Busted XR-1200?

[Novo]

I have an XR-1200 that has developed a waterfall (lacking better descriptors) sound when I run A and B up. The more the mains are up channels are up the louder the sound. The amps run fine plugged in directly...bypassing the mixer and the eq. I re-did the voltage regulators (on the main board) and a diode about two years ago.

I need it working or I need it out of the shop...

Thank you,


Novo

P.S. Peavey said clean the input/output switching jacks...did that. Also tried unplugging connections between them and the main board....no luck.

[Enzo]

I responded to this where you posted it somewher else.

Your power amps are clean, so zero all the channel faders, bring up the masters. If the masters still are noisy, it isn't from the channels so look for a noisy op amp in the master section. With the masters up, bring each channel fader up then back down to see if it is particulaly noisy. Don;t forget the trim controls. If individual channels ir pairs of channels are noisy, probably a noisy IC. If they all are equally noisy, then likely that is the stock noise level.

[Novo]

Busted xr1200

I responded to this where you posted it somewher else.

Your power amps are clean, so zero all the channel faders, bring up the masters. If the masters still are noisy, it isn't from the channels so look for a noisy op amp in the master section. With the masters up, bring each channel fader up then back down to see if it is particulaly noisy. Don;t forget the trim controls. If individual channels ir pairs of channels are noisy, probably a noisy IC. If they all are equally noisy, then likely that is the stock noise level.

First off, thank you so very much for your help!

Oh, checked output from mixer to another amp...same distortion.


OK, finally got around to doing some real testing. First off, channel b amp, all things down has what sound like a 60hz hum. Channel a, all down, no hum. Take either channel up at the mains and I get the hiss like an un-tuned radio. Take levels up, it gets louder. Channels 1, 11 ans12 don't want to play at all, but that is for later. I get monitor sends on both channels fine...with b still humming. EQ in and the out to a amp is great. EQ b in and out to amp still hums, but no am noise.

When I turn it on the led level indicator lights up to 6 and then gradually drops to nothing.

So, how do I test for a noisy IC?

Thanks again,

Novo

[Novo]

From speaker terminals a channel, I get neg 2.6 with meter set at 200m dcv. On channel b amp out I get .6 with meter set at 200m. At power to the master board I get 16v with meter set on ACV.

[Enzo]

We are still isolating the problem though. When you turn the masters up and down and the hiss goes up and down with them, that means the hiss is coming from before them. SO that is why I asked if it still hisses with the master up but ALL the channels at zero.

We also wanted to know if all the input channels are equally guilty or of there are only one or two that hiss. So we want to turn the masters up so we can hear it, then with all faders at zero, bring each one up to listen then hack to zero, and move to the next. You have determined that three channels don't work, but are the others noisy individually or all about the same?

How do I test for a noisy IC? I scope at its output. But mainly what I do is isoloate the problem to the IC. If the noise comes out of it, but was not going into it, then it pretty much has the be the problem. And at that point I ssimply replace it and find out.

[Novo]

Busted xr1200

We are still isolating the problem though. When you turn the masters up and down and the hiss goes up and down with them, that means the hiss is coming from before them. SO that is why I asked if it still hisses with the master up but ALL the channels at zero.

We also wanted to know if all the input channels are equally guilty or of there are only one or two that hiss. So we want to turn the masters up so we can hear it, then with all faders at zero, bring each one up to listen then hack to zero, and move to the next. You have determined that three channels don't work, but are the others noisy individually or all about the same?

How do I test for a noisy IC? I scope at its output. But mainly what I do is isoloate the problem to the IC. If the noise comes out of it, but was not going into it, then it pretty much has the be the problem. And at that point I ssimply replace it and find out.

If all the channels are down and 0'ed the hiss/static goes up and down with the main level control. The channels do not seem to affect the volume of the hiss...as in I take up channel 2 or eight and the hiss does not get louder until I change the main volume control. A channel, all down, still has a slightly louder than normal background hiss while channel B has a hum (60hz?) while Zeroed out and then a hiss like on channel A when you up the level. Again, as far as I can tell the channel levels don't seem to affect the hiss...but I see what you mean...it has to come in before the master level controls.

Thank you for your help and guidance.

Novo

[Novo]

My daughter and I ran her I-Pod through a couple of channels and we have clear but slightly bright audio on top of the hiss on channel A. Channel B has that hum as well as the hiss and the audio, to my ear, is slightly muffled. Could this be a dreaded jack issue?

[Enzo]

Jacks don't make hiss. You may have more than one issue, but let us work on one at a time.

We have now determined that the hiss comes from before the master controls and after the channels.

Looking at the schematic, I see U1 before the master volume controls and the inputs to U1 are the channel busses. So I suspect U1. Aren't the ICs in sockets on this board? Look between the two main faders, should be two small 8-leg ICs. The one near the top is U1. Right above it is U2, between the monitor A and B controls. It is the same type. Try swapping them and see if the hiss moves to the monitors and the mains get more quiet.

[Novo]

Sorry to have dropped off the face of the earth...Switching the ICs did not change anything. I did notice while testing that the channels do impact the loudness of the hiss somewhat. I also noticed that the case was bleeding a little electricity... I get a slight shock which I know is not normal. I am going to check how much with the meter.

Thank you,

Novo