BeoGram

Re: Beogram 4004 won't stop or lower arm

yachadm — Tue, 08 Sep 2009 13:34:41 GMT

I forgot to mention -

This can also be due to a too-low voltage-condition in the system, and there is one main culprit for that.

On the main control PCB, under the platter, at the top left is D2 - a 24V Zener diode.

If you have less than 22V on D2's cathode, replace the diode - 1N4749.

Menahem

Re: Beogram 4004 won't stop or lower arm

yachadm — Tue, 08 Sep 2009 04:12:55 GMT

I've just been through this same fault on a BG6000 I finished restoring today.

I'll write it up in more detail on a separate thread, but in my case, it was caused by the tonearm not being aligned exactly 90degrees (even 89.5degrees is not good enough!), which caused the slitted metal shield (on 0R1, at the right-end of PCB3), to not line up with the sweet-spot on the sensor, so the arm never dropped.

Don't try bending any metal to align it - please!!!!

A little patience, and I'll get pictures up on what to do.

All the lamps on this BG can be safely replaced with LED's, with appropriate resistors.

Menahem

Re: Beogram 4004 won't stop or lower arm

Dillen — Tue, 19 May 2009 14:34:43 GMT

Well, yes and no.
As you already noticed, there are many different versions and not all Beograms act
exactly the same way when a fault occurs so it's hard to diagnose exactly without
actually having it on the bench.

Generally, a tangential Beogram won't lower the tonearm onto the platter, because the
pulses from the radial streaks of the rotating platter will prevent it, that's right.
You can, however, sometimes get it to lower the tonearm just outside a 12" record by
starting play and then back out the carriage using the >> button and then press down, but
since this will be outside of the rotating platter, it won't risk damaging the needle.
Should the needle fall off the outer edge of a 7" record, the needle will hover above
low "valleys" in the radial streaks so it won't be damaged by this either (if all
adjustments are correct).
The same goes for 10" records, there are "valleys" for this as well.

If it turns out to be an IR in your Beogram, the light emitter is by far more prone
to failure than the light receiver.
If you have light, you will have to measure through the circuit from the receiver to
see where the signal gets lost.

Martin

Re: Beogram 4004 won't stop or lower arm

tournedos — Tue, 19 May 2009 09:05:34 GMT

zorro349:

So if I get home and the emitter is emitting IR light, then the receiver wouldn't be working.

Do bear in mind that some versions have a normal light bulb there (like my BG6000, for example).

Martin, can you elaborate why the arm wouldn't or couldn't lower outside the platter? Mine certainly does. As I understand it, the only signal the Beogram gets to make a go/no-go decision on this comes from the detector arm, and all it can detect is the moving black bars of the platter. On a record, outside the platter, and a non-working detector arm circuit would be just the same for it -> arm lowered when asked to?

Edit : I see 4004 is completely different in this regard at least from my early 6000. I'll get me coat regarding this detail

Re: Beogram 4004 won't stop or lower arm

zorro349 — Tue, 19 May 2009 08:32:25 GMT

So if I get home and the emitter is emitting IR light, then the receiver wouldn't be working. Should I just try and replace the receiver or try and replace both receiver and emitter? I am not quite sure how to get at the emitter as it seems it is inside of the black rubber thingy (technical term of course) ???

Zorro

Re: Beogram 4004 won't stop or lower arm

Dillen — Tue, 19 May 2009 08:29:39 GMT

Most digital cameras (and cell phone cameras) will show IR light as a pale blue shine.
This will be a quick way to tell if the LED emits light or not.
Same trick can also be used to check if the laser in a CD player is emitting light (never look directly into a laser!).

Martin

Re: Beogram 4004 won't stop or lower arm

zorro349 — Tue, 19 May 2009 08:10:14 GMT

So after reading the service manual I know for sure that the ruler sensor is not working correctly. If I hit start after a very short time the speed will change to 45 rpm way before the large black portion of the ruler is in front of the sensor. Is this an LED IR emitter and receiver? Is the receiver located in the black rubber looking thing?

Also, I am able to snag the scope from work and will put it on the tracking sensor that I can get from 1TR6-C, which I found on the main circuit board correct?

Thank you all for your help!

