Phoenix Gold Phorum

So I've got a 500.4. One front channel has no volume and one rear channel is full volume. I have the amp all apart. Wondering where I should start looking to fix this fine machine

Remove the heat sinks and see if there's any obvious heat damage. I would follow the bad channel specifically to see if there's anything obvious. If nothing obvious then start testing the resistors on that channel to check for continuity. Some of the resistors work as a fuse and can blow without leaving any indicator.

When you were testing it, were you playing music or sine waves?

Was the xover on LP/HP or Bypass?

Are all 8 red LEDs inside on?

I wa using a variable tone generator. Tried all crossover pos. and I'm pretty sure all the lights were lit.

Okay here's the thing about these amps along with ZXti, ZX, ti amps that use the same 8 gang pots for the xover fhz. Those pots act up and not to mention they are 10% in tolerance so while a few pots may be at 5k there will be one or two that will be around 4.2K or 5.8k this lead me to believe that not all ch's are xover EXACTLY at the same point.

So if you use sine waves you'll notice around the fhz xover point that some channels will have more or less output then others.


Did you test it with the xover by passed? Did all four channels have equal/balanced output?

I think your both on to something. The one full boar channel goes normal on bypass. Also found 4 of the 8 resistors next to the big fets have no reading with my dmm.

Any one know the value of this resistor. The 2 gold bands are throwing me off.

Weaklink wrote:Any one know the value of this resistor. The 2 gold bands are throwing me off.

Not trying to be rude here...but there are more of those resistors in the same spots around those transistors. Check ALL of them and you'll see which ones are open/blown and which ones are good, as well as the value of resistance.

But thats a 2.2 flameproof (fusible) resistor, if your going to replace it MAKE sure you buy the same kind otherwise your board may get damage (a little black smoke and goop).

If that's open than likely the outputs for that channel are shorted. Quick tip, each channel has their designated number on the board...for example CH 1 would be Q111 or R111 while CH 2 will be Q211 or R211, this is just and example but will make it easy to determine which channel it is and which components to test.

I checked all that were around then and found 4 that were open. All with that code.

Post of picture of the whole board and circle the open resistors...that way we can figure out which channel that may be.

When you put the xover in bypass did 3 channels produce sound and 1 was dead? We'll worry about the xover later once you got the amp running, by the way also post a picture of the xover board in case you have any open resistors (the resistors on the xover board will show damage unlike the flameproof/fusible type).

I got some 1/2w ones on the way home. Is that going to be too big? I'll take pics as soon as I can.

Ok so the resistors with arrows have no reading. With crossover on bypass. Front left sounds scratcy. Front right sounds normal(the one that goes full gain if crossovers are on). Rear left has no sound. Rear right sounds scratchy. So if 2&3 ea have one bad resistor do they sound scratchy because they are only getting half the music. Also tested with an iPod this time.

Okay here's the scoop.

Ch Front Left is 3xx
Ch Front Right is 4xx
Rear Left is 1xx
Rear Right is 2xx


Check each channels Qx16 and Qx17 as those resistors you show are tied to those transistors. Q118 may be shorted thats the big Toshiba transistor on the top you have masking tape on, if not shorted then the resistor next to it is causing it not to have output main reason why you have no output on the 1xx (right left ch).

1/2w are a bit too big, unless they come in the right package (size). I would try to stick with 1/4watt.

Tested all and no shorts between any combo of the 3 legs on any.

On that zx475ti that I sold you I replaced all of those resistors and all of those SEMIs. When in doubt replace it all, that's the best way to know it'll work right. Lol

No this a 500.4 I got. Both the zx475ti's work great.

Those large output Toshiba's are not cheap, just replacing all 8 of them would cost around 40.00. Replace all those 2.2 resistors and when you power it up make sure you use a 5-10 amp fuse and also a current limiter (12v bulb in series) just in case something else may be bad you don't blow up the board.

Will try to get the resistors replaced tomorrow and let you know. Thanks for all the help so far by the way.

So I finally got a bit of free time and replaced all 8 resistors just to be safe. All channels work now. One thing left is now the front right channel is not affected by the crossover switch. It is fine in bypass but gets quieter in hp or lp and still full range. The front left acts proper on all the crossover settings.