Anyone have a deep understanding of the philips CD control and decoding system? The SAA7341 Decoder IC?
I am trouble shooting a CD player that has a problem with the CD motor control. The CD spin's backwards and won't read a disc(i believe it does not have any PWM motor control). Looking at the Datasheet for the SAA7341 it is a bit cryptic on how it controls the PWM to the CD turntable motor. the datasheet reads as if it ONLY controls the motor on acceleration. but does not give any info if it controls the motor during play?
In the attached photo. pin 28 of the SAA7341 is the PWMA output that is connected to the MC68 Micro controller and the TCA0372 Power opamp that controls the turntable motor.
i am trying to understand the joint operation between the 7341 and the MC68 controllers. I believe one or the other is not putting out the PWM signal to control the motor. one or both IC's may have failed...OR...the problem might be further upstream. is there a Laser/focus/radial error causing a loss of PWM? how do i tell...etc
Is there anyone here that has a solid understanding of these old machines?? Please PM me.
I am trouble shooting a CD player that has a problem with the CD motor control. The CD spin's backwards and won't read a disc(i believe it does not have any PWM motor control). Looking at the Datasheet for the SAA7341 it is a bit cryptic on how it controls the PWM to the CD turntable motor. the datasheet reads as if it ONLY controls the motor on acceleration. but does not give any info if it controls the motor during play?
In the attached photo. pin 28 of the SAA7341 is the PWMA output that is connected to the MC68 Micro controller and the TCA0372 Power opamp that controls the turntable motor.
i am trying to understand the joint operation between the 7341 and the MC68 controllers. I believe one or the other is not putting out the PWM signal to control the motor. one or both IC's may have failed...OR...the problem might be further upstream. is there a Laser/focus/radial error causing a loss of PWM? how do i tell...etc
Is there anyone here that has a solid understanding of these old machines?? Please PM me.
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Hi, this question intrigued me, as I was an IC designer on the optical disc products at Philips Semiconductos/NXP quite a while back, so wondered if I recognised this device (or had even worked on it). However, looking at the datasheet, it looks to be a very early device as it has a very low level of functional integration and will have been partnered with quite a few other ICs, so I think it even predates my time there.
It does have this diagram in the datasheet, so maybe it could be instructive to look at all these signals around what seem to be some external discretes. There can as you might imagine be many reasons why the motor control can fail, apart from the output driver, as it relies on modulated data being read from the disc to sense the disc speed as an input signal for the motor control
It does have this diagram in the datasheet, so maybe it could be instructive to look at all these signals around what seem to be some external discretes. There can as you might imagine be many reasons why the motor control can fail, apart from the output driver, as it relies on modulated data being read from the disc to sense the disc speed as an input signal for the motor control
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the transport itself works perfectly fine in another CD player so I know the laser is good. But there could be problems between the laser and the decoder chip. there is a TSA1301t disc drive servo chip that could have problems also.
looking at a Philips CD910/920 service manual which uses the same transport and IC's has little troubleshooting info on the subject. I know there is a service mode but i am not sure how to use it and there are not many details in the service manual.
other than just shotgunning all the IC's and hoping one of them fixing the problem, I would really like to understand better how this works. it actually kind of interesting.
looking at a Philips CD910/920 service manual which uses the same transport and IC's has little troubleshooting info on the subject. I know there is a service mode but i am not sure how to use it and there are not many details in the service manual.
other than just shotgunning all the IC's and hoping one of them fixing the problem, I would really like to understand better how this works. it actually kind of interesting.
Oh yeah, the 7341 chip can be put into two modes for Motor control. Single ended which this deck uses, just uses the PWMA port. or a 4 wire mode.
Ah the good old TDA1301 DSIC (Digital Servo IC, this function was later fully integrated into the main CD controller chip). It is only responsible for the laser positioning on the disc using the photodiode LF data, the speed control will be using the photodiode HF data from the data pit/lands on the disc. This looks like it comes into the slicer on the SAA on the HFI pins 38/39. Following these back there may well be another IC which is splitting the HF from the LF data
Depending upon which Player yours is (you don't give the Model Number) many Philips Players which suffered from this symptom had a failed Oscillator Signal which I seem to remember was developed right at the DAC end of things.
Looks like Pin71 of the SAA7341 (which I understand is the DAC) is 'Xin' and so I would assume should have a clock on it. Many Players using this IC have a Crystal across Pins 71 and 72 but your Schematic doesn't show this and the Signal is coming from the right and in Philips Service Manuals that often means towards the O/P. The 7341 being the O/P must mean that the Clock Signal is derived elsewhere (Digital Filter maybe?).
Can you let us know the Model of the Player?
P.
Looks like Pin71 of the SAA7341 (which I understand is the DAC) is 'Xin' and so I would assume should have a clock on it. Many Players using this IC have a Crystal across Pins 71 and 72 but your Schematic doesn't show this and the Signal is coming from the right and in Philips Service Manuals that often means towards the O/P. The 7341 being the O/P must mean that the Clock Signal is derived elsewhere (Digital Filter maybe?).
Can you let us know the Model of the Player?
P.
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For reference purposes look at the Philips CD910/920
the 7341 is a Decoder chip, the DAC comes after this chip
the 7341 is a Decoder chip, the DAC comes after this chip
I think those Philips Players use a Crystal to derive the necessary Clock. (I'm having to work from memeory as I appear to have reached my alloted download quota in Hi-Fi Engine (didn't know there was one!!)) whereas the circuit you posted earlier (Post#2) shows the Clock coming from somewhere to the right.
