400SII popped and died

[Gepetto]

What is attached to the Output and Ground test point on each backplane?

 

[FredR]

Confused by the labeling on the capacitor terminal boards. Is polarity correct?

 

[Gepetto]

Confused by the labeling on the capacitor terminal boards. Is polarity correct?

Hi Fred, if you are referring to bulk caps, yes that all appears correct.

 

[WOPL Sniffer]

DUDE!!!!! Your output wires 1 and 2 on the backplanes of both channels are FUNKY and bare They are an accident waiting to happen if they didnt already

 

[WOPL Sniffer]

As I said, inspect your soldering with a scope and if it looks like crap, reflow ALL OF THEM or your amp will not last. Pull that thing apart.

 

[WOPL Sniffer]

Some of your PEM standoffs on the back plane are pretty rough as far as soldering. They should be reflowed and "Go Easy On the Solder". Too much is sometines worse that too little.

 

[Jess]

Alright, thank you guys. I'm pulling it apart now and will get those fixed tomorrow.

On a side note, I want to replace the shielded wire from the inputs to the front panel pots and back to the control board. I was going to do this when I bought the light boards but since it's all apart now I may as well just do it. From forum searching, it sounded like RG316 was a good replacement?

 

[Gepetto]

Yes RG316 is a good option, small diameter, high quality, no shrink back.

 

[Jess]

Yes RG316 is a good option, small diameter, high quality, no shrink back.

Thanks! I picked some up along with new pico fuses. I only had one spare so I haven't replaced them yet. Got a bunch of extras just in case.

 

[Jess]

Hey guys. So I reflowed a bunch of the PEM nuts and a few other things I was concerned with. I'm happy with most of them, some look ugly but I'm pretty sure they're solid. Fixed a bunch of the wiring as well and put the new pico fuses in.

I just brought up the amp to 60V with 100W DBT and the 10k ohm resistors and I'm getting around +/-41.8v at B+/- locations and on 11&12L/R, and no voltage at output test points now. At 120V I'm at +/-84V at all locations and I'm seeing 0.5mV on the left channel output test point and 0.1mV at the Right output.

Should I add the control board+dcp+next row of transistors now?

Joe to answer your question earlier I was out of alligator clips so I soldered the 10k ohm resistors to some copper wire to make wrapping them on the test points (for Step 15 in the bring up recommendations) easier. They're now on clips.

 

[laatsch55]

Leave the DCP out for now. How does the bias look?

 

[Jess]

Leave the DCP out for now. How does the bias look?

After letting it warm for 5 minutes and the bias pots set to their minimum, I have 0.289 on the right and 0.271 on the left.

 

[laatsch55]

Observe the readings as you move the pot to each extreme, just dont leave it for long in the high extreme..

 

[laatsch55]

Just looking to see if it will adjust..

 

[Jess]

Observe the readings as you move the pot to each extreme, just dont leave it for long in the high extreme..

Both sides increase steadily with the left maxing out at 0.505 and the right at 0.484.

 

[laatsch55]

Looks good. I'd put in another row.

 

[Gepetto]

After setting the bias back to minimum that is.

 

[Jess]

After setting the bias back to minimum that is.

So I shouldn't leave them at 0.350?

 

[Gepetto]

Move to minimum until you successfully get all rows in then move it up to 0.350V after warm up time

 

[Jess]

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