Hi.
I am working on a audio stage monitor. It blew its fuses. The amp, a uPC1238, was shorted.
Had trouble finding one on the internet, so after some research I decided to try substituting it with an LM1875 or TDA2003 which I ordered from Futurlec.com. Tried using the LM1875 but got a loud hum from the speaker, and the part heated very quickly. Tried power on only for a few seconds at a time. With a couple dozen trys, ther were a few times when it did power up okay, quietly. Had light bulb in series with power cord (40 or 100W) to limit current.
Tried more things with the LM1875T in the Monitor, but no help. Finally hooked up the scope and found that the amp was oscillating at over
100kHz, as I suspected. The specs say that the LM1875 is unstable for a gain of under 10. The gain appears to be about 9 in this design.Tried a TDA2003 Amp in the Monitor, and got a similar hum in the speaker. But this time it was not oscillating, but the output was stuck on the negative rail. Anyone have any idea whats going on there?
Decided I needed to get the correct part. I did find one finally - waiting for order now. But the negative rail had me puzzled.
Any thoughts would be appreciated.
Harvey