I've got a T1500-1bd on the bench. Came in with the usual R2035 falling off the board and the LM5110s blown.
I believe the client had this unit mounted on his sub box or something, because all the little heat stakes holding the plastic lid are broken, and when I asked him why he said "the music", though he claims the amp is mounted properly. Inspecting the board doesn't reveal any obvious lead breakages on the heavy components.
Repaired the stuff in the output section, getting HF oscillations at the output transistor gates, but there's an AF oscillation coming from the crossover card (apparently: it's at the output of that card going into the EQ card, and it doesn't seem to be present at the differential input to XOVER, but it's hard to tell with all the common mode noise there thanks to the ingenious placement of the AF preamp next to the rail capacitors...) The frequency is dependent on the setting of the crossover pot, and the amplitude is dependent on the gain pot.
Pulled the HV rectifiers to make the thing safer to handle and less prone to burst into flames, still there.
I had the XOVER card out, and powered it from the bench supply for testing. The oscillation was present but lower amplitude. Was seeing an odd DC bias about the last op-amp in the chain on that board, replaced that, it looked better. Soldered it back in, it still oscillates.
Before I pull that card again (or tell my client to buy a Hifonics), anyone seen this and solved it?
I believe the client had this unit mounted on his sub box or something, because all the little heat stakes holding the plastic lid are broken, and when I asked him why he said "the music", though he claims the amp is mounted properly. Inspecting the board doesn't reveal any obvious lead breakages on the heavy components.
Repaired the stuff in the output section, getting HF oscillations at the output transistor gates, but there's an AF oscillation coming from the crossover card (apparently: it's at the output of that card going into the EQ card, and it doesn't seem to be present at the differential input to XOVER, but it's hard to tell with all the common mode noise there thanks to the ingenious placement of the AF preamp next to the rail capacitors...) The frequency is dependent on the setting of the crossover pot, and the amplitude is dependent on the gain pot.
Pulled the HV rectifiers to make the thing safer to handle and less prone to burst into flames, still there.
I had the XOVER card out, and powered it from the bench supply for testing. The oscillation was present but lower amplitude. Was seeing an odd DC bias about the last op-amp in the chain on that board, replaced that, it looked better. Soldered it back in, it still oscillates.
Before I pull that card again (or tell my client to buy a Hifonics), anyone seen this and solved it?
I've seen defective crossover pots cause this in other amps. I've never had this problem in a Rockford amp, as far as I can remember.
Did the amp work perfectly when you bypassed the crossover board when it was out?
ChipQuik makes getting these boards out much easier.
Did the amp work perfectly when you bypassed the crossover board when it was out?
ChipQuik makes getting these boards out much easier.
Hi, thanks for the reply.. running it without the XOVER in (bypassing the + side of the diff input of XOVER to the input of EQ) produced no oscillation but noisy output, which I attributed to the common mode noise there. Replacing the input op-amp (the one on the main board behind the jacks) fixed it, even though the diff output coming from there looked OK and free of oscillations. shrug