On 11/01/2014 13:00, dave wrote:
On 01/10/2014 07:28 AM, N_Cook wrote:
Just in case someone out there other than myself dares to take on these,
and any ideas. All the previous times as far as the PAs are concerned
just matter of replacing SMD fusible resitors and powerFETs. This time
done that but unit goes into protect mode. With known good PA only or no
PA in there, then no flashing green power LED = protect mode.
I bench test these little 2 ounce, 250W, "digital" PAs as far as
quiesence is concerned and with +/-30V supply rails , sits there happily
with normal , for this minimal test, 0.7mA balanced current draw.
Cold testing DVM-D fashion has shown up no difference to the known good
PA SMDs.
I suspect something in the protect monitoring part of the pa has gone
wrong at the original failure but its a workup to make extenders etc to
probe these amps in full live circuit. At least the schematics etc are
out there for these amps.

Have you checked for oscillation?

As distinct from bench testing without the clock signal input I suppose.
Will do that but as bench current drain is only .7mA looks as though
I'll have to defeat the ERR line from this bad amp and add some droppers
in its power lines. At the moment the little bad PA is unplugged and
powered from the bench ps. This amp , like the other ones of 150W rating
, when on +&-30V settle with the speaker output at about -1.5 to -1.7V
and both sets of gates , and D settle to near enough always the same
readings. Then properly in circuit with +&-48V and clock , but still no
speaker load they settle to 10mV DC or so.
With bad amp in hte unit and powered up and before it cuts out I will
monitor for oscillation. Unfortunately with triggering of this protect
you have to wait 5 minutes for a cap to discharge, I must locate that so
I can manually discharge it.
Changing the preset value on this one makes no difference to the -1.6V.
I may try a bench oscillator fed to the clock of this amp, unusual
exercise if nothing else