Hi

It sounds as if you are another member of the club of people who have arm lowering difficulties on this machine – not uncommon as you have probably gathered.  In your case, something serious must have happened in the past if R56 has been cooked and I cannot guess what other parts in the solenoid circuits may have been damaged at the same time.  My approach would be as follows:

First check the movement of the solenoid to confirm that it is free and moves properly – it sounds as if you have already done that during the general lubrication stage.

Switch the turntable on and when the arm arrives at the park position, measure the voltages on the two terminals of the solenoid.  They will probably measure the same and around +40V.  This confirms that you have power at the solenoid and the winding is OK.

My next test would be to quickly ground the line from the solenoid to the collector of the 0TR4 through a 10ohm resistor.  That should actuate the solenoid and demonstrate that the solenoid and the general arm mechanics are working properly.  Before you do that, make sure that the arm can lower onto an old disc because things might not move in the way that they should.

If everything is OK at that stage, then at least you know that the solenoid works.  You will then have to start examining the solenoid control circuit to find out the reasons for your specific problem.

Regards

Geoff

Hi Remy,

Yes, there are 2 problems here - one on the main PCB, which there is not enough current flowing to drop the arm - you must resolder ALL the PCB joints. There's nothing to check there, just do it.

Certainly replace the 4 orange electrolytic capacitors with good-quality Panasonic or Nichicon units. Those capacitors are now acting as resistors and are impeding current flow.

Then, in order to solve the problem that the arm arrives to the correct point, but does not lower, you must look at your left-right photo-sensor (it has a thin slit in it, which you cannot see). You you can see it circled in red in this picture.

As you can see, I have replaced the whole circuit with an LED (unless you are competent, please do not try it - the procedure is already detailed in one of my posts which you mentioned above).

Anyway that light must be perfectly aligned, before the arm will drop.

So you need to release that screw, and rotate the sensor left/right very slightly, antil you see that the arm drops consistently with success.

Then retighten the screw.

This requires a lot of patience to get it just right!!!!!

And about that 1N4004 diode - it is mounted UNDERNEATH the PCB, not on top! Did you actually measure and check with your meter that there is no diode current between the 2 points, before you mounted the UF4007?

I put the UF 4007 on top, in the picture to illustrate it better. Of course, it doesn't matter if it is mounted above or below, but in your case, there is no point in having 2 diodes on the same circuit.

Menahem

yachadm wrote:

Anyway that light must be perfectly aligned, before the arm will drop.

Hi Menahem

I was interested in your reply to the solenoid lowering problem and there is something that I would like you or anyone else to clarify for me.  You stated that the slide transport sensor has to be carefully adjusted before the arm will drop and you normally repeat the adjustment until the arm drops consistently.  This is not how I understand the control logic but I could well be wrong. 

In the Type 5501 schematic, the signal from the slide sensor 0R1 passes through two diodes 1D41 and 1D19.  1D19 uses the signal to drive the slide motor after the solenoid has lowered the arm onto the disc.  The arm is always in the raised position when 1TR18 is closed (0V) and this condition will effectively ground 1D41 preventing the photosensor having any effect on the slide motor.  Hence my interpretation of the control logic is that the solenoid must be activated first before the photosensor can drive the motor.  A faulty slide motor photosensor should have no effect on the solenoid operation.  The bad news is that if the solenoid lower the arm and the photosensor is incorrectly adjusted, the slide motor can drag the arm across the disc, making a nasty mess.  On the other hand a badly adjusted photosensor might not move the arm at all and this messes up the disc as well.

So my question for you is, “is the slide motor photosensor configured as an interlock that affects the operation of the solenoid or is the solenoid configured as an interlock that affects the slide motor operation?”.  I am always very interested in the views of the technical people who have been trained and worked on this fascinating machine.

Thanks for your help, Regards

Geoff

Geoff,

I'm not going to guess, so I'm going to tell you only what I know from practical experience. If that left-right rotating sensor (in the above picture) is not properly adjusted, the arm will not drop, even though the arm may be in the correct position.

That's the first place I look, if the arm doesn't drop, and of course, that's after I've taken care of all other issues - lubrication, electrical function, etc.

So to take it to its conclusion, that sensor appears to act as an interlock.

Menahem

I suggest trying what Geoff suggested first.
See if the solenoid is working.

It works together with a switch (to the left of the solenoid). This switch shorts a resistor
elsewhere and allows for full power to activate the solenoid and lesser power to hold it while playing.
If the switch contacts have oxidized (or the little flat bent spring between the contact pins is missing),
the switch will not short the resistor and the solenoid will not receive enough power to activate.

There are several different versions of decks and boards. The one seen in the photo is a BG6000,
yours may be very different in both the solenoid and main board. It may even be a version without the
above mentioned switch.

