Cold start problems with CD transport

[dnsey]

I had a similar fault (laser not reaching TOC track), nad after much investigation it turned out to be due to a nearby (small) mains transformer. The magnetic field was influencing the mechanism to an amazing extent - I wouldn't have thought it possible! Re-orientating the transformer completely removed the fault.
If in doubt, try your player well away from any other equipment.

[Cobra2]

It sounds like a weak (power-)servo, maybe an op-amp, that controls the swing-arm, or too little start-up current?

Arne K

[phimor]

Hi,
I had a CD200, (CDM0) which did not start at all. Turned out to be a shorted 27nF cap near the radial opamp. The opamp would go into shortcircuit protection and shut down. No radial movement, no play.

I mention this because until I found it, probing around the opamp for the focus would cause the swing arm to move (radial), which made diagnosis a little tricky. (I have no electronics training)..

Perhaps you have a cap that is just starting to go bad, then 'heals' as it warms. If I was to do it again, I would start by changing all caps near those opamps.

Cheers

Philippe

[DoctorWho70]

Hi to all,
Thanks in advance for the help...
yesterday i have dismounted the rf/servo board another time to make some modify.
I have changed all the el caps of the power supplies increasing they in 220u from 47u, i have decoupled all the power supplies near the ic with 100n multilayer, and also for all the el caps.
i have redone all the solders (all for being sure ).
I changed all the old dish capacitors with murata multilayer ceramics of the same value.
Remounted, retrimmed the two trimmers for the good laser values.
At the first power on (before trimming the laser 50mV which was 57mV) inserting a cd, the sevo makes a 1/8 turn counterclockwise and the toc is reached....
but, after i had regulated the 50mv i had extracted the cd, put another and when inserted, no movement of the motor and error, no toc...
I tried to press play (after some seconds) moving the cd with a finger during focusing start and the toc had been reached...
I have seen after some hours (waiting to cold the electronics) the same thing... no movement of the cd no toc, little movement counterclockwise toc ok...
Is this normal this movement counterclockwise of the cdm when i insert a disc?
I have seen also that if the cd is just inserted at the power on the drive not moving but reach the toc...
The motor drive is in another board downside the motor in the cdm and the opamp wich drives the motor is near the saa7310 in the processor board... i'll try to dismount this board and make something on it...
I've checked many of the signal of the rf/servo board with the scope after the cdm started, without seeing nothing wrong...
I've not followed the path of the cdm service manual but the hf and servo focusing and other signal results at the same level of the service manual.
Bah... i have downloaded the two datasheet of the cdm ics (tda8808t and tda8809t, i can't attaching because they are 120kx2) if someone need it...i can post they by mail
I've tried to read they but i'm a bit confused if this ics are controlled by the processor or in the start they had to start automatically with some circuit hardware startup, as i have read.
Please i need if someone expert of cdm explicate me if this movement of the cd during focusing is natural, has to be ccw or cw and inducted from who...
Thanks in advance
DoctorWho70

[DoctorWho70]

Probably i've found the problem...
reading the service manual manual i placed the cd in service mode 3, then pressing play the display write error 2 as written in the manual: no TL pulses at start up; check TL, HF,photodiode signal processor (tda8808) and if the cd is present...
So i focused my attention to the tda... but with the scope i didn't see nothing strange in the HF and TL, the only problem is the absence of the motor spin to reach the toc...
One strange thing is that measuring the wave of the starting cap (22nF) with the probe the cd didn't stard also when hot, and without the probe all was ok... very strange for the very low capacitance of the scope probe, the starting cap have a time of charge of about one second... so i've changed all the polyester capacitors around the tda8808 (in the HF path and the tda working related capacitors).
This evening i remounted the board and after a cold restart the problems seems disappeared...
The motor spin immediately in every condition and reaches the toc without problem... the laser power trimming and the focus voltage remained on the same values.
also the sound seems to be changed a bit... little more bass precision and a bit in sound stage, but seems turned a little bad in the higher frequencies and transient...
I'll wait for some hours of burn in... and i'm not so sure that tomorrow the problem won't appear...
answer: better to use polypropylene caps in the hf path instead of normal polyester? i've placed also some multilayer ceramic capacitor instead original polyester and some wima MKS....
This capacitors in the hf/servo board of the cdm could really influence the sound???