Beogram 8000: Utilizing the Workshop Beogram 8000 to Test a Board

It is time to put the Workshop Beogram 8000 to work.

I received some Beogram 8000 main boards (with their microcomputer boards attached) for testing and this post will show an easy use of the Workshop Beogram 8000. 

That is to do a restoration on the main circuit board and the microcomputer board then check that it works.
Since my Workbench Beogram 8000 is fully tested and working, swapping out the main PCB should result in the Beogram still fully functional...if the restoration is all good :-).

First though...A bit of caution regarding board swapping on a Beogram 8000.
Anyone that has worked on a Beogram 8000 will have noticed that there seems to be a lot of modification work on the electronics of these units. As a comparison, the Beogram 8002 electronics typically have no modifications.  My guess is that with the Beogram 8000 being a totally new design (especially technology-wise) from the previous Beogram 4002/4004 tangential arm turntables there were a lot of post-production hiccups that had to be addressed with service bulletins and mod kits.
One such modification was when B&O changed the speed sensor assembly in the Beogram 8000.
Beolover has a really good explanation of this issue as he ran into it in this 2020 blog post.

The important thing to take away from that is DO NOT put a Beogram 8000 main board that has the circuit modification for the newer speed sensor into a Beogram 8000 that is using the older type speed sensor assembly.  The reason being is that the newer circuit board is expecting the resistor between +15V and the speed sensor light source to be on the speed sensor assembly.  The older speed sensor assemblies DO NOT have a resistor there. They expect the resistor (R46) to be on the main board.
The result will be damaging (blowing) the speed sensor light source if this pairing is done.

Here is a photo of the two types of speed sensors.

You can see in the photo that the newer speed sensor has the addition of a small board with two resistors moved from the main PCB.

These next two photos show a board configured for the original speed sensor assembly and one configured for the new speed sensor assembly.

In my case of restoring this first board that was sent to me I don't have to be concerned about a conflict with the speed sensor assembly as my Workbench Beogram 8000 currently is fitted with the newer type speed sensor and the board sent for restoration is designed for the newer type speed sensor. 

Here is the current speed sensor assembly on the Workbench Beogram 8000.

To make the Workbench Beogram 8000 capable of testing both configurations of the main boards I will need to make a modification of my own to this test setup so I can quickly and easily change speed sensors. 

But first I will finish this first Beogram 8000 board set.

Here are the "before" photos.

The electrolytic capacitors will all be replaced. Board connector mounting points will all be re-soldered.

In the case of the small microcomputer board I removed the microcomputer IC so I have more room to work on the C28 capacitor and also to upgrade the 40-pin IC socket for the microcomputer IC.

Here is the board ready to begin work on.
As usual I pulled the mounting base off the large 2200uF capacitor so I can re-use it on the replacement capacitor.

I like to start with the microcomputer board assembly and get that part out of the way.

Here is the microcomputer IC back in place (in its new socket) and the new C28 capacitor.

The rest is just selecting and fitting capacitors and soldering.
Here is the board set completed and ready to install in the Workbench Beogram 8000.

Hooking up the transformer, connectors, control panel then plugging the Beogram in brings up the reassuring Standby dot LED that things are going good.

I pressed the Play button with the platter empty and observed the Beogram search for a record and automatically switch platter speeds.  Not finding a record, it returned home and stopped.

After that initial test I verified the power supply voltages on the board. They were all good.
As a final check I put on a record and checked out the record play handling.
Initial set down and drive through the lead-in groove was perfect.
So was the run-out groove and end-stop detection.
I also tested the Pause memory function and it worked correctly.
That is where you press Pause while playing a record. Leaving the Beogram with a record on the platter in the Pause mode for a few seconds will cause the Beogram microcomputer to think you stepped away for a bit. The Beogram will return the tonearm assembly to home and go into Standby mode.
When you press Play again the Beogram will return the tonearm to the spot you paused the previous play and resume from there.  Quite a nice feature.

I believe this board set is complete and ready to send back to its owner.

The next set is one with the circuit for the original type speed sensor assembly so I will need to change that sensor assembly for that project.