Marantz Model 18

[monkboughtlunch]

So... Did someone scrap this parts 18 because of the HV winding? Sad....

Hi txturbo,

How many 18s do you have, and how many of those (if any) had an issue with transformer HV winding? I'm wondering how common the transformer problem is.

Another issue I read about is the power switch failing. Has anyone tried using a soft start thermistor to prolong life of the original switches?

 

[tonebells]

One last thing to check.. I vaguely remember a connection around the stereo threshold pot on the MPX OSC board getting shorted out. If you look at the bottom center of the board there are a couple of soldered connections. One of them was shorted to the pot and it killed the reception or activated the muting or something bad . It's a slim possibility.

I can see how that could happen. Not on this one.

Tony

 

[txturbo]

Hi txturbo,

How many 18s do you have, and how many of those (if any) had an issue with transformer HV winding? I'm wondering how common the transformer problem is.

Another issue I read about is the power switch failing. Has anyone tried using a soft start thermistor to prolong life of the original switches?

No failed transformers or power switches on 5 of them.

 

[tonebells]

I was going back-and-forth on the tuner parts found the limiter to be part of the issue. I started to small an odd odor. Before I know it there was a bit of smoke coming from the transformer. So close.

Tony

 

[tonebells]

I swapped out the the limiter and have much better volume. It still sound distorted and the muting light does not light up.

Tony

 

[RV59]

Where did you source the transformer?

Here: http://www.audiophonics.fr/en/?controllerUri=index
But I need to start a thread for explain what it's need to buy exactly and how to procede for the installation.

 

[RV59]

I swapped out the the limiter and have much better volume. It still sound distorted and the muting light does not light up.
Tony

Don't hesitate to change MPX Oscillator board if you have one.
This card is important with regard to muting functions.
But warning with R25 resistor, wich has been mounted in flying wire on first version,
and mounted on MPX Oscillator board on last version.
What is Serials Numbers of your 2 Models?

 

[tonebells]

3012 project



6314 parts


Resister is on the trimmer.

Tony

 

[tonebells]

On the 350uf caps is it better to go with 330uf or 470uf?

Tony

 

[tonebells]

Here: http://www.audiophonics.fr/en/?controllerUri=index
But I need to start a thread for explain what it's need to buy exactly and how to procede for the installation.

Please do.

Tony

 

[tonebells]

I swapped the MPX oscillator and matrix boards and the tuner is mostly working. The muting does not work but that will have to wait. The more I look into this unit the more repairs I find. The right channel is distorted on all inputs. The outputs test good and the signal is good up to the driver board.

Tony

 

[txturbo]

The muting problem is typically caused by a bad LDR. You can replace it with a neon tube and photo cell that's rated for over 200v. I have some info somewhere... I'll see if I can dig it up.

 

[txturbo]

Check this posting for info on the LDR...

Basically the photo resistor eventually craps out and light from the neon tube won't activate it. You can replace it with a new neon tube and photo resistor shrink wrapped together. There are newer LED based units however they don't play nice with the high voltage that drives the neon tube without circuit mods.

 

[tonebells]

Thanks txturbo

Tony

 

[tonebells]

The light sensor in your post is disco. The data sheet does not have the same parameters as the parts at Mouse. Would one of these do the trick?

http://www.mouser.com/Search/CompareProducts.aspx

Thanks

Tony

 

[tonebells]

Driver board voltages. 1004 & 1006 test good in circuit.

 

[txturbo]

The light sensor in your post is disco. The data sheet does not have the same parameters as the parts at Mouse. Would one of these do the trick?

http://www.mouser.com/Search/CompareProducts.aspx

Thanks

Tony

The one that I used had a 1M dark resistance and 29K on resistance. I am sure there are others that would work.

This is one that you can get at Mouser:
http://www.mouser.com/ProductDetail/Adafruit/161/?qs=/ha2pyFadugRELlGV3EJvhiJsyG6/jztqGMot59Rgn9/JAtRYbFvdw==
https://cdn-learn.adafruit.com/assets/assets/000/010/127/original/PDV-P8001.pdf

It's off resistance is 200K and on is 3-11K. Ideally you want as high as you can get when the circuit is off and as close to ground as you can get when on.

If the resistance when off is too low you may drive the signal down.

You can still get the one I used but you need to buy in qty 5..

http://www.ebay.com/itm/VT935G-Ligh...430479&hash=item3f6ad6964d:g:dmcAAOSwYIxX2HmY

 

[tonebells]

I ordered the ebay parts.

Thanks

 

[tonebells]

I found the cause of the distortion on the right channel. Pin 10k on the driver board is loose.

Tony

 

[txturbo]

Nice work!