Beocord 9000: Rebuilding the Pinch (Rubber) Roller

The final crowning task to be completed on the Beocord 9000 that I am restoring right now was to rebuild the pitted and cracked pinch roller. Most of these decks have this issue. After all they are more than 30 years old! That is definitely exceeding the life expectancy of most rubber based products. I think a rebuild of the pinch roller is a must if one wants these decks to perform as new.

Luckily, there is Terry Witt at Terry's Rubber Rollers & Wheels. He is the world expert on rebuilding tape rollers and has a widely acknowledged authority on this topic...just visit some 'tape heads' blogs and chat rooms...;-). I think he does an outstanding job for an entirely reasonable price. So, don't bother buying second rate stuff on eBay with bad bearings and plastic wheels etc...just extract your original B&O quality rubber roller and send it to him! He is absolutely reliable and trustworthy! I made a short video about this procedure for the Beocord 9000. It shows how to get the roller out and put it back in. Enjoy!:

Beocord 9000: Restoring the Peak Program Meters with SMD LEDs

I recently successfully rebuilt the broken (4 missing segments) Peak Program Meter (PPM) of a Beocord that I had received for some TLC. Since this procedure was straight forward and had a nice result, we decided to also do it for the other Beocord 9000 I am working on, which still had an original PPM with all the segments working. I initially did not want to touch its PPM since I had never done one before, so like any good doctor I aimed to 'do no harm', while surgery was not absolutely necessary.

However, since the technology is the same as in the 7-segment counter display it is likely that some of the segments would have broken in the near future. So, while I still have it on my bench I think it is a great idea to do it now that I know how to make sure there are no issues in the near future.

Here are a few impressions of the procedure on this unit. Please, check for details in my original posts (post 1, post 2, post 3). As a fan of 'kaizen' I made a small further changes to the process by adding some glue to the restored plastic discs that hold the PPM covers down.

The original PPM still installed:

After removal:

Removing the covers by gently prying off the small plastic discs that hold them to the PCB:

Now they come off:

 This time I also removed the light guide for the scale illumination. It comes off anyway when one cleans the PCB with ethanol after soldering:

Now I was ready for soldering the SMDs in. This shows the green ones lined up for installation:

This shows them all installed and ready for testing:

At this point I usually do a 24 hrs test to make sure they are all o.k.

Now it was time to put the covers back on. So I clamped the covers and the light guide down and then recreated some resemblance of the small plastic discs by pushing the remaining stubs down with my soldering iron set to 200C. That just softens the plastic enough to be able to press it flat:

After this I put some small drops of Aleene's glue on the areas

and let them dry. This glue can be removed after soaking in ethanol for a while, so this is completely reversible.

I think this is a pretty good solution, at least for the Beocords since their displays are tightly held in place by the bezel that gets clamped over them, i.e. even if one of the spots came off, the covers would not be able to fall off.

Then it was time to install the rebuilt PPM. This required replacing the original current limiting resistors of the segments with larger values to account for the much higher efficiency of the new SMD LEDs. This shows the original resistors:

And here the new ones:

And after installing the PPM across the resistors.

Then I gave it a spin with a standard 1Vpp 1kHz signal at the inputs and the recording volume slider set to ~6. That gave me a nice full range on the meter. Beautiful these big segments!

That is it. All we need now is the rebuilt pinch roller that will soon come from Terry's Rubber Rollers. Then this baby will be ready for prime time!

Beocord 9000: Total Recap - Replacement of all Electrolytic Capacitors

I also did a full recap for my earlier Beocord 9000 restoration. While I think it is less urgent for Beocords and Beograms due to the generally lower operational temperature (than amplifiers/receivers), a replacement of all electrolytic capacitors is always a good idea if long term stability is desired. While the Beocord 9000 contains quite a few electrolytic capacitors, the good news is that its design is pretty service friendly. They definitely learned something between the 70s and the 80s. Even in comparison to the Beomaster 8000, the Beocord offers much easier access. In my opinion it is best to simply leave the main PCBs in the unit and instead remove the front and back panels. Here is a picture with the front panels removed. Their removal is straight forward and described in the service manual. Here is an impression of the top after removing the control panels and the glass cover:

The bottom PCBs can be accessed in a similar way by removing the bottom panel:

A good 'service position' for exchanging the capacitors is to put the unit upright opened like a book:

I put it on a towel, which allowed me to turn and move the unit while in this position. Once in this position it is time for some patience and concentration. One after another the caps are removed and new ones soldered in (in the correct polarity - as I said: concentration!! listen to some calm music and you will find some BeoZen in this..;-). Here are a few pictures:

Board #11 (DAC) is one of the two boards that need to be removed for the recap since they are sandwiched on top of another board:

 Before:

After:

The other one is #13 (Oscillator Detector)

Before:

After:

The following boards can be done while installed in the frame:

#8 Microphone Amplifier:

Before (the shield needs to be removed; it simply comes off when unsoldering the two spots that hold it in place):

After (shield already installed again):

#3 Rec/Play back circuit:

Before:

After:

#6 Rectifier

Before:

After:

It is worthwhile noting that the big 5000 uF cap was very close to be out of spec. It only yielded 4000 uF. This is still good enough for stabilizing the supply, but it shows that doing the recap was probably a good idea.

#4 Power Supply:

Before:

After:

#1 Microcomputer/display circuit:

Before:

After:

There is one cap on the upper part of this board. This shows it after replacement:

#2 Dolby circuits:

Before:

After:

O.k. done!

