BeoGram

Re: Different arm behaviours BG6006/8000

chartz — Mon, 04 Jan 2010 03:37:51 GMT

Hi Martin,

Problem solved!

Not very elegant perhaps, but I just cut off the plastic part where the old IR diode was, and soldered a new, 5 mm one I had in stock. No trouble, no fuss.

You're the best.

Grazie mille !

Dillen:
If you like to make sure, you can put a voltmeter across the servo motor leads and compare the two decks.

That will tell you if one deck has a too tight running mech.Martin

I checked that and guess what, the 8000 is actually a bit tighter! And it's the one that works best...

Re: Different arm behaviours BG6006/8000

Dillen — Sun, 03 Jan 2010 14:58:56 GMT

Yes, that will be the reason.
The sensor in the arm next to the tonearm detects a record but the carriage is not allowed to
stop and the tonearm to be lowered before a certain amount of pulses has been counted.
No pulses = no stop and no lowering.

You can replace it with a good IR LED of almost any type though you may have to drill or cut
a bit out of the plastic housing. Like this:

Martin

Re: Different arm behaviours BG6006/8000

chartz — Sun, 03 Jan 2010 12:12:11 GMT

No luck!

The trick was so obvious... You are an ace Martin! The LED doesn't shine at all (I checked on a remote control and it shone violet). There is voltage though, but it's high at 4.9 V. Can one change it easily? It's not a common type, and the detector seems specifically designed in one item (the LED and the receptors). So, is this the problem preventing the μprocessor to drive the arm properly then, according to you?

Re: Different arm behaviours BG6006/8000

Dillen — Sun, 03 Jan 2010 11:48:29 GMT

Yes, there are several minor production changes to add to the fun.
Both in the coding and hardware.
BTW: The threaded shaft is not the same on all 50Hz and 60Hz machines either.
It was something with tiny vibrations from the mains transformer causing
the threaded shaft to resonate audible in standby on 60Hz, so it was made slightly
thicker (or thinner, I don't remember) to compensate.
Carriage bushings likewise. They are wonderful machines.

The shaft pulse counter opto IR LED could be bad or dusty.
Check it with f.e. a digital camera, it will usually shine up a
light blue if working.
The plug for the IR LED sits right next to a power connection on the main board
so any shorts here will burn the IR LED instantly.

Martin

Re: Different arm behaviours BG6006/8000

chartz — Sun, 03 Jan 2010 08:11:10 GMT

Platter pattern okay, as per SM. I'm confused. I also checked the three transistors that amplify and shape the signal. The cap (C15) is new. What about the carriage motor sensor counter then? Does this fail? Does it send any information to the processor that could be related to my problem?

The platter will turn forever in pause mode (33 or 45), but it will stop in play mode after 30 seconds.

By the way, I think the 6006 and the 8000 a similar but different animals.

First, the carriage shaft motor is different, the pulley is bigger on the 6006, and the motors sound different.

The PCBs are different too on my examples, it is difficult to follow a diagram on the SM!

Next, the suspensions are set differently: on my 6006 it will bounce nicely with the platter 1.5 mm above the plinth, as on my 8000 it will have to be level with the plinth (actually both seem to exist when you google BG pictures!). On the 6006, the arm moves quickly and decidedly; on the 8000 it seems as if it takes its time sensing the beginning of the record, then settles nicely. For what it's worth anyway.

Once again, happy New Year to Beoworld members!

Re: Different arm behaviours BG6006/8000

chartz — Sun, 03 Jan 2010 06:33:00 GMT

CPU box solders (I saw one bad, but I did the lot anyway) done. Still no go.

I'm afraid the scope isn't with me now. Anything else I can check upon?

I can activate "play" with no disc!

Re: Different arm behaviours BG6006/8000

Dillen — Sun, 03 Jan 2010 06:11:05 GMT

Did you also check for cracked solder joints inside the CPU casing ?
I see this more and more, especially at the CPU socket itself.
Use a microscope, look carefully or simply redo the lot.
Else, put a scope to the sensor signal path and see if you can
reproduce the platter rib pattern.

Martin

Re: Different arm behaviours BG6006/8000

chartz — Sun, 03 Jan 2010 05:05:12 GMT

Good morning!

Well after opening the deck to measure a few things, the arm detection has suddenly stopped working on the 6006. Damn.

No disc detection, no 45 detection, no end of side detection. Detector bulb okay. All solders, continuities and contacts triple checked at least.

Re: Different arm behaviours BG6006/8000

Dillen — Sun, 03 Jan 2010 04:38:40 GMT

If you like to make sure, you can put a voltmeter across the servo motor leads and compare the two decks.
That will tell you if one deck has a too tight running mech.

Martin

Re: Different arm behaviours BG6006/8000

Dillen — Sun, 03 Jan 2010 04:36:45 GMT

If that's a millimeter at the extreme cartridge end of the tonearm, I wouldn't worry too much about it.

Martin

Re: Different arm behaviours BG6006/8000

chartz — Sat, 02 Jan 2010 16:36:26 GMT

Thanks. The belt is fine. The shaft turns very freely (I checked that on my other deck), and the carriage moves accordingly too. There is nothing else that can be adjusted?

If I remove stylus pressure it needs a fair amount of pushing the arm towards the detector arm for it to react (I'd say one good millimetre). You can see that at the end of side: the motor is always a bit late.

Re: Different arm behaviours BG6006/8000

Dillen — Sat, 02 Jan 2010 16:14:31 GMT

Seeing a Beogram of this series with a constantly moving arm is rare.
They usually move in tiny steps, a quarter to a third shaft rotation
at a time. Hardly enough to actually see the carriage move unless you have
very sharp eyes and really look for it.
If it runs in larger "chunks", like several rotations at a time,
it's probably because it's lacking lubrication to the threaded shaft
and bushings in which case it will take a slightly larger amount of
power to rotate the shaft, which again means greater opening of
the tracking opto is needed to start the rotation.
Could also be a too tight servo motor belt.

Martin

Different arm behaviours BG6006/8000

chartz — Sat, 02 Jan 2010 15:44:03 GMT

Hello,

I can "see" the arm on my BG 8000 moves constantly (one rotation of the shaft/platter turn or thereabouts: I can't see the arm move really, like a clock!) as on my 6006 it moves every two or three turns of the platter (sometimes more), and I can see the arm move. I've tried adjusting the aperture screw but it only gets worse (either turning left or right). I'm not sure it's a problem. Also on the 8000 the arm clearly slows down when it arrives in position, but not so on the 6006, where the arm arrives directly at the correct position before lowering down.

My 8000 has all the original caps!

Any thoughts?

Thanks,

Jacques