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.