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.
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.
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.
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.
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.
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.
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.
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.
Do you have a 'scope.
C2251 ? 220mfd, just dab another across it, anything 100mfd to 1000mfd to see.
Check those safety resistors haven't gone high, the 6.8 ohm mainly.
If C2251 is OK and you have -28volts on emmiter of transistor then the reg is OK.
You could still get a DVM to read -28volts with faulty C2251 though, so you must "prove" it's not that first. If the 4.7volt zener is OK (4.7ish volts dropped across it) ... prove if your not sure by substitution, then it's looking like the display
C2251 ? 220mfd, just dab another across it, anything 100mfd to 1000mfd to see.
Check those safety resistors haven't gone high, the 6.8 ohm mainly.
If C2251 is OK and you have -28volts on emmiter of transistor then the reg is OK.
You could still get a DVM to read -28volts with faulty C2251 though, so you must "prove" it's not that first. If the 4.7volt zener is OK (4.7ish volts dropped across it) ... prove if your not sure by substitution, then it's looking like the display
Mooly said:Do you have a 'scope.
C2251 ? 220mfd, just dab another across it, anything 100mfd to 1000mfd to see.
Check those safety resistors haven't gone high, the 6.8 ohm mainly.
If C2251 is OK and you have -28volts on emmiter of transistor then the reg is OK.
You could still get a DVM to read -28volts with faulty C2251 though, so you must "prove" it's not that first. If the 4.7volt zener is OK (4.7ish volts dropped across it) ... prove if your not sure by substitution, then it's looking like the display
I have a scope.
I missed that 4.7v zener. I just had to look closely to see it lol.
I'll check that.
Mooly said:
I reduced the value of the 10R resistor (3848) which is connected to pins 44/45 of the VFD down to 3.3R (possible a little too low - but the filaments are not glowing too much!
I think the correct term for this is filament, and I was wrong to refer to it as a heater (although I think it performs the same function?).
Mooly said:
IIRC that was a little high (low?), at around -23v
Originally posted by Mooly http://www.diyaudio.com/forums/images/icons/icon12.gif
Scope across C2251, remember ground lead to POSITIVE end of cap. Any ripple ? anything over 0.5 volt or so may be problem. The emmiter of transistor should be "clean" but will probably show small HF component due to multiplexing of the display.
C2251
I shall try that cap just as soon as the family leave the dining room - we've all just finshed our "tea" and I use the dining room table as my workbench!
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