BeoGram

Re: Beogram 8000/6006 cueing

tournedos — Thu, 28 Oct 2010 04:53:46 GMT

Since your schematic cut-out above seems to be from the older(?) service manual scan, have you looked at the other one we have on site (larger file size)?

It mentions a modification to the raise/lower circuit (you seem to have it though if your turntable matches the schematic you quoted) and also shows an extra 10n cap across B/C of TR9. Dunno if that has any effect on your problem, but just a thought...

Re: Beogram 8000/6006 cueing

chartz — Thu, 28 Oct 2010 03:55:31 GMT

Hello,

Since this was never solved, I'd like to know whether someone has another hint, or the same problem...

As a reminder, when I double the value of C9 the arm's descent is slow but the muting relay never clicks. LM324 is fine. Passive components are fine, no cracked tracks or joints.

Are you sure the coil is not damped?

Re: Beogram 8000/6006 cueing

Dillen — Wed, 13 Jan 2010 12:32:52 GMT

Yes, but don't rule out a broken PCB track. I've seen too many.

Martin

Re: Beogram 8000/6006 cueing

chartz — Wed, 13 Jan 2010 10:36:32 GMT

Thank you.

I will look further into this and shall keep you informed of course. But I'm beginning to think this is a purely mechanical issue.

Re: Beogram 8000/6006 cueing

tournedos — Wed, 13 Jan 2010 10:14:48 GMT

OK, I see what you mean... But the muting signal is taken directly from the output of the integrator op-amp, while there is still T9 before the signal reaches the coil. It might be useful to observe the voltage/current across the coil, but you will need a scope or an analogue meter for that to make any sense. And I'm still very suspicious about how replacing C9 would affect anything if the integrator circuit is working correctly.

Re: Beogram 8000/6006 cueing

Dillen — Wed, 13 Jan 2010 10:12:01 GMT

It could be a little dust or other debris or it could rub on something.
Hard to diagnose per remote.

Martin

Re: Beogram 8000/6006 cueing

chartz — Wed, 13 Jan 2010 09:06:43 GMT

Yes, it is an LM324N. And yes, the muting circuit depends entirely—and only—on the signal given by the lift/lowering circuit. So the delay circuit works fine for me. If the IC was defective, the muting relay would not work at all, or the delay would be wrong. Which then excludes the amp/delay circuit failure! Back to mechanics then? Well I don't know, because for me everything is fluid and free. The unknown part is that coil though...

Re: Beogram 8000/6006 cueing

Dillen — Wed, 13 Jan 2010 08:49:09 GMT

If it is indeed a LM324N, it consists of 4 identical circuits. That's 4 individual OpAmps that can be set to work in each their function.
One circuit (or part of one circuit) can easily go bad with the other three working normally.
Nothing strange about that.

Martin

Re: Beogram 8000/6006 cueing

tournedos — Wed, 13 Jan 2010 08:49:06 GMT

As far as I can see from the schematic cut-out, the the muting relay circuit doesn't care about what speed the integrator works at, it just trips at a certain voltage.

Re: Beogram 8000/6006 cueing

chartz — Wed, 13 Jan 2010 08:42:01 GMT

Thank you both.

Okay then, but the same circuit triggers the muting relay too, doesn't it, and that works just fine. There's something I don't quite get here. I know I am being a pain, but I hate it when I can't figure things out... All solders triple-checked by the way! Also, do you think the dampening is purely electronic or not?

Re: Beogram 8000/6006 cueing

Dillen — Wed, 13 Jan 2010 08:36:36 GMT

I agree.
It's a LM324N if I remember correctly, so a very cheap and common IC.

Martin

Re: Beogram 8000/6006 cueing

tournedos — Wed, 13 Jan 2010 08:29:10 GMT

chartz:

So how do you analyze the role of C9 then?

I have no idea of the specifics of this Beogram, but that is a pretty standard integrating amplifier constructed around an op-amp (a lowpass filter of sorts, if you wish). C9 and R58+R61 determine the time constant, while D12 makes it shorter for the other direction (arm going up I suppose).

This circuit may be affected by the leak current of the original cap. It's negligible in a new cap of course, but perhaps some other marginal component or other problem has altered the operation point. I would double check even the passive components in the circuit and all solderings of course. If IC1 is some cheap and common type, I suppose you could try replacing it as well.

Re: Beogram 8000/6006 cueing

chartz — Wed, 13 Jan 2010 08:09:28 GMT

So how do you analyze the role of C9 then?

Re: Beogram 8000/6006 cueing

Dillen — Wed, 13 Jan 2010 02:13:07 GMT

Hmm..
Cooling spray on the components could maybe shed some light on it.
Or on the board itself, I've seen lots of cases where a copper track has breaked away from
a solder pad, right where they meet, and the symptoms can then easily be temperature dependant.

Martin

Re: Beogram 8000/6006 cueing

chartz — Tue, 12 Jan 2010 16:46:57 GMT

The screw doesn't stick, I've checked this.

The relay always clicks after the stylus has reached the disc.

When the deck is cold, it is normally dampened, no problem at all. But after a few minutes' use, it falls quickly, almost freely.