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Old 18th July 2008, 06:23 AM   #11
Mooly is offline Mooly  United Kingdom
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Hi,
Page 10. Pin 1 should go LOW during focus search. This is the 2 or 3 secs that the lens "bobs" up and down. If it does measure the volt drop carefully across the 22 ohm resistor connected to the emmiter of the transistor and calculate the current and compare to the value on the pickup. If it does not see whats happening on pin 19 "LD" on from the system control chip. This could be either active high or active low.
At the beginning did you mean YOU unsoldered the link or it was already missing ?

Edit -- Just to clear pin 1 will only be low for that initial couple of seconds the lens is performing the focus search operation. Be careful measuring around there, no shorts or "spiking" the LD.
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Old 18th July 2008, 01:58 PM   #12
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pin 19 is from 4.65 to 0 after three lens moving up and down.
pin 1 is always 4.85v.

The way I test the laser manually is disconnect base off the circuit and tie it to low and I saw the red beam comes on.

Is this true that the red beam should be always present doesn't matter if the Btl driver has any problem??

Looks like RF amp ic defective, no drive.
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Old 18th July 2008, 05:46 PM   #13
Mooly is offline Mooly  United Kingdom
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Hi,
Pin 19 sounds OK. You may unknowingly have damaged the laser. The laser diode has a built in photodiode on the same die connected to pin 2 of the IC (it's marked PD). This forms an auto power circuit, the IC varying how hard the transistor is turned on in response to the laser light falling on the diode. By just turning on the transistor you put the full 5 volts across the laser limited only by the 22 ohm. Did you just short the base to ground without a base current limiting resistor ?
I have had the PNP transistor fail once, can't remember the make or model now. Its worth replacing it if in doubt. A final check you can do is to measure the volts dropped ACROSS the emmiter base junction during focus search. It should be around 0.6 to 0.7 volts DC. If that happens the IC laser drive is probably OK. Measure across the transistor pins, not from ground to each pin.
The IC is always the last thing to suspect ( although it could be faulty ) Did you also measure across the 22 ohm during focus search. What was the voltage --- thats a big clue
The normal start sequence is the laser diode is turned ON. Focus search commences (the lens bobing up and down 3 times) with the disc stationary (some players do spin the disc however) as it is easier to focus on a stationary disc. When focus is achieved (which is signalled by the correct outputs from the photodiode array) the system control IC receives a "Focus OK" signal and then the disc is spun roughly to speed at which point the disc speed is crystal locked via a PLL. If no "Focus OK" signal is received the Laser is turned off.
Measure that volt drop over the 22 ohm in focus search
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Old 18th July 2008, 09:49 PM   #14
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disconnect base off the circuit, jump voltage with external power supply which was set at 0v. I saw the beam at this point and stopped.
ic pin 2 very small voltage change during the 3 up and down.

Voltage across BE is 0.23v all time. not conducting, no current will go though 22 Ohm.

pin 1 is always 4.85v is not normal??
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Old 18th July 2008, 11:23 PM   #15
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Changed RF amp ic, same situation.
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Old 19th July 2008, 12:56 AM   #16
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Found a old working sony cdp-ce305 from my collections have the same rf and servo circuitry.

swap the rf ic, no luck with the rotel.
check the pin I/O 1, 2 there is an ac signal 16Mhz found in the working sony. Not with the Rotel.

anyone has the Rotel RCD-951 service manual can help????
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Old 19th July 2008, 02:00 AM   #17
anatech is offline anatech  Canada
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Hi fastvideo,
Hang on and review what you have found out so far. What Mooly has said so far is correct. You can damage the laser diode and still see a red light. It may not be a laser any more. In truth, I rarely see a blown laser diode unless a tech has been in panic mode.

This chip is a combined servo / RF amp. I think I may have had to replace a couple so far. That's from the time when CDs where introduced. Therefore, they are very reliable and unlikely to be the fault.

Did you check to see if the DC supplies where the proper voltages and had no AC noise on them. If the laser supply has an RF signal on it, it will actually modulate the laser beam. The result will be a failure to read the disc.

Sorry, no manual. You should be able to service that machine with the IC data sheets and a similar unit to compare to. I think you need to go back to basics and list only things you know to be true. No guesses or conclusions, only things you can measure. That will keep you on the right track. List each fact as you perform whatever test you do to confirm each item. Also ask yourself if there is any other thing that can cause a section not to work instead of condemning a part straight off. Remove and check that transistor for a start. An E-B short could cause your problem. Then, your original mech is either okay, or the new one may be toast as well.

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Old 19th July 2008, 06:46 AM   #18
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Hello Chris,
Hows it going , sound advice as ever. I don't think there's much it can be now, having replaced the IC, and pin 19 the laser on command seems OK. This part of the circuit is prety much self contained.
Change the transistor, nearly any general purpose small signal PNP will do, if you pinch one out of another player make sure you dont choose a "Digital" transistor. Whazzat !!! One with inbuilt resistors.
Also as Anatach says, do check the supplies to the IC on the pins themselves.
I have a feeling that you might be going in circles, with two faults. The player initially failed ( maybe the transistor ) you replace the Laser --- still no good --- so you short the base of the transistor to ground which is able to turn "on" the failed part and this zaps the laser.
Right at the beginning you said the solder blob was unsoldered.
Was this by you or was it already removed ?
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Old 19th July 2008, 11:58 AM   #19
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This is the exact same problem from day 1 I open it up, missing laser beam.
Then I ordered a laser unit but it comes with the complete chassis, so I unsolder the protection link and installed it, same problem. Assuming all motors and laser from the new chassis is good. This where I started to troubleshoot the RF circuit.
The transistor measure good, I already tried with another pnp tr, no luck. RF amp ic is good swapping between a working unit.
Measure all supply line, looks good, no abnormal noise.

It is time for a 2 opinion
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Old 19th July 2008, 05:14 PM   #20
Mooly is offline Mooly  United Kingdom
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Hi,
Sorry I can't really add any more without actually working on the unit and measuring for myself. I do know you will kick yourself when you find the fault. The laser has to light first whether or not there is any other problem.
You could always try unpluging the optical unit and soldering an LED + resistor, say 120 ohm give or take from the collector of the transistor to ground and see if it gives a brief light when focus search is in operation. You could overide pin 19 to turn the LD on all the time. If you were to feed a current ( very tiny ) into the PD input that should vary the brightness of the LED but thats all getting a bit heavy really.
Can I ask, did the player just fail "naturally" in use or has it a history

Edit, Have looked again at the data sheet just to confirm this is a totally "analogue device" -- no data lines, clock pulses, I2C --- anything. It's got to work as it is, nothing external can influence it. Pin 19 is active high meaning it should be tied to 5 volts to permanently enable the laser. It's has to work -- it's something silly this !!!
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