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Old 5th March 2013, 08:47 AM   #1
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Default YBA CD2 alpha : laser diod don't light up.

I have a problem on a YBA CD2 alpha player. The laser diod and the YBA blue LED don't light up. Trying to initialize a new CD, the pick up moves correctly to the center of the disc to the position switch. Then the lens moves up and down to search the CD but the laser does not light up.

This happened after I disconnected and reconnected the mechanism (pick-up + spindle motor + sled motor + switches) from the main board.

The pick-up is only two years old and had been replaced and adjusted by YBA. I swapped the whole mechanism with a spare one got from a TEAC PD-365 but it didn't change anything.

As far as I know, YBA never published any service manual, so I've got the one of the CEC 780-880CD which is built on the same base : a SF90 (with 2 6 pin connectors) Sanyo pick-up and a Sanyo mainboard.

According to the service manual, the laser diod is controlled by the Sanyo LC6554H microprocessor. When the pin 43 is low, the laser emits the beam. In addition of the player state, two conditions must be met : the tray must be closed and the pick-up position switch must be closed. As there is no tray on this player, YBA shorted the tray switch so as it seems always closed.

I checked that both signals came properly from the mechanism to the LC6554H on pins 18 and 19. I checked also all the components on the laser control circuit from pin 43 to the pick-up connector and the laser power supply circuit. The only problem I found is that the pin 43 is always high (+5V) even in initialization time.

Did anyone experience such kind of problem ? Might be something wrong with the LC6554H ?

Thank you for your help.
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File Type: jpg YBACD2.mainboard.JPG (149.3 KB, 90 views)
File Type: jpg YBACD2.mechanism.JPG (88.7 KB, 90 views)
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Old 5th March 2013, 12:23 PM   #2
Mooly is online now Mooly  United Kingdom
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If the "blue YBA" led is a cosmetic indicator then why not troubleshoot that first.

It sounds more like you have lost a rail. The uprocessor is the last item to suspect.
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Old 5th March 2013, 02:30 PM   #3
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The the blue led is located close to the laser diod on the pick-up head. They always light up together. I guess they are simply connected in parallel.
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Old 5th March 2013, 05:29 PM   #4
Mooly is online now Mooly  United Kingdom
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The fact it does a focus search routine but doesn't pull the LD on pin low is a bit disturbing.

Could the micro have got zapped when you were working on it ? I hope it was all unpugged from the mains while you were connecting/disconnecting ribbons. I wonder if a rail was charged and the ribbon made contact somehow.
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Old 6th March 2013, 09:58 PM   #5
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The player was unplugged when I was disconnecting/connecting the ribbon. But, at a certain point, I plugged the main on without the ribbon connected. May be this brought some confusion to the µproc and for some safety reasons, it has locked the laser beam. Yet, this is not documented in the service manual.
Another thing could be that some components from pin 43 to the ribbon didn't like that the circuit was open. They are not so many of them : capacitor C051, 2 transistors used as switches Q12 and Q13 and 4 resistors. I wonder if some damage on one or several of these could maintain the pin 43 in +5V, which is the same voltage as the one on the transistors's emitters and bases. This could explain why the focus works properly.
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Old 7th March 2013, 06:34 AM   #6
Mooly is online now Mooly  United Kingdom
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I doubt the uP has locked anything. That would imply a backup 5 volts and /or non-volatile RAM somewhere. (Sometimes where that is the case then discharging all caps and then pressing tinfoil hard on to the PCB covering all uP pins can remove residual charge and provide a "reset") I don't think anything like that is happening here though.
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Old 10th March 2013, 08:58 PM   #7
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I tried with the tinfoil but it didn't change anything as expected.
I decided to check again all components on the laser control circuit, especially transistors and capacitors which may be tricky to check. I found out that a capacitor was zapped (the capacitance measure was right, so to be clear in one's mind about it, I made a little circuit to check the tension and the time of charge/discharge under the condition of the original circuit). I will tell you when I will get through all of this.
In the meantime, a new picture of the famous blue diod soldered on the SF-90 head. In the background, the zapped capacitor (1) added by YBA ,another capacitor on the laser power circuit (2) , and the two transistors for light up control by the µproc (3 - 4).
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File Type: jpg YBACD2.mainborad and mech.jpg (192.6 KB, 63 views)
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Old 11th March 2013, 07:37 AM   #8
Mooly is online now Mooly  United Kingdom
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Without actually seeing the correct circuit and having the unit to work on its very difficult to diagnose what could be happening. If you have found a faulty cap then that may be a clue.
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Old 11th March 2013, 02:33 PM   #9
maxpou is offline maxpou  Canada
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Hi WhiteBalise,
Michel is a good guy for you, find it and send a PM. Maxpou
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Old 3rd April 2013, 05:32 PM   #10
Michel is offline Michel  Canada
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Hi WhiteBalise,

Are you still having problems with your YBA CD2 Alpha?
If so let me know as I am pretty sure I can help you as I have repaired lots and lots of them.

Michel
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