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Old 30th May 2011, 03:58 AM   #1
DQ828 is offline DQ828  Australia
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Default NAD Display Very Dim

I have an old NAD C521i CD player that I use occasionally & the display is VERY dim, in fact I thought it was dead but eventually noticed there was still some life left in it.

I have downloaded the manual but really for me it's like trying to read a foreign language.

It's not worth sending to the shop to get fixed, but I was hoping to keep it going if I can.

Does anyone have any idea what the problem might be?

I did find a thread from 2006 that I thought was going to get me there but it turned out the capacitors that the fellow replaced to fix his problem dont seem to exist in my player.
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Last edited by DQ828; 30th May 2011 at 04:05 AM.
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Old 30th May 2011, 04:27 AM   #2
GoranB is offline GoranB  Poland
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Quote:
Originally Posted by DQ828 View Post
I have an old NAD C521i CD player that I use occasionally & the display is VERY dim, in fact I thought it was dead but eventually noticed there was still some life left in it.

I have downloaded the manual but really for me it's like trying to read a foreign language.

It's not worth sending to the shop to get fixed, but I was hoping to keep it going if I can.

Does anyone have any idea what the problem might be?

I did find a thread from 2006 that I thought was going to get me there but it turned out the capacitors that the fellow replaced to fix his problem dont seem to exist in my player.
I think there should be a voltage of 3.3 - 4 V and another oven higher abt 40V, meassure the secundar winding on your trafo.
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Old 30th May 2011, 09:50 AM   #3
Mooly is online now Mooly  United Kingdom
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The big question is whether this is an LCD or a VFD display.

The LCD is backlit via small filament bulbs... a common problem.

The VFD (vacuum flourescent display) can suffer with low emmision, usually some segments are brighter than others and can "recover" after many hours use.
This type of display often suffers from "capacitor trouble" in the supplies derived to feed it... very common across all types of equipment that use this type of display.

If you post the circuit we can advise...
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Old 30th May 2011, 10:00 AM   #4
Mooly is online now Mooly  United Kingdom
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Seems this uses an electro flourescent display.

These would be my first suspects... check by substitution.
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Old 30th May 2011, 10:05 AM   #5
Mooly is online now Mooly  United Kingdom
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R709 in that diagram appears to be a preset pot... I assume to set the brightness of the display ?
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Old 30th May 2011, 10:12 AM   #6
DQ828 is offline DQ828  Australia
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Quote:
Originally Posted by Mooly View Post
R709 in that diagram appears to be a preset pot... I assume to set the brightness of the display ?
WOW your fast, thanks, it will be a couple of days before I get the chance to pull it apart.

What do you mean "check by substitution".

I have no idea what R709 does but I will have a play when I get it apart.

THANKS

David
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Old 30th May 2011, 10:20 AM   #7
Mooly is online now Mooly  United Kingdom
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Without using a scope to see if there is any high frequency noise or ripple on the supply the only sure way to test the caps is to remove and replace with new (check by substitution).

R709 varies the supply available to the transistor Q520. I haven't read the manual... there may be a procedure for adjusting it but I would still change the caps first before doing anything.

Q520 forms a simple oscillator (with transformer M501) to generate a high voltage for the display.

Good luck... any questions just ask.

I'm not saying the display isn't faulty... it may be... but caps are such a common problem that it makes sense to check them first.
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Old 30th May 2011, 10:48 AM   #8
DQ828 is offline DQ828  Australia
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Quote:
Originally Posted by Mooly View Post
Without using a scope to see if there is any high frequency noise or ripple on the supply the only sure way to test the caps is to remove and replace with new (check by substitution).

R709 varies the supply available to the transistor Q520. I haven't read the manual... there may be a procedure for adjusting it but I would still change the caps first before doing anything.

Q520 forms a simple oscillator (with transformer M501) to generate a high voltage for the display.

Good luck... any questions just ask.

I'm not saying the display isn't faulty... it may be... but caps are such a common problem that it makes sense to check them first.
How important is it to match the capacitor values exactly?
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Old 30th May 2011, 10:51 AM   #9
Mooly is online now Mooly  United Kingdom
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No matching required at all... just stick to the original values and choose at least as high a voltage rating as the originals.
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Old 30th May 2011, 11:03 AM   #10
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This is the PCB location,
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