nashou
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Post by nashou on Nov 1, 2016 10:21:45 GMT -5
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Post by mastertech on Nov 1, 2016 11:18:06 GMT -5
That looks fine.  |
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nashou
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Post by nashou on Nov 1, 2016 12:26:11 GMT -5
Thanks Mac. Not sure how to procede with this amp. I got the Dual Fets and replaced them but the voltage went down again on the -25 volt rail again.
I posted over on Audio Karma more info.
Nashou
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nashou
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Post by nashou on Nov 1, 2016 12:58:06 GMT -5
I ordered these diodes as well just to have on hand for this amp.  |
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Post by mastertech on Nov 1, 2016 18:02:23 GMT -5
Never hurts to have extra parts on hand.
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nashou
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Post by nashou on Nov 11, 2016 17:18:18 GMT -5
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Post by mastertech on Nov 12, 2016 11:29:34 GMT -5
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nashou
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Post by nashou on Nov 12, 2016 16:15:58 GMT -5
Yeah I have looked at those parts. Might try the cheap ones till it works. I did take two apart and made one good one.
One thing that is weird is that in my parts tester if i flip the pins around they identify the source and drain on the ends in the same fashion. so no matter what orientation it is the source always stays on slot 1 in
my parts tester. It seams from my research that it doesn't matter with N channel J Fet's . the source and drain are reversible . SO i will try the jerry rigged part tonight and see if it blows. I don't see why it will again, the -14 volt
on the S or D seems with in range of the Fet.
Nashou
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nashou
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Post by nashou on Nov 12, 2016 18:57:55 GMT -5
Ok this is where I am. With the Gerry rigged sk146( TR108 made from two good half's ) I got the proper voltages for that channel( Right).
But TR107 blows out the half that is connected to TR105 .
At the Gate of TR107 I get about -4.57 volts where it should be 0. and fort he source i get -11 or a bit more. it changes the longer i keep it there. it use to be stable at 13.66
the other half seem fine except for the Source since its connected to the other half of the N J-Fet.
I changed D109 and D110 to be safe that wasn't the issue, I also pulled TR105 and it tested good. But could it be bad or leaky causing the one half of TR107 to blow?
Reading back I think I pulled and tested almost every Transistor.
Not sure where to proceed from here. But at least I now know which half of TR107 is getting damaged.
Edit: Just to mention with TR108 removed and TR 107 removed I got the same -13.66 at the sources for both Transistors but the gates were different.
Posted this same find over at AK as well.
Nashou
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Post by mastertech on Nov 12, 2016 22:33:09 GMT -5
Pull TR107 and TR105 and having all other components installed. Then test the voltages on the pads of these 3 devices (9) points. Give me these 9 voltages.
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nashou
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Post by nashou on Nov 13, 2016 7:17:09 GMT -5
Pull TR107 and TR105 and having all other components installed. Then test the voltages on the pads of these 3 devices (9) points. Give me these 9 voltages. Well TR107 was pulled when I tested. And I did test with TR 105 out but forgot the numbers. Will do this later today after work . Nashou |
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nashou
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Post by nashou on Nov 13, 2016 16:40:29 GMT -5
Ok ,
TR107 has 6 pins row one connects to TR103 which is still populated.
On bottom side of PCB from right to left I believe the pins are
Row 1
D=.3 mV, G=7.6 mV, S=-11.14 VDC
Row 2( connected to TR105 removed)
S=-11.14 VDC, G= -3.97, VDC D=.5 mV
Now TR 105
E=.5 mV, C= +24.75 VDC , B = -4.82 VDC
Looks like the -4.82 at the base of TR105 should be a positive voltage. Hmmm
Athanasios
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Post by mastertech on Nov 13, 2016 18:36:44 GMT -5
Test voltage on both sides of R113.
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nashou
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Post by nashou on Nov 13, 2016 18:51:53 GMT -5
Test voltage on both sides of R113. On the side connected to the base of TR105 its -4.8 and on the other side it's as it should be +24.74 Athanasios |
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Post by mastertech on Nov 13, 2016 19:20:24 GMT -5
That does not look right. If you can, lift 1 leg of that resistor, the side to TR105 and then do value test and then voltage test again on lifted leg of resistor.
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