Input socket or something else on amplifier is broken - diyAudio
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Old 25th April 2015, 06:03 PM   #1
diyAudio Member
 
Join Date: Apr 2015
Default Input socket or something else on amplifier is broken

Hi to everybody
I hope i have placed this in the correct section. I have read the rules.

I have a Skytec PA 2500 amplifier. It has two speakers connected via speakon cables.
The audio source is connected to the amplifier via a mini jack stereo cable on one end and then 2 X mono jack (1/4) into the amplifier. I have tested both cables and i have come to the conclusion that one of the sockets is not working. Maybe it is not the socket itself but some part inside the amplifier, that's why im here now.

I have taken some pictures of the amplifier and the faulty socket.

This is the back panel of the amplifier if it means anything:
Click the image to open in full size.
The faulty socket(it's the socket on the left of the photo):
Click the image to open in full size.
This is the left/right socket circuit board, i just took this picture because one of the solder points has that brown around it;
Click the image to open in full size.

Can anyone please help me?

I really miss being able to use this system for parties.
I would be very gratefull and if it is allowed in this forum i can give my helper a small bitcoin donation, don't expect a huge amount. It would be a gesture more than a "salary".

Last edited by BreachOfEuphoria; 25th April 2015 at 06:26 PM.
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Old 26th April 2015, 03:44 AM   #2
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
First, what exactly is wrong? You suggest the input jack is bad, but is the problem that nothing comes out one speaker?

Use the system to isolate the problem. I assume one side works? So right side is dead and left side works? So do this connect the system and power up. Put a signal into the amp and we expect sound from the left speaker. First we verify the speakers are OK, so unplug the speaker cord from each channel and plug it back into the other channel in each case. In other words the left channel now is connected to the right speaker and the right channel to the left speaker. Does the other speaker now remain silent? or does the same speaker remain silent? That will tell us if the speakers and cords are OK.

Assuming the speakers are OK, then restore the connections to original state. Now we have sound out the left again. Now trade places with the input cords. Did the problem stay with the right or did it move to the left. if it moved, then the source is the issue.

But if we verify the source and speakers are OK, then the amp has the issue. I can't read what the switch is for in the rear. is that a bridge/stereo switch? Is it in stereo mode then? You are using 1/4" inputs, have you tried feeding the amp with the XLR input on the same jack? Are there VU meters on the front? or maybe a signal indicator LED? If so is there indications of signal on the right or only the left?

When you first turn the amp on, is there normally a speaker relay clicking in? if so do you hear both channels or just one clicking in? If no relays, is there any thump or pop at turn-on in the right side? Once it is on is ther any background sound in that speaker to let you know at least the amp is alive? Got volume controls? Turn the right one up and down, does the background sound go up and down with it?

You appear to have the input jack board out of the amp chassis, so with the amp running and the volumes up, look where the cable from that board back to the main circuit board connects. You should be able to tell which connections are left, right, and ground. Touch left and right connections right there, one side at a time. use something metal, like a probe tip or a small screwdriver. A working channel ought to make some small hum when you touch. if the good channel does this, so should the other, if the amp works. If both sides work like that, then you probably do have a jack problem, but if the right side still makes no hum, then likely the jacks are not the issue.

Without schematics it is difficult to advise further, but wwith signal applied to both, you might scope at the volume controls to see if signal gets that far. And if it doesn't you could probably inject a signal at that point to see if the rest of the channel functions.
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Old 26th April 2015, 04:16 AM   #3
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Join Date: Mar 2013
Quote:
Originally Posted by Enzo View Post
First, what exactly is wrong? .
X2. We know you think you have an input connector problem but why do you think that? The position on that switch on the back near the power cord is important as is whatever indicators and controls the amp has on the front panel, and it is also important to know exactly what the amp is and is not doing in terms of sound output, so fill in those blanks and maybe we can help sort it out.
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Old 26th April 2015, 02:34 PM   #4
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Join Date: Apr 2015
Thank you for your answer

Quote:
Originally Posted by Enzo View Post
First, what exactly is wrong? You suggest the input jack is bad, but is the problem that nothing comes out one speaker?

Use the system to isolate the problem. I assume one side works? So right side is dead and left side works? So do this connect the system and power up. Put a signal into the amp and we expect sound from the left speaker. First we verify the speakers are OK, so unplug the speaker cord from each channel and plug it back into the other channel in each case. In other words the left channel now is connected to the right speaker and the right channel to the left speaker. Does the other speaker now remain silent? or does the same speaker remain silent? That will tell us if the speakers and cords are OK.
It's definitely something on the amplifier. Both the speakers and both the cables are working fine.
Quote:
Originally Posted by Enzo View Post
Assuming the speakers are OK, then restore the connections to original state. Now we have sound out the left again. Now trade places with the input cords. Did the problem stay with the right or did it move to the left. if it moved, then the source is the issue.
The problem stayed with the right.
Quote:
Originally Posted by Enzo View Post
But if we verify the source and speakers are OK, then the amp has the issue. I can't read what the switch is for in the rear. is that a bridge/stereo switch? Is it in stereo mode then? You are using 1/4" inputs, have you tried feeding the amp with the XLR input on the same jack? Are there VU meters on the front? or maybe a signal indicator LED? If so is there indications of signal on the right or only the left?
It's a "Signal ground lift/Ground" switch.

