advertisement


Another Naim CDi repair - with some questions...

J

jpk

pfm Member
I got a CDI for a good price and grabbed it since it has a CDM4. I already had repaired a CDM4 based player, so knew how to to swap out a dead laser etc. The CDI had no fault but needed recap. I changed all lytics and tants and created this BOM:

in3AeEZ.jpeg


Here is the BOM in "shopping cart mode":

097DJUE.jpeg


In place of the usual 10uF tants I fitted 47uF tants at the input and output of the -5V supply for the DAC. Also I tried a 10uF Wima on the TDA1541A between the -5 and -15V pins but didn't like the kind of harsh sound, so removed it again. After recap I checked the voltages and compared them with the numbers shown in this post. Here are the voltages of my CDI:

5dGkTV9.jpeg


Question: as you can see I get over 60 degrees C at the heat sinks, is this still OK? I adjusted laser power and focus offfset:

YLHFeXo.jpeg


Question: the 400mV is the average of multiple discs, is that the way how it should be adjusted? The voltage across the resistor of my CDI reads 44mV for most discs and goes higher only for some CDs. The RF eye pattern looks good:

OfpVX63.png


I took it from here:

JH2kH4u.jpeg


The player works perfect and sounds great. I added SPDIF output:

397vc0q.jpeg


Schematic:

AAIKlD2.jpeg


The signal at the BNC looks good:

XglAGgC.png


The front fascia logo LEDs stay off at power on until mute is cleared. That is normal according to the manual:

pohOT9T.jpeg


But the logo flickers very faintly when disc playback is started: it seems it indicates mute. I never noticed it before, but I hope this is normal...?
 
Last edited:
Not normal on CDM9 CDi’s, but that’s all I have experience with, sorry.
 
Thanks for the information! I double checked everything, didn't find anything, so I removed the logo LED daughter board and did a reflow of all solder joints (on all PCBs) including the SMD chips. Now the machine runs flicker free. The Naim logo indeed indicates mute condition as stated in these posts:

martin clark said:
It's the relay circuit in the output being set-off by some very low bass/DC on the disc. 'Sees a 'dc' offset, mutes teh output. The flashing logo tells you it has happened.

The CDS 1 has the output connected via muting relay, which is also controlled by a circuit which senses LF content <5Hz and disconnects the output. The time constants got revisited in later players - Cdi, CD2 etc and don't work in quite so aggressive a way. Don't worry about it, it; just a disc out of red-book spec.
Click to expand...

MJS said:
This is completely normal. The display shows the state of the DC servo on the output stage - there are no capacitors in the signal output path. It has a long time constant so can take up to 50 seconds or so.
Click to expand...

wylton said:
The problem to which you refer is generally caused by DC offset which is present on the CD. The CDS is sensitive to DC offset and has a protection circuit which prevents DC from being passed through the amplifiers to the speakers (which would fry the voice coils). When offset is present, the circuit cuts in; this mutes the sound, and the logo will momentarily dim.
Click to expand...
 
The DC offset servo applies specifically to the first generation CDS. The CDI uses a DC blocking capacitor and doesn't use it.
However the mute and display circuit seems overly complicated. There's a simple time delay circuit based on those in every Naim preamp, but it's also over-ridden by an output from the CD micro processor. I have not seen this behaviour in a CDI before, but good to see a reflow has fixed it. You have a CDM4-based player there. Lasers and motor boards are still available from donor players, but they're pretty bullet-proof and last years. It is worth putting a heatsink on top of the DAC to keep it running cooler.
 
Thanks a lot for the input! I have heatsinks of the correct size, but how do I fix them to the chip? And does the SAA7220 also benefit from a heatsink? It runs quite warm. Speaking of heat: the two 3pin regulators on the main PCB that have heatsinks run hot, I read some 67 degrees C on my cheap infrared meter - is that OK?
 
In my experience the DAC chips fail far more often than the SAA7220. Just glue one on with superglue or a bit of epoxy. There are a couple of 5V regulators than run really hot but there's not much you can do about that.
 
The SAA7220runs at about 1watt of dissipation..! but seems to tolerate it.
The DAC runs ~ half that dissipation - but, is far more sensitive/ easily damaged.

I glued small heat sinks to mine as @MJS suggests, as a result. Still running>20yrs later....
 
This site contains affiliate links for which pink fish media may be compensated.
  • Like
Reactions: jpk
Thanks for the input, I will install a heat sink to the DAC chip as soon as I receive my thermal glue :)

I noticed some strange behaviour of the door switch, please let me know if there is any reason to worry. I will try to show what I mean with the following 3 videos:
  1. This video shows my CDi when closing door without a disk. Looks normal to me.
  2. With disk my CDi behaves exactly like the CD3 shown in this video. Also normal.
  3. When opening the lid sometimes this happens: not normal...?
 
This CD player's hush circuit drives the signal from the display panel, and the LED display is synchronized to drive. There are two LM317s fitted with heat sinks that are extremely hot. It is recommended that you mount them on aluminum panels below the PCB for heat dissipation or add more radiators. The capacitance near LM317 LM337 on the circuit board is all to be checked, preferably replaced.
 
  • Like
Reactions: jpk
Today I dismantled the lid mechanism, gave it a very basic clean, adjusted the spring loading of the lid and made the micro switch a bit more responsiv by slightly bending it's lever - after that it seems the CDi is finally behaving well. I adjusted the 7segment display a tiny bit less bright and glued a heat sink to the TDA1541A-S1. Pity the crown isn't visible any more...
 
You must log in or register to reply here.


advertisement


Back
Top