Beomaster 6000 (2702) restoration: indicator and power supply circuit

Next in line in this full restoration project is the indicator PCB (stereo, FM signal strength & balance) together with the output power supply circuit. They are connected together with a metal L-frame. 

The first thing I noticed was that the leads of one transistor where not cut off! Or it came out of the factory like that, or someone replaced the transistor and forgot to cut of the leads (more likely...). Anyhow, this is dangerous situation and can lead to short circuits.

I replaced the trimmers with encapsulated ones since this area does collect a lot of dust. I  always check the settings of the trimmers and "copy" the values to the new ones. Obviously, all settings need to be checked again later on during calibration of the unit.

The hard wires between the two PCB's have been replaced with flexible ones. New glass bulbs (12V / 30mA) have been placed as well. One had already a broken wire.

After the output stage restoration, this one was quick and easy !

Beomaster 8000: Continuing the Board Recap

Three more circuit boards are now recapped...old electrolytic and tantalum capacitors replaced with new 105°C electrolytic capacitors or polyester (WIMA) capacitors where applicable.

Here is the Beomaster 8000 preamplifier board (from various angles) before recapping.

Here is the board after the recap.

Along with the capacitor replacement I also reflow the solder joints on all of the board connectors and on this board I cleaned the input trimmer contacts with contact cleaner. The solder joints on those trimmers were also reflowed.

Next to the preamplifier board are the FM and FM Interface boards so they were next to be recapped.
Here is the before picture.

Here are the after pictures.

The last board in this set of board recapping is the Tone Control and Filter board.
This is the before recapping picture.

This is probably the simplest board to recap in the Beomaster. Here is the after picture.

That leaves just the display and microcomputer boards to do before this Beomaster will be ready for a test drive.

Beogram 4002 (5513): Final Adjustments and Test Drive with Freddie Hubbard's Liquid Love

After installing the Beolover 4002 Commander remote control and internal RIAA pre-amplifier it was time to do the final adjustments on this deck and then give it a first spin. First I adjusted the tracking feedback:

The blue trimmer on my tracking sensor LED light source is very helpful for fine tuning the feedback after doing the coarse mechanical adjustment of the sensor housing relative to the sensor aperture.

The next step was to adjust the subclasses and platter height followed by adjusting the arm lowering limit:

The goal here is to adjust the lowering limit the the needle can go below the record but does not hit the ribs of the platter, should the record detection circuitry ever fail. Then it was time to adjust the tracking weight to 1.2g. I usually replace the flimsy circlip that holds the counter weight screw in place

with a M3 nut and a washer:

This allows fixating the counter weight in place in a way that survives the rigors of shipping. Once that is done the weight adjustment mechanism can be calibrated with a digital balance:

Most B&O cartridges are specified for a 1.2g tracking weight, i.e. it is best to calibrate for that weight.

The final step was to replace the original worn keypad with an almost pristine original pad that I recently was able to acquire:

And then it was finally time to put on a record and give this restored Beogram its first spin of its new life! I selected a recently acquire Freddie Hubbard record from 1975, "Liquid Love". This record is among the less highly rated ones of his output, but it is rapidly becoming one of my favorites. Especially the track "Lost Dreams" is quite lovely. Here is an impression:

I always enjoy playing a Beogram with my 4002 Commander remote installed. In case you wondered how the IR signal makes it from the Apple remote to the Commander receiver board: This shows the IR receiver as it protrudes from beneath the plinth when the deck is fully assembled:

Almost invisible (and fully reversible). Beolovely!

Beomaster 6000 (2702) restoration: re-assembling the output subframe

Before putting the output stage PCB back into the subframe there are a few things to take care of. First is cleaning the frame, the heat sinks and the plastic spacers. To remove the glue on the frame I used paint remover followed by some alcohol cleaner and water with detergent. I looks almost as new again!

And after the cleaning...

The warping of the output PCB has been mentioned a few times already and to avoid the common short circuits between the subframe and the solder side of the PCB I decided to use a permanent shielding in between. I used a sheet of 1mm thick plastic that I cut to size and glued on the inside of the subframe. Several cut-outs need to be done off course to fit everything back later and to give the wires, screws, etc. the space they need.