Zorro

Re: Beogram 4004 won't stop or lower arm

Dillen — Mon, 18 May 2009 16:28:09 GMT

The Beogram won't allow for lowering of the tonearm if no record is sensed.
You cannot force the Beogram to lower the tonearm outside of the record or onto the platter
if no record is present (or the sensing is not working), even by using the up and
down arrow buttons.
I don't have the lamps specs right here. They are sometimes mentioned in service
manuals but not always and may differ according to version.
The tracking lamp, I seem to remember as a 24V 25mA or so. That'll be the one
in the plastic housing at the base of the carriage, detecting the tonearms tracking
angle.
The ruler lamp is an IR-LED (or UV) if I remember correctly, at least in some machines.
There are countless different versions, even territory-specific versions.

Martin

Re: Beogram 4004 won't stop or lower arm

zorro349 — Mon, 18 May 2009 11:01:33 GMT

So,

If I lower the arm manually with the UP/DOWN button there are no permissives for this? I should be able to measure voltage over the solenoid that lowers the arm? Mechanically is seems like it lowers pretty easily with all of the linkage and such. It seems like there are a few problems with this TT. Hopefully I will be able to figure it out with your help.

Thanks!

Re: Beogram 4004 won't stop or lower arm

tournedos — Mon, 18 May 2009 10:40:47 GMT

Just to clarify, I was talking about the bulb that shines through the "ruler", the clear plastic bar with black stripes that moves along with the carriage. Martin meant the one inside the base of the tonearm, which you can't really see without removing some parts. It may shine through a little from some angle.

But anyway, neither of these being out will prevent the tonearm from being lowered manually on a record. That will be another problem. Could be an electronic problem (I think Martin already gave you hints on that), or mechanical - the joints responsibe for lowering the arm have a tendency to get stuck. These are around the solenoid. Have you tried measuring if it gets any power when you attempt to lower the arm manually? It should be possible with the platter removed (contrary to how many people first think about it, the detection arm doesn't detect the presence of a record - it detects the platter bars not moving under it).

Re: Beogram 4004 won't stop or lower arm

zorro349 — Mon, 18 May 2009 10:08:59 GMT

So, it seems that the sensor for the tracking arm isn't working, but also the lamp for the position sensor isn't working. Martin, is it true that you have replacements or know where to obtain one? I am an electrical engineer and would be able to order one from digi-key or some other company if it was a commercially available component. It seems that my abilitiy to troubleshoot at the component level isn't very good due to mentality of just swapping out complete modules that I see everyday at work.

Thanks for all your help,

Zorro

Re: Beogram 4004 won't stop or lower arm

tournedos — Mon, 18 May 2009 10:00:59 GMT

As far as I understand, you should still be able to lower the arm manually outside the platter (or on a record) if the position sensor isn't working. But, you're right in that it will definitely hose the automatic functions - since the deck never "sees" the landing zones, the arm will go on and on until the end limit switch aborts the mission (automatic stop probably wouldn't work either if the trailing groove of the record doesn't go far enough.

If you cannot lower the arm at all, you must have more problems than just this. Anyway, if you cannot find the correct bulb (I believe Dillen can supply them), it's possible to replace it with a led and a resistor. Getting the correct brightness might require some experimenting.

Re: Beogram 4004 won't stop or lower arm

Dillen — Mon, 18 May 2009 09:59:20 GMT

No, that would cause another fault and make the Beogram unable to track (the carriage follow the groove) as the
record is played.

Martin

Re: Beogram 4004 won't stop or lower arm

zorro349 — Mon, 18 May 2009 09:04:56 GMT

After further inspection the lamp on the postion sensor (one under deck) is no longer functioning. What would be a good replacement for this part? Does this seem like this lamp could be my problem with not even stopping to try and lower? (Since it can't find the 33 position?)

Thanks,

Zorro

Re: Beogram 4004 won't stop or lower arm

Dillen — Sun, 17 May 2009 23:52:15 GMT

Welcome to Beoworld !
Thanks for joining as a silver member, your support is greatly appreciated.

Put an oscilloscope to the sensor (receivers) electronic circuit and look for the pulses
made by the radial streaks of the platter with no record on it.
You should be able to see the pulse train very clearly.
There are different versions of the BG4004, but in most versions TR6(C) is a good
place to measure.
If it's frozen around ground potential, a record is not sensed and the reason is often
tantal C19.
Depending on the exact version, a capacitor kit is available. If one tantal is bad, the rest is probably
marginal.

Martin