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: Restoration of the Peak Program Meter Scale Illumination

While the scale illumination light bulb was still working in the Beocord 9000 display that I am rebuilding right now, my customer decided to replace the bulb anyway to make sure that there are no unwanted surprises during return shipping. I can only agree since these light bulbs have a tendency to break their leads of during high vibration-situations (think speeding FedEx truck and a bunch potholes...;-). Once one is in there, I think it is best to simply replace everything and be done with it.

I did this procedure already once in the last Beocord 9000 that I rebuilt, which had a broken bulb.

Here are a few pictures to document the process for this particular unit:

This photo shows the original light bulb held in place by the 'cork' that sticks through the PCB

and from the back:

This is the PCB that I implanted. It is the same that I use in the Beogram 4000 to replace the position-scale incandescent bulbs.

It has almost the same width as the 5 mm bulb that they used in the Beocord 9000. I only use one red-green LED on the board for this application, i.e. I bridged the second LED position with SMD jumpers ("000"). It is important to replace incandescent bulbs with red-green LEDs if the light is being filtered or reflected by red or green features (like in this case where the scale is both green and red).

This picture shows the LED board inserted into the bulb space.

And from the back. It can directly be soldered to the solder points of the bulb, the polarity matches:

Here is a picture of the test drive:

On to the 7-segment display.

Beocord 9000: Restoration of the Peak Program Meter with SMD LEDs (III)

This is the third installment of my report on how to rebuild the peak program meters (PPM) of a Beocord 9000. The first two posts report on the installation of SMD LEDs to replace the original faulty LEDs on the PPM PCB, and the re-attachment of the plastic covers. This post demonstrates the installation and brightness adjustment of the rebuilt PPM.

The first step was to replace the original current limiting resistors with the correct values for the modern SMD LEDs. Modern LEDs typically need much less current and achieve higher brightness than the original LEDs. This is reflected in the much larger resistor values that my initial experiments yielded to achieve similar or slightly increased brightness with the new LEDs. The original values were 180 Ohm for the red and 120 Ohm for the green ones. The SMD types required 470 Ohm for red and 330 Ohm for green for slightly enhanced output (see first post). The resultant currents were in the 10 mA range, while the original LEDs easily draw 40 mA, while having a lower intensity.

Here is a picture of the original resistor bank (the 8 leftmost resistors)

This shows the new resistors installed. Despite the PPM having 16 LEDs there are only 8 resistors. This is due to the fact that the two left and right PPMs are multiplexed at 60 Hz, i.e. only 8 are on at a time. This is seen in the signals of the two common anodes (pin 1 and 2 on the display board) which each drive one of the PPMs:

This shows the new resistors installed:

And here after installation of the rebuilt PPM:

And in action:

It turned out to be a good idea to fix the two display boards in sequence, i.e. leave one in while taking out the other. this allows to realign the one that was out with the one that is still in when putting it back. That way it is easy to get it back into the right position that it fits perfectly into the plastic bezel. Another helpful thing to do is to mark on the headers of the displays how far they were inserted into the PCB. This is important to get the right slant of the displays that matches the cover.

On to replacing the scale illumination bulb with a red/green SMD LED.

Beocord 9000: Restoration of the Peak Program Meter with SMD LEDs (II)

The 24 hrs test of the rebuilt Peak Program Meters (PPM) of the Beocord 9000 display that I am rebuilding was successful:

So I set out to reattach the red-green covers. Encouraged by my recent rebuild of a Beocord 9000 counter display, I decided to rely on melting the plastic posts of the red-green covers with my soldering iron set to 200C to recreate the original attachment method. First I needed to clamp the display together, however, to ensure that the covers would make a tight bond with the PCB to avoid light escaping through cracks at the bottom:

I applied the clamps in a way that the cover posts were still accessible and then I melted them by rolling the solder iron tip cone over them. This worked quite nicely:

When I cleaned the PCB with ethanol after soldering the SMD LEDs, the glue that held the light guide down dissolved. This told me that this clear glue was most likely some kind of polyvinyl ester based carpenter glue. So I used 'Aleene's Original Tacky Glue', which is my mainstay for bonding speaker foams to the cones. This glue dries clear, recreating the original look of the bonds:

After the glue was hardened, I put the display again to a 24hrs test to ensure that nothing bad happened during the reassembly:

What a beautiful design! I can't wait until I can make a test-recording with this deck using these lovely big rebuilt PPMs.

Beocord 9000: Restoration of the Peak Program Meter with SMD LEDs (I)

While I am waiting for the pinch roller for the Beocord 9000 I am finishing up, I started working on another 9000 that needs the displays rebuilt. Cassettes are definitely back! I hope they will start manufacturing new tapes again (and SONY decides to restart the production of the Walkman II...but that is an entirely different story...;-).

