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Old 8th February 2010, 05:11 PM   #1
fbc is offline fbc  United Kingdom
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Join Date: Feb 2010
Default need help with phoenix gold xs2300

I've just got a phoenix gold XS2300 off ebay and it doesn't work

I wired it up to some 6x9's i had lying around to test it, the power light comes on ok but the sound coming out of the speakers (one more than the other) was fierce crackling. The speaker cone was going crazy and after about 10 secs i see the dreaded smoke from the voice coil .

I've never done any real electrical repairs before so i need all the help i can get. I've been reading up on various websites and it seems these symptoms are most likely due to blown output transistors.
What else is likely to have gone with the output transistors? can i check the power transistors while they are on the pcb or do they need removing? How can i test the input side of the amp is ok?

Pcb:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.


Also there is a burnt resistor (circled) but i cant read the stripes on it to replace it.

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Old 8th February 2010, 07:37 PM   #2
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Wow! this one has seen better days... Well to begin with the burnt resistors are the current limits for the 16 volts lower rails as i recall they do appear to be directly in front of the two zener diodes for this supply located dead center of the board.
I would ohm these out to see what they read or if they are open, and if the 16 volt zeners are actually supplying their rated voltage. LMK what you find there please...We will need to get this functional to see if the front end op-amps are blown also. This supply is tightly designed so if there are any defective ICs in the front end the supply will drop below the 16 volt designed output and it will smoke these big resistors along with the diodes in front of them.
The little resistor in the middle that is burnt black is most likely the ground connection inside the amp and it must be replaced and I believe its a 10 ohm or 1 ohm 1/2 watt carbon film 5% tolerance. I will look see if I can find one of these in my scrape pile to compare with. Since its been a few years since I repaired one of these.

Next thing we will visit the channel outputs. I would again ohm these out looking for shorted mosfet power transistors mounted on the sink. Any of these reading less then 300 ohms I would consider suspect, and you will most likely see them reading dead shorted at 4 ohms or less across any two of the three terminals of each device.

Now this amp uses a unique bias drive circuitry that uses zener diodes to keep its bias and drive as linear as possible thus improving overall SQ and also making this little amp a very powerful amp also. I have seen them drive subs, and mids and tweets alike by owners.
The big draw back to the design (IMO) is that when you lose a output you most likely have zener diode damage also and a few of the mpsa transistors also get severely damaged. < they run warm to the touch normally, so under duress they get too hot and become leaky or short out completely.
The good news is that all these little parts are dirt cheap, so even if you have to gut the channel its only a few bucks to do so.
And except for the time involved its financially a pretty painless ordeal to rebuild the channel.

Now most of the resistors in this amp are 1 or 2 % tolerance and here again you must use these same tolerance parts or the channel will give you issues on rebuild. It was a fairly precise design by PG, and so it requires the same precision on rebuild to get like new results.

I am guessing out loud that this amp ran subs well into clipping in its lifetime by the looks of the damage. If you have bad outputs you can try to swap in new parts, but by my experiences on these you will get un controlled bias and rising idle current draw issues due to more defective circuitry on the board, I.E. the driver bias circuitry is most likely toast also. I have never seen one that did not have some level associated driver circuitry damage. So just doing a output swap most likely result in failure of the work, and a re-bench to reconsider what was missed.

I have looked closely at your channel outputs and when you have a failure here the large gray ceramic resistors tend to toast up and there solder joints also turn gray matte finish as they go bad. It appears that I only see one channel exhibiting this behavior and its the channel located near the speaker connection side. You will notice one of the resistors has discolored possibly from bad outputs, maybe.. This can also happen from constant clipping the amp also.

If the outputs are all good then all the damage may just be those three burnt resistors in the middle of the board. I have seen a few lucky breaks on these since PG designed them to break in a safe manner by engineering then to burn resistors not the whole amp. Perhaps this one will be like that.

