"Packrat" wrote in message
...

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