Beomaster 2400: Power Supply Checks and No-Load Current Adjustment

The lamps are now all replaced and tested.  I am ready to move on to the power supply checks.

First however, I installed the Beomaster 2400 control panel and rechecked the operation of the touch buttons and lamps. This panel is sometimes tricky to install as there is a spring contact for each of the touch control buttons.  Those must all align properly to their metal posts.

Here are photos of those checks. Note that the color of the indicator lamps isn't accurate to how they actually appear in person. It is always difficult to capture lighting pictures and still have enough light to see the audio component in the photo.

...and finally...Standby

Now for the voltage checks.

First is the +15VDC power.  Here is the +15V supply reservoir capacitor. 22V at the reservoir capacitor is a good value. Next is to adjust the output of the +15VDC regulator.

The service manual says to use the 2R151 trimmer to set the +15VDC supply to +15.0V making the measurement at 2TP15.

No problems adjusting that. Now to measure the Beomaster 2400 ±31VDC supplies. I measured those voltages at the two large 5000uF reservoir capacitors (0C7 and 0C8).

I have a couple of wires connected to the test points for the Beomaster 2400 no-load current adjustments.  The space is too cramped to easily attach measurement probes across the emitter resistors (2R256 and 2R356) for this adjustment so I like to temporarily solder some test wires for the no-load adjustment. Both channels easily dialed in to the service manual stated 12mA with the multi-turn trimmers I installed earlier.

Everything tested good so I can finish up the re-assembly of this Beomaster 2400 unit.

Beomaster 2400: Indicator Lamp Checks

Now the project gets to the fun part...reassembly and testing.

First thing is to put all of the parts I removed back and turn the Beomaster 2400 on.

I want to see if the replaced lamps all work and I will want to measure the Beomaster power supplies.

This post will show the testing of the new lamps.  The volume level indicator lamp module and the Bass/Treble/Balance module have to be re-soldered in place first. 

Here is the volume level lamp module reinstalled.

...and here is the Bass/Treble/Balance lamp module.

With the Beomaster powered on these two lamp modules illuminate.  

The source and FM tuning indicator module has two connectors so no soldering is required to reinstall it.

The lamps on this module all worked except one, the FM3 source selection lamp.
It turned out that I had the LED replacement lamp installed with reverse polarity.  I switched it around and then it too worked.

I was curious as to how I got the polarity wrong on the FM3 source indicator board. I used the previous Beomaster 2400 restoration project as a reference so the polarity should have been correct.
Looking at the previous project I now see that this indicator lamp panel has differences more than just the two board connectors.

Here is the Beomaster 2400 Type 2902 indicator board from my previous restoration project. The FM3 lamp (between the two board connectors) does not have the jumper that the current Beomaster 2400 does.  The same is true for the Beomaster 1900 Type 2903. The wiring path for that lamp is indeed different...as I found out.

On to the power supply and no-load current adjustments.

Beomaster 2400: Lamp Replacements

This post shows my Beomaster 1900/2400 lamp replacement method.

I replace the two volume level indicator lamps with new incandescent type lamps. These lamps are part of the the volume level circuit and need the lamps to be the incandescent type of lamp.

This is the board with the original lamps.

Here is the board with two new incandescent lamps installed.  I source them from Martin Olsen.

Next is the update to the Beomaster 2400 source selection and FM indicator lamps.
Again, here is the original lamp board for the source selection and FM indicator lamps.
I marked the positive side on the lamps I will be replacing with LED type bulbs.

First is the replacement of the three incandescent bulbs for (FM Stereo indication and FM tuning).

Next are the replacement of the source selection indicator lamps with LED modules.
These are a bunch of my homemade LED assemblies. The single ones are for the Beomaster 1900/2400 source indicator lamps. The dual LED assemblies are for the Bass, Treble and Balance position indicators.

Last are the replacement of the incandescent lamps for the Bass, Treble and Balance indicators.
Here is a picture of the board with the original incandescent lamps.

I always change these lamps to LED type lamps.  I often find that the plastic position indicator masks that fit over these lamps are damaged due to heat from the lamps. The LED replacements operate at a much lower temperature so should be better for the long term and are not damaging to the plastic indicator masks.

In the next post I will reassemble the Beomaster 2400 next and check the results of the restoration work so far.

Beomaster 2400 Type 2902: Lamp replacement and voltage checks

This Beomaster 2400 has reached the final stages of the restoration.  I replaced the indicator lamps and performed the first voltage checks on the receiver today.

On the Beomaster I replace the lamps that are only for illuminating a display function with LED devices. There are five lamps that are part of the circuit that they display the state of.  Those lamps must remain incandescent type bulbs. I typically get my incandescent lamps from Martin Olsen as I know he will source me the correct type.

Here is the before picture of the Beomaster 2400 volume indicator lamps.

....and here are the replacements. These are two that must be incandescent type bulbs.

Next are the tone control lamps (Bass, Treble and Balance).  These are lamps that can really benefit by changing to LED type bulbs. The sliding indicator masks on this Beomaster unit are deteriorated from the heat of the original incandescent bulbs.

The replacement LED lamps give off a lot less heat and should not damage the replacement indicator masks I am going to install.

Here are the original lamps.

Here are the replacement LED assemblies I created. Note that the polarity has to be correct on the LED lamps.

The LED lamps must have a current limiting resistor.

The source selection display board is the last board to replace lamps on. Here is the original configuration.

The far left bulb and the two incandescent bulbs on the far right must remain incandescent type bulbs.
The rest will be changed to LED devices. The red LED for Standby indication doesn't need to be changed if it still works.

Time to test the lamp replacements.

Standby works

The Standby lamp is a good indication that +15VDC is good on this Beomaster.  Time to check the power supply voltages.

Here is the +15VDC reservoir capacitor. The voltage here looks good. It is prior to +15VDC voltage regulation.

Selecting a source (i.e. FM5) I see that I have +15V so I performed that service manual adjustment.

While the Beomaster is still open where I can (barely) get to the left and right channel no-load current adjustment pots I performed those adjustments.

It is too difficult to place probes across the emitter resistor from the component side of the board while it is installed so I attach my probe wires on the trace side.

Now I can easily measure the voltage across one of the left and right channel emitter resistors for the no-load current adjustments.

Both channels dialed in easily. Well...relatively easy.  The trim pots for this adjustment are not the easiest to reach.

Note that I had the polarity of the probes reversed on the right channel measurement. It doesn't matter for this adjustment check. I am only concerned that I set the voltage on the meter to 12mV.

I also checked the ±31V rail voltages for the output amplifier. They measured good...probe polarity is important here :-).

The final service manual voltage checks I performed were the tuning voltages. There is one adjustment for FM1 and another for FM5.

So far so good on the reassembly and electrical checks.

I will finish reassembling this Beomaster then take it over to the test bench for some functional testing. I did perform a sneak peak by connecting up an FM antenna and an iPod Nano to the Tape source and listened to music via the headphones jack. The Beomaster 2400 is playing music again. Tone controls all work so a nice milestone has been reached on this project.

I will leave the Beomaster 2400 playing an FM station while hooked up to a pair of Beovox S75 speakers I keep in my workshop.  While it is busy doing that I can work on assembling the new display indicator masks for the bass, treble and balance controls.