Marantz CD5000 - display very dull - help? - diyAudio
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Old 18th July 2009, 04:27 PM   #1
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Default Marantz CD5000 - display very dull - help?

I have just acquired a Marantz CD5000 with the intent of modifying it. However, upon delivery, the display is very dark. There doesn't appear to be a dimmer option on the remote, so all I can assume is there is a fault.

Can anybody offer any guidance as to where I should start looking? Unfortunately I don't have a schematic, otherwise I could look there first.

I suspect this might be some kind of 'stock' fault with a quick fix.

I can see the diisplay if I cup my hands around it, but only just - however it is working - just not bright enough.

Can anyone help please?

Thanks, Tony.
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Old 18th July 2009, 10:53 PM   #2
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I have now got a service manual for this player.

It's identical to the Philips CD-753.

However... all the voltages around the display appear to be correct.

If I increase (what I think is the heater) voltage, the display brightens as expected. But it is still not as bright as I think it should be.

I cannot see anything in the CPU that can vary the brightness - so could this mean the display is faulty?

I would have thought it would stop working altogether if that was the case?

Any input anybody?

Thanks, Tony.
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Old 20th July 2009, 05:30 AM   #3
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On the filament ac voltage, you should see about -22.5V DC riding on the 5V AC. If not, check the -27V VKK supply. In that unit, it's only halfwave rectified, so a weak filter cap will make that drop real fast. If the voltages are all ok, then the FL display may be simply fading from age, but I doubt it.
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Old 20th July 2009, 06:53 AM   #4
Mooly is offline Mooly  United Kingdom
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I would go with stephensanks suggestion. Not familiar with the player but have worked on many dim FL displays over the years, usually a dried out cap etc.
Duff displays usually have uneven brightness, often looking better in horizontal lines under each of the filament heaters.
Displays that haven't been used in years can be like that, but often "recover" in use.
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Old 20th July 2009, 01:09 PM   #5
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Thanks guys.

I have checked the -ve supply (VKK) and it's around -27v.

The display is even - so that kind of rules out a duff display.

Needless to say, I'm still quite confused.

I can't see any leaky caps - however substitution might be a worthwhile excercise I guess...

Tony.
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Old 21st July 2009, 04:35 PM   #6
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Note that the VKK is fed to the F lines via a 4.7V zener diode & a resistor voltage divider network. So, you need to see that this is yielding about the right voltage of dc bias on the F lines; somewhere around -21V I'd estimate. Also, on the display board, there are 10ohm resistors feeding the supply to each end of the filament, PLUS, strangely, a 10uf cap on each end coupling the dc biased F voltage to the +5VDC line. Either of those leak any current and you'll dim the display & cause hum on the +5VDC line. First thing I would do is replace all of the caps involved with Nichicon or Nippon Chemicon.
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Old 21st July 2009, 05:31 PM   #7
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Quote:
Originally posted by stephensank
Note that the VKK is fed to the F lines via a 4.7V zener diode & a resistor voltage divider network. So, you need to see that this is yielding about the right voltage of dc bias on the F lines; somewhere around -21V I'd estimate. Also, on the display board, there are 10ohm resistors feeding the supply to each end of the filament, PLUS, strangely, a 10uf cap on each end coupling the dc biased F voltage to the +5VDC line. Either of those leak any current and you'll dim the display & cause hum on the +5VDC line. First thing I would do is replace all of the caps involved with Nichicon or Nippon Chemicon.
I have replaced both the 10uF caps (even tried leaving them out of circuit). I have also checked voltages around the zener and transistor. I really cannot see this being anything other than the display at this stage.

Many thanks for the suggestions.
Tony.
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Old 21st July 2009, 05:41 PM   #8
Mooly is offline Mooly  United Kingdom
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I don't know how "bright" the display on this model is.
Is it pretty unreadable ? are you sure it's faulty ?
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Old 21st July 2009, 06:09 PM   #9
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Quote:
Originally posted by Mooly
I don't know how "bright" the display on this model is.
Is it pretty unreadable ? are you sure it's faulty ?
It's totally unreadable, even during the evening under a 60w light bulb! And no - I'm not partially sighted!

Tony.
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Old 21st July 2009, 06:12 PM   #10
Mooly is offline Mooly  United Kingdom
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OK.. Had to ask some displays are "dimmmer" than others.
Would have to see circuit to comment more.
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