The Smoked 400

[laatsch55]

R76 was responsible for the smoke...

 

[laatsch55]

A 21193 shorted emitter to collector..

 

[laatsch55]

Smoke cleaned...

 

[WOPL Sniffer]

Lots of corrosive flux left on them boards.

 

[laatsch55]

Yep, got some cleanup...

 

[FredR]

Damn

 

[laatsch55]

Yep Fred...God Particle got me again.

Also both B- pico fuses on the backplanes.
And they are first generation backplanes, the outputs are soldered in.

 

[BlazeES]

You smoked THE 400?

 

[laatsch55]

Yeppers...

 

[laatsch55]

The 21194's on the right channel were OK..

 

[laatsch55]

All outputs desoldered and out. Only had on PNP blown. I'll go back with 95's and 96's...

 

[laatsch55]

Q1 thru Q10 check Ok in circuit...might have got lucky on this one...

 

[mlucitt]

R76 was responsible for the smoke...

So if R76R is there to limit current going to the base of Q7R, the Minus Drive Signal transistor, did the current limiting circuit of Q8 and Q9 work to protect the rest of the outputs and only the one PNP 21193 shorted because it was still/just conducting?

 

[laatsch55]

That's what I think.. the miracle is q7 and 10 are ok.

 

[WOPL Sniffer]

Lee, the soldered in outputs were fun to remove and replace were they not?? Do you plan on putting in the newer backplane rev's?

 

[Gepetto]

That's what I think.. the miracle is q7 and 10 are ok.

With the RevE and up board, there would not be a thought of any miracle. The robustness of the MJE15034/35s are 4X what the predecessors in the RevD and earlier boards were.

The 5A AGX rail fuses should have lost this tug of war though.

 

[laatsch55]

Lee, the soldered in outputs were fun to remove and replace were they not?? Do you plan on putting in the newer backplane rev's?

Perry it was a pain the ass. I used 2 soldering irons after doing the solder sucker and my problem was the grease on the mica insulators. they wouldn't just drop out. Had to have a 3rd hand so Jani was drafted. After that it went well....
I'll leave these backplanes in for now.

 

[laatsch55]

With the RevE and up board, there would not be a thought of any miracle. The robustness of the MJE15034/35s are 4X what the predecessors in the RevD and earlier boards were.

The 5A AGX rail fuses should have lost this tug of war though.

And they did Joe. I remember in the A and C boards a slip up like this we would have a lot more collateral damage...

 

[Gepetto]

The trick is to hang the magnet tool from them when you heat them up and they should come out with all that added weight.

 

[laatsch55]

Well shit....fuckin brilliant Joe..