Anyway, here is a picture of the sad state of this display:

Not shown here, but the TIME CAL bulb is also dim, like on the other 9000. I decided to attack the VU or 'peak program' meter (PPM) first, since I never did this type of display before. Beolover excitement, no doubt! After opening the Beocord up, the first step is to remove the display bezel that covers the boards and also holds the translucent windows:

After taking the bezel off:

The I unsoldered the PPM board:

The next step was to remove the plastic covers. It turned out that there are black cardboard strips inserted between the covers and the light guide for the scale illumination:

The plastic covers were fixed to the PCB by melting their protruding plastic feet and flattening them, which creates round shaped 'seals':

These must be removed before the covers can be lifted:

I decided to leave the light guide in. Here is a picture after taking the covers and strips off:

For the fun of it, I piped some light in from the side where the scale illumination bulb sits. One can see nicely that the triangular cutouts in the bottom act as mirrors that reflect light to the positions where the scale numbers are:

After playing with this I started working on the rebuild. The first task was to determine the right resistors for the new SMD LEDs. First I determined the values needed to achieve an identical brightness to the original LEDs. For this I replaced a red and a green one of the four broken LEDs with SMD LEDs (Newark 75K1441 (red 14MCD 2.0V) and 75K1440 (green 18MCD 2.1V):

then I rigged the setup with resistors and ran it:

And with covers on:

It turns out that values of about 1k Ohm for red and 670 Ohm for green at 6.2V yield similar brightness. Note that the red LEDs had a similar brightness difference as the green ones, but the camera was not able to show this very well.

My client decided to ramp the brightness a bit up that the displays are better visible in brightly lit rooms. So I determined values that will make them match well with the higher brightness 7-segment display of the counter and indicator light SMD replacements that I usually use.

Here is a picture of the higher brightness version in comparison with the original LEDs:

The values that do the job are 330 Ohm for green (yielding 12.6mA) and 470 for red (9.4mA)

After this tests, I replaced all LEDs with SMD versions:

And running at 6.2V with the above resistor values in series:

Beautiful!! I will let this run for 24hrs before I reattach the covers to make sure that there are no problems.

Beocord 9000: Peak Program Meter Scale Illumination with a Red/Green LED

After I put in the rebuilt 7-segment LED display back into the Beocord 9000 that I am restoring right now, I had to realize that the light bulb that illuminates the dB scale of the peak program meter broke off one of its leads. This happens often to these old light bulbs. They seem to mostly die this way. The leads oxidize and then break off when stressed. And there was definitely a bit of stress when wrangling the display bezel back over the display PCBs.

This is how it looked before the repair. No numbers show in between the PPM LEDs:

I examined the situation. The bulb sticks into a total internal reflection wave guide that feeds light into the space between the PPM LEDs. Matching the positions of the numbers in the mask in the bezel the surface of the wave guide is roughed a bit to diffuse some light out, hence back-illuminating the numbers. Here is a picture of the bulb as it sticks its head into the guide:

The bulb is held in place by a 'cork' that is pressed into an orifice below the bulb. Here is a picture from the other side of the PCB:

I extracted the bulb and the cork:

I aways try to replace these sensitive bulbs with LED based replacements to achieve better shipping survivability as well as longterm stability (I hope they will still sell cassette tapes in 30 years...;-). The bulb has a 5mm diameter, and the waveguide has an opening that is a bit larger. I encountered a similar situation when I upgraded the tonearm position indicator illumination of the Beogram 4000 that I rebuilt recently. For that case I developed a special PCB that holds two red/green SMD LEDs to achieve an incandescent look and a red scale indicator. I checked and found that these PCBs perfectly fit into the cavity in the waveguide. So I adapted one of them by just soldering one LED on it and bridging the space of the second one that is in series on this board.

The Beocord 9000 scale illumination also needs red and green LEDs since the positive dB values show in red, while the negative ones appear in green. An amber LED would not work since LEDs generate their light by a semiconductor transition, i.e. there is only the specific wavelength of the particular LED color present. So if red or green light is filtered out to achieve red or green scale illuminations amber does not fit the filters, i.e. the light will be suppressed or show amber at a low intensity, but not red or green.

Here is a picture of the adapted PCB:

I used a high brightness red/green LED (Newark 75R0619)  in combination with a 499 Ohm resistor for the red LED and a 2k resistor for the green one, which has a higher luminescent efficiency. This adapted the LEDs to the 6.2 V bulb supply and achieved the proper brightness.

This picture shows it in action after soldering it into the light bulb spot: 

It is held securely in place by two strong leads from below. Luckily the for-Beogram 4000-designed PCB had the "+" and "-" tabs in the right orientation, so the jumpers are not crossed:

Here is a shot of the wave guide under LED illumination:

And with bezel installed:

For comparison: This is the display in my own Beocord 9000 that still has the original light bulb:

Very similar appearance. The LED version is actually a bit more color-true since incandescent light bulbs are not very good at making green light. The LED illumination is also a bit more even since the light is piped into the guide in a directed fashion due to the narrow emission angle of LEDs.