Can you give the Model of your Player?
P.
Can you give the Model of your Player?
P.
So the circuit in post #2 is not your player?
Am I not right in thinking the Philips CD910/920 uses a Crystal across Pins 71&72?
P
Am I not right in thinking the Philips CD910/920 uses a Crystal across Pins 71&72?
P
there is a crystal just off screen that feeds pin 71 in only. so that is different. But. what is your thinking? that the crystal has gone bad?
Well, certainly on their older players, when that Clock went missing it caused your exact symptoms.
I presume the Tray is working and you can insert a Disc OK, pointing to the fact that the Motor's Supply is OK?
But when the Disc is loaded it starts to spin the wrong way as you describe in your first post.
I firstly would check this Clock and then check all your Supplies.
They all must be good and clean.
Do you have an oscilloscope? I think this is going to be a necessity for this unit.
P.
I presume the Tray is working and you can insert a Disc OK, pointing to the fact that the Motor's Supply is OK?
But when the Disc is loaded it starts to spin the wrong way as you describe in your first post.
I firstly would check this Clock and then check all your Supplies.
They all must be good and clean.
Do you have an oscilloscope? I think this is going to be a necessity for this unit.
P.
I will check that. and yes I have a full lab with several scopes!
and yes, the tray opens and closes, you can insert a disc but no TOC pops up. just says ERR and if you press play the disc spins backwards. and you migt be on to something. the crystal goes through a logic IC and then to the decoder chip, but it also connects to a chip for the SPDIF output port on this player. if there was a power surge. static or lightning strike, it could have come through the SPDIF port and wiped out that chip. that could block that crystal reference from making it to the decder chip...hmmmmm
and yes, the tray opens and closes, you can insert a disc but no TOC pops up. just says ERR and if you press play the disc spins backwards. and you migt be on to something. the crystal goes through a logic IC and then to the decoder chip, but it also connects to a chip for the SPDIF output port on this player. if there was a power surge. static or lightning strike, it could have come through the SPDIF port and wiped out that chip. that could block that crystal reference from making it to the decder chip...hmmmmm
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Ok, I have checked that all the crystals are working and that they are feeding their respective pins. I have also replaced EVERY IC in the thing and made sure that all the power supply voltages are where they should be and no change....so I am missing something. there is a shorted cap or something someplace
OK, let's start from scratch.
Power ON. No Disc. What's the Spindle Motor doing?
Open Tray. What's the Spindle Motor doing?
Disc in Tray and Close the Tray. What happens? Disc immediately starts to spin backwards as soon as it hits the Motor? (Because the Motor is already spinning?)
Or, the Laser Focuses on the Disc and recognises there is a Disc, but starts to spin it backwards?
P.
Power ON. No Disc. What's the Spindle Motor doing?
Open Tray. What's the Spindle Motor doing?
Disc in Tray and Close the Tray. What happens? Disc immediately starts to spin backwards as soon as it hits the Motor? (Because the Motor is already spinning?)
Or, the Laser Focuses on the Disc and recognises there is a Disc, but starts to spin it backwards?
P.
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I will double check, I know that once you power on, the disc doesn't move, the laser tries to focus, then the cd spins backwards.
I can see Brief PWM pulses at the input of R79 before the cd starts to spin backwards.
I will go through the whole start up procedure tomorrow and figure out whats going on. I found out this era of Players is known for bad circuit boards. open and shorted traces so I am guessing there is an open trace someplace.
Zc
I can see Brief PWM pulses at the input of R79 before the cd starts to spin backwards.
I will go through the whole start up procedure tomorrow and figure out whats going on. I found out this era of Players is known for bad circuit boards. open and shorted traces so I am guessing there is an open trace someplace.
Zc
Ok, No disc, power on. turntable motor hums for 1 second and the laser jumps up and down then the turntable motor starts to run backwards for a second then stop. display says "No Disc" as expected.
open tray, insert disc, close tray, disc spins backwards, and "Err" is displayed and then disc stops and display says "Loaded". I cannot see the laser.
If you press play at that point. the disc spins backwards and the display just says "Err"
I have started manually testing every trace
open tray, insert disc, close tray, disc spins backwards, and "Err" is displayed and then disc stops and display says "Loaded". I cannot see the laser.
If you press play at that point. the disc spins backwards and the display just says "Err"
I have started manually testing every trace
as stated before. the transport works fine, i can swap it into another player and it works fine so I know the motors) and laser are fine etc.
I assume you have the schematics, right?
Make sure the signal coming from pin 13 of IC7700 is healthy - is the 4Mhz ceramic oscillator (1700) signal healthy?
IC7102, pin 27 drives (speed reference) the turntable motor, (together with the above control to start and stop the spinning of the motor).
The linear OP amplifier TCA0372 can go bad, which will send the turntable to max speed.
Also, make sure that the standby signal coming from pin 11 of IC7700 is correct AND the two transistors are okay (7140 and 7141)
Make sure the signal coming from pin 13 of IC7700 is healthy - is the 4Mhz ceramic oscillator (1700) signal healthy?
IC7102, pin 27 drives (speed reference) the turntable motor, (together with the above control to start and stop the spinning of the motor).
The linear OP amplifier TCA0372 can go bad, which will send the turntable to max speed.
Also, make sure that the standby signal coming from pin 11 of IC7700 is correct AND the two transistors are okay (7140 and 7141)