Underbias = set bias too low. It will always go up when you run it to full supply voltage, and you don't want to overshoot. You want to start low, and adjust it up, not have it too high and have drop it in a panic.
Drive to full output should be self-explanatory. Crank it till it clips. Without speakers until the amp can fully be trusted. A sine wave generator and oscilloscope would be a more scientific approach, but music will do.
Drive to full output should be self-explanatory. Crank it till it clips. Without speakers until the amp can fully be trusted. A sine wave generator and oscilloscope would be a more scientific approach, but music will do.
So, a couple things.
Z1 is fine. It lives.
I have the bias trimpot turned down to 0 ohms, and I'm still getting voltage on the output. About 15-16v. If I turn the trimpot the other way, the voltage starts going up, and if I'm running through the dim bulb tester, the bulb gets brighter. So bias is adjustable... but something is still wrong, because I can't adjust the bias low enough with that trimpot.
Charles.
Z1 is fine. It lives.
I have the bias trimpot turned down to 0 ohms, and I'm still getting voltage on the output. About 15-16v. If I turn the trimpot the other way, the voltage starts going up, and if I'm running through the dim bulb tester, the bulb gets brighter. So bias is adjustable... but something is still wrong, because I can't adjust the bias low enough with that trimpot.
Charles.
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I afraid the inputs suffert so much that the offset isn't right anymore, making the amp.output far from zero.
Or there is to much leaking between the pins caused by overheating the print while exchaging the IC.
Mona
If the bias current is set to high it get very hot.On the emitter resistors in the output (0.33 Ω) better not more then 25mV.
It's possible there is something else wrong besides the opamp.In that case it will try the pull things right by outputting the max.at pin 6 ,normaly if everything is ok around -2V.
Mona
It's possible there is something else wrong besides the opamp.In that case it will try the pull things right by outputting the max.at pin 6 ,normaly if everything is ok around -2V.
Mona
With that much voltage at the speakers why is the protection relay not doing it's thing? Also Phase Linear amps usually don't have any voltage across their output emitter resistors that's why the bias is set measuring across the driver emitter resistor. I think the input IC is kaput, it's responsible for the output offset. Are the power supply voltages correct at the IC?
Craig
Craig
the manual said when the amp draws excessive current at turn on, to short the emitter and collector of the bias transistor. I'm guessing that's Q2, which is attached to the heat sink. I did that, and suddenly the current draw disappeared.
So I replaced Q2.... and it still does the same thing with a brand new transistor in there. I also replaced Z1 again, but no dice there either. Double checked the output transistors, they all test good.
Charles.
So I replaced Q2.... and it still does the same thing with a brand new transistor in there. I also replaced Z1 again, but no dice there either. Double checked the output transistors, they all test good.
Charles.
OK, when you short the emitter and collector of Q2 you basically turning off the driver and output stages. Since the current draw goes away that proves that everything after Q2 should be OK and the problem is somewhere before Q2. What are the DC volts on pins 4 and 7 of Z1? Should be +15VDC on pin 7 and -15VDC on pin 4.
Craig
Craig
Two more things for Phase Linears in general. 1. Check for oscillation. Many times the oscillation goes away when you turn the driver/output stage bias OFF (shorting Q2) and comes back at "normal" bais settings resulting in high current draw. This can be tricky to fix. 2. If C6 is leaky it can do all sorts of stupid things. Normally, the bootstrap cap is connected to speaker out, not the driver stage output. In this configuration, any leakage current gets amplified. With the bias set to zero, that amplification is removed. Pull the cap and see what happens. It will sort of run without it. If it turns out to be at least part of the problem, put a new one in.
"Check for oscillation" isn't something I have the equipment or knowledge to do.
R11: +12.8/+17.5
R8: -12.3/-17.4
With Q2 jumper wire installed (bulb no longer taking most of the current load)
R11: 63/15
R8: -63/-15
Q5&Q6:
E: 6.4
B: 7.5
C: 17.7
Again, those readings are because the bulb is shining brightly and taking the load.
Charles.
R11: +12.8/+17.5
R8: -12.3/-17.4
With Q2 jumper wire installed (bulb no longer taking most of the current load)
R11: 63/15
R8: -63/-15
Q5&Q6:
E: 6.4
B: 7.5
C: 17.7
Again, those readings are because the bulb is shining brightly and taking the load.
Charles.
Check to see if R101/102 are getting hot. If the amp is oscillating, it will be dumping current into the zobel. If it's not (or if it's at a low level), it won't.
You're supposed to use an oscilloscope, but a finger on the zobel resistor gives a pretty good indication. Also, you could make sure those resistors aren't already burned out. Which could make it oscillate.
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