Just opened up a GFA-545 with a blown fuse.... Oh boy the ammonia smell is wonderful and corrosion is all over the right channel board. Yep cat pee killed the amp, well half of it anyways.... YUCK!
I started the de-population of the board and am going to replace everything that looks corroded....
From the Fuse holders to almost the other side where D601 and D603 reside. Due to the amount of scrubbing I've taken off a little bit of the silk screen.
Does anyone have a board layout that someone can actually read? The service manual is so blurry I cant use it. I'm comparing vs the schematic and i can't seem to find the disc cap 47pf that goes from D607 to R639. hmmm?
Thanks for the help,
Eric
I started the de-population of the board and am going to replace everything that looks corroded....
From the Fuse holders to almost the other side where D601 and D603 reside. Due to the amount of scrubbing I've taken off a little bit of the silk screen.
Does anyone have a board layout that someone can actually read? The service manual is so blurry I cant use it. I'm comparing vs the schematic and i can't seem to find the disc cap 47pf that goes from D607 to R639. hmmm?
Thanks for the help,
Eric
Pee isn't so corrosive that it destroys components; it's just a wee bit conductive and made the fuse blow. So scrub the board with soap and water, and see what caused the fuse to blow?
A wee bit conductive could get a small current flowing where it shouldn’t be, resulting in a large one somewhere else. Like turning on both drivers enough to effectively short the outputs across the supply. You pretty much have to check everything for collateral damage.
This is looking better! Time to start populating.... Good thing the other channel is in tact and i'll use as a reference.
OMG! Although in the cat's defense, I see more evidence of bird than cat....
New rule: Not commenting on anything until I see pictures!
New rule: Not commenting on anything until I see pictures!
I checked everything on the board without corrosion and verified it was in spec... That included just a couple resistors,the drivers, thermal breaker and outputs.
Still trying to find the missing 2 caps on the schematic. both are labeled "47" and of a ceramic disc style. Both are sitting across the drivers (Q621 and Q623) from their base to respective collector. It must have been an after-thought since they don't have dedicated holes drilled for them!
Those caps are 47pF compensation caps across the drivers. The PCB is missing pads for these, so you'll see them jammed into the holes with another component. The GFA-555 has these but they are 68pF.
It's this cap! (And it has a twin on the other driver.)
I'd replace with an NP0/C0G ceramic or if you prefer, silver-mica, polypropylene or polyester are good choices too.
It's this cap! (And it has a twin on the other driver.)
I'd replace with an NP0/C0G ceramic or if you prefer, silver-mica, polypropylene or polyester are good choices too.
Alrighty, got the parts ordered I didn't have onhand.. and installed the ones I did have. Also "Upgraded the Jumpers" on the board since gold won't corrode as bad as tin/copper.. WITH CAT PEE!! LOL
Anyways here's the Q replacement list.
Q601,Q603,Q605 2SC2362 KSC1845 (HFE MATCHED)
Q607 2SA1016 KSA992
Q609,Q613 2SA1208 KSA1381
Q611,Q619 2SA608 2N3906 (PINOUT CHANGE)
Q615 2SC2910 KSC3503
Q617 2SC536 2N3904 (PINOUT CHANGE)
Anyways here's the Q replacement list.
Q601,Q603,Q605 2SC2362 KSC1845 (HFE MATCHED)
Q607 2SA1016 KSA992
Q609,Q613 2SA1208 KSA1381
Q611,Q619 2SA608 2N3906 (PINOUT CHANGE)
Q615 2SC2910 KSC3503
Q617 2SC536 2N3904 (PINOUT CHANGE)
FWIW, ...For Q617/Q619, the bias spreader, I use, and have always had good results with KSC1845/KSA992 for the same duty in my BFA-555 circuit board kit. They should work great for the GFA-535 too. I'm not saying the 2N3906/06 won't work well, but these are proven IMO.
Also I use KSA992 for same job as Q611. Again, not critiquing your choice, this is just what I've always used with good results.
Actually, here's the whole BFA-555 for comparison.
Actually, here's the whole BFA-555 for comparison.
Don't forget there should be a 1uF poly cap bodged in parallel to the 47uF cap, C609, that AC-couples and refers the negative side of the LTP to ground. It doesn't have to be exactly 1uF, just something that will bypass at high-frequencies where the electrolytic starts to look like an inductor.
This is an heroic restoration by the way!
I once had a customer send me an amp with cat pee in it and I threw it in the trash in disgust. Can't pay me enough to clean that up! 🤣
I once had a customer send me an amp with cat pee in it and I threw it in the trash in disgust. Can't pay me enough to clean that up! 🤣
I agree with Phloodpants above comment.
Heroic job, and you'd need to dig deeeeep into your pocket for me to touch it.
Cat pee is fowl.
Heroic job, and you'd need to dig deeeeep into your pocket for me to touch it.
Cat pee is fowl.
YESSSSSS!!!! It's done, and sounds great. I almost feel bad for not restoring the other channel, But I guess we wait for the cat on that.
Changed the 2n3904/06 to the 1845/992 combo for that bias spreader, so no funky criss-cross applesauce for those transistors. Thanks @Phloodpants
6.5 & 6.6mVDC at the test points. ~55vdc +/- on the rails
Tool's "Forty Six & 2" sounds awesome on this amp with some Episode speakers. Ear tickling goodness!
Changed the 2n3904/06 to the 1845/992 combo for that bias spreader, so no funky criss-cross applesauce for those transistors. Thanks @Phloodpants
6.5 & 6.6mVDC at the test points. ~55vdc +/- on the rails
Tool's "Forty Six & 2" sounds awesome on this amp with some Episode speakers. Ear tickling goodness!