Exciting! Newly manufactured circuit boards for the GFA-565 just arrived!
Why create new boards for an old amp? Exploding capacitors, that’s why.
A little background; The GFA-565 is infamous for sending speakers up in smoke, due to a bad batch of Elna capacitors that tend to explode and spray conductive electrolyte all over the board. (Pretty much every 565 ever made has this problem.) The fluid residue is conductive, making connections where there should be none, which causes a DC offset to appear on the speaker outputs. The DC smokes the speaker’s voice coil.
Repairing the board is no fun at all! The electrolytic fluid is vile and pernicious stuff—extremely corrosive, turning copper traces turn to crust, and blackening the board. It leaves an invisible conductive film and it’s very easy to miss a spot. It soaks into through-holes, and even gets on component leads. It’s a mess.
So, I had a customer with a pair of GFA-565’s with DC offset that had already been unsuccessfully serviced by another shop. (Frankly, it was poor quality work throughout. Electrical tape falling off bodgy solder joints, inappropriate replacement parts, etc. A cheap DC protection board was hacked in.) The offset was only 100mV or so, but the GFA-565 has a DC servo circuit, so it should be near zero. The DC servo was pegged to one side trying to correct this fault.
I stared in dismay at this disgusting circuit board. Besides the mangled copper traces, how can I be absolutely sure I’m removing every speck of electrolyte? The original evidence was gone.
I can’t be sure. So make new boards!
I stripped all the components off the board, and sanded the copper side down to bare metal, and scanned it on the flatbed. The copper turns out white in the image, so I flipped the color, and used the curves tool to split the image into a 2-color B&W image.
But it was a fuzzy image that needed many hours of editing to get the clean result you see here.
I call this one “Surprised clown / angry clown”.
They arrived today! Beautiful quality!
Can’t wait to try them!
Board is populated!
I found a bunch of minor errors along the way—hole sizes, lead spacing, clarity of text, and whatnot—and corrected them in Eagle CAD for the next batch of boards. But I’m confident this board will work great.
They work! On the first try too.
The torroid in the foreground is not original. This 565 has a custom power supply with 2x1000va transformers in place of the original 1250VA.
Rev 2.0 boards arrived and they are even better! I can now say that these are better quality boards than the originals! These have plated through-holes for a more solid solder connection, and greater pad strength. They are also less affected by heat cycling. Even with poor soldering, a plated through-hole is extremely reliable.
UPDATE 5-22-17: These are the latest revision.
And here’s one installed versus the crusty old board.