Hi Folks!

After many years I am now the proud owner of my first B&O product.  Hmm...one problem though...it doesn't work!

Having browsed through the forum I know this topic has been covered several times, but I still can't find the answer I need.  Basically the arm doesn't lower.  It cues and finds the record and stops at the start.  I can also cue in and out manually.  If there is no record on the deck it cues to the end and returns to stop.  That part is fine, but the arm stays up.  Mechanically everything seems free.  I can push the solenoid in by hand and the arm will lower, but I don't really want to stand holding the solenoid in while listening to my LPs.

I have no voltage getting to the solenoid.  Firstly, can anyone tell me what voltage operates this solenoid?  I have traced the circuit back to transistors 0TR4, 1TR10 and 1TR11 that I assume in my basic knowledge operate the solenoid.  I have no voltage readings on any of the terminals of these transistors.  Can anyone advise where to go from here?

Also, there is a bulb on the underside of the main circuit board that doesn't make sense why it should be there.  I haven't seen it light up so I don't know if it's faulty, but could this have anything to do with the problem?

Any help would be appreciated, thanks.

Alex

Hi Alex

I have never worked on the BG4000 but recently overhauled the BG6000 which does appear to be fairly similar in many respects.

I am not sure whether you have access to the service manual but I presume so because of your knowledge of the relevant transistors.  0TR4 provides the main switching capability for the solenoid.  When the BG6000 is in the off state, the collector reads around 25 to 30V and the emitter is grounded.  If you haven’t got this high voltage on the collector then your problem is back at the power supply but since the turntable is working normally, I think that this is not going to be the problem.

If you have 25 to 30V at 0TR4c, then this transistor is not being activated properly or it has failed.  Again, in the off state, the base of 0TR4 should be grounded. It rises to ±0.7V when it gets the signal to lower the arm.  Check out these basic functions and the results should start to point to your problem area.

I agree with your curiosity on that bulb, I wondered what it was for as well.  Perhaps one of the BG4000 experts will provide us with a good answer and shed more light on your solenoid problem as well.

By the way, welcome to Beoworld and have lots of fun.

Regards

Geoff

Hi Alex:

This is a crap shoot... but I had exact same problem on a BG4002 that I repaired.

Follow the solenoid to the transistor. Along the control signal path there is a zener diode the feeds the transistor. I don't have my notes handy (I'm thinking 24 volts but I don't remember!). This diode was bad in my unit.

Perform a diode test. If this is your problem, send me a note and I'll look up the correct value for you.

Derek

geearr:

I agree with your curiosity on that bulb, I wondered what it was for as well.  Perhaps one of the BG4000 experts will provide us with a good answer and shed more light on your solenoid problem as well.

It belongs to the Wien bridge sine wave oscillator that generates the driving signal to the platter AC motor. It is not supposed to light up, it operates as a kind of current / temperature dependent resistor and stablizes the frequency. This is an old trick that was first commercially used by certain gentlemen Hewlett and Packard in their first product, a precision sine wave generator.

Oops!  I'm a little embarrassed here folks as it appears I do have some voltage readings at some of these points.  I rechecked them again this morning and I can only suspect that my meter probably didn't have a good ground connection.  Thanks for your help so far guys, it has given me an idea where to start looking.  Geoff, I have the circuit diagram that I acquired with the unit - I don't know if this is the full service manual or whether that contains any additional information.

This is what I have with the arm cued and ready to lower:

0TR4 emitter  0v

         base      6v approx

         collector 43v

solenoid has 43v at both terminals

1TR11   emitter   6v

             base      6v

             collector 6v

1TR10   emitter   0v

             base      0v

             collector 6v

The fact all voltages across 1TR11 are 6v brings me to resistor 1R28 that I am about to remove and check for open circuit.  The other side of this resistor is 0v - in fact this is the point where I am grounding my meter.  Please let me know if you think my diagnosis so far is correct.

Result!  Removed 1R28 only to find the value was fine around 150ohms.  Replaced it back into the board and now it works!  Must have been a dry solder joint though it looked ok before I removed it.

