Beocenter 9500 CD Decoder Board Repair

[auric]

Hi:

I have BC 9500 with a faulty CD decoder board.

The CD mech is working and functions in another unit. No problems with the special blue axial cap.

When I hit play, the laser in the mech will move to seek to read the TOC, but the CD spindle motor will not spin up.

I get 9V, 5v, -6 and -9V rails supplying voltages to the mech.

Any suggestions on where to start looking?

Derek

 

 

[chartz]

Hi Derek,

Long time no see!

Have you replaced the blue cap?

Location: Burgundy

[auric]

Hi Jacques:

The famous “blue” cap is on the servo board of the CD mechanism.

The fault in my system is in the controller / DA decoder board.

Derek

[Die_Bogener]

You have the repair manual?

The motor only needs 4 pins.

+9V, -9V, ground and a DC control voltage for the rotation speed.

That’s all … easy to check.

The motor itself is a 4-coil stepper motor.

[auric]

Hi Die:

I have the schematics for the servo and decoder board  from the BC9500 service manual.

It’s the decoder board at fault. (Picture attached). The cd mechanism works fine. CD mechanism plays fine on another 9500 chassis.

Just when the decoder board was failing, it would spin the CD slowly in reverse.

Derek

[Die_Bogener]

Hmmm, where is the blue Philips…???

Or, more precise: Are they all gone on vacation? Or all dead…?

 

It will not work without these blue Philips or Vishay/BC.

[Dillen]

And apparently, some ICs were replaced as well.
I may be able to find a working module in the dungeons if needed.

Martin

[auric]

Well that’s actually my working decoder board.

I know there is some controversy over the Philips/Visay axial blue caps having gone through the archived posts on whether they are specifically required.

Since I have very limited experience with the Philips CDM series transports, I won’t challenge anyone who knows a lot more about these things than I do.

All I can say is someone replaced them years ago and the board has been playing fine on my working 9500 unit. I also noticed that on the early Beocenter 2500, also a Philips CDM4  transport, there are no blue Philips capacitor inside.

The decoder board on the non-working 9500 that has now gone bad is stock original. I really don’t like shotgun replacing all capacitors. Are the blue caps suspect? All voltage rails are present and at the right levels.

 

Derek

[orava]

IF i remember right, I did have to change some transistor times ago… Maybe worth to check them?

[auric]

Thanks Orava:

There is one transistor, BC 818 that regulates the -9V rail that is prone to fail and I know to check it.

Its really strange that all of the other power supplies are on the big heat sink or implemented with higher current transistors. The BC 818 is a surface mount under the PCB.

On this occasion its not that one.

Right now the laser will seek, but the motor won’t spin. I may move a few degrees but won’t spin up.

Derek

 

 

 

 

[orava]

Also, you probably noticed that those wire connectors are terrible and cold loose connetion.

[auric]

Hi Orava:

Yep. I reflowed all off the solder joints on the connectors. So far still no luck.

 

Derek

[Die_Bogener]

The Blue Philips is something special. It is not a  “Low ESR” type.

More or less the opposite… it is something like a “High ESR” type. Ideal for slow R-C Filter units and working pretty linear.

All CD units need a slow working filter for drive speed, rotation, focus and so on… to get all filters at the same time working in spec.

LOW ESR DOES NOT WORK. At least, not reliable…

 

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