Is this normal appearance for and amplifier IC??

[dan newberry]

I'm in uncharted territory (for me, anyway). I'm a radio tech--and don't find much in a CB I can't tackle...

But I have a Pioneer surround sound home theatre amp that's kickin' my butt.

(that's what I get for doin' a friend a favor). :O

Anyway, the first symptom was no power-up. Just a flashing LED on the front panel. When you press the power button... nothing. The LED stays on steady for about four seconds and then begins flashing again.

Checked the input voltage. 110 VAC goes two different places. Part goes straight through a rectifier arrangement on the main board, and the other part goes to the power transformer. Found an open primary on the power transformer, and figured that was it. Ordered a new part (cost me about 75 bucks . I installed the new transformer, and IT DIDN'T FIX IT! Now, the 110 VAC which goes to the power transformer is being shunted--I guess--at the board. I probably did a no-no, but I jumpered 110 to the transformer and good DC voltage appears at several places on the board. So the transformer is working.

The owner said that the amp quit while he was "rockin' out really loud."

The two main IC amplifiers (PAC011A's, 50 bucks each from Pioneer) do not look the same. One has a flat surface--table top level. The other is slightly "humped" in its center. You've got to be looking really close to see it, but it's got a convex bow to it.

Here's my question, or questions, as it happens...

Is this appearance of the "bowed" surface of the amp chip an indication that it is toast? Or is it normal to see them other than perfectly flat?

Secondly.

Would a bad amp chip cause the unit to stay in shut-down--and not power up? I even took that bad amp chip out of the circuit (major, royal pain working on this thing)--and I tried powering up with the suspected bad chip out of circuit. No dice--it still wouldn't power up. No display, no "clicking relays..."

Help me out here guys--please? By the way, service manuals are 30 bucks. The owner has capped me at 150 dollars, so I'm working blind here--for the time being anyway.

Dan

[Larry E]

Hi, the blinking led on the front panel is telling you that you have a short
in thee amp, the bulge is a dead give away that it is blown, bad news is,
you should never replace just one chip, you should always replace
them as a pair, Larry E

[THE GREAT OZ]

HELLO, Well this sounds like a big no sound problem. Yes the IC's commonly refered to as the finals are no doubt destroyed. However please take the time to check any emmitter resistors that may be involved. These are generaly the flameproof type and may not always look damaged but will increase in value. Before you blow another set of finals check them and be sure to use dummy loads and a good waveform analizer to look at the clip rate and distortion values. Todays amps with feedback loops are critical. Good luck OZ

[Guest]

when you have repaired it check out his speaker system for shorts because he may get a repeat performance

[Guest]