Beomaster 4400 - Australia Project - Reassembly and Power Check

Since the last update I finished the capacitor replacement tasks on this Beomaster 4400.

In addition to that, I replaced four incandescent lamps for the front panel. Those were the Overload Indicator, Power On and the two Tuning Indicators.

I cleaned the front panel along with applying some Deoxit to the four slide controls - Volume, Bass, Treble and Balance.

I also reattached the Beomaster 4400 heatsink assemblies with new SIL Pad thermal conductive material on the power transistors.

Here are the before and after photos of the IF Section PCB (PC 2).

Next is the Stereo Decoder and Indicator Circuit PCB (PC 3).

Last is the Pre-Amplifier PCB (PC4).

The next few photos show the indicator lamp replacement in the Beomaster 4400.
The front panel indicator lamps consist of a plastic base with contacts for the power wire and ground, a slot for mounting the lamp fixture (onto a bayonet on the front panel) and a socket for a 60ma-80ma lamp.

It takes a bit of patience and care to replace these lamps.

Here is the Overload Indicator lamp.

Here is the Power On lamp.

Here are the two Tuning Indicator lamps.  The flexible wire that connects power to the two lamp fixtures makes removal and insertion a little tricky.

The front panel controls cleaned up good after the Deoxit treatment on the slider controls.

The next two pictures show the Beomaster 4400 with it's circuit boards re-installed.
The photos show the SIL Pad thermal conductive material behind the transistors mounted to the heatsinks.

This is the point during the restoration where I can test that the Beomaster 4400 has electrical power.

I first plugged the Beomaster 4400 to my Dim Bulb with Variac tester.
That allows me to check that there isn't anything shorted that will draw a bunch of power and damage other electrical components.

With the Beomaster 4400 plugged into the tester, I turn the Beomaster on, then start applying AC with the variac.  I monitor the current draw of the Beomaster as well as the light bulb of the tester to see if any problems begin to appear.  That allows me to stop and shut power down if I see the beginnings of a problem.

The Beomaster 4400 powered up clean without any issues.

Assured that no shorts exist I plugged the Beomaster 4400 into a normal AC socket.

My first step was to check the power supply voltages.  I measured the +15 VDC voltage regulator output, the +35 VDC supply, the two +24 VDC, +33 VDC, -12 VDC supplies and the +-35 VDC rail voltages for the power amplifier.

Here is the +15 VDC check

Transistors 5TR3 and 5TR4 regulate +24 VDC to the Right channel tone controls and Left channel tone controls respectively.

There is a 35 VDC regulated voltage to the IF Section (PC 2).

After the the Beomaster 4400 volume and tone control circuits there is a Bessel Filter circuit just prior to the output amplifier.  That circuit uses a -12 VDC reference voltage.

The output amplifier circuits have rail voltages of +-35 VDC.

The last voltage check I made was the 33 VDC regulator circuit on the preamplifier board.

The voltage checks were all good so I performed the No-Load Current Adjustment for the Left and Right channels.  The service manual says to adjust the respective channel trimmers for 10mV to 15mV across each channel's emitter resistors.  For now I set them to 10mV.

This Beomaster 4400 is ready for some performance testing.  I will setup some of those tests for the next post.

Beomaster 5000 Type 2323: Reassembly and initially power on test

The Beomaster reassembly went smoothly.  You do have to remember to reassemble things in the reverse order they were removed as the order is important.

Once the components were all put back in place it was time to try the always fun initial power on test.

On this initial test my plan is to verify some key voltages like the +5 VDC to the Microcomputer PCB and the ±40 VDC rail voltages for the output amplifiers.  I also will adjust the idle current trimmers for the output amplifiers per the service manual.

With the Beomaster 5000 plugged in I turned it on by selecting a few of the source selections.

That is always a good sight to see.

Obviously the Microcomputer is working but I still measured and adjusted the +5V power supply for it per the service manual.

Next I adjusted the output amplifier idle current to 11mV across each channel's emitter resistors per the service manual.

The multi-turn trimmers make those adjustments very easy.

The final test on this initial power up was to check the 40V rail voltages on the output amplifiers.

The initial power on checks all look good.

I can move on to the next round of testing which will include playing some actual music content through the Beomaster and driving some speakers.  I will also hook the Beomaster up to some test equipment and check what the audio signals are looking like on the analyzer.

Beomaster 2400 Type 2902 - Canada Project Power Supply & No-Load Current Adjustment

 The hard parts of the Beomaster 2400 are completed. It is time to put the receiver back together so I can do some basic voltage checks.  

First though I need to re-attach the four output amplifier transistors that mount to the Beomaster 2400 heat sinks. I like using the Sil-Pad thermal interface product rather than the white thermal paste in these low profile receivers. The Sil-Pads do a good job and don't have the mess that paste does.

At this point I decided I wanted to check the Beomaster 2400 restoration I had done so far by powering up the Beomaster and performing some basic service manual tests.  In order to do that I re-attached the Filter & Tone Control board along with the Beomaster 2400 lamp boards.

If you think your eyes are playing tricks on you in the above two photos they are not. I didn't really like the new replacement 2C92 2200uF, 25V capacitor for +15VDC in the Beomaster.  The markings on that capacitor were kind of strange. It wasn't as clear as it should be about which end of the axial capacitor was positive and negative. Normally the (-) marking is a distinct arrow pointing at the negative end. This capacitor looks like it points in both directors and the data sheet on it wasn't any help...so I switched it out with a Vishay 2200uF, 25V, axial capacitor that has clear polarity markings.

Plugging in the Beomaster 2400 and turning the master power switch on resulted in the red Standby LED illuminating.

The first test I performed was for the +15VDC supply. I adjusted it to the required +15V per the service manual.

Next were the left and right channel no-load current adjustments.
The space for attaching measurement wires and adjusting the trimmers is very cramped in the Beomaster 2400. My method of performing the adjustment is to mount the measurement wires across the emitter resistors from the bottom of the Beomaster 2400 main board.

That provides the leads I need to attach my DMM for the no-load current measurements.
I adjusted the left channel for the target 12mV across the emitter resistor test points.

Then I adjusted the right channel.

So far everything looks good.

I want to measure the Beomaster 2400 muting circuit while I have the cover off and the original lamps still attached. That is the volume muting that occurs when the music source is switched.  Pressing one of the Beomaster music source switches should send a volume mute signal to the volume control until the source switching is completed.

I soldered on some test wires so I can watch the muting circuit in action with an oscilloscope.

Tomorrow I will measure what goes on with the volume muting circuit.

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.