I'm going to take some pictures again and edit this post or include them in my next post to try and answer the rest of you questions.
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Old 27th April 2015, 03:10 PM   #5
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Join Date: Apr 2015
Quote:
Originally Posted by Enzo View Post
But if we verify the source and speakers are OK, then the amp has the issue. I can't read what the switch is for in the rear. is that a bridge/stereo switch? Is it in stereo mode then? You are using 1/4" inputs, have you tried feeding the amp with the XLR input on the same jack? Are there VU meters on the front? or maybe a signal indicator LED? If so is there indications of signal on the right or only the left?.
There are no VU meters on the front. This is how the front looks
Click the image to open in full size.

Quote:
Originally Posted by Enzo View Post
When you first turn the amp on, is there normally a speaker relay clicking in? if so do you hear both channels or just one clicking in? If no relays, is there any thump or pop at turn-on in the right side? Once it is on is ther any background sound in that speaker to let you know at least the amp is alive? Got volume controls? Turn the right one up and down, does the background sound go up and down with it?

You appear to have the input jack board out of the amp chassis, so with the amp running and the volumes up, look where the cable from that board back to the main circuit board connects. You should be able to tell which connections are left, right, and ground. Touch left and right connections right there, one side at a time. use something metal, like a probe tip or a small screwdriver. A working channel ought to make some small hum when you touch. if the good channel does this, so should the other, if the amp works. If both sides work like that, then you probably do have a jack problem, but if the right side still makes no hum, then likely the jacks are not the issue.

Without schematics it is difficult to advise further, but wwith signal applied to both, you might scope at the volume controls to see if signal gets that far. And if it doesn't you could probably inject a signal at that point to see if the rest of the channel functions.
I'm sorry for the very blurry photo
Click the image to open in full size.
The switch reads; "Signal ground lift/Ground"
The fuse is a 10 A.

I have tested the left and the right channel with the screwdriver trick you advised me.
The top circuit board is for the left output channel
The bottom circuit board is for the right output channel.

Click the image to open in full size.
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Old 28th April 2015, 12:21 AM   #6
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
Right above and below the "PA2500" on the front panel, I see two rows of what look to be LEDs. Are they not volume indicators? That is a form of VU meter. A VU meter doesn't have to be an actual meter with a moving needle. So we are wondering if those indicate signal on both channels or only the good side.

So what happened when you touched those inputs?

Am I correct that the two volume controls and the peak lights near them are all on a smaller circuit board? Can that board be taken off the panel for access while the amp is running?
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Old 29th April 2015, 07:50 PM   #7
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Join Date: Apr 2015
Quote:
Originally Posted by Enzo View Post
Right above and below the "PA2500" on the front panel, I see two rows of what look to be LEDs. Are they not volume indicators?
No they are just holes, maybe ventilation holes.
Quote:
Originally Posted by Enzo View Post
That is a form of VU meter. A VU meter doesn't have to be an actual meter with a moving needle. So we are wondering if those indicate signal on both channels or only the good side.

So what happened when you touched those inputs?

Am I correct that the two volume controls and the peak lights near them are all on a smaller circuit board? Can that board be taken off the panel for access while the amp is running?
Yes you are correct, they are on a smaller circuit board. Yes it can be taken off while the amp is running, i just gotta make sure it stays put so i don't electrocute myself.

Well i had my head under my arm the other day when i wanted to remove that little circuit board and i managed to rip off the volume potentiometers (if that's what they are). I'm sorry Enzo.

Now i'm trying to find somewhere to buy these electronic components again.
These are the "volume knobs" (not really i know)
Click the image to open in full size.
One person i asked believed they were 10k audio taper potentiometers.
Another person believes they are variable resistors.

This is the circuit board they were attached to. The two potentiometers were attached to the two black components on the circuit board in the lower left and lower right corner ( but i'm sure you allready knew that ):
Click the image to open in full size.

I'm going to try to find the schematics, because you mentioned it and also so i can try and contact the manufacturer.
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Old 29th April 2015, 09:27 PM   #8
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
One of the controls I can see printed on it that it is 10k audio taper.

If I take a small board like that out of a chassis while it is running, I usually fold up a towel or maybe use a magazine or newspaper to put under it so it won't touch anything else and short out.
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Old 21st May 2015, 01:52 PM   #9
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Join Date: Apr 2015
I have gotten the amplifier to work now! I'm sorry for taking so long to respond in this thread.
It was a broken potentiometer that caused the right channel to be dead

In the end it was a good thing that i ripped off that circuit board.

I ordered some new logarithmic potentiometers that needed some adjustments before they would be able to be soldered onto the circuit board but i made them both fit.
Both left and right channel works again now

I just need to find some QUALITY speakon to jack cables now. Anyone knows which brand is worth buying?

I can understand that the whole "Gold plated connectors" and "oxygen free" marketing technique only improves sound quality marginally.

Thank you for your help Enzo !
My offer for the BTC donation still stands but thats up to you.
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