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Beogram 4002: Restoration of DC Motor Video Published - Check It Out!

By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...

Thursday, October 18, 2018

Canada Beomaster 8000: Display Board Segment LED Restoration Part 1

The last board to complete in the restoration of this Beomaster 8000 project is the display board. With power supplied to the Beomaster I could see there were some LED segments that were not illuminating. To really if all of the display segments work or if there is a bad connection I pull the display modules and place them on my home built test jig. Using a bench power supply and the test jig I can turn all of the display segments on at the same time. This will reveal any faulty segments.

Here is the display board before removing the display modules.





















The highlighted, dotted lines mark the display module leads that need to be desoldered for removal of the display modules.






















Here is the board with the display modules removed.

























The test jig reveals that there are four display segment LEDs that have failed.



So it is on to the display module repair.

Canada Beomaster 8000: Microcomputer Board Completed

I completed the electrolytic capacitor replacement on the Beomaster 8000 a few posts back. When I changed the two capacitors on the microcomputer and display boards I said I would return to the two boards later to finish their restoration tasks. I did that because I wanted to test the Beomaster power supply voltages first. Now that the power supply tests are out of the way I returned to the microcomputer board and completed the last task there.

The final microcomputer board task was to replace the two 2 MHz crystal oscillators with new ones. We like to replace the two oscillator devices because the Beomaster 8000 is such a heavy and expensive component to ship. Beolover first ran into a problem with the Beomaster 8000 2 MHz oscillator devices in a 2016 restoration. Since then we decided to make that replacement on all of our Beomaster 8000 restorations that involve shipping. Think of it as insurance.

The replacement is not terribly difficult but care must be taken to not damage the two microcomputer board processor devices.

Here is the board as I left it after the recap. The crystal oscillators and their related capacitors are highlighted.























This is a closer look at the 2 MHz oscillator devices and their 12pF ceramic capacitors.
























Before de-soldering and removing the existing 2 MHz oscillator devices the leads are shorted and the two processor devices (9IC3 & 9IC4) are removed. The red alligator clip connects the board ground to my shop power ground and my electrostatic discharge wristband. It is important to protect against static discharge when working with integrated circuits. Especially when some of these integrated circuits are not available anymore.






















This picture shows the oscillators removed.






















The new crystal oscillator devices are 2 MHz oscillators but their spec sheet specifies that they require 18pF capacitors instead of the 12pF capacitors the old oscillator devices required.






















The metal lids are then reattached to the microcomputer board shield box and I tested that the Beomaster microcomputer board still works.
























The control panel still functions so the microcomputer board looks like it is ready to go.

The display has some failed segments. To verify that I will remove the four segmented display modules and see how they do on the test jig.

Saturday, October 13, 2018

Texas Beomaster 8000: Power Check Milestone

After I finished the capacitor replacement on the final two boards for both the Beomaster 8000 from Canada and Texas my next task was to connect the components up and check out the power supplies.  In my last post I successfully tested the power supplies on the unit from Canada. I am happy to say the Texas Beomaster has also reached that milestone.

There was a slight difference in being able to run the tests on the Texas Beomaster. When I completed the recapping of the microcomputer board I was not pleased with the state of the solder joints on that board. It had been worked on before and there were several places on the board where the soldering was not good. I didn't want to wait until I resoldered that board to check the power supplies. So I used one of my spare Beomaster 8000 microcomputer boards as a substitute in the Texas Beomaster for the power supply checks.

But first I had to reassemble components in order to try powering up the Beomaster.
























Here is my substitute microcomputer board. It is a fully restored and known good board.






















The Beomaster is ready to try powering up.





















With my DMM connected to the +5 VDC regulator I plugged the Beomaster in to an AC outlet.






















Success. The red LED standby dot is illuminated and I have +5 VDC at the power supply +5V regulator output.

I pressed the TP1 (tape 1) button on the control panel and the Beomaster came to life.






















Continuing on the +5V, ±15V and ±55V supplies all checked out.



















































































As on the Beomaster 8000 from Canada this is a big milestone. It's great to know that the supply voltages are all good on this Beomaster.

While the Beomaster was on I checked out the display board. Interestingly there were initially some segments out but later they started working. In the following photo I also turned on the Beomaster Filter button as indicated by the illuminated incandescent lamp.
























I will have to check that out some more later.  The next task on this Beomaster is to get its original microcomputer board resoldered and into shape where it is controlling the receiver.

Friday, October 12, 2018

Canada Beomaster 8000: Power Check Milestone Reached

I mentioned in the last post on this Beomaster 8000 from Canada restoration that my next step was to check the restoration work so far by performing some power checks. That means connecting up all of the boards, plugging the Beomaster power plug in and checking the DC supply voltages.

That milestone has now been reached. Plugging in the Beomaster yielded no surprises and the expected red dot standby LED illuminated.






















Pressing the PH (phono) button on the control panel illuminated the volume level and PH segments on the display.






















The Beomaster appears to have power so it is time to measure the DC supply voltages.

First is the +5 VDC supply reservoir and the output of the +5 VDC regulator.
















































Very good. That check was pretty much redundant as the red LED dot would not have illuminated if the +5 VDC supply wasn't working. But I like to see what the actual voltage is.

Next are the ±15 VDC supply reservoirs and voltage regulators.
































































































Those all check out. Now for the ±55 VDC rail voltages for the left and right channel output amplifiers.



































































All voltages are present and accounted for. That is a major milestone in the Beomaster 8000 restoration. From here it is to return and complete the work on the microcomputer and display boards.  After that I will reassemble the Beomaster 8000 for functional testing.

With the power applied to the Beomaster I was able to see that there are some failed display segments. The plan was to rebuild those displays anyway so that confirms it is necessary.


Tuesday, October 9, 2018

Beogram 4002: DC Motor Restoration

A Beogram 4002 DC motor from London in need of restoration recently arrived. Most Beogram 4002/4004 DC motors are in need of getting their Oilite brass bearings re-infused with fresh oil at this point in time. The oil stored in these porous brass bearings is drawn out over the years, resulting in dry bearings that are the main cause of RPM variations in Beograms. This shows the motor as received:
Extraction of the bearings requires disassembly of the motor:
The two small donuts on the black pad are the bearings. I put them in motor oil and pulled a vacuum:
The air bubbles emerging from the bearings indicate the air drawn from the bearings due to the vacuum. This makes room for oil diffusion into the bearings. After about 48 hours the bubbling stopped and I extracted the bearings from the oil:
Then I re-assembled the motor and installed it in one of my Beogram 4002s for a 24 hrs RPM stability test with my BeoloverRPM device,
which allows logging of the RPM over extended periods of time. A great tool to check the health of a platter motor, since RPM fluctuations usually are inconsistent over time, and it is difficult to pinpoint issues by listening to records alone.
This is the RPM graph that I obtained after about 24 hrs:
This is as good as it gets...this motor is back in business and will soon travel back to its Beogram in London!