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Naim CDi servo board problem
Naim CDi servo board problem
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Old 3rd July 2017, 08:20 AM   #1
iqpi is offline iqpi  Australia
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Default Naim CDi servo board problem

Hello everyone I've just bought a Naim CDi with issues (that how the previous owner described it). Up on powering the unit up I noticed the motor spins immediately and fairly fast CCW, it just spins and spins no matter what I press, with or without CD. The laser tried to focus and stay in inner-center position but the warp speed made it chucked out an error.

Further inspection revealed that for some reasons someone tried to scratched out two electrical traces. One of the traces leads to the 220uf caps the other leads to the lid switch-connector and the red wire that goes to the collector of transistor 8c338. Right now I have reconnected the traces with solder wires (temp fix) and fired it up. The speed is the same but this time the laser goes all the way out to the edge and stays there and no focus whatsoever. To put insults to injuries I think I smelled that beautiful electrical fume coming out from one of those 220uf caps

I'm not sure what I should do next..any help is greatly appreciated.
Aaron

Edit: The schematic show where the traces are cut and the positions of the 220uf caps.

Click the image to open in full size.

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Last edited by iqpi; 3rd July 2017 at 08:29 AM.
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Old 3rd July 2017, 08:31 AM   #2
Mooly is offline Mooly  United Kingdom
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Naim CDi servo board problem
Welcome to diyAudio Aaron

I've no magic fixes I'm afraid. Firstly, cut print like that is commonly seen as part of manufacturer modifications... not saying that is what has happened here... but worth bearing in mind. So that could be original.

The disc spinning at speed suggests a missing rail or a missing clock signal.

Your best bet is to identify which Philips player this is based on (because that board looks very Philips to me) and then try and identify all the rails that need to be present and work from there.
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Old 3rd July 2017, 08:44 AM   #3
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Hi Mooly thank you for the warm welcome.
You are right this is based on the Phillips CDM4/27 and definitely right about the cut being manufacturer mod. Google also confirmed this.

This servo uses the following three ICs:

a. TCA0372dp2 Dual Op-Amp - driving the Laser Focus?
b. TDA8809t Radial Error Processor - signal processor for motor?
c. TDA8808t Photo-Diode Processor - signal processor for laser control?

Would it be correct to say the 8809 is not receiving the clock signal or itself-is-fried?
Aaron
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Old 3rd July 2017, 08:55 AM   #4
Mooly is offline Mooly  United Kingdom
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Naim CDi servo board problem
I wouldn't condemn any chips just yet. Shorting that print out (and smelling burning) may well have caused further problems I'm afraid.

Firstly you need to check all the supplies are correct. Philips love using fusible resistors and the overload just created may well have caused one to either fail or go high in value. So that has to be the first step. If you haven't a full manual for the Naim then you will have to drag up the data sheets for all the chips and locate the power supply points and confirm them that way.

Secondly, the most common issue on the Philips radial pickups is failure of the 33uF caps (if it is that model and type) on the servo board under the pickup. The 33uF's are favourite but on something this age any of the small axial electrolytics that Philips use will be suspect.
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Old 3rd July 2017, 11:22 AM   #5
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I have replaced all the electrolytic caps and I found one open 1ohm (probably fusible resistor) so I took it out and bridged the connection with a piece of wire of roughly 1ohm and sure enough it is back to how it was when I first turn it on. So I guess I'm back to square one.

I will need to grab a correct resistor tomorrow, will a 1ohm 5% .25W suffice as replacement?
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Old 3rd July 2017, 11:28 AM   #6
Mooly is offline Mooly  United Kingdom
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Naim CDi servo board problem
The standard resistor should be OK for now. Safety (fusible) resistors don't smoke and burn when overloaded in the way that a standard carbon or metal film will.

If you haven't already done so then you still need to check all the supplies are correct. Beyond that you need to concentrate on the observed fault. If the platter motor is spinning then look at the drive amplifier, its supplies and then any inputs to the chip. You then work back from there seeing if there is any obvious reason for the platter drive chip to be receiving a 'spin' voltage.
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Old 5th July 2017, 09:00 AM   #7
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Bit of an update:
I checked the voltages on the servo and they checked out alright. Since then I have moved to the main board because with or without the servo board connected the motor still spins upon turn on and the motor cable is connected directly to the main board. I didn't wanna touch the main board before because Naim made it difficult to disassemble the board from the chassis.

I measured 4.9V at VDD of the 7220 IC and the regulator supplying the 5V is also giving 4.9V so thats all good. Pin 9 clock out put from 7220 IC is giving 1.7V so thats good too. Now I have traced pin 9 to 7310 IC and have continuity at pin 26 of 7310 (as pictured). I dont have the schematic for the main board so it is a bit difficult to trace especially when the trace runs underneath another component and disappeared into oblivion.

Reflowed solder at the crystal oscillator and the two caps made no difference...
Aaron

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Old 5th July 2017, 09:43 AM   #8
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Voltages from the regulators, they look ok to me.

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Old 5th July 2017, 11:44 AM   #9
Mooly is offline Mooly  United Kingdom
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Naim CDi servo board problem
You are really going to need the correct circuit diagrams I suspect. You have to work with what you can see and observe as being faulty... which is the motor spinning.

If you locate the motor drive amp and can confirm that it is either spinning in response to an input voltage or spinning when no input voltage is present then that is a start.

I think this is going to be an uphill struggle tbh, but you have nothing to lose in seeing what might turn up.
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Old 5th July 2017, 12:00 PM   #10
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Mooly, thank you for your help s far

I took out the crystal oscillator and the symptom persist so most likely clock related?
I will try to do as you suggested, I could not find the schematic for the life of me. I dont think Naim ever releases the schematic for the CDi.
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