Beogram 8002: Glueing on the Aluminum Panels, Installing the Hood and a Test Drive with Chico Hamilton on Impulse!

Time to put this Beogram 8002 back together! It came a bit as a kit with the hood removed and the aluminum panels detached. As usual I glued the panel around the platter on with epoxy using 4-40 washers to bridge the gap between the plastic shell and the panel:

After the epoxy had hardened it was time to glue on the panel:

After this it was time to put the hood back on. It simply clips into place around the back part of the plastic shell of the enclosure. The only sweat producing part is to get the leaf spring inserted the correct way while attaching the hood. This shows how the spring is to be inserted:

since I only have two hands, I fixed the spring in place with some Scotch tape:

This helps a lot since the assembly is upright during this attachment operation. Once the hood assembly was in place it was time to attache the smaller aluminum panel.

As usual, I attached it with three layers of double sided tape. That shimmed it up to the level achieved with the 1980s style foam adhesive tape B&O used back then to attach these panels to the plastic parts.

After all this it was time to give this 8002 a spin. I selected a recently acquired original pressing of Chick Hamilton's gorgeous "Passin' Through" album (Impulse A-29).

The second side is an amazing, almost psychedelic experience that would probably convert the most ardent digital music purist that vinyl is the way to go! Such a direct, warm and vibrant experience! Absolutely amazing! I wish I could find a time machine and go see a Hamilton performance live in the 60s!

Beogram 8002: Mechanical Adjustments and a Scraping Sub-Platter

After bringing the electronics up to spec it was time to put this Beogram 8002 also mechanically back to perfect functionality. I usually clean the carriage mechanism and re-lubricate everything, replace the carriage drive belt and adjust the tonearm parallelism. This Beogram also had the 'scraping subplatter issue' that seems to be fairly common.

Let's start with the carriage mechanism. This shows it taken apart.

After cleaning off the old grease and replacing it with a modern synthetic grease it was time to adjust the arm, which was pointing upward:

This is the situation after the adjustment:

On to the scraping sub-platter. This is caused by a compressed plastic disc at the bottom of the main bearing that holds the weight of the platter. This disk can suffer during transport if the platter is not taken out. To get to the disk the spindle needs to be take out:

This is done by loosening the screw in the silvery clamp on the right and rotating the arm that holds the sensor assembly that reads out the tacho disk clockwise:

The main bearing is in the center of the photo. This shows the plastic disc pushed up via the small hole in the bottom of the bearing that can be accessed from the underside of the enclosure:

The small orange disk on the right is a 3D printed part that I developed to shim up the white disk by ~0.5 mm. This elevates the sub-platter a bit and the scraping stops. It can be inserted under the white disk without having to take it out. Just flip it vertical with the small rod or similar that is used to push it up and insert the orange disc, then put everything horizontal again with fine tweezers. 

After this operation the platter ran smoothly again. On to installing the "liberated" aluminum plates and the putting the hood back on.

Beogram 8002: Repair of a Dead Display Digit

Another issue plaguing the Beogram 8002 that I am finishing up right now was that the fourth digit of the RPM display was dead. This shows the sorry state of affairs before my repair:

Since all segments of this digit were not working the most likely root cause of the issue was a missing strobe signal for this digit. A measurement with my oscilloscope at the strobe pin (14) on the display confirmed this hypothesis. Time to 'follow the signal', which is not the most straight forward thing to do in this setup since the unit must be running to do the measurements. I installed some micro-grabber leads in the microcontroller can at strategically important points and then did the measurements with the board installed. It turned out that the trace that connects processor pin 13 to the base of IC6 (the Darlington that drives digit 4) was interrupted midway (between the solder points of the white and ground leads):

The way this looked suggested that this was probably the result of 'human interaction', and of course one wonders what may have compelled anyone to poke around there with a sharp object causing the trace to come off. Anyway, I reestablished contact with a piece of magnet wire:

and the display digit came to life again:

Time to put the hood back on, do the mechanical adjustments and then do some 'reliability testing' (= listening to some awesome vinyls I recently bought...;-) on this lovely Beogram 8002.