Beocord 9000: Replacing the RAM Battery

The Beocord 9000 has a 3V battery that supports the 16 word memory chip (an interesting MCM144102 chip that is mentioned as a peripheral memory unit in the Motorola 6804 manual, but whose detailed data sheet appears to be unavailable on the web). This chip stores the calibration settings (and may also back up the system time...not sure at this point - need to play a bit more with it). Here is a snapshot of the circuit:

The good news is that the battery is secured against connecting it with reverse polarity via D27. This suggests that replacing it with a battery holder instead of a soldered in tabbed version is a good way to proceed. 

The battery is located right underneath the TIME CAL indicator cabinet. The original battery started leaking the Li compound from the inside (that is the green-grey stuff around it). When I unsoldered the battery I suffered a small explosion due to this leaked compound. One should keep in mind that Li  is a highly reactive compound where a bit of heat immediately causes an exothermal reaction with the oxygen in the air. Luckily, I wore a magnifying visor and glasses, so nothing bad happened. But I would definitely recommend to cut the battery off with a wire cutter before starting to remove the tabs. Also wiping the area with ethanol would probably be a good idea to remove as much of the stuff as possible. Anyway, here is a picture of the vacated battery location after cleaning it as good as possible:

I used a 1/3N battery holder since tabbed 1/3N batteries are rare and pretty expensive. Also, a battery holder will enable to replace the battery in a few years without much fuss (the glass panel is removed very quickly without the need of a screwdriver, and then the battery can be accessed). Here is a picture of the new battery and the holder:

And the holder (Newark 25T0455) magnified:

Here is a picture after soldering it in. It is important to note the correct orientation that the + and - symbols match up with this on the PCB to avoid confusion down the road:

And with battery inserted:

Looks nice! Like it was designed that way (sort of strange to find a soldered battery in such a rarefied device, but then engineering of consumer devices usually assumes a 10 year use horizon...).

Beocord 9000: Repairing a Cracked Clutch Arm

This is a follow up to my initial entry about replacing the idler wheel rubber 'tires' in a Beocord 9000 tape deck. One of the issues I had was that the clutch arm showed a crack where the clutch shaft bearing is press-fitted 

It seems that many of these decks have this issue. A design weakness. While I thought that this is maybe not too dramatic since the strain was released via the crack and the bearing seemed stably in place, I felt that a proper restoration should not leave such a crack unattended. There is an interesting thread on Beoworld.org that was started by Sonavor, who is an expert on these decks. His approach was to buy some fitting copper pipe and cut off small rings that he was able to force over the cracked plastic part. While this is a really pretty looking and solid fix, the disadvantage is that one has to take the clutch apart. I did not want to risk to break the part, so I came up with a different approach:

I designed a 3D printed two-part ABS sleeve that I glued together under pressure using acetone-ABS slurry. This makes a virtually bulk material-strength bond since it dissolves the material at the interface and after evaporation of the solvent an almost uniform piece emerges.

Here is a picture of the parts together with the clutch:

While it was hardening I forced the parts together with a pair of grip pliers

And here is the end result:

I installed this in the Beocord and it works very nicely.

Beocord 9000: Exchanging the Rubber Parts in the Tape Mechanism

I made some more progress with the Beocord 9000 that I am restoring right now. I recently received the rubber 'tires' for the idler wheels in the tape drive mechanism and so I set out to install them. The reason I went ahead to do this was that the deck would not rewind properly. At the end of the rewinding process, when the power to the motor is reduced by the microcontroller the winding process became very slow and, depending on the particular tape, it also stopped in some cases. Of course this was not acceptable, so I looked around, and what came up on Beoworld.org suggested that the idler wheel rubber tires can harden over time reducing the friction and hence the transport becomes slow.

It turned out later, after I took the mechanism apart that a previous 'repair' effort on the mechanism bent an important friction pad, which in effect caused the problem. Well, now we have new idler wheel tires in the drive but also a straightened out tab that functions properly again. I think it is part of any decent restoration to refresh the rubber for long term stability, so I do not think the replacement was a useless effort. Anyway, I made a video about the replacement of these idler wheel tires (that can be obtained from Dillen of Beoworld.org...what would we do without him!!...;-). Here is the video (pay attention to the part where I discuss the bent pad - this can happen very easily if the drive is assembled without knowing about this issue):

It is worthwhile pointing out that I had a couple of issues during the rebuilding of the tape drive:

1) The plastic fixture of the clutch had a crack. This seems to be a standard issue with these drives. There are several posts on Beoworld about it and how to fix it with sections of brass pipe. I went a different route, since I did not like that one has to take the clutch apart for fitting the brass segments. My solution was to print a two-part ABS plastic sleeve that I then glued together around the part using Acetone-printer filament slurry. I will make a separate post about this in the near future.

2) After I plugged the drive back into the Beocord, it behaved erratically. When I pressed 'play', for example, it would go on 'fast forward' instead, rewinding ceased to work altogether. It turned out that pulling the plug of the ribbon cable that goes into the microcontroller board caused the board-mounted header to crack several solder points, and that caused intermittent behavior. To I desoldered them, and that fixed everything. This shows the header with the cracks. If you look closely you can see the ring shaped hairline crack around the top pin:

I added some flux and solder to the points and that fixed the problem:

After this I tested the drive, and it performed flawlessly. I measured the fast forward and reverse times for a C90 Maxwell tape:

FFD: 1:44 min with the motor power reduction coming on at about 1:37 min

FRV: 1:40 min; motor power reduction at 1:33 min

The spec from the manual is C60 takes 70 sec in either direction. So I think we are pretty close at ~100 sec for a C90. You guessed it: I do not own C60 tape...never understood their purpose...;-)

What is left to do is to get the rubber pinch roller rebuilt by Terry Witt. While it still performs o.k. it shows a bulging cracked surface, i.e. needs to be fixed to make this a 'full' restoration. Here is a picture: