I don’t mean to clog the forum up , but was hoping to get a quick answer on this Marantz 4240 as my brother is leaving for Spokane tomorrow evening and I’d like to send this with him.
I’ve done an overhaul on it, when I got it only had output on the front right output whether in 2 or 4 channel mode. So full recap, cleaning, Bourne 25 turns for the bias and offset, etc. After the rebuild I still had no output on the rear channels and the left front was now there but much lower in volume and out of phase. After finding a few bad components after tracing a signal I’m down to my last issue: the ground.
So Marantz runs the ground through a selector switch on the back that lets you choose either 2 channels of 40w power or 4 channels of 17 watt power. It bridges two of the four channels when in two channel mode. When in four channel I get good continuity from the speaker negative out to chassis, about 0.2 ohms on all channels. When in two channel mode the front channels (only ones used) the resistance jumps to about 145 or so ohms on each channel. This gives me a horrid looking wave form on the scope. If I ground my scope leads to the chassis it then gives perfect looking wave forms.
I can’t see why they would run the ground through the switch as you want good continuity from chassis to neg input. So with that high of resistance I’m not getting output. Can’t I just solder a lead from the negative output to the chassis? I don’t want to damage anything by doing so, so I thought I’d ask here.
Oh and yes, I’ve cleaned the switch several times and I’m not exactly sure what’s going on with it.
Dan
I’ve done an overhaul on it, when I got it only had output on the front right output whether in 2 or 4 channel mode. So full recap, cleaning, Bourne 25 turns for the bias and offset, etc. After the rebuild I still had no output on the rear channels and the left front was now there but much lower in volume and out of phase. After finding a few bad components after tracing a signal I’m down to my last issue: the ground.
So Marantz runs the ground through a selector switch on the back that lets you choose either 2 channels of 40w power or 4 channels of 17 watt power. It bridges two of the four channels when in two channel mode. When in four channel I get good continuity from the speaker negative out to chassis, about 0.2 ohms on all channels. When in two channel mode the front channels (only ones used) the resistance jumps to about 145 or so ohms on each channel. This gives me a horrid looking wave form on the scope. If I ground my scope leads to the chassis it then gives perfect looking wave forms.
I can’t see why they would run the ground through the switch as you want good continuity from chassis to neg input. So with that high of resistance I’m not getting output. Can’t I just solder a lead from the negative output to the chassis? I don’t want to damage anything by doing so, so I thought I’d ask here.
Oh and yes, I’ve cleaned the switch several times and I’m not exactly sure what’s going on with it.
Dan
