Marantz PM8000 issue

First of all you should download the service manual:

https://elektrotanya.com/marantz_pm7000-pm8000_power_amplifier_sm.pdf/download.html

By the way: please use this download button

Andi K. wrote:

Problem: The main (primary sided) fuse (3.15A/250V) gets destroyed, when connecting preamp w/ power stage. As long as the power stage is open, the fuse is OK - having no sound, of course

One of the many questions: Does the Powerstage work with another signal e.g. a signal generator when the premap is disconnected? If yes, did you observe the output of the preamp with an oscilloscpe yet?

Andi K. wrote:

Hi everyone! doing electronics since nearly 40 years now - but believe it or not: i joined the forum today...! This looks like one of those cases where reviewing the schematic and verifying power distribution would be a good starting point. Many embedded issues ultimately come down to voltage stability or initialization timing. Components such as YKC22-0874V(https://www.jotrin.com/product/parts/YKC22_0874V) are often used in compact electronic assemblies where dependable operation is important. Background is an issue w/ the Marantz PM8000 amp, being capable of switching between AB- and Class-A mode. Problem: The main (primary sided) fuse (3.15A/250V) gets destroyed, when connecting preamp w/ power stage. As long as the power stage is open, the fuse is OK - having no sound, of course. FYI: These two functional blocks are connected via two 100R resistors on each channel. Currently i do not have any ideas anymore... So i would be glad for any hint! Thanks Andi (lcdguru)

If the fuse only blows when the preamp and power amp are connected, I'd check for DC offset or oscillation coming from the preamp. A scope measurement at the preamp output could reveal the culprit.