As per my original post.... is there an equivalent IC I can replace this
with?

"Mark D. Zacharias" wrote in message
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"Arfa Daily" wrote in message
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"Packrat" wrote in message
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Those voltages are not necessarily wrong, it is the midpoint volts that
are important. This will likely be at the junction point of two very
low value resistors, which are often integrated into a single 3 pin
item for each channel on Pioneers. The midpoint from each channel, will
be the actual speaker output, so will head on up to the protection
relay contacts. I would start by looking at what is on the midpoint of
each channel, to see if it is really a problem in one of the output
stages, that is causing the protect circuit to remain inoperative.

Those midpoint voltages you mentioned are way off, about 30VDC to be
exact. I spent quite a bit of time trying to figure out where that 30V
was coming from, and the problem only went away when I removed that
preamp IC..... so I'm wondering if the IC may be faulty. Or perhaps the
previous owner did something really stupid, like trying to apply AC into
the speaker terminals or something?


As a slight aside, are the transformers that you've fitted, the genuine
110v article for that model, or some 'appropriate' substitutes ? The
reason I ask, is that some protection circuits monitor power supply
outputs, and sometimes AC feeds from the power transformers, as well as
the output stages, so if anything was amiss with the replacement
transformers, or your wiring in of them, this might cause you a problem
with the protect circuit that doesn't really exist. Did you try feeding
the amp with 240v before you started on the conversion, to see if it
originally worked, or were you already aware that it didn't ?

Arfa
Unfortunately I didn't power it with 240 before converting, but I'm
very certain my conversion is correct because all the power supply
voltages match the schematic within 1 - 2%.


It's quite possible then that the preamp 'IC' is faulty. Is it one of
those hybrid voltage amplifier modules that look a bit like a small STK
device ? If so, then I have had them cause problems like this. The
midpoint volts should be zero, or close enough that it doesn't matter. A
very large midpoint offset such as you appear to have, is usually as a
result of a missing rail ( I'm assuming that you have both the HV+ and
HV- rails making it to the output transistors ), a short circuit output
transistor with an open circuit emitter resistor, or sometimes incorrect
drive as you think that you have. If the midpoint volts drop to zero when
you remove the IC, that would tend to suggest that you are right with
your diagnosis. Good luck with it.

Arfa


The PA0016 is a 16 pin (IIRC) DIP IC. They do go bad, but usually only if
there has been an associated amplifier failure.

I'd still be looking for power supply issues, especially a floating
ground. For example a broken eyelet at a power transformer, where they
solder to the pins of the transformer.

Mark Z.