All of the above info is either from experience or details I garnered from PG directly over the last 20 years or so. I myself was a big PG fan for this time period. PG was recently sold off to AAMP/ Stinger out of Florida USA. Perhaps a phone call or a kind request will get you the support documents from them.
LMK what you find and I will try to give a much help as I can to your efforts. But if you not a tech then you might want to look up Marko on this forum as he is a resident of your country and I know he has some experience with Pg amps, perhaps a PM to him may also be helpful, tell him I sent you, he will remember me I think...
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Old 8th February 2010, 11:55 PM   #3
fbc is offline fbc  United Kingdom
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wow thank you for such a detailed reply.

Quote:
Originally Posted by 1moreamp View Post
Wow! this one has seen better days... Well to begin with the burnt resistors are the current limits for the 16 volts lower rails as i recall they do appear to be directly in front of the two zener diodes for this supply located dead center of the board.
Quote:
Originally Posted by 1moreamp View Post
I would ohm these out to see what they read or if they are open, and if the 16 volt zeners are actually supplying their rated voltage.
I didn't think these looked burnt myself , I've put an meter across them and they read around 240ohms. seem reasonable??

As for testing the zener diodes, where should i take a volt reading from?

Quote:
Originally Posted by 1moreamp View Post
The little resistor in the middle that is burnt black is most likely the ground connection inside the amp and it must be replaced and I believe its a 10 ohm or 1 ohm 1/2 watt carbon film 5% tolerance.


Right that is a big help, i've put the meter across it and its reading around 100 ohms so something aint right. I cant see what colours the bands were to find out what it was though.

Quote:
Originally Posted by 1moreamp View Post
Next thing we will visit the channel outputs. I would again ohm these out looking for shorted mosfet power transistors mounted on the sink. Any of these reading less then 300 ohms I would consider suspect, and you will most likely see them reading dead shorted at 4 ohms or less across any two of the three terminals of each device.


none of the power transistors or output transistors read below 300 ohms between any two of their 3 terminals.
But do i need to remove them from the pcb to read them properly though? While they are still connected the meter might be reading parallel components? i dunno?


Quote:
Originally Posted by 1moreamp View Post
I have looked closely at your channel outputs and when you have a failure here the large gray ceramic resistors tend to toast up and there solder joints also turn gray matte finish as they go bad. It appears that I only see one channel exhibiting this behavior and its the channel located near the speaker connection side. You will notice one of the resistors has discolored possibly from bad outputs, maybe.. This can also happen from constant clipping the amp also.


now you point it out, both channels have dull solder joints on 1 or more of the large grey resistors, I've put the meter across them aswell and the two together (on both sides) read about 2.8 ohms, and the one on its own (again both sides) reads about 195 ohms.
Any idea what they should be?

Quote:
Originally Posted by 1moreamp View Post
If the outputs are all good then all the damage may just be those three burnt resistors in the middle of the board. I have seen a few lucky breaks on these since PG designed them to break in a safe manner by engineering then to burn resistors not the whole amp. Perhaps this one will be like that.


Well thats good, at least there is some hope for me then

Quote:
Originally Posted by 1moreamp View Post
PG was recently sold off to AAMP/ Stinger out of Florida USA. Perhaps a phone call or a kind request will get you the support documents from them.


I have e-mailed PG asking for a schematic, havent heard back yet though.

Quote:
Originally Posted by 1moreamp View Post
LMK what you find and I will try to give a much help as I can to your efforts. But if you not a tech then you might want to look up Marko on this forum as he is a resident of your country and I know he has some experience with Pg amps, perhaps a PM to him may also be helpful, tell him I sent you, he will remember me I think...


Thats very kind of you, and no i'm not a tech but i would like to learn more about this, i have time on my hands at the moment so i dont mind putting the hours in to learning more, it is nice to have someone take the time to explain it to me though, you clearly know your stuff!
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Old 9th February 2010, 03:40 AM   #4
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Ok from the top to the bottom with reply's.

