G'Day All,
Wondering if I could get some help please with this NAD CD player - its VFD is very dim.
Back story to this unit - when I got it, it had the 'no disc' error. Tried cleaning the laser, performed the service bulletin 'fix', and eventually had to replace the laser assembly.
Plays beautifully now. Whilst working on the unit I noticed some components had green corrosion on their leads, so I went about and replaced those as well.
Now for the frustrating (and brutally honest) part - I can't remember if the display was always dim, or whether it only became dim after the surgery I have performed...All I know is it's nowhere near as bright as it should be.
My knowledge is pretty limited and so I've reached the limit of what I'm able to figure out. I've gone through and checked as much as I can with regards to voltages and related components, but I feel I must be missing something...
So here's what I have: In addition to the parts in the 'back story', I've replaced the following components with values as per the service manual:
D505, D510, D511. R394, R520, R523. C560, C561.
If anyone's game to take a look I've linked the service manual, the service bulletin (and also the service manual for the C541* unit) below.
(*this player appears almost identical and the service manual is far easier to read
Thanks heaps,
Matt
C540 Bulletin
C540 SM
C541 SM
Wondering if I could get some help please with this NAD CD player - its VFD is very dim.
Back story to this unit - when I got it, it had the 'no disc' error. Tried cleaning the laser, performed the service bulletin 'fix', and eventually had to replace the laser assembly.
Plays beautifully now. Whilst working on the unit I noticed some components had green corrosion on their leads, so I went about and replaced those as well.
Now for the frustrating (and brutally honest) part - I can't remember if the display was always dim, or whether it only became dim after the surgery I have performed...All I know is it's nowhere near as bright as it should be.
My knowledge is pretty limited and so I've reached the limit of what I'm able to figure out. I've gone through and checked as much as I can with regards to voltages and related components, but I feel I must be missing something...
So here's what I have: In addition to the parts in the 'back story', I've replaced the following components with values as per the service manual:
D505, D510, D511. R394, R520, R523. C560, C561.
If anyone's game to take a look I've linked the service manual, the service bulletin (and also the service manual for the C541* unit) below.
(*this player appears almost identical and the service manual is far easier to read
Thanks heaps,
Matt
C540 Bulletin
C540 SM
C541 SM
C510 is one to replace.
If the -22 volt rail is correct and clean and the filaments are floated away from that by the 5v6 Zener (so you should see 5.6v across that diode) then its either the VFD that is dim (low emission), or it is in fact normal for that player. The segments should be equally lit without bright spots where the filament passes over them.
Also make sure the display is clean and the window and any filter material is clean. You Might be surprised how bright the display is without the front on.
If the -22 volt rail is correct and clean and the filaments are floated away from that by the 5v6 Zener (so you should see 5.6v across that diode) then its either the VFD that is dim (low emission), or it is in fact normal for that player. The segments should be equally lit without bright spots where the filament passes over them.
Also make sure the display is clean and the window and any filter material is clean. You Might be surprised how bright the display is without the front on.
Thanks Mooly.
I've replaced C510 now as well, still no change. I measured the 5v6 Zener and its pretty much bang on @ 5.56v across it. It's also showing a stable -22.2v at the anode end, so I think that means the -22v rail is ok?
Out of curiosity I also measured V across D510 and it came up at -/+22.8v
(note: the parts list in the SM suggests this zener should be between 21.52-22.63V... schematic says 22v so that's what I've put in)
Are VFD's sensitive to voltage? eg: would that 0.2v make a difference to the brightness?(assuming that D510 affects the VFD circuit)
Are there some other points I should be checking voltage further up the chain?
Thanks agan.
I've replaced C510 now as well, still no change. I measured the 5v6 Zener and its pretty much bang on @ 5.56v across it. It's also showing a stable -22.2v at the anode end, so I think that means the -22v rail is ok?
Out of curiosity I also measured V across D510 and it came up at -/+22.8v
(note: the parts list in the SM suggests this zener should be between 21.52-22.63V... schematic says 22v so that's what I've put in)
Are VFD's sensitive to voltage? eg: would that 0.2v make a difference to the brightness?(assuming that D510 affects the VFD circuit)
Are there some other points I should be checking voltage further up the chain?
Thanks agan.
They are not very sensitive to voltage. Ultimately the voltages on the electrodes set the brightness but is not critical.
VFD's do go low emission (they are a thermionic device after all) and they also can suffer from low emission caused by lack of use. In that case they usually brighten up after a few 10's of hours of the segments being lit. If all the voltages are correct this is the most likely cause. There may be a test pin on the driver chip to light them all up at once.
You could try something like a 24v Zener and see if that helps but don't go to high as the driver chip sees this voltage.
I've heard reports that you can improve emission by over running the filament for a few seconds to rejuvenate it. You need a variable PSU and gently bring the voltage up until the heaters are visibly glowing to quite a bright level. Hold it like that for a few seconds and then try the display.
Note... I have never tried the above for this problem and there is a risk of damaging the display heaters if you go to high but I have powered heaters on old displays to see how bright the filaments go and its pretty impressive.
VFD's do go low emission (they are a thermionic device after all) and they also can suffer from low emission caused by lack of use. In that case they usually brighten up after a few 10's of hours of the segments being lit. If all the voltages are correct this is the most likely cause. There may be a test pin on the driver chip to light them all up at once.
You could try something like a 24v Zener and see if that helps but don't go to high as the driver chip sees this voltage.
I've heard reports that you can improve emission by over running the filament for a few seconds to rejuvenate it. You need a variable PSU and gently bring the voltage up until the heaters are visibly glowing to quite a bright level. Hold it like that for a few seconds and then try the display.
Note... I have never tried the above for this problem and there is a risk of damaging the display heaters if you go to high but I have powered heaters on old displays to see how bright the filaments go and its pretty impressive.