Sunday, June 25, 2017

Reliable failures

A while back, I'd showcased the failed cathode drive amplifier for my main monitor.  This hybrid circuit had failed due to thermal stress because the alumina substrate had detached from the thermal tab.  Grey, sandy solder on full display, I'd mumbled about "metallurgical nuance".

Well, I guess it happened again.  Sort of.

boing
Again, the green channel failed, this time due to fractured solder between a transistor's thermal slug and the substrate.  The solder is black and gritty and won't reflow at all.  I ended up mangling everything just trying.

And then I tried to replace the entire amplifier section with part from the last failure.
what are you dooooooing
I flowed the new amplifier into place and gently held it square with tweezers while the solder froze... and then bumped the bond wires off of one of the transistors.

Wholesalers want about $90 for this stupid IC, and the only place I can find cheaper only takes orders by phone... in Polish.  I guess I'll just have a bicolor monitor from now on.

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