A Pair of Beomaster 1900 Receivers for Restoration: Unit #2 Reassembly and Power Supply Checks

This second Beomaster 1900 unit is ready for reassembly and its initial power supply checks.

I put the power transistor heatsinks back in place on the four output transistors. I used Sil-Pad insulators for the thermal insulation material.

As a reminder, here is what the power transistors looked like at the start...prior to the capacitor replacements.

Here they are now after the restoration.  Installed with their new thermal insulation.

This photo shows the trace side mounting of the heatsinks.

While I had the heatsinks installed and the Beomaster 1900 turned over I soldered on some test leads for the No-Load Currrent measurements I will be adjusting later.

Next is the reassembly of the indicator lamp boards. I use dual LED lamp assemblies for the Bass, Treble and Balance slider position indicators.  For everything else I use replacement incandescent lamps.

While access is easy to the Beomaster 1900 touch button posts I cleaned the posts and treated them with Deoxit.

I had to resolder the power transformer secondary wires that supply the Beomaster 1900 +15VDC power supply.  That is because I intentionally desoldered them to protect them while I was moving the board around during the capacitor replacment.

Power could now be applied to the Beomaster and the standby lamp indicates there is +15 VDC power.

I tested and adjusted the Beomaster +15 VDC supply voltage per the service manual first.

The voltage coming in from the transformer secondary was the usual voltage of over 22 VDC.

I then performed the service manual adjustment to set the regulated +15 VDC supply to +15.0 VDC.

Next I did a quick check to verify the +-31 VDC rail voltages were present...and they were.

The power supplies look good so it is on to making an initial No-Load Current adjustment.

Per the service manual I adjusted the no load current for the output amplifier emitter resistors where the DC voltage across the emitter resistors is 12mVDC.  That measurement is also made without any speakers connected (no load) and with the volume level at zero.

This is a good start to the Beomaster 1900 restoration wrap-up.
Tomorrow I will finish the service manual checks and run some performance checks.

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.