Just for the record the voltage at the base of 0TR4 when activated is a little over 3v.  The voltage at the solenoid is 31v and 34v referenced to ground, so it only needs 3v to work, but it is possible that it needs a higher peak voltage to draw it in.

Now I'm going off to google Wein bridge sine wave oscillators...

Thanks for your help guys!  I guess this was a pretty basic fault, but without your help and knowing roughly what voltage readings should be I'd have been p***ing in the wind.

Now onto the next project...I've got my eye on a faulty BG2200 on ebay...not in the same league as the 4000 but...SOMEONE PLEASE STOP ME NOW!!!

alexb1406:

Now I'm going off to google Wein bridge sine wave oscillators...

You will get better results with Wien bridge (as in Vienna), not Wein or Wine

Good work, enjoy your Beogram! Be warned that there is no escape

Thanks tournedos

I continue to learn something every day

Regards

Geoff

Hi Alex

Thanks for your voltage measurements, they have cleared a few things up.

Firstly, you have 40v on the collector of 0TR4 and both terminals of the solenoid so you don’t appear to have a power supply issue.

Second, 0TR4 has 6v on the base and 0v on the emitter and is not conducting.  Hence there is a good chance that 0TR4 is cooked. 

You measure 6v on the three terminals of 1TR11.  When the signal is sent to activate the solenoid, 1TR10 should be off, providing the 6v to the base of 1TR11.  My guess is that 1TR11 is in the correct state and 1R28 could well be OK.  I am assuming that you are measuring to the nearest volt and are not seeing the 0.7v drop that exists across the transistor.

When the arm is being instructed to drop and the solenoid is being activated, the base of 1TR10 should be low and that seems to be the situation from your measurements.  My money would be on a faulty 0TR4 at this stage.

Regards

Geoff    

Hi Geoff,

I think you may have misunderstood me.  It now works after refitting 1R28 - hence why I suspect it was a dry solder joint.  I now have a range of voltages across 1TR11 and 3v at the base of 0TR4 when the solenoid is activated - 3.37v to be precise, but I don't fully trust the accuracy of my meter so I have rounded off all the figures I provided.  Across 1TR11 I have 3.37v, 4.05v, and 5.87v again when the solenoid is activated.  When the arm is in the up position the voltages are 0v, 0.73v, and 0.08v.

Of course this is purely academic now and I am only providing these voltage readings in case it may help someone else in the future.

I have however since fixing it discovered another problem for which I may start another thread - that is once lowered, the arm cues across the record very quickly and skates across the surface.  Is this likely to be an adjustment of the arm that moves across the photoelectric sensor?  I don't want to mess with it until someone can confirm this.

Well done Alex

I must have missed your follow up post, the one after you reported the readings.  It probably came along while I was compiling my replies.  Anyhow, at least you have a solenoid that works and an arm that drops when required. 

Yes, I would have a look at the adjustment of the photosensor - I had that problem on my unit as well - it was fairly simple to fix.

Geoff

Thanks Geoff, photosensor now adjusted and working.

Guess what!  I have another problem!

With everything reassembled and no record on the platter, the arm sometimes travels to the very end and then drops onto the empty platter.  Sometimes it works ok and returns without dropping, but every so often it will come down.  This is after the search light goes past the end of the platter ribs, so is it still searching for the start of a record?  Once it goes past the end of the ribs it must think it's found the record.  Fortunately I realised what was happening before I replaced the cartridge.

I have looked at all the switches under the arm and they all seem to be operating ok.  I can even work them manually and so far I have not been able to recreate the problem.  It seems that the end switch may not be working, but the arm looks like it presses it down - in fact when it does work it only has to touch it and the arm instantly reverses.

I've had enough of it for one day.  I'm away for the weekend but I plan to return to the task on Monday - refreshed and ready for another battle...!!!

Hi Alex

That is just typical for these machines, you fix one problem and only end up identifying the next one.

Unfortunately, you have reached a point where your BG4000 loses its similarity with my BG6000 - I have no complex switching system to fiddle with, so I can't help you with that one.  I am sure that someone on the site does know the nuances of your machine and will follow your progress with interest.  I am sure you will end up fixing it - it only takes time.

