Marantz 250 restoration query

[catrafter]

Be Aware, one side is upside down from the other.

Tom

 

[quadmatrix82]

Be Aware, one side is upside down from the other.

Tom

Thanks Tom I noticed the sides are upside down so do the outputs then should be in opposite order from the other?

 

[quadmatrix82]

Been a while since my last post life has got in the way done a check on resistors values on the boards make sure no issues nearing completion and went back to check work to make sure no issues before power on - want to double check have I installed the pre drivers correctly? I couldn’t find an exact service manual for this board to confirm ?

 

[GRonald]

 

[GRonald]

This is from the 1200 and should be the same as you 250 power amp board.

 

[quadmatrix82]

Thankyou!

 

[quadmatrix82]

Both channels up and running! Dc offset adjusted however I’m not sure where the bias test points are on this board? Can someone identify where to test bias ? Thankyou!

 

[quadmatrix82]

I get no bias reading on both channels on the coil resistors shows 0 voltage have I selected the right location to test bias on this board?

 

[GRonald]

You should get bias in mv from 2.5 mv upwards with the bias pot turned fully anticlockwise. You need to test across those .1 ohm coil resistors with the multimeter connected to the side of the resistors close to the center of the board.

 

[GRonald]

If your board has the diode under the pre-driver, check the orientation of the diode attached a picture I have on record showing the diode.

 

[quadmatrix82]

Great Thankyou I’ll try and get back to you

 

[quadmatrix82]

View attachment 2392979 You should get bias in mv from 2.5 mv upwards with the bias pot turned fully anticlockwise. You need to test across those .1 ohm coil resistors with the multimeter connected to the side of the resistors close to the center of the board.

Thankyou it is biasing well now at 12mv and stable within half a milivolt

 

[quadmatrix82]

Sounding great so far, is it normal for the vu meters to bounce when switched on?

 

[quadmatrix82]

The Marantz 250 is running great the past few days Thankyou to everyone that has helped me with this restoration couldn’t have happened with the expert advice here! Can anyone recommend any led lights that lighten the meter so you can see the meters move better? These led installed already are dark looking and don’t seem to lighten the whole meter too well?

 

[EastPoint]

Those look like Royal Blue/Ice Blue lights to me. You want "Cool Blue" or possibly warm white or cool white, if the meters are already tinted blue enough.

 

[quadmatrix82]

T

Those look like Royal Blue/Ice Blue lights to me. You want "Cool Blue" or possibly warm white or cool white, if the meters are already tinted blue enough.

Thankyou! I’ll look around for some of these instead

 

[quadmatrix82]

I

Those look like Royal Blue/Ice Blue lights to me. You want "Cool Blue" or possibly warm white or cool white, if the meters are already tinted blue enough.

Im not sure what colour type I got bought the led many years ago do you think warm white will brighten it up better than it is now?

 

[goldswimmerb]

I

Im not sure what colour type I got bought the led many years ago do you think warm white will brighten it up better than it is now?

Warm white should be brighter than stock, and brighter than blue, but keep the look original. Cool white, to me usually looks brighter but the color can be off.

 

[quadmatrix82]

Cool thanks I’ll go warm white then I prefer the original look too!

Warm white should be brighter than stock, and brighter than blue, but keep the look original. Cool white, to me usually looks brighter but the color can be off.

 

[quadmatrix82]

Is it normal for the meters to bounce to the end when the amp is switched on? My 250m doesn’t do this or Marantz 140?