Hello,

Man is this frustrating, I just did a capacitor replacement on a Beogram 4002 that I thought would fix the table. The tone arm goes across the record but does not set down and then returns to the starting position and shuts off. It will not decend even using the down button. Everything else that I can check out seems to work. I do notice two things which I have no idea of their significance. The foto resistor at the base of the tone stays lit as long as there is power to the table even in the stop position. Also the lamp that is part of the optical-sensing circuit (behind the plexiglass ruler) does not light. I have another turntable I could swithch this out with that has a different type of lamp in it. The one on this table has a cylindrical metal case around the lamp the other is a bare bulb on the parts table. If anyone has had a similar experience and any suggestions it would be appreciated.

John

There are many different versions of the Beogram 4002 and different
types of lamp/sensors for the ruler. The lamp assy's are not directly
interchangeable.
One type uses IR, which is light you cannot see.

Check the lamp inside the sensor arm and its position with relation to the
lens system, check also the signal from the sensor. The radial streaks on the
platter makes for a good signal for a scope check.
If it sees no record, it will not lower the tonearm.

Martin

Hi,

If your Beogram 4002 has the IR detection (like mine!) you can actually see it glow with a digital camera, on the back LCD (in the dark). It will apprear blue-violet. I think Martin himself gave me this trick!

On my 4002 the shutter bulb was fine, but there was a bad solder joint. This could also happen within the detector arm I suppose.

The foto resistor at the base of the tone stays lit as long as there is power to the table even in the stop position

This is not normal at all. Have you checked the stop switch? Are you sure nothing is preventing the carriage to actually reach its real resting position?

I don't advise replacing with LED's by the way, don't believe what some say!

Hello Martin and Jacques,

Thank you for the reply. I checked out the IR detection as was suggested and I do see the blue-violet light in the dark. One other thing of note is that the end of the sensor arm does not light up as the arm travels which may mean nothing but I am mentioning it anyway.

My table was one that had dual capacitors and there was a little confusion on the hook up by me but I think that I have that correct. I am including an image of the hook up of the two capacitors if it means anything. The negative terminals on both capacitors are connected together with the black wires. The orange wire is connected to the positive terminal of the 1000uF and the white to the postivie terminal of the 4700uF. In the picture it looks like the positive and negative terminals fo the 1000uF art wired together but they are not. Also the orange leads are resting on the metal strap only on the insulated part of the wire so their is no contact. 

Not sure what else to do at this point except to check out what Martin suggested with a scope which I don't have so would need to go elsewhere. Any other thoughts would be appreciated.

John

jfrancis:

 One other thing of note is that the end of the sensor arm does not light up as the arm travels which may mean nothing but I am mentioning it anyway.

Oh that's good news!

It should light up actually, as soon as you press "START"! It should show the B&o logo in red too...

Gently slide the black extremity of this detector arm out of the arm and test the bulb...

Hello Jacque,

Thanks for the encouragement with this suggestion. How might I test the bulb and I assume a continunity text with a meter could be used to do that? I certainly will check this out as possibility but I have a question. Do you think the foto sensor at the base of the arm alway being lit even when the table is in the stopped position and this are somehow related? I don't want to do any more harm at this point by pullin on wires if I don't have too, but maybe I have nothing to loose.

I actually put the old dual capacitor back in place of the two new ones to see if my hookup of the new capacitors might have been the problem but the operation of the table was unchanged.

Thanks again,

John

Hi, 

There is no link between the two bulbs.

But as I told you, on PCB 4, there is a leaf switch for the shutter bulb which turns it off when the arm is in its resting position.

Either the switch is dirty or more probably it is misaligned. You normally clearly hear it when it triggers.

Hello Jacques,

Again my thanks but just so that I am clear, is the leaf switch you refer to the same one that stops the arm from going any further at the rest position and the platter from rotating? Both of these things stop when the arm returns to the resting position but the light remains on. I even tried manually pushing the switch so I could hear an audible click but the foto light remains on under the tone and sensor arms. If it is another switch where is it found?

Thanks,

John

If the SO switch works then there should be no power supply at all because it grounds the command of the first power transistor. Are you positive that the switch operates?

So when the arm comes to park, there is an audible click, the arm stops (with no sound of the servo motor straining), the deck stops spinning and the speed select lamps go out however the lamp at the base of the tone arm is still lit? Fully lit or does it dim in brightness?

