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Beogram Commander Remote Control: Maybe This is the Final Version!..;-)

This is a follow up to my recent post about the redesigned Beogram Commander remote control board, which now works in both (DC-motor) Beogr...

Thursday, April 28, 2022

Beomaster 4400 Type 2419: Reassembly and Power On Test

The hard work restoring this Beomaster 4400 unit is starting to pay off.
I reached the milestone of reassembling the Beomaster and testing its power supplies.

In the last post the Beomaster 4400 reassembly had begun but left off needing the output amplifier transistors to be mounted on the heatsinks. 

The transistors are now installed on the heatsinks with SIL pad thermal insulators.

I also wired up the power switch and mounted an arc suppression device like I usually do with these amplifiers.

The arc suppression device installation required tapping a couple of M3 holes in the Beomaster bracket that secures the large filter capacitors.

I started installing these devices after one Beomaster 4400 had arrived with severely charred switch contacts.  Because these power switches can no longer be sourced (other than stealing on from another Beomaster 4400) I think it is worth a little more effort to protect them.

Before plugging in and turning this Beomaster 4400 on for the first time I plugged it in to my Dim Bulb/Variac tester.

That tester allows me to slowly apply AC power to the Beomaster while monitoring how much current it is drawing.  The light bulb draws current away from the amplifier if too much is present.
Doing that protects the Beomaster from having more component damage if there is a short circuit somewhere.

Here is a good example of why it is good to start out with this type of testing.

This Beomaster started drawing too much current right away as I dialed up the AC voltage on the variac.
It reached about 400mA by the time I was at 50 V.

I stopped and removed power.

After going over the wiring of the Beomaster I found and fixed the problem.

Running the test again I now have a clean power up of the Beomaster unit.

Around 260 mA with full input power applied.
That matches what I get with other Beomaster 4400 units.

With the Beomaster 4400 able to power on safely I performed a number of power supply voltage checks.

Here are the +15 V and +35 V reference voltages.

Next is the -12 V reference for the audio muting circuit.

Here is the reference voltage for the Phono, Tape 1 and Tape 2 preamplifier circuits.

Here are the 24 V Left and Right channel reference voltages for the preamplifier tone controls.

Here are the power amplifier positive and negative rail voltages.

Finally, here are the Left and Right channel no-load current checks and adjustments for the output amplifier.

The service manual says to measure across the emitter resistors and adjust for between 10 mA and 15 mA.

For now I will roughly set them above 10 mA.  I will adjustment them more precisely later.  Probably at 12 mA.

It feels great to finally have this Beomaster 4400 amplifier powering on again.

In the next post I will start in on some bench testing that is include some actual music listening tests.

Monday, April 25, 2022

Beogram 4002 (5513): Complete Restoration Including a Refurbished Keypad and Commander Remote Control Module

This post describes the complete restoration of the Beogram 4002 (5513) from Arizona that I initially assessed here. This shows the unit as received:

As usual, my first step was starting the platter motor bearing oil infusion. This shows the extracted motor:
I disassembled it to get the bearings (two small donuts on black pad) out:
Then I immersed the bearings in motor oil and pulled a vacuum. Immediately strong bubbling started as the air was drawn from the porous emitted bearing material, making room for fresh oil to interdiffuse back into the material:
While the infusion process was taking place (usually takes 2-3 days until the bubbling stops), I removed the moving parts of the arm lowering and carriage transport mechanisms for cleaning and re-lubrication:
This shows the cleaned components:
After re-assembling the mechanisms, I replaced the cracked plastic carriage pulley with a machined aluminum replica:
Then I replaced the incandescent light bulb of the tracking feedback mechanism with a LED based replacement. The black box in this picture shows the original part in place:
This shows the replacement. The blue part is a trimmer that allows adjusting the intensity of the LED, which is useful for fine-tuning the tracking mechanism:
The final aspect of the carriage restoration was to remove the damper-to-tonearm linkage and lubricate its pivot point. For this one has to remove the sensor arm. This shows the arms assembly from the back.
I removed the sensor arm assembly
and removed the linkage
As usual the small copper plate that reduces the lateral arm friction when the arm is up was only loosely attached and fell off after a light tug:
Originally, it is attached with double sided tape, which after 40+ years is usually degraded. I epoxied the part back into position:
This concluded my work on the carriage/arm lowering mechanism. The next step was rebuilding the main PCB. A while ago I started replacing all the power transistors and Darlingtons on this board since I had a couple returns to my bench after one of these transistors failed. So it seems they are also affected by the aging process. That much for 'silicon is forever'!...;-). It is best to replace the two on top of the board while the board is still bolted in. This shows the original TIP107 Darlington that drives the solenoid, 1IC4: 
I replaced it with a TIP107:
After replacing these devices, I removed the board. This shows the component side in original condition:
This is a detail shot of the original RPM section, consisting of the Siemens RPM switch relay and the two RPM trimmers for tuning the platter speed:
I exchanged all the electrolytic capacitors, the RPM section, and the sensor arm circuit, as well as the transistor that supplies the platter motor with power:
This shows the rebuilt RPM section. I use 25 turn encapsulated trimmers. This allows a much more consistent adjustment of the RPM:

The next step was rebuilding the output board, which houses the output relay and the delay circuit that makes sure the relay only triggers after the needle has safely landed in the groove:
This shows the rebuilt board. I also installed a (red) switch that allows connecting system and signal grounds in case there is a hum issue.
My next focus was on replacing the degraded transport lock bushings:
This requires removal of the floating chassis so one can vacuum all the fragments out of the enclosure. They can impede the floating chassis movement when they get stuck underneath. Due to the elegant flatness of the Beogram design there is not much room for the chassis to move. During this step it is a good idea to also remove the original reservoir capacitor:
This shows the emptied enclosure:
I vacuumed the enclosure and prepared the bushing replacements:
They are 3D printed. They install as a two-part assembly, where one half goes in from the bottom and the other from the top. this makes installation a snap. This shows one of the locks after installation of the new bushings:
Here a shot of the new reservoir capacitor assembly. This Beogram came with a two-capacitance unit since it is a CD-4 board ready design, where the CD-4 board has its own reservoir capacitor. These dual-capacitance units are no longer available, and so I replace them with two modern capacitors that are common grounded:
After this chapter of the restoration it was time to replace the remaining incandescent bulbs with LED assemblies. First I focused on the RPM panel. This shows the extracted panel with the original bulbs still installed:
These are the recently updated LED based replacements:
They solder directly to the solder points of the original bulbs. Beolovely!:
This shows one of them in action:
The final bulb to replace was the one in the sensor arm. This shows the original bulb and the replacement:
I installed the replacement. This shows the LED in action:
After replacing the light source in the sensor arm it is a good idea to check the sensor signal without a record on the platter. This is the trace I measured:
An amplitude between 4-6V is acceptable that the circuit functions reliably. This is important to protect the stylus from accidentally being lowered on the empty platter.
In the meantime the bearings had concluded their infusion process. I extracted them from the oil:
and reassembled the motor. Now it was time to measure the longterm RPM stability with the BeoloverRPM device:
It allows logging the RPM once every 10s for extended periods of time.
This is the curve I measured after about 24hrs:
This is about as good as it gets with the DC platter motors in Beograms!
A routine check of the fuses compartment revealed that one of the fuses was 'embellished' with some aluminum foil. Not something the Beolover would advise to do at home!
I installed new fuses. 
This is generally a good idea, since many of the old glass bodied fuses have loose metal parts, i.e. the fuses are not sealed anymore. This can lead to corrosion and blown fuses without a real reason.
Now it was time to do the adjustments. After adjusting the platter height, arm horizontality and height, floating chassis position and platter centrality I focused on calibrating the tracking force. The first step is usually the replacement of the flimsy circlip that holds the counterweight screw in place
with a M3 nut, which allows fixating the counterweight in place that it can withstand the rigors of shipping without voiding the calibration:
Then I calibrated the weight scale to be accurate around the 1.2g mark:
After this I adjusted the arm lowering limit to make sure the stylus would miss the ribs on the platter in case of an accidental arm lowering due to technical malfunction of the control circuitry:
Another important adjustment is the tracking feedback, which makes sure that the carriage correctly and smoothly tracks the inward needle movement during record play:
At this point this restoration was coming to a close. The final technical touch was the replacement of the corroded original RCA plugs with modern all-metal units with gold plated terminals. This shows the original plugs:
And their replacements:

The final steps of this restoration were cosmetic: This Beogram had rusty chassis springs:
My customer suggested to use Loctite 'Extend' rust neutralizer on them. I decided to get a jar of this compound and give it a try (these were not the first rusty springs that appeared on my bench). I brushed the neutralizer on the rusted areas:
After a couple coats and 24 hrs curing, I spray painted them with some matte lacquer. Definitely looks better than before!:
An now the crowning touch! After a long period of trial and error and experimenting with a number of coatings and providers, co-Beolover Beomazed came through and provided the first re-coated keypad, which makes this restoration a very happy moment for the Beolover! I replaced the badly worn keypad:

And now this Beogram does not only play like new, it also looks awesome! Perfect! I celebrated this moment with a recently acquired 'Return to Forever featuring Chick Corea' album from 1975, "No Mystery" (Polydor PD6512), which was of course ultrasonically cleaned with a CleanerVinyl ProXL setup. Beautiful!:

I will play this Beogram a bit more, and if nothing further comes up it will soon be time for it to return to its owner in Arizona!