Control board voltage problem

roccus

roccus

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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?
 
Check D81 for short. Should read normal with the meter set for diode check.

(I just went through this myself but with the positive 15 volts):cheers:
 
roccus said:
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?
Click to expand...

You cannot realistically check VR2, it is an integrated circuit, not a transistor.
 
Gepetto said:
You cannot realistically check VR2, it is an integrated circuit, not a transistor.
Click to expand...

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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roccus said:
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.....
Click to expand...

That is not the way to look at it Ray. If it is not regulating, VR2 is your likely problem.
 
Gepetto said:
That is not the way to look at it Ray. If it is not regulating, VR2 is your likely problem.
Click to expand...

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??
 
roccus said:
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??
Click to expand...

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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Gepetto said:
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.
Click to expand...

Thanks think I got it I will also do as JB suggested and check D81
 
And check Pad 12 for negative rail voltage as Joe suggested. You have to know if you have voltage enough to regulate..
 
laatsch55 said:
And check Pad 12 for negative rail voltage as Joe suggested. You have to know if you have voltage enough to regulate..
Click to expand...

Thanks Lee I did check the rectifier at the power supply and it is ok.... so something in between there and Q2 is toasted
 
Guess I may have to order a TL431
 
roccus said:
Thanks Lee I did check the rectifier at the power supply and it is ok.... so something in between there and Q2 is toasted
Click to expand...
The Pico fuse on the backplane is open if you do not have -78v at PAD12
 
Gepetto said:
The Pico fuse on the backplane is open if you do not have -78v at PAD12
Click to expand...


Thank you Joe will check that as well... I hadn't considered the backplanes into this
 
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 :(
 
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
 
i
laatsch55 said:
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
Click to expand...
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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