It is difficult to really diagnose without seeing it but to me the problem sounds like it could be the motor itself. The play speed (voltage) does come from the Beogram amplifier board though so it could also be electronic. The easiest way to tell is to swap out the platter motor if you have access to another Beogram 400x with the DC motor.  Is your 4002 a DC or AC motor type unit? If you don't have access to a spare I would pull the motor and see if Beolover can look at it. He is also set up to re-infuse the bearings of those type of motors with oil and repair them. So if the motor is the culprit he will be able to fix it. If the motor tests good then you will know the problem is in your board. Are you certain the belt is not involved with the problem. You can swap the belt with your 4002 as they are the same belt type.

sonavor 

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Thank you for the knowledgeable response.

I do have a 4002, but either never noticed or if I did, inconveniently forgot if the motor was AC or DC. If mine is an early model it will be DC, otherwise AC like the 4004.

I did replace the belt (from Martin) about 3 years ago. While I am not certain about the belt, it is an unlikely source for this ”issue.” I specifically pressed hard on the record with my hand and it had almost NO effect on the record speed. If the belt was weak, I imagine the platter would have actually stopped.

A bad motor is certainly a possibility however this has been going on for at least 3 years, so with regular use, I imagine a bad motor would have failed by now.

After this morning’s near stop mid-record on 45RPM I have been on a marathon of record playing for the last 4 hours, playing one 33 1/3RPM record after another and the performance is flawless.

What this 4004 won’t do is dependably play a 45RPM record. Worse for remote diagnosis is that it starts at near or about the correct speed, then mid-record drops in RPM/s dramatically, only to “catch its breath” towards the end of the record.

It is the changing speeds on 45RPM’s that throws me coupled with the perfect performance on 33 1/3RPM’s.

Let me ask another question, so let’s say it is the amplifier board that has an issue, could this problem only affect 45RPM’s?

I have no problem in sending out the amplifier board or motor for proper repair, but I have had God-awful luck with shipping Beograms, that I am extremely disinclined to ship the entire Beogram.

Thanks again for the helpful tips. I gotta give this some more thought.

Jeff

P.S. Martin did in fact find those 1600 belts I needed.

I would suggest to just ship the motor and/or board if it comes down to those. On the Beogram 4002/4404 (types 5523/5526) those components just unplug. So no need to ship the whole turntable and risk any damage in shipping.

You have the DC and AC motors confused. The original Beogram 4000 and subsequent Beogram 4002 (Types 5501 through 5503) have the AC platter motor.  After that Bang & Olufsen changed up the design and went to the DC motor. So your 4004 has a DC motor for sure and if your 4002 is a type 5513 or higher, then it will also have a DC motor.

Since you have been changing the belt I take it you have been running it with the deck covers off. Can you observe whether anything is obstructing the movement of the platter belt and/or tonearm assembly? Is the belt staying in place and in the middle of the motor drive shaft?

I wasn't clear from your first posting about 33 1/3 being perfect. I understood that 45 RPM had problems but switching to 33 1/3 also wouldn't work right (occasionally). If the failure is always on 45 and never on 33 1/3 then I would suspect the electronics and not the motor. The Beogram changes speeds electronically and that circuit is on the main board so, yes, it can be a board issue.

sonavor

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Before I get into this, I want to thank you sincerely for all your time AND expert advice.

 I am tremendously embarrassed that I managed to get the AC and DC motors backwards, as I really should know better having a Beogram 4000. To err is human but this is FAR from my first mistake.

The belt was changed three years ago, so no; I am not running the turntable with the cover off.

Today I played the Beogram 4004 essentially nonstop for 4 ½ hours (I was upset by this development and had the time….) and it played every record at 33 1/3 perfectly, no exceptions.

I am no expert (far from it) on these Beograms, but after that long duration without problems I assume it is a flaw in the main board that affects the 45RPM play. The mechanicals I can deal with, but electronics mystify me completely.

Before I pull out the board I will spend a bit more time on this 4004. For reasons of no interest to this forum I am actually forced to use this 4004, so it will get all my attention in the immediate future.

Again thanks for pointing out the two possible problems. 🤒

Jeff

Sure, no need for any embarrassment. The internals aren't something an owner should have to deal with (at least not very often). The problem does seem to point towards the board as the most likely suspect. As I said, the board can easily be removed and sent to someone for repair so you don't have to worry about shipping the whole turntable. Once the board is repaired you will be able to adjust the trimmers to dial in the precise speed.

sonavor

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This is an excellent option.

This has been an unfortunate and totally unexpected week of B&O failures. Like some terrible Gypsy curse. Three to be exact, and the 4004 misbehaved at a very inconvenient moment to make problem number 4.

Once I get the “other” issues taken care of, I will want to have this board repaired.

You really have been an amazing help.

Thank you. 🙂

Jeff

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OK, it pretty much official, it is the board.

I checked the belt and it looks virtually new.

I played this 4004 for 4 hours yesterday and 5 hours today without a single hiccup. If it were the motor I believe a fault would have shown up with this much "work."

So am I satisfied with 33 1/3RPM only play? No, but priorities dictate that I have 3 other repairs done first. As 99% of my records are 33 1/3RPM's and with the 4004 performing so well, I don't feel pressed to have this repair performed immediately.

Thank you for directing me to this problem.

Jeff

Resurrecting an old thread.

Did you ever manage to get the speed problem fixed? My 4004 (#5523) is showing exactly the same behaviour, albeit not as severe as yours. My 45 rpm fluctuates between 42-46 as measured with a tachometer. 33 rpm is solid.  BTW, I already switched out the r15, r16 with those new trimpots but that didn't help.

I wish I could be of help, but not at this time.

My problem disappeared completely about 3 weeks ago. Whatever is wrong is still wrong.

I had planned to send the board off to my shop near Atlanta, GA, but with with no malfunction, that seems rather pointless.

When the problem reoccurs I will post an update, but for now, there is nothing to report.

That said if you make progress with your 4004, I surely would like to hear about it. The problem (I believe) is with the motherboard.

One question, do you use your 4004 with the remote control? I am not sure why, but this feature really "turns my crank." 😁

Jeff