Beomaster 8000: First Power Test

The Beomaster 8000 boards are all recapped. The output amplifier boards were exercised and passed their bench test. The remainder of the components have to be tested reassembled in the Beomaster so I think now is a good time to see where I am actually at with this restoration.

I want to check the Beomaster power supply with everything back in the cabinet. I also want to see what the condition actually is on the microcomputer and display boards. Since this Beomaster arrived in a non-working state I don't really know if those two boards have any issues aside from the electrolytic capacitors.

So here goes...
It is difficult to really document clearly with pictures where every cable connection goes. The best thing to do is label the connectors as you are disassembling them and take lots of pictures.

Here are a few pictures of the reassembly of the Preamplifier, FM, FM Interface, Filter & Tone Controls and Microcomputer boards.

After a double and triple check of the wiring I plugged the Beomaster power cord into my bench AC power strip. This looks promising. It means I at least have +5V power.  The Beomaster correctly comes up in Standby mode.

Time to check the voltage regulators.
First the +5V even though I know it has to be working. I still want to measure the input and output of the regulator.

Very nice.

Now to check the ±15V regulators. I like to use TP1 or TP2 mode to first take the Beomaster out of Standby.  I selected TP2 in this case and that quickly reveals the display segments do have faulty LEDs.  I was expecting that but it needed to be confirmed.

Checking the -15V regulator I can see its input and output are good.

Not good news on the +15V regulator. The output is bad.

That isn't a big deal though as these regulators are easy to come by and the location of the component makes it easy to replace.

I also checked the ±55V reservoir capacitor voltages. This picture shows that it is at 56V which is fine.

I am happy with the test results. Nothing major.  Importantly, the microcomputer appears to be great. The display board has bad segments but the plan was to change those LEDs out anyway. The +15V regulator failure should be easy to deal with. I will replace the regulator, proceed with the display LED replacement and perform the preventative measure of replacing the microcomputer crystal oscillator devices.

That should keep me busy for a while. Once those steps are complete I should be able to put the Beomaster in operational mode, recheck the no-load current and DC offset in the output amplifier and give the receiver a listen.

Beogram 8000: Initial Voltage Checks

Now that the required electrical work is done I am able to connect the Beogram 8000 components back together and see what the main voltages look like.

Here is the test set up I always use for Beogram 8000 and 8002 turntables. It is nice that every component I would need to get to is easily accessible for measuring.

Plugging in the power cord the Beogram standby light came on as expected.

Next I tested the 33 ⅓ RPM and 45 RPM speeds. The turntable speeds look like they are working but the bottom segments of the display is not working. Usually that indicates a problem with one of the 4.7nF capacitors on the microcomputer PCB. I will have to dig into that after these initial checks.

I observed one other functional problem I will have to investigate and that is with the record play. The tonearm moves to the start of a record but the fixed arm sensor is not detecting an empty platter.

Other than those two things the electronic functions look to be in good order.

On to the voltage checks for the Beogram power supply.  Here is the schematic for the power supply.

I checked the C24 capacitor on the main board for the voltage supplied to the Beogram +5 VDC regulator and the +5 VDC voltage at the microcomputer IC. Both measured good.

The C27 main board capacitor and +15 VDC supply voltage also look good.

So do the C29 main board capacitor and -15 VDC supply.

Overall good news on the electrical parts of this Beogram. Next I will look for the display segment problem and check the signals coming from the various sensors. That should point me to the culprit on the platter non-detection.

Beomaster 1900 (Type 2903): Replacing The Bass, Treble and Balance Slider Potentiometers

Now that the Beomaster can power back up I performed the 15 volt supply check and adjusted the No-Signal Current setting for the left and right channels.

Since the left and right channel No-Load Current adjustment went smoothly I expected the Beomaster to be able to finally play music again. I used an ipod Nano as the source to the Beomaster Tape input and a pair of Beovox S55 speakers for the outputs. To my surprise I had no sound in the left channel. After some quick debugging I found that the Nano source signals were present in the Beomaster up to the balance slider. It is common for the bass, treble and balance slider potentiometers to develop problems in these receivers.

Checking the balance slider I found that it was the culprit.

Note: The tabs shown by the red arrows below have to be bent straight in order to disassembly the potentiometer.

I thought about doing a creative repair with some glue but figured there must be a better solution.
As it turns out, Martin at Beoworld makes a replacement part for the black slider housing that moves to change the output. That black slider housing is the piece with the broken tabs the potentiometer contacts are secured with. I ordered a set of three replacement parts as all three slider potentiometers (bass, treble and balance) have a broken contact mounting tab.

Since it will take at least a week for the parts to come from Denmark I wanted to keep going with the Beomaster restoration. I pulled the bass, treble and balance slider potentiometers from a Beomaster 2400. The Beomaster 2400 turned out to have nice, intact slider contact assemblies so they will do nicely and I have new assemblies on order. In the exchange of parts I will only take the contact assembly as the Beomaster 2400 Bass slider potentiometer is 20KΩ and the Beomaster 1900 Bass slider potentiometer is 50KΩ.

I cleaned the potentiometer contact strips and contacts with a fiberglass brush and some Deoxit Fader Lube.

With the Beomaster 1900 slider pots cleaned and rebuilt it was time to test the Beomaster 1900 for sound again.

Sly's voice came out beautifully on both Beovox S55 speakers. All of the slider potentiometers really needed that restoration.