Recently, I tried to play a CD on the Beocenter 8000 I have at the office. No sound came out, so walked up to the machine, opened the CD lid, and was greeted with a putrid puff of smoke *cough*

I opened the unit today. No obvious faults anywere else, but two 10 ohm resistors on the servo board are clearly damaged, and badly off value (on the right in the picture, above & below the two transistors). I dug up another same type servo board I have (probably faulty), and even on that one of these resistors has gotten brown and the resistance is too low.

These obviously belong to the spindle motor control. I tried rotating the motor by hand, it doesn't seem any tighter than normal, and whirrs away quite nicely with a 3V battery. Any ideas? I could start by replacing those resistors, but would rather not shoot in the dark and risk more damage...

While separating the servo board from the mechanism, one of the spindle motor wires came off the motor with no force at all, so there might have been a bad solder there.

Does anyone have the schematic for these later type of servo/mechanisms that have a two-wire spindle motor? I think I've gone through all relevant service manuals on site, and all of them only discuss the earlier types that have the motor control board attached to the motor itself. I could draw it off the PCB but would rather not...

Yes.

Not the best quality but this is what I have at present and I think it'll do.

If those two resistors are gone, the two transistors are probably toasted too.

Martin

Ähmmm, check the transistors, the schematic is wrong... it's a BC328-25 (!!!)  and a BC338-25. Or there will be more smoke ;)

But usually they can survive... but replace them for safety.

Replace the 10 Ohm resistors, disconnect the motor and test it, measure the voltage on the output and the voltage over the 10 Ohm resistors... or test the heat with your finger. They should not become hot.

Edited... : not BC337... it's a BC328-25 for TR6125  

Thanks! I'll take a better look at the patient tomorrow. From the looks of the schematic, it seems there'll probably be no other damage than the transistors and resistors, hope the opamp is OK. I'll check the +/-9.5V supplies first, though... and BC338 probably can't be an NPN and PNP at the same time The PNP one must in reality be BC328?

Do you have an idea why the original resistors are 0.1%? Doesn't seem that critical to me.

Oh, never mind, I'll just nick the transistors from the other board if they still measure OK

The resistors are specified: 10 Ohm, 10% and 0,3 Watt. Nothing special, just normal resistors used as a fuse.

Thanks, guys - it wasn't quite this easy though; -9.5V apparently gets overloaded and can't keep its level. Either the transistors are faulty after all, or TR6314 under the decoder board (the only thing between raw power supply and this rail) has had it. I'll need to get proper replacements before trying again some other day, the Blu-Ray player will have to take care of the CDs until then

I have a Beocenter 8000 with the same problem. Changed both resistors and a transistor that messured out of range. Now the CD spins up and keeps spining at a speed near light:), after 3-4seconds the lid opens. Before doing any "repairs" the cd did maybe move for 3/4 of a round. Anybody who have a clue?   

Back at work... -9.5V was missing completely. The transistor regulating it (BC818, SMD and located conveniently under the decoder board) had burned and I replaced it. The power supply works now.

Then, I replaced the two driver transistors with correct types and the resistors as well. Still no luck - at least one of the resistors gets very hot so I powered down. I measured the current consumption of the spindle motor with 3 VDC (it rotates seemingly normally); without a disc it stays at 30 mA or so and with a disc first jumps a little and comes down to 60-70 mA when it has gotten up to speed. Does this sound normal? I have another (broken) mechanism, and the motor seemed to give about the same values.

What's next

Lo and behold - I connected a multimeter inline the motor circuit to measure the actual operating current, and the darn thing works now! I have tried stopping and restarting the CD a number of times to find out if the spindle motor has some position where it gets stuck, but no. The motor - or perhaps the CD holder - makes a slight ticking noise however, so it might have a mechanical problem...

How much work is it to swap the spindle motor, as I have the other mech I could part out? The hub seems just pressed on the axle?

amr:

I have a Beocenter 8000 with the same problem. Changed both resistors and a transistor that messured out of range. Now the CD spins up and keeps spining at a speed near light:), after 3-4seconds the lid opens. Before doing any "repairs" the cd did maybe move for 3/4 of a round. Anybody who have a clue?   

You probably shouldn't believe anything I say , but I seem to remember that this happens when the focus offset adjustment is way off. DON'T touch the the other trimmer - laser current - though, if you know the CD has worked earlier with its current setting!

I suggest you replace capacitors BEFORE readjusting anything. An adjustment won't just go out by itself, it's far more likely to be one or more dried out capacitors. Could also be a cracked solder somewhere, especially in the voltage regulator areas.
Depending on the deck version capacitor kits are readily available for the servo board (or one can be put together).

Martin

I dont think it has do with the focus offset. Today I took a look at the Beocenter again and I messured the current to the cd motor. -7,4V, which means that the cd spins the wrong way? Am I on to anything now?:)

Ok, in the beginning you see the circuit plan for the motor. It's a dc motor, usually it works with around 3-5V. If you measure negative voltages, then something is wrong... rotating in the wrong direction.

This BC8000 board shown above is almost identical to the CD6500/7000 controller board.

Let's check some things first: The circuit plan is wrong, TR6125 is a BC328-25, not a BC338.

Replace first: 

TR6124=BC338-25

TR6125=BC328-25

R3212 + R3213 = 10 Ohm

C2138, C2140 = 220uF 16V

C2103=33 or better 47uF 16V, axial, MUST be blue PHILIPS or blue BC, other caps will cause problems!

C2104, C2107 = 47uF or better 100uF 16V

Replace ALL electrolyt caps, replace the bipolar C2159 1,5uF cap by a Wima MKS-2. This cap can fail and has already failed several times! 

Remove the motor plug and measure: R3212: +9.5V, R3213: -9.5V

Pin 7 of the IC6103=NJM4560 must be the same voltage measurement like the output pin for the motor. Check it.

Pin 8 of the chip= +9.5V, pin 4 = -9.5V. If one of these powersupply voltages is missing, a savety resister is burnt (R3210 + R3211 =  1 Ohm)

The signal MCES means MotorControlEnableSignal... simple Motor_On. It is a pulse wide modulated signal (140us, 5-50% varation). Check it. checked with a dc multimeter (this is just wrong, but try it...), it must be active around 2.5V

But.... i'm pretty sure, that the focus DOES NOT WORK, probably another resistor or chip is burnt. Check IC6104=L272. Pin 16=-9.5V, Pin 2=+9.5V

Ground is chassis frame.

Thank you for your help, I will get to work

:)