I bought this really nice looking, cheap BC8000 in which - can you guess - the CD wasn't working. I was expecting an easy C2103 job, but not so. Somebody had been in there before me, replaced a number of caps with seemingly good low ESR types, then forgotten(?) to solder C2138 and -40 in place(!!!) and put it back together.

Anyway, I fixed that and replaced the (already replaced) C2103 with the same 4x10uF parallel system that worked great in my CD6500, but it still doesn't work. The test program gives "-2" (focus trouble). Is there an easy way to check if the laser has already fried or if I should bother experimenting further? (CDM 4/57, by the way).

I re-read the previous workshop and noticed that it might be possible to replace just the laser arm with a donor from a similar cdm4 mechanism. Where could I find those, if need be?

You should be able to see the laser on a piece of white paper if you switch the room lights down.

Have you checked the laser pre sets? Someone may have changed them.

Well, not on paper, but in a darkened room I see a definite red glow on the lens, so I guess there's hope. The lens goes up and down too while hunting for focus, so I believe the control and mechanics are basically OK.

I'll read a little more on this to find out where to measure and what before turning anything, I remember the warnings about the laser dying in seconds with incorrect current settings. I was afraid that the trimmers had been rotated randomly. 

Edit: seems like C2159, originally 1.5 uF bipolar and recommended by Martin to be replaced by a 1.5u plastic cap, seems to have been replaced by a 2.2u plain electrolytic by the previous adjuster I should've looked around more carefully before assembling the unit.. I'll do something about that before attempting anything else.
 

C2103 should be a blue Philips axial type - 33uF like the original. Many other types will not work and you can forget about low ESR types - they won't work.

Don't look directly into the laser, you will risk damage to your eyes. The laser normally shines a pale blue if seen using a digital camera (or cell phone camera). Remote control IR LED's can be checked the same way.

Measuring the voltages on the pins of the driver transistor is the safe way to tell if the laser is OK.

Martin

Hello Martin,

Do you know why C2103 must be the Philip 33uF Blue one? They are not easy to get hold of!

Elsewhere on the forum, I've learned that the old Philips cap range now belong to BC Components of Vishay, and this particular cap family is called 138AML. Available globally from www.digikey.com, www.segor.de apparently sells the same stuff; I just ordered today a bunch of them and an assortment of plastic caps for my other current & future B&O projects, for a total of around 100 euros

I don't know why this particular cap is so critical, but I believe the experts...

I don't know why, that's just the way it is.

I've serviced countless machines and I have tried different types of caps but the mentioned one is the only type that works. I know that Martin from Germany (Die_Bogener) has come to the same conclusion. Often, the defective cap, when measured out of circuit, seems fine but a new cap cures the problem.

Remember to check the laser current after changing the cap ! Theoretically, replacing the cap shouldn't affect the laser current, I know, but experience proves otherwise.

Speaking of capacitors, just yesterday I had to replace an 6,8nF sealed polyester cap in a Beomaster 3000. It's one of the grey types, squares-ish with rounded corners. Normally, these are extremely reliable components but this one had completely lost its capacitance (or internal connection). Working together with a resistor as a 19KHz MPX filter in the signal path, it wasn't even in a stressed position. Nothing visually wrong - just no go.

Martin

I agree that alternatives don't work all the time and I am at a loss to explain the reason. I will try one of the suggested websites.

OK, got my caps from Segor today. I went on to replace C2103, and the supposed-to-be-bipolar other cap too (with 1,5u MKS). Still don't work.

However, I overlooked something last time. There's nothing connected to P36, I can't find the motor control board anywhere, and the spindle motor leads are soldered directly on the servo PCB. The BC9000 service manual on the site doesn't specifically mention BC8000. Did it use a simpler spindle motor arrangement, or am I looking at a completely botched up repair job by somebody before me?

(and if yes, what stuff do I need to look for to get a donor for the missing parts?) 

Not a botched repair as far as I am aware. I have seen several soldered spindle motor wires like yours. I think they used a cheaper spindle motor on this version of the CD mech. I remember that I had one of these with a problem with thrust washers on the motor worn and not allowing the motor to turn. I remember canibalising another motor but can't remember where the donor bits came from!

The motor control must be on the servo pcb.

Good to hear, Graham. The servo PCB doesn't quite match the ones described in the service manual so I guess I'm still happy

Anyway, I already bought a CDM 4/19 on ebay so I can transplant the laser arm if need be. This centre is just so good looking that I want it to work, too...