Here's a quick rundown of what I worked on since March 2020:
GK 400RB: Bad volume pot. Sold for profit.
800RB: Shorted output transistor, likely counterfeits that somebody else put in there. Arcing power switch. Sold for profit.
Aguilar SL112 cabinet: Broken crossover PCB, broke the plastic mounting posts. Drilled new mounting holes and jumpered a broken trace and mounted it to the inside of the cabinet with nylons standoffs. Kept it for a couple months, then sold for substantial profit.
800RB: More counterfeit output transistors. I was able to rub the silkscreen off with my finger. Fixed and sold for profit.
Fender Rumble 200: Smelled like basement and cat piss and the knobs were covered in sticky gunk. Bleached the shit out of it. Measured DC offset going into the off-the-shelf Icepower Class-D module. SMD ferrite bead was getting hot under the thermal imaging camera and -15V rail was collapsing when the fan kicked on. Common problem on these modules. Replaced with a wire jumper. Ended up keeping this one for band practice duties, as it actually sounds really good and is pretty light.
Carvin BX700: This one was kinda rare, I guess. Never seen another one like it before. Active-clamp flyback power supply had a shorted clamp MOSFET. Spent a lot of time troubleshooting this one before shotgunning a bunch of parts into it to get it working. Ended up finally buying a cheap hot-air rework station also. Sold for a small profit, after considering all of the time I spent on it.
Ampeg SVT-3 PRO: "Partially working." Just needed the output transistors rebiased. Common problem with these. Replaced three broken EQ faders also. Took about 2 hours total, sold for profit.
JBL 306P MKII:
Sold my JBL 708P studio monitors (for over double what I paid 3 years ago) and bought a pair of 306Ps instead, for 1/10th the cost. The 306Ps are definitely in the budget category, but they get you about 80% of what the 7-series does.
I really liked the 708Ps, but they were slightly too tall on my stands, so the tweeters weren’t at ear level. They’re also designed for more mid-field listening, from about 10 - 12 ft away. My desk is set up for nearfield.
A common complaint with 3-series is the resonance around 240 Hz that makes them sound a little boxy. People have tracked it down to cabinet resonance, and adding internal bracing helps. I cut a couple of dowels and glued them in there.
I also added mass to the plastic front baffle with some fire putty (basically non-hardening clay) I had left over from building the studio in Nashville. Then I filled in the chambers with siliconized latex caulk, the heaviest I could find.
I stuck some Peel & Seal (the hardware store equivalent of Dynamat) to the metal backplate to damp the ringing of the thin panel. In total, I added about 3 lbs to the whole speaker, or about 20% more mass.
I did one speaker first, then set up a blind A/B test to see if I could tell a difference with the unmodified one. Bass is tighter, less boomy, and a frequency sweep sounds less peaky.
Orange OR15: “No output” Well, yeah, there’s not going to be any output when the HT fuse is blown. So I replaced that. Somebody also attempted to install a Mercury Magnetics output transformer, but they had their primary side wires mixed up and it was only outputting about 350 mW before clipping. Swapped the wires and cleaned up their horrible soldering job and everything’s working now. Sold for significant profit after an hour of work.
Another 400RB: Cold solder joint on master volume pot. Sold for profit.
Another SVT-3 PRO: Blown output transistors. Sold for profit.
I also completely redid another drum kit, but I'll save that for another thread.
