Marantz 18 scope fixable??

[Dearslayer]

Hey guys I know this is a long shot question without more info but looking for some opinions and thoughts on a unit I have an opportunity to purchase. It's a minty unit and apparently works fine except the scope doesn't gyrate much. It does have a trace as seen in the photos. A friend of mine is offering it up. I know nothing about these scope units but have read that it's a common issue to have problems with them. Is it fixable given the fact that the scope at least works?

 

[RV59]

Of course it's fixable, the problem is to know where is the failure.

 

[Dearslayer]

Thanks RV59. I guess my concern from doing some research on these older units, was more about maybe some parts being unobtainable. It most likely be beyond my capabilities so I'm just try to get a handle on repair cost based on if it is indeed repairable. Apparently everything else on this unit is working fine except the scope isn't as it should be.

GT.

 

[txturbo]

The scope may get a bit dim or have some dark spots but almost never fails. In this case you can see that it displays something so I would say the tube is good. The problem is most likely in the transistors that drive the tube, very common problem.

 

[jstang]

Likely vertical drive....

 

[Dearslayer]

Would replacement transistors be available then?? Please forgive my ignorance but what would Vertical Drive be? I've restored a few Marantz units but I'm not sure messin with a scope is within my abilities.

 

[jstang]

Scope units have very high voltage.....no place for a beginner.

Yes it most likely can be repaired.

Johnk

 

[Dearslayer]

Picked it up today and not home with it just yet. Will have a look see later tonight and post Picts.

 

[Dearslayer]

She's home. Hooked up and it sounds great. Seems to be in really good condition aside from a little dust. As previously mentioned the scope does work however more of a straight line. Any suggested basics I can check myself or as as you suggest Jstang ..I should just stay the heck out of it.

GT.

 

[txturbo]

Thats a nice example!

Your picture shows a typical mono signal yet the stereo light is on. Try and connect an ipod or something to the AUX input and select the audio display on the scope.

Also what happens when you push the tape monitor button?

This is from the Marantz 18 manual:

 

[Dearslayer]

Well tried the Aux with my iPhone, Audio Display pushed in and the display bounces to the beat of the music much better. When Audio display button is out the trace fades to a small dot in the crosshairs. Sound disappears when tape monitor button pushed in as expected. Difficult to see ( photo taken with my iPad ) but it's no longer a straight line.

 

[txturbo]

When used with an Iphone does the display look like this?

 

[Dearslayer]

Yes very similar just not quite as large. Volume isn't very hi as all are sleeping here.

 

[txturbo]

The size of the displayed image will depend on the max volume level from the iphone. In any case it seems as if the scope is working.

Plug in a set of headphones to the 18 and see if your are actually getting an FM stereo signal. Push the mono button and see if you can hear a difference. It may be that the MPX section needs an adjustment.

 

[Dearslayer]

With headphones plugged in there is no difference with the mono button when on FM. No difference without the headphones either on FM. There is a difference with the iPhone though when engaging mono with or without headphones.

 

[txturbo]

Ok... Let me look at the manual..

 

[txturbo]

Soes the stereo light go on and off as you tune?

 

[Dearslayer]

Yes it does, mine you I'm not getting the best reception in the basement.

 

[txturbo]

Before you start messing with the tuner you should check the AMP driver DC balance and bias.

Have you downloaded the service manual?

 

[Dearslayer]

I have the manual minimized on my iPad for now. I will print it tomorrow at work as I've done for every unit I have. When you say balance you mean offset? Sorry I'm not exactly an old hand at this. Old yes but not experienced like you guys. Wish I did this stuff years ago instead of waiting this long. Getting late now but maybe will check the bias before bed. I'll check back as soon as I can. I want to say thank you txturbo for all your help thus far.

GT.