BeoGram

Re: Beogram 6000 prematurely ends play

tournedos — Tue, 19 Feb 2008 11:58:43 GMT

Thank you, thank you. Tomorrow I'll need to raid the flea markets in search of something new to play

A final observation, which I'll post in case it might help someone searching the forums for troubleshooting information later: at first I was scratching my head over why the selection of record size & speed for 45 rpm singles only worked every other time, i.e on the first time the arm always tried to lower at the LP landing zone. Then it occured to me that the worn out belt was slipping, and the platter didn't reach correct speed in time for the detector circuit to "see" it! On the second try, it was already turning... there's a filter in the detection circuit, and it needs the correct frequency of moving bars under the sensor. Wicked people, those Danish engineers!

-mika

Re: Beogram 6000 prematurely ends play

camshaft — Tue, 19 Feb 2008 11:21:38 GMT

Wow, really happy to hear you got it sorted out!

Re: Beogram 6000 prematurely ends play

tournedos — Sun, 17 Feb 2008 12:36:44 GMT

Final update, I hope - I fiddled with the position of the detector arm light bulb to get the maximum platter signal amplitude and tweaked R35. Now even the disc detection and speed selection work The signal is quite marginal, though; I guess the bulb is pretty worn. It does get the correct voltage.

-mika

Re: Beogram 6000 prematurely ends play

tournedos — Sat, 16 Feb 2008 17:39:16 GMT

Just an update, in case someone is still interested - I've been playing through a good part of my LP collection today, without a single hickup. Dunno what happened, but I'm not complaining I'll carry the oscilloscope back to work on Monday (and list the Dual CS5000 for sale)...

-mika

Re: Beogram 6000 prematurely ends play

Dillen — Sat, 16 Feb 2008 07:52:42 GMT

Mika,

You have a PM !

Martin

Re: Beogram 6000 prematurely ends play

tournedos — Fri, 15 Feb 2008 16:25:16 GMT

I don't think so - at least not completely. I tried it a few times in a completely dark room with no noticeable difference. I'm starting to suspect the sensor itself might misbehave when it's in the dark. I was thinking about the moving wirings from the carriage too at first, but since the problems are strictly on the black bars now, I think I can rule them out.

Now that I have all the covers on the deck it has played a few sides without problems... maybe it likes the warmth

(BTW, I'll need a new belt sometime soon and my local supplier doesn't carry belts this long anymore. Please drop me a PM with instructions, if you have them... )

-mika

Re: Beogram 6000 prematurely ends play

Dillen — Fri, 15 Feb 2008 16:14:08 GMT

Strange fault, it's not because ambient light can fall on the sensor ?

Martin

Re: Beogram 6000 prematurely ends play

tournedos — Fri, 15 Feb 2008 15:17:01 GMT

I never found out where the spurious pulses come from while the ruler is at a black stripe. Possibly induced by the servo firing. The first transistor stage still amplified them to full level anyhow.

I added a couple of power supply decoupling caps (the mainboard doesn't have any from the factory!), reduced the sensor-amplifier coupling cap to half of its original size and made the pull-up on the amplifier base heavier so it would need more pulse energy to turn off. Now the deck gets past the 45 rpm landing zone maybe two times out of three.

I'll put the covers on (how stylish!), clean up this mess, and return to the project some sunny day...

-mika

Re: Beogram 6000 prematurely ends play

tournedos — Thu, 14 Feb 2008 17:18:06 GMT

Progress, I think - the machine isn't imagining the OFF command, it really accumulates the "run-off" signal voltage at the test point over C33 from pulses coming from nowhere, while the ruler sensor is in the dark. But not always :-/ (Wish the nice folks at B&O had designed the machine so that I could probe with the oscilloscope while the platter is on...). Other than that, the pulse decays seem right all around.

At this point, I think I'll crack a beer and listen to CDs for the rest of the evening

-mika

Re: Beogram 6000 prematurely ends play

Dillen — Thu, 14 Feb 2008 17:16:12 GMT

Usually, the sensor either works or don't. The lamp is what becomes weak in most cases, it could also just be out of focus with the lens system. The lamp should be in a position very near the lens, in some cases actually touching, and with the filament centered with respect to the lens.

When I said IR related to the ruler, it's because an IR system is used in some versions and that just came to mind. There seems to be a lot of different versions, easily 25 or more and I'm getting older.

Martin

Re: Beogram 6000 prematurely ends play

tournedos — Thu, 14 Feb 2008 15:50:02 GMT

Thanks, tried that. Didn't help :-/ (actually didn't bend them as they're on plastic holders, I just adjusted the ruler as close to the sensor as possible)

Ummh... IR? We are talking about the same 6000 (a.k.a 4002), right? This has an incandescent light and I guess an LDR...

The analogue control logic is diabolical and defies human mind. I think I'll replace it with a microprocessor At least I've found out why the platter detection doesn't work, the signal coming from the arm is very weak, only about one volt after TR9 (should be six). I guess the sensor is out...

-mika

Re: Beogram 6000 prematurely ends play

Dillen — Thu, 14 Feb 2008 14:56:29 GMT

Clean the ruler and gently bend the IR sensor and emitter as close to the ruler as possible without touching.

Martin

Re: Beogram 6000 prematurely ends play

tournedos — Thu, 14 Feb 2008 13:58:17 GMT

After some experimenting, I noticed that the problematic positions aren't random at all any more. They are invariably

right after start, even so that the arm doesn't have time to lower
at the 45 rpm landing zone

...i.e exactly where the wide black stripes are located on the position encoder bar, or whatever it's called. I removed it temporarily, and now the deck doesn't know where to lower the arm nor where to really stop, but doesn't stop by itself either. Apparently the logic is confused of when it's running and when it's seeking.

I guess I'll continue by spending some quality time studying the schematic. Must be a shorted/open diode, or something...

Re: Beogram 6000 prematurely ends play

tournedos — Thu, 14 Feb 2008 12:39:18 GMT

Gee. Now I've replaced the two large power supply caps, as well as every single electrolytic (including tantalums) on the main board and the one on the sled. The machine still makes spontaneous automatic stops at seemingly random positions, though perhaps not so often. Anyone care to comment on what to check next?

Re: Beogram 6000 prematurely ends play

tournedos — Tue, 12 Feb 2008 16:09:15 GMT

OK, now I've been inside the deck, and cleaned and lubricated the two fixed tracks of the transport, as well as the worm track. This actually helped a lot, now I've been able to play two consecutive record sides without the machine cutting out, but the problem still remains.

I noticed that the tone arm "leads" a bit while playing, it's closer to the detector arm at the moving (cartridge) end. Is there an electronic tracking adjustment somewhere, or am I really supposed to loosen the clamp in the base of the tonearm pivot and turn the reflector block around? This might be the only problem, since the deck most often cuts out right after lowering the arm, when it is supposed to run fast on the leader of the record...

-mika