marantz 4300

[mrmodify]

I have a old marantz 4300 i am trying to resurrect. The outputs are fried with a few other parts. I was checking the transformer voltage which all was fine. I checked resistance and voltage output on secondary taps, all were fine. There are 3 different secondary windings two sets with center taps 1 set of orange leads read .4 ohms when checked to chassis. The yellow set of leads does not. I think and have not checked yet but think center tap on the orange leads are grounded to chasiss. I checked voltage from chasiss to my bench 120vac ground side of plug and got 30vac. took scope and got a sign wave of 10 volts. took amp reading from chasiss to 120vac plug ground shows no amperage. the unit does not have a three prong power cord. The outputs are removed during this test. There is a 3 amp fuse currently in unit and it is not blowing. The unit is suppose to have a 8 amp fuse in it and for testing I am using the 3 amp. I am missing something here.

 

[Resqueline]

??? Try explaining your problem again..

 

[mrmodify]

Thanks for replying, The transformer has three primary leads white goes to chasiss. The blue and red wires go to the AC line. On the secondary side you have seven wires. two green @ 7vac (lighting). two yellows @ 76vac (?) and two orange leads @ 56vac (goes to outputs). one black wire is center tap I think. The schematic shows the yellow set and the orange set to have a center tap. The secondary leads except for lamp circuit are disconnect from power supply. Both amp sections are out of unit because of shorted parts. I am trying to make sure other circuits work before I start repairing. With a DVM red lead to chasiss and black lead to ground on a 120 vac house recepticle I get 30vac on meter. If I take a scope and place the ground of probe to a 120vac house recepticle ground and probe to chasiss I get a sine wave of 10 volts. Take DVM on ac amps and put positive lead to chasiss and black lead to a 120vac house recepticle ground i get nothing. Ohm readings on transformer all seem to be ok. when orange leads are checked I get .4 ohms to chassis. Sorry im long winded hope i explained it better. I dont think transformer is bad but am confused why scope and DVM show voltage across house ground and chasiss.

 

[Resqueline]

Well, that is called leakage current and is caused by the small inherent capacitance between the primary winding and the core (chassis). This is perfectly normal and the current is so small that only your voltage range is able to pick it up. The DVM shows more than the 'scope because the DVM is 10M ohms whereas the 'scope is 1M ohm. If your DMM had had a uA AC range it would have been able to show the actual current. Unless the blue & red wires show a resistance to chassis ground it's ok.
Measuring voltage from chassis to yellows & oranges should show half their total voltage if they're centertapped & ok. Blown outputs rarely affect anything else.

 

[mrmodify]

Thanks Resqueline, I thought for a while there I was going to have to ditch the old girl. I stumbled on this site late last night. I think it is great, Who ever created or had part of this site. Cheers to you all. I am a person who likes to tinker. took electronics in high school many years ago. I like the on line training keep it up Thanks Again!!