The Workbench

Re: BeoGram 4000 Restoration

Andre — Sat, 05 Nov 2011 21:28:20 GMT

Menahem

Very impressive work. Makes my own labours seem like a half-dead fish flapping around in mud

dauphine/andre

Re: BeoGram 4000 Restoration

yachadm — Sat, 05 Nov 2011 12:18:42 GMT

Electrolytics - Nichicon HE, Panasonic 220uF SU Bipolar, Panasonic TSHA (the 3900uF 63V to fit nicely)

4.7uF and smaller - Wima MKS2

Many resistors also required replacement, and as I mentioned also transistors and diodes.

I can put together a kit of most of the pieces for you - contact me offline.

Re: BeoGram 4000 Restoration

filip_kbh — Fri, 04 Nov 2011 14:06:31 GMT

Any chance you could tell us what types of capacitators/Electrolyts you have used.

I have two BG4000 decks and though they both work, I am worried about the caps, and I would like to change them. I hope this is not too difficult.

Re: BeoGram 4000 Restoration

yachadm — Tue, 01 Nov 2011 07:12:53 GMT

Solved .

Sometimes I don't do what I know I should do, and it prolongs the troubleshooting process.

The AC versions of the BG4000, 4002 and 6000, all have a very similar circuit with regard to the solenoid activation of lowering the arm.

The /\ or \/ signal comes from the keyboard in a very similar way, and is then passed to the solenoid via 2 driver transistors (on the BG4000 1TR10 and 1TR11), and 3 on the AC 4002/6000 1TR14, 1TR15, 1TR16.

I'd already had experience on the BG4002/6000 with the effects of these specific leaky transistors, which are badly stressed by the original large grey capacitors drying out.

Visually, in the past I have seen the immediate benefits of replacing these: having connected the TT via a 60W lamp in series with the main AC line, when the solenoid is activated, the lamp lights up indicating excessive current draw. Yes, the TT works, but it's not correct. Replacing these 3 transistors always caused a great improvement, with the lamp barely illuminating with the solenoid activated.

So here on the BG4000, as always, I connected the series lamp, and of course it lit up. But, I didn't think of applying my past experience to this circuit, until I'd exhausted the other possibilities of the FCH chips being faulty (which of course they weren't).

Then I decided to replace TR10 and 11, just like I always do with the appropriate transistors on the 4002. Immediately after connecting AC, of course the solenoid didn't activate , and when it did (correctly) upon reaching the LP, the lamp barely illuminated.

Measuring TR10 after the fact showed an hFe of 9 (instead of about 150).

So, I can recommend when restoring these TT's, replace the solenoid's driver transistors without even thinking twice.

Menahem

Re: BeoGram 4000 Restoration

Rich — Thu, 27 Oct 2011 18:01:01 GMT

I wish I could offer help; alas, I can't, but I offer best of luck.

My 4002 after service had many a night of flawless playback, one weird night where it had an attitude, then flawless operation since. I hope my 4002 gremlin didn't find its way to your deck.

Re: BeoGram 4000 Restoration

yachadm — Thu, 27 Oct 2011 09:37:04 GMT

It's worked flawlessly since I finished the restoration, but suddenly......

This morning, when pressing ON, immediately the solenoid activates and lowers the arm. ie, it doesn't wait until it reaches the beginning of the LP to lower the arm.

It plays fine, but when it comes to the end of the LP, the arm stays lowered, and drags the needle back across the LP (I caught that real quick!), and only raises the arm again at the At-Rest position.

Pressing the <, >, /\ or \/ buttons has no effect on lift/lower - ie the arm does not lift in response to these buttons when they are pressed.

Also, I connected the scope directly to the solenoid, and then pressed the /\ and \/ buttons - the waveform jumps, so the buttons are OK and their signals are getting to the solenoid.

So, something is forcing the solenoid down at application of power ON, and preventing the other normal circuits (buttons, end of LP position) to raise the arm appropriately.

I've checked for any broken wires / solder joints etc, but I need help to know where to start looking.

Menahem

Re: BeoGram 4000 Restoration

Dillen — Thu, 29 Sep 2011 12:56:28 GMT

Bring it in for service.

Martin

Re: BeoGram 4000 Restoration

filip_kbh — Thu, 29 Sep 2011 10:23:50 GMT

But the thing is that even though I turn the dial to the max position (1.5) I cannot get more than 0.8 if I'm really lucky - and that is clearly not enough for any of the B&O styluses I have. The gauge is very precise and this is not a problem on my other Beogram 4000.

Re: BeoGram 4000 Restoration

Dillen — Thu, 29 Sep 2011 09:59:29 GMT

I suggest you use a tracking force gauge more suitable for the Beogram.
B&O made some nice ones that were included with some cartridges but
they can be a bit difficult to get hold of.
Something like this will probably also do fine:
http://www.amazon.com/Shure-SFG-2-Stylus-Tracking-Force/dp/B00006I5SD/ref=sr_1_1?ie=UTF8&qid=1317308043&sr=8-1

And then, don't trust the dial on the adjustment, it will be somewhat off by now.
Trust the gauge and never mind the dial.

Martin

Re: BeoGram 4000 Restoration

filip_kbh — Wed, 28 Sep 2011 14:53:30 GMT

Here is a short film of my problem. As you will see the weight platter is too close to the arm, leaving no room for the arm to be able to lower. I suspect the arm was once replaced and that the platter was not - but how will I find out?

Anyway - take a look at the video here:
(Please visit the site to view this media)

Re: BeoGram 4000 Restoration

chartz — Wed, 28 Sep 2011 08:38:04 GMT

Believe me, the eye is very, very accurate when it comes to define whether two arms are parallel or even slightly in/out!

BUT the black plastic of a record, when in contrast with the alu parts, CAN be misleading!

So trust your eye but don't get sick about it alright!

Re: BeoGram 4000 Restoration

tournedos — Wed, 28 Sep 2011 03:12:47 GMT

filip_kbh:
And also how does one get this tool for adjusting the lenght of the arm?

Hardly anywhere, unless you get to raid an old service establishment. You'll just need to duplicate its function somehow. For all that I can see, it is essentially a 90° gauge pivoted at the center of the platter.

On the other hand, I really don't believe there'll ever be any practical or audible difference if you just do those adjustments by eye. The goal is simply that the arm is perpendicular to the travel of the stylus, which should cross the center of the record.

Re: BeoGram 4000 Restoration

filip_kbh — Tue, 27 Sep 2011 14:00:09 GMT

Hi - yes, that's it. I'm sorry I didn't have the service manual at hand when I suggested you take a look at the circuit.

However, I have another question for the service manual. How does one do this: What is a bearing frame?

And also how does one get this tool for adjusting the lenght of the arm?

Re: BeoGram 4000 Restoration

yachadm — Tue, 27 Sep 2011 12:50:39 GMT

Filip,

I can't offer any opinion, because I don't know - that's why I'm asking.

Has it something to do with this adjustment?

Re: BeoGram 4000 Restoration

filip_kbh — Tue, 27 Sep 2011 12:31:55 GMT

I had the same problem on one of my two BG 4000s. Somebody in here said that it wasn't these contacts as they supposedly only control where the arm should be lowered. Instead there should be a circuit detecting the run-out groove, meaning that when the arm travels fast, the circuit will give the command to lift the arm and return.