Best of luck and have fun

Geoff 

Thanks Geoff for your help so far, and everyone else for that matter, it has been invaluable.

Although I'm not at home at the moment I have sneaked a few minutes away from other duties to browse the forum.  I'm being summoned to bed as I write - but I'll leave that one there in case I get moderated...the bug has definitely got hold of me...

I just couldn't recreate the problem before I left home so I decided to box it all up and be wary of it in case it happens again.  I'll just have to test it every now and then and see what happens.

All I need to do now is make an adapter lead up to connect the DIN plug to my RCA input.  I haven't actually played it through an amp yet.  Am I right to think it will be ok to plug into any phono input, or do I need any other type of preamp?  I have two cartridges with it, an SP15 and an MMC20E.

alexb1406:

I haven't actually played it through an amp yet.  Am I right to think it will be ok to plug into any phono input, or do I need any other type of preamp?  I have two cartridges with it, an SP15 and an MMC20E.

Depends on whether your amp has a RIAA preamp in the the phono input. The Beogram 4000 doesn't have this fitted, Steve at Soundsheavenly & Lee at LifeStyleAV can both supply a preamp kit with all relevant cables to do this.

The SP15 is quite a rarity as it was the 1st in this B&O range of integrated cartridge/stylus design & the chances are it may be goosed due to age as much as anything else - worth keeping though just for the rarity value. The MMC20E will also be quite old but is likely to be the best candidate for a decent performance but, hey ho you won't know until you give them a whirl.

Chris.

Thanks Chris, I have with the SP15 the original box that it was supplied in dated 1973, cleaning brush and scales - I haven't fitted these back in the box yet as they were given to me loose but it looks like there are compartments underneath inside the box for these.  There is also a graph that looks like it might be the performance chart, I assume for this specific cartridge from the factory.

Coming back to the RIAA, please correct me if I'm wrong but I thought phono inputs were, by definition, designed to have the preamps in the amp.  If the preamp was in the turntable then you would have to connect it to an AUX input.  My amp, an AKAI AA-1175 (nearly as old as the BG4000) has both phono and aux inputs.  I presently have two other turntables connected via a switching box to the phono input.  So I presume that there must be a RIAA built into the phono input of my amp...am I right?

Amplifiers of that vintage normally have the RIAA built in as you surmise. My SP15 still performs well so certainly worth a try - very similar to the MMC20EN and hence better specified than the black 20E.

Thanks Peter, you've confirmed exactly what I thought.

I'm trying to get the bits together to make up the din/rca converter lead.  Our local Maplin didn't have a female din plug.  I've found one in another store but I can't collect it till Monday.

Well, we're up and running!

Made the link lead up yesterday and plugged it in, and after I connected a ground lead with a couple of crocodile clips to cure the mains hum (it's missing altogether) it sounded great.  Anyone have any idea where this lead originally connected to on the Beogram?  Finicky maybe, but I'd like to make it look as original as possible.

As predicted the SP15 doesn't work at all.  If Soundsmith can do anything with it I may be tempted to let them overhaul it as I believe this would have been the original cartridge fitted to the BG4000.  And I have another project on the way that is missing a cartridge and the MMC20E would be a good candidate for it...yes, the temptation was too much - I bought the BG2200 that I had my eye on...EBAY, THOU ART TEMPTATION...

Any psychologists on our forum, can you please set up an ebay rehabilitation program...or more appropriately, a B&O rehabilitation program...

alexb1406:

Made the link lead up yesterday and plugged it in, and after I connected a ground lead with a couple of crocodile clips to cure the mains hum (it's missing altogether) it sounded great.  Anyone have any idea where this lead originally connected to on the Beogram?  Finicky maybe, but I'd like to make it look as original as possible.

There was no separate ground lead - the sleeve of the DIN connector and the outer shield of the cable create the shield ground connection. It connects to the chassis inside the Beogram.

I don't think anyone will overhaul the SP15 if the coils are broken, apparently both Sound-Smith and Axel from schallplattennadeln.de only fix the suspension (and Axel replaces the entire cantilever/stylus). It was indeed the original cartridge, I would just keep it as a display piece as the whole set with the factory test charts is quite rare.