CD servo board problem

15 replies
TO
Offline
tournedos
Bronze
Posted February 2, 2009 at 11:39 GMT
#1754868

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...

link

DI
Offline
Dillen
BronzeModeratorFounder
Posted February 2, 2009 at 12:02 GMT
#1754869

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

DI
Offline
Die_Bogener
Bronze
Posted February 2, 2009 at 13:02 GMT
#1754870

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  

TO
Offline
tournedos
Bronze
Posted February 2, 2009 at 13:06 GMT
#1754871

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.

TO
Offline
tournedos
Bronze
Posted February 2, 2009 at 13:09 GMT
#1754872

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

DI
Offline
Die_Bogener
Bronze
Posted February 2, 2009 at 13:18 GMT
#1754873

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

TO
Offline
tournedos
Bronze
Posted February 3, 2009 at 11:47 GMT
#1754874

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 🙂

A(
Offline
amr (archived)
Bronze
Posted February 9, 2009 at 13:50 GMT
#1754875

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?   

TO
Offline
tournedos
Bronze
Posted February 11, 2009 at 10:39 GMT
#1754876

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 😕

TO
Offline
tournedos
Bronze
Posted February 11, 2009 at 11:06 GMT
#1754877

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?

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