Jacques

"I don't advise replacing with LED's by the way, don't believe what some say!"

I respect your opinion to differ, but such a blanket statement as this can get you into hot water.

Yes, I have been doing the LED replacement on tens of BG4002/6000's for well over a decade, and they all work flawlessly, as expected.

What I didn't know many years ago, when I designed the LED mod for these turntables, is that B&O had actually made this modification themselves on the production line, and EVERY SINGLE late model BG4002 Type 5513 (DC motor) had LED's, instead of incandescent lamps, as did the earlier models.

No, I don't know at which Type 5513 serial number the switchover was done, but I have already had 2 units in for repair, with the factory LED's fitted.

So, with the B&O factory's backing, I'm going to contradict you - politely ;-) , and advise any owner who wants to mod his unit with LED's has the factory's blessing.

Here is a component picture of a late-model BG4002 with the factory LED installed.

Menahem

Assuming all electrical functions are fine, there is one remaining cause which will give this result.

The step sensor – in the picture – is misaligned.

Do this as a last resort, because it is extremely finicky and time-consuming.

Untighten slightly the screw which secures the metal belt around the cylinder, so that the metal belt is free (but still stiff) to move laterally around the cylinder.  

Rotate the square box (and the belt) a hair's width clockwise, and try again. Within 2 or 3 hair's width, you should be OK.

If that is the cause, you will then be OFF with the initial set-down position, and further alignment is necessary.

But take one step at a time.

Menahem

Dear Menahem,

Yes I know, my 4002 has a LED but it is infrared, not white light.

However, I would be interested to have a diagram of a 4002 or 4004 with a LED in the shutter or in the detector arm. If such mods are possible, please let us know how B&O did them. On later Beograms (6006, 8000, 8002) there aren't any LED's to be found.

Is the LED in your picture original?

Jacques

That is the original, virgin, untouched original factory-fitted LED!

And, it's not critical whether it has an infra-red LED (factory-fitted), or a modern LED (per my modification) - in the appropriate circuit of course (Do not replace the infra-red with a modern LED - and you should not need to, anyway). Both LED's work equally flawlessly.

On the BeoGram 4002, Type 5513 / 5523 Service Manual, page 2-3 and 2-4, you can see exactly this circuit, with an excellent (as usual) description by B&O.

I have it in PDF, and i don't know how to upload a PDF here - it should be downloadable from this site anyway.

Menahem

I believe B&O's motivation for the LED modification in this position was not to get rid of the incandescent bulb, but the RPY58 photocell at the receiving end. Apparently it was a problematic component even back then.

Yes Menahem, but we were discussing about the detector arm and shutter lamps.

I saw somewhere (not in one of your posts) that it was possible to fit LED's in those places, but I couldn't achieve normal behaviour. So if you have a reliable solution it will be useful to everybody here. 

I already have the SM for my 4002 and yes it shows the IR LED.

I just dismantled a late model BG4002 for spares and it had the factory fitted LED.

I have to confess to trying this mod Jacques (I was curious :) ) and in defense of Menahem, I have to say the results are favorable so far! There are certain B&O circuits that do not allow this mod (not without modification at least!) such as the record arm sensor and other examples where the rest of the circuit somehow relies on the bulb, so led's should not be inserted whereever possible. I would also argue leds may alter the quality of light in some situations that might not be desirable. However, IMO in this example I cannot see why there should be too much objection! Certainly not a mandatory upgrade, and the overall difference in performance is perhaps not ground breaking in any way, but I would suggest it is slightly more reliable in the long term. Also don't forget the only safety built into this part of the circuit is a slightly over-rated bulb to allow for a longer life, if it fails the player will continue but without servo assistance and will result in a situation that is not good for the stylus...

I wonder if B&O didn't upgrade the led because they were hardly more use than point-indication back in those days, and more light is clearly needed in this case!

I have also done the indicator bulbs in my Beomaster 6000 behind the volume, looks just fine !

chartz:

Yes Menahem, but we were discussing about the detector arm and shutter lamps.

I saw somewhere (not in one of your posts) that it was possible to fit LED's in those places, but I couldn't achieve normal behaviour. So if you have a reliable solution it will be useful to everybody here. 

