400SII popped and died

Jess said:
I installed the second row and the left bias min/max was 0.290 - 0.508 and the right was 0.280 - 0.497.

I installed the third row and around 30v I noticed my 100w bulb started glowing. I checked rail voltage and B- was around 0.5v and B+ was at 1.2v
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Appears you may have a leaker in the third row you installed. Don’t adjust the bias up to max after you install the second row of outputs as you risk cross conduction and damage to outputs. Leave at minimum until all installed and no glowing bright DBT
 
Hey, just wanted to thank you all for the help. I appreciate it a ton. I had press pause on this for a day but hopefully I'll get back on it tonight or tomorrow.

I did try swapping the 3rd row set of transistors with the last set I had yet to install just to see if it behaved differently and it did not. Is it worth it to swap out transistors one at a time to see if there's a bad one or do you think leak is coming from a cap on the boards?

I have the resistors on the output+ground test points, DCP isn't hooked up yet so the speaker posts aren't connected.
 
Jess said:
Hey, just wanted to thank you all for the help. I appreciate it a ton. I had press pause on this for a day but hopefully I'll get back on it tonight or tomorrow.

I did try swapping the 3rd row set of transistors with the last set I had yet to install just to see if it behaved differently and it did not. Is it worth it to swap out transistors one at a time to see if there's a bad one or do you think leak is coming from a cap on the boards?

I have the resistors on the output+ground test points, DCP isn't hooked up yet so the speaker posts aren't connected.
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Hi Jess
You are only swapping in the transistors, the caps are always there so if they were leaking (very doubtful) you would be experiencing the leakage all the time, not just when you installed the next row of transistors. Your DBT should behave the same way for each row of devices installed. From your message it seems that is not the case in your amp so you should try and weed out the offending transistor(s)
 
Hey all!
It's been a while but I wanted to post an update to this and give thanks for all of your input and help. A bunch of stuff happened after my last post and Joe graciously helped me over email. The short version is I ended up cutting one of the silpads while inserting a screw which caused a short on the collector and shot sparks in my face. I took everything to my cousin who helped me diagnose near every component and fix a few solder joints. I ended up replacing 3 output transistors. Bring up was smooth and after 24 hours of nonstop music through it, I'm cautiously optimistic that the next time I open it will be to install a new meter board lol.

Anyway, thank you all again for the help and I hope everyone is staying safe out there.
Jess
 
Jess said:
Hey all!
It's been a while but I wanted to post an update to this and give thanks for all of your input and help. A bunch of stuff happened after my last post and Joe graciously helped me over email. The short version is I ended up cutting one of the silpads while inserting a screw which caused a short on the collector and shot sparks in my face. I took everything to my cousin who helped me diagnose near every component and fix a few solder joints. I ended up replacing 3 output transistors. Bring up was smooth and after 24 hours of nonstop music through it, I'm cautiously optimistic that the next time I open it will be to install a new meter board lol.

Anyway, thank you all again for the help and I hope everyone is staying safe out there.
Jess
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Thanks for the update. I think it would be a good practice for all of us to do a transistor case (collector) to chassis ground check after both screws on all the installed output transistors have been torqued to the proper specification (I think that was 6-8 inch-pounds).
 
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