Protronics

09/04/2026

Noisy Cerwin Vega home stereo speaker repair, no soldering iron required, just some blocks of wood, wood glue & a clamp. This speaker has a noise when certain bass frequency notes thump at volume. There are no cleats in the corners inside, and the right side is loose, so 2 cleats will get glued in upper & lower right side to stop the rattling on certain sounds. The cleat getting glued inside is same size as the blocks under the clamp jaws.

08/17/2026

FAKE TRANSISTORS — Not in my shop
They look the same, but what's inside is a very different story.

Back in 1980, when I started buying MJ15003 transistors to repair Peavey amplifiers, there was no internet, no cheap counterfeit parts. I bought my parts from Motorola distributor Hamilton Avnet in Irving Texas, and I knew I was getting factory-original components.

Fast forward to today, servicing an amplifier for a customer who had just paid someone else to repair it, and it didn't even last a day before it failed. The soldering & parts replaced looked OK, so what happened?

I suspected counterfeit output transistors. So I cut one open to see what was actually inside.

The difference was shocking. The MJ15003 is rated for 250 watts. Looking at the counterfeit, the semiconductor die inside was less than ¼ the size of the genuine original part. That's the part that actually has to handle the power. A smaller die simply isn't built the same way to handle those rated specs.

The picture shows the difference for themselves. I have 2 original On Semiconductor parts on the left, 1 cut open, the fake on the right & circled the die in the middle with red.

08/01/2026

A few of the 47uF capacitors leaked a bit of corrosive electrolyte, like many early SMD caps do, all 47uF caps were replaced. One small purple wire added to reconnect where corrosion did damage on the far right. Board was cleaned some before photos, old capacitors sitting above board. More corrosion hiding under some of the black & gray jacks on the left. Short test video at end sweeping sine wave, as connected to power amp & woofer only, w/out satellite speakers.

07/31/2026

Look at these beauties. We just wrapped up a full acoustic restoration on these classic 70s JBL L65 Jubal home stereo speakers. Reconing both woofers to restore the bass and thorough cleaning of midrange & tweeter controls, fully restored crossover output so they sound as good as new.

07/23/2026

Finishing up work on this awesome 1960s Sunn 1200S bass amp! This beast came in with a "triple threat" of intermittent issues: motorboating, high-frequency oscillation, and a stubborn hum—three completely separate noise problems.
After adressing all issues, she’s running clean, quiet, and strong. Since it's an Ultra-Linear tube output circuit, it stays remarkably clean with tons of headroom.
No bass guitar in the shop today to give you a proper low-end demo, but here’s a quick peak inside the chassis at all that vintage goodness!

07/11/2026

Blue Sky Sat 5 MKII studio monitor speaker in for repair. Midrange driver voice coil melted & deformed when LM3886T output IC shorted & put DC to the driver.

07/11/2026

Blue Sky Sat 5 MKII studio monitor speaker in for repair. This is the shorted output IC you see cracked on the right. Tweeter IC on left is OK. When it shorted, it put out DC to the voice coil, and it heats up the copper coil & melts the Kapton form it is wound on.

07/11/2026

Blue Sky Sat 5 MKII Studio Monitor speakers in for repair. Voice coil melted when midrange LM3886T output IC shorted & put DC voltage across the windings. Tweeter output IC is OK and on left. Will attempt to rebuild the woofer with new voice coil & spider, if a voice coil with same specs can be found, and try to reuse cone & rubber surround. Two new woofers is easier option, but originals are no where to be found.

05/16/2026