Michigan Beogram 8002 Restoration: Sensor Measurements

The Beogram 8002 from Michigan is performing very good with its turntable functional tests.

I connected some test leads to the Beogram's position sensors, speed sensor, record detection sensor and the forward servo drive signal (IC2 Pin 7).  Reference Beolover's post on the servo motor check.

Here are my test points on the Beogram 8002 PCB 1 board.

First, the position sensors (1 & 2) along with the IC2 Pin 7 output to the servo motor.

This picture shows the signals when the Beogram 8002 is doing a forward scan over the platter.

The image on the left is of the Fast Forward Scan and the image on the right is the Slow Forward Scan.

I placed a test record on the platter and measured the sensors again while playing a record.

The servo IC2 Pin 7 signal varies as the servo motor advances the tonearm assembly to track the record groove.  It does this once every revolution of the platter.

The tonearm controls worked perfectly and the Beogram 8002 record play was great.

Next I swapped out the test lead on the Position 2 and IC2 Pin 7 test points with the Speed Sensor and Record Detection test points.

The Record Detection on the Beogram 8002 is interesting compared to the Beogram 8000.
The Beogram 8000 platter is very similar to the Beogram 4002/4004 platters so the platter detection in the fixed arm just measures a series of pulses by detecting the platter ribs.

With the Beogram 8002 B&O designed a special laser engraved platter with two different sections of black markings as well as a flat gray section.

Here are the Beogram 8000 and Beogram 8002 platters side by side.

The Beogram 8002 platter design results in a different record detection signal than the Beogram 8000.

Here are photos of the Record Detection sensor measurements and the Platter Speed sensor measurements.  I kept the Position 1 sensor as a reference.

This first set of images is with the platter speed at 33.33 RPM.
I actually set the speed to 33.33 RPM to show the Record Detection sensor at the black marking level and at the gray section level.  The photo on the left shows the Record Detection sensor over the black markings.

Here is he platter speed set to 45 RPM but I only captured the signals over the gray section of the platter.

I am satisfied that this Beogram 8002 is functioning properly now.

I will play a couple of records with the components still removed from the cabinet just to test the sound and make sure the audio mute relay is working.

Then I will do the cabinet repairs and reassemble the Beogram 8002 to complete the project.

Michigan Beogram 8002 Restoration: Scanning LDR Assembly

Here is a quick update on the Beogram 8002 restoration project from Michigan.

I left off with the Forward and Reverse scanning control not able to adjust to the values specified in the service manual.

To fix that I knew I would have to replace the two LDR devices and/or the light source.

It turned out that the two LDR devices measured pretty close to each other when testing them after I removed them.  The problem appeared to be with the light source.

I removed the original incandescent lamp and installed an 5mm LED with a 3300 ohm current limiting resistor.

I also tested a couple of new LDR replacements but none of them were as good as the two original devices.

The new LED light source worked great and I was able to adjust the forward and reverse scanning voltages to very close to the target 620mV for the "off" state of the buttons.

I tested the basic Beogram 8002 Play, Stop, Forward, Reverse operations with this updated control panel and it performed just as I expect it to.

With the Beogram 8002 components opened up like this I will solder on some test wires to measure the position sensor, record detect sensor and the platter speed sensor.

Looking at those on an oscilloscope will show how healthy those signals are.

The results of those tests will be in the next post.

Beogram 8002: Arm Moves a Few mm and Then Stops - Replacement of Photo Resistors and Bulb in the Keypad

I guess I celebrated the Beogram 8002 that I recently restored a bit too early. After playing a few albums it gave me the 'after pressing start the arm only moves a few mm and then stops without dropping' phenomenon. This is usually an indication that one of the photo resistors in the keypad is on the frizz. A while ago I made a comprehensive post about this phenomenon and how the << >> scan system works.

So I opened the Beogram up again and extracted the keypad:

Then I removed the circuit board (it slides out to the right after removing the small screw that locks it in place):

I should have done this right away after adjusting the scan voltages, since the two screws that control the base line light intensity on the photo resistors were at fairly different levels, indicative that there is a difference between the resistors: 

Anyway, I opened the assembly up, which revealed the photo resistors, the apertures that are moved by the << and >> buttons, as well as the light bulb at the center of the assembly:

I exchanged the photo resistors with GL5549 types (widely available on ebay), and I also replaced the light bulb with a white LED (Newark 14N9428) and a 1k resistor in series:

Then I installed the keypad again in the Beogram and adjusted the scan voltages. After the adjustment both of the screws were about at the same position as it should be!

After this it played again perfectly. I hope this is the last time I have to open it up again!

Memo About Scanning, Enlarging and Printing Circuit Diagrams in High Resolution

I received my original Beocord 5000 service manual a few days ago. Before I start working on a B&O unit I always like to have all the documentation that is available...just so much more fun that way. I also like the circuit diagrams enlarged on separate sheets. That way one can read the circuit description while looking at the diagrams. Also enlarged is better for markup. Unfortunately most manuals available on the internet are fairly poorly scanned. Today I spent a bit of time trying to get it right. I recently obtained an EPSON 'Perfection V37' photo quality scanner and a 1200dpi Brother HL-2240 printer. Today I experimented a bit with their settings trying to get a perfect reproduction of the two circuit diagrams of the Beocord 5000 manual.

Here is what I ended up with: The scanner is best set to 'Text' (i.e. essentially to "bitmap") and 1200 dpi resolution. The 'image correction setting' needs to be set two notches towards lighter density. This prevents the bleeding of smaller text and numbers, and the resulting scan is very close to the original in appearance and density:

Multipage diagrams need to be reassembled in Photoshop before they can be printed on multiple pages ('tiled') that can be assembled into a large poster-like print of the diagram. Photoshop unfortunately cannot do this, and Illustrator requires a post script printer for high resolution output, which the cheap Brother apparently is not. I was able to work around this using a $4.99 app from the Apple Appstore, called "Mindcad Tiler". In difference to the Adobe products, this app obeys the printer settings, i.e. the HD 1200 dpi mode of the Brother can be used. It also is very easy to use for the tiling process...simply select paper orientation and number of rows and columns of paper sheets, and it scales the PDF file automatically to fit the pages...very nice!

Here is a screen shot of the printer settings that I found to produce the best output:

It is important to select HQ 1200 as resolution and under Advanced/Graphics Quality/ the setting 'text'. Without it the printer will do some dithering and blur the precise quality of the scan.

After the pages printed, a bit of scissoring and Scotch taping produces nice large diagrams in pristine resolution:

O.k....now I am ready to work on the Beocord 5000!