Martin

How similar is the 4000 to the 4002?  I recently had the same problem with my BG4000 and found the problem in a dry solder joint on the main board.  If the circuits are similar you may be able to check voltages on the various transistors in the circuit.  Have a look at:

/forum/beogram/beogram-4000---arm-doesnt-lower

I provided the voltages both before and after the repair - they may be of use to you.

Hi Menahem

I have tried to put down my thoughts on the solenoid operation to help get to the bottom of this problem solving exercise.  First of all, I think that Martin has a very valid point when he mentions the number of model variants that we might be thinking about or have been working on.  In my case, my experience tends to be based on the extensive repair work that I have carried out on the BG6000 Type 5505. 

The machine with the problem that we are trying to address in this thread is the BG4002 Type 5501.  From the schematics that I have available in the service manual for Type 5501-5002, the 5505 seems to have many of the basic features of the 5501.  In particular, the circuits controlling the solenoid appear to be very similar.  The component numbering is however different.

I have spent a lot of time studying the service information that is available for these units and I think that it is important to put the following points on the record for others who are faced with the same problem of a solenoid that doesn’t want to lower the arm.  The problem solving section in the service manual clearly spells out the possible causes and the areas to check if the solenoid fails to operate when the arm is sitting in the correct position at the start of a record.  These are the logical places to start looking and they cover the following parts of the circuit: 

Power supply faults

Detector circuit faults

Electronic switching faults

Pulse generator faults

Solenoid physical faults

The test points will of course vary from one model to the next so I’m not going into any further detail at the moment.  However, I do have the test points for the BG6000 Type 5505 and I will always check these areas first.  In my case, it was the detector circuit that was faulty and a burnt out transistor was the cause.

One thing that the problem solving chart does make clear is that the slide motor operation (including its photosensor) is only investigated after the solenoid has lowered the arm.  This means that the solenoid has to lower before the slide motor can work and can be checked.  Hence the solenoid is an interlock for the slide motor and to me, there is no logical way that the slide motor can affect the solenoid operation.

The adjustment of this photosensor is extremely important as it controls the rate of advancement of the arm.  The adjustment procedure in the manual focuses on setting up the threshold voltage for the stepping motor and when this is done properly, the shutter is locked in position.  There are no indications that this procedure can influence the operation of the solenoid.

I have checked all of the relevant voltages on my BG6000 and when the arm is in the correct position at the start of a record and the arm is raised, the solenoid control voltage at the collector of 1TR20 is grounded to zero.  Hence the voltage at the cathode of 1D19 is also zero and the voltage on the anode side is around 0.7V.  Under these conditions, there is insufficient current flow to operate the slide motor.  If you move the arm from side to side in this position (equivalent to changing the shutter position), the voltage always stays around 0.7V and the motor will never operate.  This is a totally logical result because the designer doesn’t want the slide motor controller to be operational when the arm is in the raised position.

The arm drops when the solenoid control voltage changes from zero to +18V.  The cathode of 1D19 is now 18V and the anode voltage now has freedom to vary from zero to 18.7V.  When the arm is in the perpendicular position, the shutter is closed and the voltage is low – around 1V.  As the arm moves towards the centre of the disc, the light exposure increases and the voltage increases to around 5V.  At that stage the motor moves, the arm straightens and the voltage drops back to 1V.  During normal operation, this voltage simply cycles between 1 and 5V.

If the shutter is way out of position and the photoresistor gets full light exposure, then the motor voltage is going to be high and the arm will be dragged across the record at high speed.  However, this can only happen after the solenoid has activated – the arm drops and immediately the slide motor runs away and ruins the record and stylus.  This has happened to me and for this reason, it is extremely important to get the shutter and the slide motor properly setup before the arm is lowered and playing a valuable record. 

I hope that this has thrown some light on the control system for this machine and I always value feedback from more experienced people.  However, from the observed operation of the BG6000 Type 5505, I have found nothing to suggest that the refusal of the solenoid to operate can be attributed to maladjustment of the slide motor photosensor. 

Regards

Geoff 

I have the opposite problem: the arm doesn't raise at end of record or when buttom ^ is pushed. Or couse it goes up when ac cord is taken out of  AC outlet.

Any suggestions?

Geoff,

Some very valid points - obviously not all the possible defects can be covered in my write-ups, simply because I haven't seen all of them. But it's a good place to start.

After covering the basic areas I described, a troubleshooter would have developed a reasonable perception of how the BeoGram functions, and assuming he has reasonable deductive abilities, he could probably solve his particular problem by asking more pointed questions on the forum and without too much stumbling. I've worked on all the 4002 series (AC and DC) and there's enough common ground in the circuit operation to transfer knowledge of one to the others.

Tim, definitely an electrical and not a mechanical problem - check functionality of the solenoid, and of the diode (hidden upside down) on the PCB directly to the left of the solenoid.

Get back to us, with progress.

Menahem