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Model 18 Scope Troubleshooting

Riddle me this: Is it normal for the visible NE2 muting neon lamp indicator in the left rear of the unit to momentarily light up when the selector knob is turned to FM (even when the "Muting Off" switch is depressed and the receiver is tuned to a strong signal)?

bktheking and hirscwi, does the visible mute lamp on your non-popping units flicker on momentarily when you first turn the knob to FM?

txturbo and fhamre, does the visible mute lamp on your popping units flicker on momentarily when you first turn the knob to FM?

My popping unit does flicker on for a moment and this coincides in lock-step with the popping noise. I wonder if there is a relationship (e.g. a resistor that's connected to that visible NE2 lamp out of spec etc).
 
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Sorry, my 18 is no longer with me. I sold it recently in order to fund a Model 19 when I can find a good one. My 18 sounded great but was a bit ragged in appearance.
 
monkboughtlunch said:
Riddle me this: Is it normal for the visible NE2 muting neon lamp indicator in the left rear of the unit to momentarily light up when the selector knob is turned to FM (even when the "Muting Off" switch is depressed and the receiver is tuned to a strong signal)?

bktheking and hirscwi, does the visible mute lamp on your non-popping units flicker on momentarily when you first turn the knob to FM?

txturbo and fhamre, does the visible mute lamp on your popping units flicker on momentarily when you first turn the knob to FM?

My popping unit does flicker on for a moment and this coincides in lock-step with the popping noise. I wonder if there is a relationship (e.g. a resistor that's connected to that visible NE2 lamp out of spec etc).
Click to expand...

Mine flickers momentarily every time it pops. If you look very carefully the tube has two electrodes, normally only one of them will glow with DC voltage and the one that glows can indicate polarity. With AC both will glow.

When mine pops, sometimes it's the opposing electrode that glows.
 
txturbo said:
Mine flickers momentarily every time it pops. If you look very carefully the tube has two electrodes, normally only one of them will glow with DC voltage and the one that glows can indicate polarity. With AC both will glow.

When mine pops, sometimes it's the opposing electrode that glows.
Click to expand...

Thanks. What about your other 2 Model 18s? Do they pop and does the neon flicker?
 
txturbo said:
Mine flickers momentarily every time it pops. If you look very carefully the tube has two electrodes, normally only one of them will glow with DC voltage and the one that glows can indicate polarity. With AC both will glow.

When mine pops, sometimes it's the opposing electrode that glows.
Click to expand...

Interesting. Thoughts on if the pop is related to the flickering muting indicator or associated parts? Dug through the schematic and pasted it below. The schematic notes this muting indicator is an NE2V. I've pasted the specs of an NE2V below from an online datasheet.

Muting_MPXOsc.jpg


mpxosc2.jpg


ne2vspecs.jpg
 
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I don't think it has anything to do with the neon lamp at this point..... I will remove it completely as a test...
 
txturbo said:
I don't think it has anything to do with the neon lamp at this point..... I will remove it completely as a test...
Click to expand...

Would it be reasonable to conclude that whatever is causing the audible pop when selector switch is turned to FM is also causing the visible neon muting lamp (NE-2V) to light up momentarily? If so, would the voltage spike observed at least be equal or exceed 90 volts DC? 90 volts DC appears to be the gas striking voltage to light up NE-2V in the datasheet above. If that's the case, are there any parts in the muting circuit that -- if they were out of spec -- might result in allowing momentarily at least 90 volts to the muting lamp to light it up?
 
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Also, could the selector switch itself be passing on the voltage spike to the MPX OSC board (and thus momentarily lighting the muting indicator) from some other issue located elsewhere?
 
The audio noise is coming from the arc that occurs across the selector switch. You can hear the arc by turning off the speakers and then activating the switch.

Why does it arc?
 
That switch has 200v on it to feed the mpx or if board , I forget which one. Carbon tracks , ie dirty selector switch could cause arcing.
 
I deoxited mine with no change. Does that mean switch contacts are beyond rehabilitation? How is the arc presented to the speakers? Is the voltage spike being sent from selector switch to the mpx osc board (and thus flickering the mute neon) and then being amplified? Will this require a new selector switch to fix? Is the Marantz selector switch custom design or do aftermarket switches exist that are compatible with the 200v switching?
 
Found this. Thoughts?

pustelniakr said:
DeOxit is not suitable for power switches and other high current or high voltage carrying contacts. for one thing, DeOxit requires a "wiping" action to clean contacts. High current/voltage contacts generally do not provide wiping action, to minimize arcing. They do arc to some degree anyway. That arcing tends to burn the residual lube left behind by the DeOxit, leaving nasty deposits on the contacts.

Switches, relays, etc, with high current/voltage contacts are best disassembled, and dressed, or outright replaced.

Enjoy,
Rich P
Click to expand...
 
When an arc occurs it's quite destructive on the surface of the contact. The surface is no longer planar and will have lots of ridges. DeOxit can't solve this issue.

The contacts need to be burnished, I will give it a try.
 
Ok.. I burnished the contacts, makes no difference.

I did notice that when I measure with the switch open on the power supply side I get a pop from touching the volt meter lead.

So basically the meter represents a very high resistance path to ground and makes a noise when I touch the power supply 200V line. Again, this is with the switch open, no power to the MPX or oscillator.

I no longer think it has anything to do with the tuner or switch.
 
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