I already have the SM for my 4002 and yes it shows the IR LED.

I will post a piccy of my mod sometime Jacques. Anyway, I think we are all muddying this post here lol I am sure the OP is not interested in led mods at this point in time!

Again yes, but this is missing the point, since we were wondering about the detector lamp, and the shutter lamp in the first place, weren't we?(sorry if I'm being thick here!)

Jfrancis told us he did have this LED fitted and that it was working anyway!

I doubt the LEDs in the detector arm and the shutter would work at all!

Oh well.

Step1:

I will post a piccy of my mod sometime Jacques. Anyway, I think we are all muddying this post here lol I am sure the OP is not interested in led mods at this point in time!

Indeed! It was working fine before the recap with the stuff that is in there currently, there's no need to start complicating things with modifications here and there.

Already in the second post by the OP, he mentions that the detector arm won't light up at all. Now focus here!

Edit: Oops, I don't actually see a mention anywhere that the deck was working before. I'll get me coat

chartz:

It should light up actually, as soon as you press "START"! It should show the B&o logo in red too...

Gently slide the black extremity of this detector arm out of the arm and test the bulb...

... with an ohmmeter of course!

To me MIka the OP is saying his table works, but will not set down (result of the detector arm bulb not working) and the shutter lamp is constantly lit. Now this should not be possible if the deck shuts down after the arm reaches the stop positiion, which is what I was trying to ascertain previously. I cannot think off the top of my head if he has possibly got a plug in wrong, but then surely this would cause other issues. The OP needs to tell us more I think!

I agree, check the sensor arm lamp and or voltage supply first.

With regards to the other discussion, see this tech-info from B&O:
http://users.cybercity.dk/~dsl42943/BGT-2_Beogram_4002_Intermittent_lift_and_run-off_to_stop.pdf

Martin

Hello,

There was quite a bit of discussion since I last looked at the forum and my post about my problems regarding the lamp being out in the detector arm and the foto sensor at the base of the tone and detector arm being on as long as power was to the table.

Step1:

So when the arm comes to park, there is an audible click, the arm stops (with no sound of the servo motor straining), the deck stops spinning and the speed select lamps go out however the lamp at the base of the tone arm is still lit? Fully lit or does it dim in brightness?

First in regard to the question by Olly and the related one by Jacques regarding the possibility of the switch not functioning properly. When I push start the 33rpm speed indicator lights on the control panel as the arm moves to the left, then I hear a click and the 45rpm light indicator lights up and the arm reaches the end of the run and returns to the starting point. There is not a very audible click but the lights for the speed indicators go out and the platter stops turning. I have manually pressed the switch with a screw driver and the platter will start to rotate but stops but the light does not go out or dim significantly. The foto sensor at the base of the arms remains lit as long as the table is plugged in.

In regard to checking the bulb in the sensor arm, does the bulb need to be disconnected to do this with an ohm meter or can this be done soldered in place?

Regarding Jacques comment:

"If the SO switch works then there should be no power supply at all because it grounds the command of the first power transistor. Are you positive that the switch operates?"

I don't know what else to do to test the SO switch outside of what I have done. If the first power transistor were defective that Jackque mentioned but the switch stilled worked would that cause this issue?

To address another comment and a thought by Olly:

"To me MIka the OP is saying his table works, but will not set down (result of the detector arm bulb not working) and the shutter lamp is constantly lit. Now this should not be possible if the deck shuts down after the arm reaches the stop positiion, which is what I was trying to ascertain previously. I cannot think off the top of my head if he has possibly got a plug in wrong, but then surely this would cause other issues. The OP needs to tell us more I think!"

I have checked the position of all the plugs against the board's printed color indicators for the wires, and how the plughs should be inserted into the boards. The table was non-working when I got it and I did not notice how the plugs were inserted before I did the capacitor replacement. If the plugs were inserted incorrectly could this have done damage to other components on the board and yet the table partly function as I have described? Regarding Martin's point about the power, I am not sure what else to check in regard to the voltage supply to the board.

I do appreciate all the responses that I have received to this problem and will check out Menahem's suggestion of maybe having an issue with the step sensor after I eliminate the issues regarding the detector arm and if possible get answers from any of yet regarding this post.

Thanks,

John