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 4000: New Arrival from Italy

Exciting! Another Beogram 4000 found its way to my bench for a full restoration! TNT brought it over to the US in an amazing three days. I extracted it from the box. It was quite well packed and arrived safely. The exterior of the unit is pretty decent. No damages to the veneer and the hood is absolutely polishable:

The aluminum trim in the back of the hood came off on one side, but that can be fixed with double sided tape. After I opened it up and removed the aluminum plates (which are in dire need of a deep cleaning) I found that the carriage pulley had come off during transport:

Luckily the parts were easily found in the enclosure:

As usual the main key of the control pad extracted itself from the spring that holds it in place. This proves that it is absolutely necessary to tape the keys down for transport. I reinstalled the pad, switched the unit to 110V and plugged it in (keenly watching for potential smoke...;-). Nothing happened, so I pressed 'ON' and the carriage set itself into motion in search for a record. It stopped as expected at the set-down point for 12" vinyls. So far so good. However the solenoid did not engage. I moved the assembly a few times up and down by hand and then tried again, and there was a life sign. Very reluctantly the tone arm lift engaged after a tired motion of the solenoid plunger...

The unit came with the indication that the arm would not lower. It is clear that this unit needs a full clean and rebuild of the solenoid/arm mechanism. Also the solenoid looks strange and may be a non-B&O part. Other than that I found that the RPM switches are oxidized and do not work every time one presses them. The restoration will cure all that. On the good news end a working strobe light can be noted. 

In my opinion one of the intriguing features of the 4000. The position indicator, which is another remarkable design feature, was already broken once and glued back together. This indicates that this unit was in 'expert' hands at some point. The glue job is fairly well, done, though. 

Furthermore, the indicator light bulbs are dead. My SMD LED replacements will fix that for good. All in all I am pretty confident about this project. This Beogram 4000 is a good starting point for a full restoration, which will take it to near-new performance and looks.

Beomaster 8000: Intermittent Display Digits - Bad Solder Joints

Oh well...While I was cheerfully listening to an episode of Car Talk on NPR on the Beomaster 8000 that will soon go to Australia, I could not help noticing a couple digits in the freshly restored frequency display fluctuating -on-off-on-off...Back to the bench with this one! It really is a nice workout, carrying the 45 pound behemoth to my electronics lab...;-).

The digits that blinked suggested a problem with the Phase 3 strobe that governs two digits in the frequency display, as well as the balance digit. I quickly found the problem: A broken solder joint at P74 that, among other signals, connects Phase 3 to pin 15 of 9IC3 (the master microprocessor). Here is a picture of the solder joints of the connector:

If you look carefully, you will notice the shadow around the leftmost joint...this indicates a broken out joint.

I re-soldered all jacks and plugs on the two joined PCBs and now all is fine. These two large, but poorly mechanically supported boards are really the most problematic area of the 8000s...whenever there is erratic behavior, it is usually some solder joints or vias on #8 or #9. I will add the re-soldering of the board-to-board connectors to my standard Beomaster 8000 restoration process. Live and learn!

Back to the living room for some more in the field testing before the long journey.

Beomaster 8000: Display Restoration with SMD LEDs - Reassembling the Display Units

The SMD LEDs that I put into the Beomaster 8000 displays survived the 48 hrs test without problems. Time to put the display units back together. I applied the method I outlined earlier in this blog:

http://beolover.blogspot.com/2012/09/beomaster-8000-display-repair-hopefully.html

After I glued the transparency foil pieces to the back of the displays, I fixed them with carpenter clamps:

And after extracting them from the clamps:

Then I replaced R14 and R16 with 3.3kOhm and 1.5kOhm resistors to adjust the display voltage to reduce the intensity of the LEDs. See this blog entry for details about the adjustment procedure:

http://beolover.blogspot.com/2012/05/beomaster-8000-display-brightness.html

Then it was time to solder the displays back in. The insertion of the displays back into the board is tricky since one needs to line up all the pins at once...patience and calm music pays here...;-). Here is the display board after installation:

I adjusted trimmer R15 to get about 3.1V keyboard strobe (yellow) and about 4V on the LED rail (blue). It is important that the keyboard strobe does not go below 2.7V (see above blog entry for a discussion):

Looks like we are almost done. The last step before I put it back together is to check on the processor board.