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AU-X1

Here is a pic of mine that I posted to Harolda's resto thread.

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MINE
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HAROLDA's (from: http://audiokarma.org/forums/index....-output-transistor-replacements.684619/page-5)
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Yours
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I'm thinking of replacing the pnp 2sa917 with the ksa1381 any input on this would be great as the previous replacement 2n5400 is now obsolete.
 
 
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I replaced all of the transistors on both F-2775 boards and all of them on F-2778 and now I have a perfect -10.5v on VR03 and VR04 and a perfect -47.5v on VR01 and VR02 and on the left F-2775 bias I have a perfect 25mv but on the right F-2775 I'm getting 0.411v I'm not sure what's up with that yet?
 
Willy6 said:
I replaced all of the transistors on both F-2775 boards and all of them on F-2778 and now I have a perfect -10.5v on VR03 and VR04 and a perfect -47.5v on VR01 and VR02 and on the left F-2775 bias I have a perfect 25mv but on the right F-2775 I'm getting 0.411v I'm not sure what's up with that yet?
Click to expand...

Good work! Things seem to be improving.

What new transistors did you install? Just hoping for info about new parts being used.
 
Willy6 said:
... but on the right F-2775 I'm getting 0.411v I'm not sure what's up with that yet?
Click to expand...

This board dialed in OK before your most recent transistor installation...YES?

Put it back on the DBT to check for faults.

Confirm the ground connection at both the bottom and top of the board are good.
(That one at the bottom that screws into the filter cap mounting plate is easy to forget.)
 
Ronito6 said:
This board dialed in OK before your most recent transistor installation...YES?

Put it back on the DBT to check for faults.

Confirm the ground connection at both the bottom and top of the board are good.
(That one at the bottom that screws into the filter cap mounting plate is easy to forget.)
Click to expand...
Yes I had both F-2775 boards dialed in before I changed the transistors.I didn't have time to look at it today but I did put it back on the dbt and it shows a slight fault the 75 watt bulb go's almost completely dim but still had a faint glow through the wire and if I disconnect the wire plug from the right F-2775 board it go's completely out so there is a short somewhere on that side either on the F-2775 board or on F-2781..
 
I found the short and it wasn't on F-2775 it was a transistor that I replaced on F-2778 that must have got bumped when I reinstalled the board?All 3 pins popped through and broke 2 pads off of the trace.I found the problem when I pulled this plug out of F-2781 and the dbt went completely out.20160830_212718.jpg
 
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When I said I couldn't adjust the bias lower then 0.411v on the right F-2775 I was measuring from the wrong two emitters :( now I can't get the bias lower then 73mv and I can't find anything wrong other then the dual 2200uf 80v caps are dead but that doesn't effect the left side it adjusted spot on.The dbt go's completely out now so no short anywhere..
 
Willy6 said:
...the wrong two emitters..
Click to expand...

I was afraid of that. But I assumed the best so I did not mention that possibility.

Do you think you might have lost a couple OP transistors by dialing past their tolerance as you tried to adjust while measuring where you did.

Test those OP transistors one more time.

Otherwise, I suppose you might have lost a connection on the troublesome 2775.
Check all wires and confirm continuity.

The duals are likely OK as they send power to other major sections of the amp and those sections would fail too if those caps fiizzled out.
 
If you can't get the bias lower than 73mV - then the problem is very likely to be in the area of TR12,13,14,15,16 (or their opposite numbers in the other channel) - something preventing TR15 and 16 from turning on enough, (thus nipping the bases of the OP transistors together thus reducing bias current), that's where you need to concentrate your investigations. (either that or one or more of your emitter resistors is out of spec).
 
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Ronito6 said:
I was afraid of that. But I assumed the best so I did not mention that possibility.

Do you think you might have lost a couple OP transistors by dialing past their tolerance as you tried to adjust while measuring where you did.

Test those OP transistors one more time.

Otherwise, I suppose you might have lost a connection on the troublesome 2775.
Check all wires and confirm continuity.

The duals are likely OK as they send power to other major sections of the amp and those sections would fail too if those caps fiizzled out.
Click to expand...
OP's are still good and the duals don't charge up anymore they charged up a few times and I discharged them with a screw driver now after warming up for 20 min when I tried to discharge them nothing there but a faint spark new ones on order..
 
Hyperion said:
If you can't get the bias lower than 73mV - then the problem is very likely to be in the area of TR12,13,14,15,16 (or their opposite numbers in the other channel) - something preventing TR15 and 16 from turning on enough, (thus nipping the bases of the OP transistors together thus reducing bias current), that's where you need to concentrate your investigations. (either that or one or more of your emitter resistors is out of spec).
Click to expand...
The emitters are 0.47 ohm and they all read .4 still soldered in place.should I remove them from the circuit and re measure or just order new ones?
 
Ronito6 said:
I was afraid of that. But I assumed the best so I did not mention that possibility.

Do you think you might have lost a couple OP transistors by dialing past their tolerance as you tried to adjust while measuring where you did.

Test those OP transistors one more time.

Otherwise, I suppose you might have lost a connection on the troublesome 2775.
Check all wires and confirm continuity.

The duals are likely OK as they send power to other major sections of the amp and those sections would fail too if those caps fiizzled out.
Click to expand...
On the multi voltage export model those Dual Caps take power from F-2781 and deliver power to F-2775 they don't send power anywhere else..
 
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