I don't known about the FT317/417s in Threshold equipment but in Ampzilla (and relatives) and in Mark Levinson that have an iffy history.
Craig
Craig
I think I have the schematic right now. It will be a few days before I get time to check voltages.
I pulled what I called transistor 6 & 7 and the negative voltage on the plus side went away. The only thing that get hot with them out is the transistor I called 16. The voltage on 16 with +/- 37 volt input are e=-29 b=-29 c=-1.4
Good. Now that you have symetric voltages on the plus and minus side, just check the power transistors.
Which transistor is "16" on the circit diagram ?
Which transistor is "16" on the circit diagram ?
If you can touch "16", then it is not problem. It was probably getting hot also when 6&7 were connected.
You can re-check it after everything is back in.
You can re-check it after everything is back in.
I still need to figure out what to do with 6 & 7. The transistors I pulled out test fine. I don't know if they are the problem. I may try a sub to see what happens. I need to see what will work in place of the MPS-L01. Any thoughts.
Well I sub a fair match for the L01s and had full voltage and things looked good. Then I shorted something. Time to start over. I definitely blow one of the L01s this time. Now I need to find a good sub.
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http://www.diyaudio.com/forums/pass-labs/55055-threshold-400a-parts-substitution-mods.html
Here NTE54/55 is offered as sub to FT317/417 and it looks same as MJE15030/31. They also offer "matched pairs".
FT317 NTE Equivalent NTE54 NPN audio power amplif... - Wholesale Electronics
NTE54 - NTE ELECTRONICS - BIPOLAR TRANSISTOR, NPN, 150V, TO-220 | Newark element14
Here NTE54/55 is offered as sub to FT317/417 and it looks same as MJE15030/31. They also offer "matched pairs".
FT317 NTE Equivalent NTE54 NPN audio power amplif... - Wholesale Electronics
NTE54 - NTE ELECTRONICS - BIPOLAR TRANSISTOR, NPN, 150V, TO-220 | Newark element14
I am still missing something somewhere. I rechecked everything and found a 300 ohm resister at 1k. Every thing else seems fine. Here are voltage readings at the transistors taken with 10 volts +/- input. Maybe someone will see something and give me a clue.
trans #
400and4000 B
trans #
To start with replace all the old electrolytic and tantalum caps before going farther.
Change the tantalums to bipolar electrolytics
Change the tantalums to bipolar electrolytics
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All caps are now film except for 47uf and 220uf at the input. Right now they are polar electrolytic. The picture with the numbers is an old one from when I first started. I needed something to keep the transistors straight.
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Transistor 8 is connected with source and collector reversed. Schematic is correct, actual transistor connected wrong on pcb.