[Mark-sf]

It is not recommended that you switch topology types as many of those changes are in notch filters and B&O likely had different drivers or a different batch that needed compensation. As far as parts quality, since all bands are in parallel and there are a lot of parts, I would focus on replacing any electrolytics in the mid and tweeter circuits with poly caps as it does not appear there are any iron-core inductors in there. Check out either the Dayton or Fast PA Series from Solen. I have had excellent results with these.

[Mark-sf]

My recommendation would be to add an RIAA board inside such as https://www.ebay.com/itm/185373986428?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=i_P7_Iv4Tsu&sssrc=2349624&ssuid=WrB3U2kWQBO&var=&widget_ver=artemis&media=COPY. This is just an example of one that can run off of the +12v single supply. I’m sure there are higher quality ones if you scout around. You can find the user and service manuals on Beocentral.com.

[Mark-sf]

I know the muting board had the additional pattern so it could be the same for the main board. It is easy enough for you to check. In any case the newer sealed ones are your long term solution.

[Mark-sf]

There is no switch involved. The direction and action is controlled by two pins, 21 and 22 on IC8 that provide a differential voltage to dual op-amp IC9. I do not have access to the service manual that may explain how end of travel is sensed.

[Mark-sf]

There are two springs that govern the damped closing of the cover. This is discussed at the end of the service manual at https://beomanuals.com/manuals/Beocord/Beocord%205000/Beocord_5000-Service_Manual-version4.pdf.

[Mark-sf]

I am afraid you need to open the top to get to the adjustment for the photo sensor. It’s described in the service manual available at https://beomanuals.com/manuals/Beogram/Beogram%206002/Beogram_6002-Service_Manual.pdf. You can also view a video on how to open it on Rudy’s site at https://beolover.blogspot.com/2017/07/beogram-8000-opening-beogram-to-service.html.

[Mark-sf]

I’m afraid you are going to need to open it up to access the adjustment. This is explained in the service manual at https://beomanuals.com/manuals/Beogram/Beogram%206002/Beogram_6002-Service_Manual.pdf. You can also check out Rudy’s video on opening it up at  https://beolover.blogspot.com/2017/07/beogram-8000-opening-beogram-to-service.html.

[Mark-sf]

My approach would be to first check out the power supply as there are multiple ones in this unit along with 4 fuses. You can get the service manual at https://beomanuals.com/manuals/Beocenter/Beocenter%209000/Bang-Olufsen-Beocenter_9000-Service-Manual.pdf.

[Mark-sf]

The belt should be 88mm in length. You can measure it by aligning it flat with just enough tension to have the two sides flat against each other and that should measure 44mm. One reliable vendor is here at https://www.beoparts-shop.com/product/platter-belt-3/ if it turns out your belt is over 1mm shorter. Also make sure that the pulley height is such that the belt runs fully on the subplatter.

[Mark-sf]

You are dealing with an AC Motor running off of the mains voltage, therefore there would only be mechanical speed adjustments and they would be in the manual. I would check that all of your play adjustments as per the manual are correct as there may be insufficient tension. All the above also assume you are not trying to use a 50Hz unit on 60Hz.

[Mark-sf]

That is fine. Check the spec for your cartridge as some need 1.2 grams.

[Mark-sf]

That relay is the stock one for 4002’s that have DC motors. Simply get the replacement kit for that type. If you want to experiment swap it with the muting relay as that one may be in better shape since DC does not flow thru it’s contacts.

[Mark-sf]

You don’t need to cut the mains. Simply carefully pick up the arm once it has moved to the record and move it back supporting it on any item that is high enough to keep the stylus from touching the top. You can also take the platter off and with the 45 adapter depressed press play and it will move over and lower.

Assuming the arm is truly lowered, then the weight should not be hitting the rear at zero grams as applying 1 gram is only 1/2 turn of the weight.

[Mark-sf]

The OEM relay is not available, but the replacement kits are readily on eBay depending on which relay you have. This is a DPDT relay that defaults to the 33 speed when unpowered. I would only jumper that side or remove it if you want to test 45 as well.  In any case, I would always replace it at this point as any cleaning fix is only temporary and the part is cheap enough.

[Mark-sf]

The arm should be in the recording playing mode and then the weight should be adjusted to zero tracking force. Then you rotate the numeric dial without moving the weight so that zero is a 12 o’clock. At that point you rotate the entire weight to the desired tracking force.

[Mark-sf]

I would try injecting a signal at the wiper of the volume control for each channel with the volume at max and then take your distortion measurements. This will pinpoint whether you have an amp or preamp issue. I’m betting on the latter from your discription.

[Mark-sf]

A relay’s contacts can corrode over the decades especially when not hermetically sealed. This introduces a variable resistance which causes the speed variation. One can affect a temporary fix by carefully cleaning the contacts since the cover is removable; however, this is only a temporary fix and its very easy to bend the thin contact supports making it worse.

[Mark-sf]

You most likely need to replace the speed switch relay. There are modern replacement kits available on eBay or Beolover’s site.

[Mark-sf]

Yup need to do some measurements instead of using your ear to answer my questions. Download a turntable App for your phone such as RPM and come back with answers to 3 and 4.

[Mark-sf]

Worn bearings would not cause a motor to run fast. I would approach diagnosing this in this way.

1. Determine if the speed is fast for both 33 and 45.
2. Determine if the speed is faster for 45 to the same extent as it is for 33.
3. Determine what specific speed range for 33 and 45 you can adjust over.
4. Determine whether the speed is steady even though fast.

From the answers to the above, one can pin down the area of the system causing the problem. Feel free to post these and I’ll give you my diagnosis.

[Author]

Posts