ground as a reference point.

Can you be a bit more specific as far as which two channels are experiencing this issue.

[johnzenobia]

Either front or rear channels have the same issue . I am guessing that only half of the power supply is firing on and not powering up the preamp board. I still have more checking to do. Thanks so much for the great advice and information.

[johnzenobia]

Update. Got the amp running for 30 seconds before blowing out IRF540 mosfet drivers. I replaced 12 caps throughout the amp and some cold solder joints.

[trickyricky]

If you are testing the amplifier outside the heat sink then that will cause any device that is/was attached to the sink to fail.

[Jacampb2]

What version of the IRF540s are you using? If you are using IRF540n, it is a a virtual certainty that this will continue to happen, in or out of the heat sink. Replace all the outputs in the channel having issues. If there is more than one parallel part, replace them all with parts from the same batch. This will ensure the closest match short of testing and matching each transistor. If you don't do this, there can be enough variation between devices that they do not share current equally and you will continually see transistors fail after a short amount of run time. Make sure you turn the bias pots all the way down (counter clockwise) after replacing any outputs, after you get the amp stable and up to operating temperature, reset the bias.

Check all the gate resistors, with a multimeter, not just visually. These are almost certainly flame proof/fusible resistors in the output section and they will most likely show no signs of having burnt open. Meter check every one, even resistors for outputs that did not fail. Do like Rick said above, replace the (iirc) A56 small signal transistors that drive the outputs. There are also several 1N4048(from memory, verify!) diodes in the driver section that you may as well swap out. Like rick said, it's peanuts in parts and it almost insures a successful repair. Check the emitter resistors (well I guess in this case they are drain or source resistors), verify they are not open. They too may be flame proof and show no visual sign of damage. Even when they are not flame proof the resistance can shift significantly if they have been over heated and they still may show no outward signs.

Good Luck,
Jason

[johnzenobia]

Thanks for the great information. Yes I ordered the IRF540. Do you know what the bias voltage and where it's measured at. I know sometimes you check it at the emitter resistors.. Thanks waiting on parts from digikey.

[Jacampb2]

I actually have a XS6600 that I need to repair still, but I haven't gotten around to it yet. A lot of PG amps, have test points for measuring while setting bias. I think the Tantrum 500.2 that I just worked on (very similar to the XS amps) did not have the test points. If there are no manufacturer specified test points then I default to using voltage drop over the emitter resistors. I normally start somewhere in the neighborhood of 1-2mv. For myself, unless I can hear crossover distortion or the idle current is abnormal, I just leave it there. If I can hear audible crossover distortion, or if I am working on someone else's junk, I will typically set the bias with the scope. It is very easy to see in the output waveform. It looks like a flat spot where the voltage passes across the 0 volt threshold.

Good Luck,
Jason

[johnzenobia]

UPDATE !!! So excited got it working. Thank you so much for the all the information it was a great help.

changed all the mosfet outputs,all the transistor drivers,8 cap0s in the power supply,4 caps in the xover section that were leaky and swelled and numerous cold solder joints. The sound on the bench with just an ipod as the source is amazing hooking up tomorrow in the truck . Plan on running the rear ch on a JL 10w0 and the front ch on the front door speakers.

[johnzenobia]

Sitting in my truck now listening to it! It's like a whole new audio system arrived! Unbelievably awesome ☺

[Jacampb2]

That's awesome Bro! In my opinion its always sweeter knowing you tracked it down and fixed the problem on your own! Its kind of like solving a puzzle and its part of this hobby that I really enjoy.

Later,
Jason

[Bfowler]

i love seeing that another xs amp is still rocking. nice work

[johnzenobia]

Just bought an XS2500 that I am planning on rebuilding. New caps , new output stage,etc. I loved the sound that XS4600 and wanted a little more power to the sub so I will be running both amps .I remember selling these amps when I worked at a local stereo shop back in the late 90's. Will keep updates coming.

[CK1991]

glad to see these XS amps are still out there. I finally hooked up the xs6600 in my van today and it kicks ass.