Crate CA15

[theguitartech]

Hi all- Im new to amp repair and looking for some pointers. I run a guitar repair shop and a client abandonded a dead Crate CA15 acoustic amp and I figure its the perfect place to get my feet wet. I have the schematic for the amp and some basic test equipment (multimeter, scope, signal generator) and a enough electrical knowledge to keep from killing myself (my dad was an electronics profesor at the local college so a bit rubbed off on me)

Here's a brief rundown of the amp-

When I recieved it the amp would power on (light up) but no sound at all

Pulled open the chassis and discovered the power amp chip had exploded. Model TDA2030 on the schematic.

Ordered a handful of replacement chips. Installed one and fired the amp up. Everything sounded fine. Messed around with it for a few minutes testing all the knobs and inputs and decided to put it all back together.

Put everything back together and fired it up- nothing but a loud hum. Smelled a little funny as well.

Took the chassis back out and fired it up again. More hum for a second then the power amp chip exploded. So Im back where I started. Amp lights up but no output.

Due to the hum my gut says AC is getting through somewhere it shouldn't be, but then again I have 0 experience with solid state amps so who knows. Any advice on where to go from here?

[52 Bill]

Hi, welcome to the place.

My guess is the hum you heard was the chip failing and putting dc voltage on the speaker output until it blew up. It may be that you had fixed the symptom but not the cause. I would suggest posting the schematic for this amp here so that everyone can follow along at home.

Does this amp have a fuse? I'm surprised that it hasn't blown with the circuit overloading like that. Is the fuse the correct value?

Do you have a lightbulb limiter? If not I'd suggest that you build one, as it will come in handy as you work on this amp and on any future repair jobs.

[olddawg]

Make sure that it is not over fused. Remove the IC and take voltage/ripple measurements at the IC pads. Make sure the rail voltages are correct. Install the new IC making sure there are no solder bridges (hint: clean the board with alcohol and use flux). Run the amp up with no load (speaker). If you do not have a variac use a light bulb limiter. If the amp is stable and running cool, turn it off and hook up a known good speaker. If it is not running cool look for dc offset and runaway oscillation. From you description I would suspect a bad (shorting) speaker load or the amp is oscillating above the audible range. It could be a few things.

[theguitartech]

Thanks for the input guys. Here's the schematic for the amp. Im going to build a lightbulb limiter today.