Hi:

My BG 4002 AC motor has developed a "knocking" sound as it rotates. I can make it go away by holding/lifting the spindle as it turns but eventually it comes back.

Does anyone know what's going on? Perhaps it needs lubrication after all these years?

Derek

Derek,

Did you check the motor phase adjustment ?

Martin

Hi Martin:

How do you adjust motor phase?

I see only motor voltage adjustment instructions in the service manual.

Derek

Yes, it's 1R29 on the main board.

I like to adjust it with everything mounted, platter, belt etc. to "simulate" normal conditions
and then simply adjust the trimmer for the smoothest motor run. It's quite
easy to hear when you hit the right spot and I've found this method works much more
reliable than the "official", which in some cases can end up quite far from correct.

Martin

Hi Martin:

Yes that is properly adjusted.

The motor still "knocks," it sounds like someone is litterally "knocking on your door" with a periodic frequency.

Derek

Lubrication then ?

Martin

Yes that's what I'm thinking.

Do you know how to dismantle the motor? Can it even be taken apart?

I don't suppose anyone on here has a spare motor?

I should also mention that it "knocks" more often when in 45 speed mode.

Derek

I may have a motor,

                                 what part number and any other markings are written on it? A photo would be better.

Chris.

Chris:

Many thanks for coming to the rescue!

But lets hold off for now as I may have solved the problem with lubrication.

Initially I just applied oil to the shaft via need applicator but the knocking didn't go away.

The next thing I did was I used a ruler to pry the pully off. Then I soaked the bearing around the shaft with a big blob of oil and let the motor overnight. When I woke up in the morning it was running smoothly and quietly again! So it appears it requires a bit of time for the lubricant to work in, but you do need to apply generously. Happily no disassembly of the motor was required.

Do you know if these AC motors are supposed to run warm? Also is it normal to hear a low level AC hum from them?

Thanks,

Derek

Derek,

Good work!

Just for the record, could you put up a photo of your AC motor, showing what "pulley" you pried off, and where exactly you inserted a blob of oil!

Also regarding the AC hum, here are the 4 caps I replaced on mine, and the hum disappeared:

1. 1x Nichicon 4700uF 25V UHE1E472MHD6

2. 1 x Nichicon 220uF 16V BiPolar UVP1C221MPD

3. 2x United ChemiCon 4700uF 50V EKMH500VSN472MQ35T - actual capacitance is 4100uF so very close to the B&O original 4000uF spec. For this, I have also used Panasonic TSHA units (ECO-S1HA472BA) on other models with excellent results, but the KMH just fits better.

All are available at Digikey.

The picture shows them before I replaced the metal hold-down bar. The 2 smaller caps on the left were subsequently hot-glued to the chassis.

I also have a limited supply of Nichicon Muse Audiophile Power Capacitors 4700uF 35V and 63V, which are perfect for the main power supplies in the BeoMasters and BeoCenters. For pics and details, please PM me!

Menahem

Hi Menahem:

Yes thanks for the info!

I changes all of the caps except fro the 150uF bipolar phase shift capacitor. I'm trying to save up enough parts to get over the Digi-Key minimum order amount. I see that you are using 220 uF. Do you think that replacing this will get rid of the hum?

I also used 4700uF capacitors as a substitute for the original 4000uf; much easier to source. They work fine.

Derek

Derek,

Yes, I used a Nichicon 220uF Bipolar - you can get it at Mouser, too (no minimums).

There was an added (unintended) benefit to that:

If you remember, I ran a post awhile back, regarding the AC motor getting really hot - well, now the motor runs just warm - a real improvement.

It appears that my BG6000 is now 101% operational, without any issues at all.

I'm really happy with it.

Menahem.

Menahem:

Thanks for that additional piece of information!

I'm close to fully restoring my 4002 which was fished out of a dumpster.

On outstanding problem that remains is the unit will not always turn of when the carriage returns to rest position. The carriage assembly hits the off switch on at rest position, the system appears to turn off, but there is still some current leakage. The sensor arm light remains very dimly lit and motor will continue spinning but at a slower rate.

I've replaced all of the electrolytics except for the bipolar. 0TR1 is new. I'm now suspecting that 1TR1 is leaking although it measures fine on the VOM. Very strange!

Derek

Derek,

Check 3D1 1N4004 - on mine it was leaky - I replaced it witha UF4007.

It's underneath the PCB - you need to disassemble the PCB to get at it.

Menahem