When I mounted the PCB I noticed something interesting:  the warping of the PCB was almost completely gone. The reason is simple: the many wires that come from the 8 darlingtons transistors are longer than needed (to allow removal without desoldering) and are "stored" on the bottom of the subframe when everything is mounted. This cable tree however pushes against the board and makes it warp. There are tiny slots on the bottom of the frame (see picture above) that are supposed to hold the board in place. But they are to small and the board jumps out easily. As a precaution (probably not really needed) I glued a small plastic spacer on the board in order to keep the correct distance between board and frame. Again, probably not needed but it helps to get a perfectly aligned and straight board and that looks nice!

Up to the the heat sinks and the output darlington transistors. To make mounting easier and avoid breaking of,  I replaced all the hard wires going the 8 darlingtons and the 4 transistors (that are also mounted on the heat sinks) with flexible wires. AWG 20 (0,5mm²) for the power darlingtons and AWG 24 (0,2mm²) for the other transistors. I tried to respect the original color code and was able to keep all but one original color. Note that the wires all have different lengths !

The mica isolators that are typically used are replaced with sil(icone)-pads. Some of the originals ones where cracked anyhow as you can see in the picture below. I know there is some debate about the pro's and con's of both. Some people stick to mica and use the needed thermal paste. Other swear to silpads. I'm in favour of the latter. It's easier and less messy since you don't need the white thermal paste anymore. I agree that one needs to be careful. These silpads can be punctured if something  (like a tiny ball of solder) sticks between the transistor and frame (heat sink). Therefore it is wise to check the surface smoothness of the transistor (usually the collector connection) and the frame. Also, do not over-tighten the bolts or screws. 

 

The plastic spacers are fixed to the subframe with a dot of glue, just enough to keep them in place.

The small driver transistors that are used for feedback of temperature and thus allow thermal stability of the power stage (the bias current) do need a bit of thermal paste since they are to small for silpads. One of them was fried on the right output channel and I replaced it with a authorised replacement (MPSA13).

Now all the heatsinks and transistors are mounted on the subframe.

Before moving on to the next phase, I checked a few things to make sure that there was no shortcircuit anywhere, that I had not mixed up the NPN & PNP darlingtons, etc. I found a fault in (again) the front right channel. Something was not measuring correctly. So I had to remove the board again and found a burned resistor 11R69 of 330 ohm that I had not noticed before.  This resistor is in series with the trimmer that regulates the bias current. I did replace all the trimmers before but never checked them for burning out. I did now, and one off course was burned out. Normal, since the driver transistor O1C6 was short circuit on all tree connections!

should be "resistor" of course and not "transisitor"

Checked again and so far so good. But no power yet applied to the board. That's for later.....

Beogram 4002 (5513): Installation of Beolover Commander MkII Remote and Internal RIAA Pre-Amp Board

The owner of the Beogram 4002 (5513) that I am finishing up asked me to install my 4002 Commander remote control as well as my internal RIAA pre-amplifier module. The Commander allows the full control of the 4002 with an Apple remote, while the RIAA gives the Beogram a high level output that can be directly plugged into any CD/DVD/AUX input on modern amplifiers. 

This shows the RIAA board together with the mounting adapter that elevates it above the headers on the output PCB:

This shows the board installed:

It is soldered into the spot where the output relay is located. The RIAA board design includes a second output relay for the non-amplified signal path, i.e. the RIAA can taken out of the signal path by simply plugging the two plugs into the original headers. See here for more detail about the RIAA board design and use. 

This shows the Commander MkII receiver unit on the bench:

The extension to the right is the IR receiver that feeds through in between the plinth and the enclosure to the outside of the deck. The MkII version has an added auto repeat function which uses a red LED (extension to the left) to indicate the auto-repeat status (LED permanently on: One time repeat, blinking: up to 10 plays and off: no auto repeat). This LED is installed beneath the CD-4 indicator in the RPM adjustment panel. This can be seen here:

The Commander board itself just plugs into the keypad connector, while the keypad plugs into a header on the Commander. One of the four screws that hold the main PCB in place doubles to hold the Commander PCB piggybacking on top of the main PCB.

On to the final adjustments and a test drive!