Beogram 8002: Record Detection Malfunction

The Beogram 8002 that I am restoring right now had issues with the record detection function. When pressing start with no record on the platter it would drive the arm to the start groove position and then lower it onto the platter. And that is of course not acceptable considering the high prices of rebuilt cartridges these days...so I had another look under the hood. Here is the relevant section of my annotated circuit diagram:

When no record is present the photocell PH1 generates an alternating current due to the intensity change caused by the black strips on the platter alternating with reflective sections. This current charges C15. The resistors R65 and 64 are there to allow the capacitor to discharge when the photocell is off. R64 allows to change the time constant of the discharging process. By optimizing R64 the AC amplitude that goes into the base of TR14 can be maximized. TR14 ad TR15 amplify the AC signal which finally charges C19 and a voltage builds up at the base of TR16. TR16 turns on and HH is pulled to ground. HH feeds directly into the microcontroller, which therefore can detect the absence of a record and prevent arm lowering and/or drive the carriage towards the center of the platter in search of vinyl.

I hooked up my oscilloscope to R71/R72 and measured the signal with the sensor arm over the rotating platter. What I saw was a signal similar to the curve shown in the circuit diagram. At the same time I measured HH, which turned out to be somewhat inconsistent, fluctuating between 0.15 and 0.5V. This pointed towards a too small pull at the base of TR16 which would therefore not turn completely on.

I tried to adjust R64, but was not able to produce a larger signal at R71/72. After some head scratching I realized that I had maxed out R64 to obtain the largest possible signal. This was strange since one would expect that R64 would be dimensioned in a way that the maximum signal would be obtained somewhere in the middle of its resistive track. I measured the resistance across R65/64 and I saw only ~3k. This was strange since in the circuit diagram 15k and 20k are parallel, which should yield 8.5k...I removed R64 and it turned out that it was a 4.7k trimmer. I replaced it with a 50k 25 turn trimmer and did the adjustment again. And this time I was able to adjust to a clear maximum (8V) of the RMS voltage at R71/72. It is a good idea to use the RMS voltage of the sawtooth since its maximum will correspond to the maximum current pumped into the the base of TR16. This is the signal I measured after optimizing R64:

The corresponding voltage at HH was now a constant 0.13V.

Pressing start now also resulted in the appropriate response of the turntable: It did not drop the arm anymore but instead drove it all the way across the platter and then back to the home position. So this may be fixed! On to the repairing the missing digit in the RPM display.

Beogram 8002: Replacing the Motor Phase Capacitor

Today I finished up the recap of the Beogram 8002 that I am restoring right now. The motor phase capacitor is hidden away in the transformer block:

This large can is a unipolar 27uF capacitor. It can be replaced with two modern back to back 47uF bipolar caps. I designed a 3D printed fixture to hold them neatly in place:

This assembly is available to other enthusiasts. Just send me a message via the contact form to the right.

After this was settled I went on to replace the two remaining power supply capacitors that are directly soldered to the small PCB that uses the enclosure as heat sink:

I soldered two new capacitors in

and that concludes the electrolytic capacitor renewal of this Beogram 8002.

Beogram 8002: A First Look and Restoration of the PCB

Another Beogram 8002 arrived on my bench for some TLC. This one came in a disassembled state:

The hood was removed and of course the aluminum panels are detached (as usual). Under the hood, it was original

except that someone had removed the relay/DIN7 output board:

Luckily, a while ago I was able to buy a 8002 for parts, and its output board will go in here.

As usual the first step of any of my Beogram 8002/8000 restorations is to replace the electrolytic capacitors on the PCB with quality Japanese 105C grade units, and to reflow all the solder points of the board headers. Bad solder joints on this board are the main reason for operational headaches of the Beogram 8000/8002 series. Especially the connector for the transformer often has intermittent pins, causing the platter to randomly stop and other issues. I took the board out

and went to work. The most tricky part of this operation is the sole electrolytic capacitor in the 'inner sanctum', the microcontroller EMI can. It is located right next to the processor chip and serves to decouple its power supply from the rest of the Beogram:

It can be a bit tricky to remove without burning the jumper wires to the small add-on board that sits on top of the capacitor. The important thing to realize about this capacitor is that its main solder connection to ground is on the component side of the board, i.e. one has to do a bit of 'microsurgery' to unsolder it. Having three hands would be helpful here...;-). This shows the board after removal of the capacitor. The small solder pad on the left is the ground connection:

And here after installation of the new capacitor:

Once I forgot to solder the ground connection...an interesting experience...;-)

Here is an impression of the rebuilt board:

And a detail shot of the reservoir caps:

After replacing the board and plugging everything back together the Beogram showed first signs of life. Two issues were immediately apparent: It did not recognize that there was no record on the platter, and then there seems to be a missing display segment:

Interesting topics for the next few posts about this Beogram 8002!