I just received my first Beogram 4004.An excellent piece of engineering.It was sold as is,not working,which is just the kind of project I like.Everything seems ok except the slide transport will not increment automatically as the arm becomes offset,and eventually the tonearm reaches maximum travel and the record just skips.I have opened it up and ran it manually moving the tonearm from center attempting to get it to trigger the transport motor,but nothing.The belt is in place and the slide works fine manually.I see what appears to be the sensor(s) for telling the transport to increment. An optical sensor,perhaps?No caps have been changed to my knowledge,and I have done no further troubleshooting.Iwas hoping someone may have seen this or could offer some suggestions to get me on the right track to troubleshooting.

Thanks

Paul

Inside a small plastic housing at the foot of the carriage, you will find a sensor, a lamp and
an interrupter that follows the movement of the tonearm.
I'm sure you will find the lamp is defective.

Martin

Excellent.Thank you.An incandesent lamp with visible light?Or an infrared LED?

Paul

Good call,martin.I have the assembly out and the lamp is burned out.Now for a suitable replacement.I Measured 22 volts on the circuit.I have a 14v .08amp lamp and a 28v .04 amp.Would either of these be suitable?I notice the schematic just list the part as "housing with lamp".

I seem to remember it being a 24V lamp 25mA or so.
It's not listed in the service manuals but I think it is in the tech notes.
Probably slightly underrun in voltage to extend lifespan.

Martin

I am considering a white LED and dropping resistor but it is a bit too much voltage to drop for my liking.

Done!

Installed a white LED with hot glue.Used a 1k 1 watt dropping resistor.Works great.It might be my imagination but this thing seems to sound better than my BG3400,using the same cartridge.

Thanks for all the input

Paul

Hi Paul

That sounds like a neat solution - I know that those lamps are very difficult to source.  Have you any photos showing how you put everything together?

Regards

Geoff

Geoff

Sorry,didn't take any pics.I'll describe.I can't claim the patent on outfitting LEDs on these machines as I have seen it done on this forum.

-First mark how far the lamp protrudes into the housing.

-Next I cut away the square block portion that is filled with adhesive holding the lamp.

-Then tack the LED in place inside the housing with a drop of hot glue,taking note of polarity,and placement as original.

-Then place masking tape,as a filler to the back section,over the leads.

-With the LED firmly in place,and the back hole sealed,I added a more generous portion of glue to encase the back of the LED and fill the back.

-After the adhesives dries,Peel away the tape.

-A dab of black paint or permanent marker to the back of the adhesive to seal out light and give a finished look.

-cut the Leads to approx .25 inches,solder a light guage wire salvaged from a 1/8 watt resistor to the negative lead for flexiblity when adjusting.

-solder a 1k 1watt resistor to the possitive lead.

-Re install everything and put a bit of a bend in both the thin wire lead and the resistor to give flexibility when adjusting.

The interesting thing about this project was the 1 watt resistor I used.It is physically the size of a 1/8 watt carbon comp.believe it or not.I accidently ordered it for a different project and thought I had either ordered the wrong part,or they had made a mistake.After looking into it,the resister is indeed a 1 watt,designed to be extra small.I was sceptical of it's use in the tube amp it was originally ordered for,but I tried it here.The small size made for a nice clean job,a full size resistor would have been a tight squeeze.I ran it non stop for a few hours last night.It seems to be working well.

If I had to do another,I would probably use epoxy as a filler for a more robust,finished look.

I regret not taking step by step pics!Oh,well..I guess I will have to buy another Beogram.

Regards

Paul

Good job Paul!

My "invention" is certainly not a patent, and I'm very pleased to see others using it!

Actually, B&O started using LEDs for these sensors in later production versions.

But that took a redesigned PCB to do the job.

Here you can see the 1K Resistor mounted

Menahem

Very nice Menahem.

Is that a vacuum tube socket I see in the background?

Yes,

On the very early production versions of the BG4002 and BG 6000, they probably still had a large stock of vaccuum sockets available from the vaccuum days, so that's what they used to connect the CD4-RIAA PCB.

More proof that the old over-engineered stuff is so much better.

In the later production versions, they used a flat socket, so flimsy in comparison!