Control board voltage problem

roccus

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#1
On the +15V test pin on the control board I am getting +15.2V so that is good but on the -15V pin I am getting +1.3V I pulled and checked Q2 and VR2 but they are both ok... maybe a diode blown?
 

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#3
On the +15V test pin on the control board I am getting +15.2V so that is good but on the -15V pin I am getting +1.3V I pulled and checked Q2 and VR2 but they are both ok... maybe a diode blown?
You cannot realistically check VR2, it is an integrated circuit, not a transistor.
 

roccus

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#4
You cannot realistically check VR2, it is an integrated circuit, not a transistor.
VR2 is a regulator with resistance right? so if it was bad it would be open on one side or the other correct? I see V2 basically as a dual resistor may be wrong.....
 
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#5
VR2 is a regulator with resistance right? so if it was bad it would be open on one side or the other correct? I see V2 basically as a dual resistor may be wrong.....
That is not the way to look at it Ray. If it is not regulating, VR2 is your likely problem.
 

roccus

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#6
That is not the way to look at it Ray. If it is not regulating, VR2 is your likely problem.
Hi Joe please forgive me for my ignorance on this... if V2 does not use resistance to regulate then how does it regulate? How can you test V2? And is V2 a standard TL431 or custom??
 

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#7
Hi Joe please forgive me for my ignorance on this... if V2 does not use resistance to regulate then how does it regulate? How can you test V2? And is V2 a standard TL431 or custom??
It is an op amp coupled with a precision voltage reference and an open collector output transistor inside that TO-92 package. Not a resistor at all. It is a sophisticated integrated circuit.


You can test if it is bad Ray
by removing it from the circuit and replacing it with a new one. It is a standard TL431AI device.

First make sure you have -78V coming in on both left and right channels on PAD 12. If you are getting plus voltage on the negative regulator, that is likely a key suspect.
 
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roccus

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#8
It is an op amp coupled with a precision voltage reference and an open collector output transistor inside that TO-92 package. Not a resistor at all. It is a sophisticated integrated circuit.


You can test if it is bad Ray
by removing it from the circuit and replacing it with a new one. It is a standard TL431AI device.

First make sure you have -78V coming in on both left and right channels on PAD 12. If you are getting plus voltage on the negative regulator, that is likely a key suspect.
Thanks think I got it I will also do as JB suggested and check D81
 

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#9
And check Pad 12 for negative rail voltage as Joe suggested. You have to know if you have voltage enough to regulate..
 

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#10
And check Pad 12 for negative rail voltage as Joe suggested. You have to know if you have voltage enough to regulate..
Thanks Lee I did check the rectifier at the power supply and it is ok.... so something in between there and Q2 is toasted
 

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#14
Checked out pad 12 on right and left channel right channel is good -83V but right channel is +3 volt looked at pico fuses on right channel backplane and the B- fuse is open... I know I don't have any of these around here so looks like my amp will be out of commission for at least another week or so to get replacement fuse :(
 

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#15
That fuse prevented the roasting of the predriver on the control board, ergo, it did it's job. As an assembler of a lot of control and backplane boards one of the first things I did was order 100 spare pico fuses. Unless a guy is doing a lot of it, it really doesn't make sense to stock up on these types of components..........................


BUT..... When you do encounter these types of problems, when ordering replacements , a few more doesn't cost much at all, but you probably already knew that....:-D
 

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#16
i
That fuse prevented the roasting of the predriver on the control board, ergo, it did it's job. As an assembler of a lot of control and backplane boards one of the first things I did was order 100 spare pico fuses. Unless a guy is doing a lot of it, it really doesn't make sense to stock up on these types of components..........................


BUT..... When you do encounter these types of problems, when ordering replacements , a few more doesn't cost much at all, but you probably already knew that....:-D
This would be very helpful if you lived next door.. never a Lee around when you need one! lol But ya when I order a part I get a few extras I have hundreds of dollars of components kicking around here but still never have the part I need :tard:
 
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