Well 240 ohms sounds good at this point, I have not found my dead amp to compare to yet, but the number sounds good. these are both showing signs of excessive heat but if they read the same we may be good enough to move on, and look back a bit later.
As for the diodes they will short out internally so if they do not read shorted with your meter again here we may be good enough to look back later to polish this area before we close the unit up. You might touch up all the solders for these devices, they got real hot and the solder may be taking a beating here.
You will need to ground your meter to the RCA shield or the center tap of the power transformer. Then using the red probe you should read both sides of each diode on voltage scale until you see which sides are grounded. The other side will show you the rail supply and it should be 16 volts give or take 5%. I have seen these voltages not be balanced I.E. not absolutely equal. In a perfect world they should be equal, again apply the 5% rule since this is the tolerance of the zener diodes.

As for the little burnt carbon film I will need to dig in the morning to get you a real number at least for now we are addressing it though until tomorrow...



If all the outputs read Ok < above 300 ohms > leave them for now. Once we get the amp powered up and in test we will determine of they are leaky or not, and pass judgment then on them, and the associated driver circuitry by testing for excessive DC offset voltage at the speaker terminals, and drifting bias drive of the output stages. This drifting will look like a rising current draw while the amp idles with no signal and load on the bench. The hotter the amp gets the worse the condition gets until failure is achieved. So if you detect this scenario then we want to keep power on the amp for limited time periods until we correct the issues and get it stable.


Big ceramic resistors... The 2.8 is close enough for now, and the 180 ohms is AOK cause its actually a 200 ohm resistor and these like to cook off and cause distorted issues. I would apply a tiny bit of electronics grade solder flux and touch up each solder connection of these three devices in each channel.
I have seen bad solder cause a weak and distorted sound issue. "remember Pg designed in resistors that blow and disconnect like fuses in over current conditions" this makes repair cheaper then rebuilding the whole amp.

PG had a habit of NOT answering emails outside the USA and were known for leaving this business segment to their offshore reps. I have no idea if their is a rep in England currently. I do know I hear from Marko a lot for the last few years so I am guessing not.


I know I sent Marko the only XS print I had for a XS-6600, I can't seem to find my copy currently. This doc would be helpful to you, but still not the exact amp you have it would give you a idea what the layout is your dealing with. Vague but still helpful just the same.

I thank you kindly for your praise, but were not out of the woods yet. I have seen these not worthwhile in the end. I am hoping we both miss that boat this time

Let me know your status tomorrow its 8:35PM here now. I need to close up a PC I am working on so it will get delivered tomorrow. We can continue more then hopefully after I go through one of my stacks and get your exact Xs amp on my bench to compare to....Best regards....C
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Old 9th February 2010, 02:10 PM   #5
fbc is offline fbc  United Kingdom
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Quote:
Originally Posted by 1moreamp View Post
You will need to ground your meter to the RCA shield or the center tap of the power transformer. Then using the red probe you should read both sides of each diode on voltage scale until you see which sides are grounded. The other side will show you the rail supply and it should be 16 volts give or take 5%. I have seen these voltages not be balanced I.E. not absolutely equal. In a perfect world they should be equal, again apply the 5% rule since this is the tolerance of the zener diodes.
ok, i have tried this and got over 15v from both zeners but have discovered a strange sound about 5 seconds after connecting the remote voltage. I didn't want to hold the power on incase it was doing more damage, so this meant i only had a 5 second window to test the zeners, so i'm not sure of an exact reading or how balanced they are.

The noise is like a fast switching sound, like a relay opening and closing really fast. I'm not sure how to describe it better really. I can try to listen for its location on the board, i just didn't want to hold it on for very long.


Quote:
Originally Posted by 1moreamp View Post
PG had a habit of NOT answering emails outside the USA and were known for leaving this business segment to their offshore reps. I have no idea if their is a rep in England currently. I do know I hear from Marko a lot for the last few years so I am guessing not.


I've had a reply from them, i'm told they dont have the schematic, only the owners manual.



Thanks again for you help, its very much appreciated.
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Old 10th February 2010, 04:36 PM   #6
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Send me a PM with your direct email, I found the document I wanted to send you....
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