Hi Menahem:

The diameter is important in that the piston needs to move freely but with limited play; we'd have to find one that matches closely.

But it isn't critical that we get it "exact."

The former should be some non magentic material. The most ideal would be same thickness but otherwise thinner would be more preferable than thicker.

When I was a kid, I wound several solenoids. I used flexible tubing as the former and a metalic rod as the core and some good strength from them.

It's not as critical as the resistance / # of turns.

Crossover inductors or voice coils would require more precision, these are much more forgiving.

Need your help again guys!

I have cleaned the contacts on the microswitch and set everything up from scratch ( the mods suggested in the service manual have been done).

When I play a record the arm drops in the correct place, plays for about 20-30 seconds and then the  arm lifts and drops and continues on playing as normal. I have not done the led conversions as yet as I didn't want to introduce another variable.

What to do???

Not sure if this has already been tried or if it's any help at all:

B&O Tech info BGT-3 describes a problem:
"It has been found that in some cases the arm raises undesireably
immediately after lowering when the set is connected to a voltage
source apprx. 10% below the nominel."
Fix: 8R6 has been changed from 1MOhm to 560KOhm
(This change was done in production from serial number 1787001)

B&O Tech info BGT-4 says:
For Type 5503 and 5513
"In case of intermittent lift/lower problems replace 1C23 (Type 5503)
or 1C20 (Type 5513)".

B&O Tech info BGT-2 says (a.o.):
Ambient light shining down on the photo-sensor (f.e. if top covers are
not mounted or reflections come from a sharp spotlight in the right angle
onto the deck), can also produce an undesired lift.
(But in my experience usually a run-off to park position afterwards rather
than a lowering).

Martin

Thanks Martin, I'll look into this tomorrow.

Dillen:

Not sure if this has already been tried or if it's any help at all:

B&O Tech info BGT-3 describes a problem:
"It has been found that in some cases the arm raises undesireably
immediately after lowering when the set is connected to a voltage
source apprx. 10% below the nominel."
Fix: 8R6 has been changed from 1MOhm to 560KOhm
(This change was done in production from serial number 1787001)

BGT-3 Does not seem to apply to my type number. My 8R6 is on the decoder board and there is no sign of such a resistor

B&O Tech info BGT-4 says:
For Type 5503 and 5513
"In case of intermittent lift/lower problems replace 1C23 (Type 5503)
or 1C20 (Type 5513)".

BGT-4 Is probably relevent to Type 5502 as well so this is worth a try - awaiting component!

B&O Tech info BGT-2 says (a.o.):
Ambient light shining down on the photo-sensor (f.e. if top covers are
not mounted or reflections come from a sharp spotlight in the right angle
onto the deck), can also produce an undesired lift.
(But in my experience usually a run-off to park position afterwards rather
than a lowering).

My problem exists even in a shelving unit which is not near a window or lights.

Martin

Sorted!! Thanks once again to that genius who is TJ.

Apparently, the new drive belt on the arm servo motor is too tight. Replaced it with the old belt and problem gone!!!

***edit***

Further investigation has revealed that the problem was lack of lubrication. The old belt was too stretched to drive the threaded shaft on a consistant basis. I have cleaned and relubricated the threaded shaft and the bushes, re-fitted the new belt and all appears well. Still testing!!

I did the training course for the 6000 system in '74, it took 4 day's!!

We used a Santana album among others to test the cd4 effect,definately the best surround system of the day (or since?)

I can still find my notes to the course,but have lost my hair and several marbles since!!

I can help if you get stuck.

Nick

Thanks Nick, all seems to be OK at present.

I'm sure you could find your marbles if required!!

4 days seems a long time for the training course although Tim does indicate that they are "thoroughly unreliable" so it was probably time well spent.

Hi Mika:

I thought I'd share my experience as this problem has consumed many hours of my time.

Yes spurious noise in the photoresistor  RPY 58 is the problem.

In a previous post I suggested flipping the sensor around. This may work. I also sourced and purchased new old stock RPY 58 and tried a few without success. There may be high variability in the noise parameters of this device. 

 B&O Tech builletin from June 20th 1975 (Issue No. BG6/75) offers the solution. (found at back of service manual on for this series on this site).

B&O suggests 2N5779 photo darlington replacement. This component is obsolete. And it does not cross reference to any other modern equivalent that I can find.

As a modern substitute, we can use Vishay BPW77NB. This has very close parameters, but different physical packaging.

B&O also specifies a new housing for the transistor. This is also obsolete. Fortunately a new housing is not necssary. Simply reuse the existing one. With a hot utility blade, carefully cut/melt off the back old plastic casing so that  BPW77NB can fit inside.You will need the slotted housing in order for reliable discrmination of the bands on the ruler.

Clip off the base lead and bend and solder emitter and collector leads to solder pads. Use pliers to align position of sensor to the light slot from the lamp on the other side of the ruler.

The rest of the fix is per the bulletin.

Works :)

Derek

Excellent Derek, thanks for sharing

I'll consider that if the problem ever bothers me again - my BG6000 has worked fine now for a long time, but it gets quite a little use.

Thanks Derek!

Excellent info!

Menahem

Thanks Derek. I'm still having very intermittent problems.

I have ignored it for now as I have been busy with other things but this sounds like it may be the fix.

Hi Mika:

Mine had little use as well after I thought I had exorcised the demon. 

Then when I went to demostrate my 4002 to people that had never seen one before, and were awed by the beauty of the design, it turned out to be a VERY embarassing situation for me!

So I had to make it go away for good!

Derek