Beomaster 4400 Type 2419: Personal Project: Initial Power Checks

I couldn't end the day with just having the board restoration work complete.

I am always curious whether the audio components will actually work now.

First step was to reinstall the preamplifier and FM boards.

The Beomaster is ready to power on. Like I always do with this type of amplifier I connect the power cord to my variac, ammeter, voltmeter and dim bulb test device.  That device will protect against any hidden short to grounds on the power signals and it will tell me if something is drawing too much current.

In this case...I got nothing. No lights, no voltage on the power supplies.

After a bit of investigation I discovered that one of the AC cable wires was not connected internally in the Beomaster.  That explains that.

I checked the other wires around it and checked for any shorts. Other than the disconnected AC wire everything else looked fine.

Here is my repair of the broken wire.

That looks much better.

On the second round of the power checks I still don't get any lights illuminating on the Beomaster 4400 but I do have power on the supplies.

Here are the +15 VDC and +35 VDC supply checks

and here are the ±35 VDC rail voltage checks

It looks like the Beomaster 4400 is ready for a quick listening check.

I did a quick, initial setting of the idle current for the output amplifiers by adjusting the left and right channel trimmers to get 10mVDC across the respective channel emitter resistors.

Once those were adjusted I connected an iPod Nano to the Tape 2 source input and used a pair of headphones to check if I had sound.

Success!

I connected up an FM antenna to the Beomaster 4400 antenna input and tried tuning a station.
Another success.  The FM tuner section is working great. The tuning indicator and stereo lamps do come on as well.

So for certain the Beomaster 4400 power on lamp is not working and the lamp that illuminates the radicator (the FM signal strength meter) is also not working.

I am not sure about the overload lamp but I can test that when I replace the power on lamp.

Texas Beomaster 8000: Power Check Milestone

After I finished the capacitor replacement on the final two boards for both the Beomaster 8000 from Canada and Texas my next task was to connect the components up and check out the power supplies.  In my last post I successfully tested the power supplies on the unit from Canada. I am happy to say the Texas Beomaster has also reached that milestone.

There was a slight difference in being able to run the tests on the Texas Beomaster. When I completed the recapping of the microcomputer board I was not pleased with the state of the solder joints on that board. It had been worked on before and there were several places on the board where the soldering was not good. I didn't want to wait until I resoldered that board to check the power supplies. So I used one of my spare Beomaster 8000 microcomputer boards as a substitute in the Texas Beomaster for the power supply checks.

But first I had to reassemble components in order to try powering up the Beomaster.

Here is my substitute microcomputer board. It is a fully restored and known good board.

The Beomaster is ready to try powering up.

With my DMM connected to the +5 VDC regulator I plugged the Beomaster in to an AC outlet.

Success. The red LED standby dot is illuminated and I have +5 VDC at the power supply +5V regulator output.

I pressed the TP1 (tape 1) button on the control panel and the Beomaster came to life.

Continuing on the +5V, ±15V and ±55V supplies all checked out.

As on the Beomaster 8000 from Canada this is a big milestone. It's great to know that the supply voltages are all good on this Beomaster.

While the Beomaster was on I checked out the display board. Interestingly there were initially some segments out but later they started working. In the following photo I also turned on the Beomaster Filter button as indicated by the illuminated incandescent lamp.

I will have to check that out some more later.  The next task on this Beomaster is to get its original microcomputer board resoldered and into shape where it is controlling the receiver.

Beomaster 4400 (2419): Reassembly and Power Checks

Today I reassembled the electrical components of the Beomaster 4400 and performed the all important first power on test. The goal here was to verify all of the board component work is correct and the Beomaster can be plugged in, turned on and all of the power supply voltages are good.

I installed the FM boards (PC1, PC2 and PC3) first.

I had removed the shield cover to the main power switch so I reinstalled those parts now.

The last board to install is the PC4 preamplifier board.

As I was tightening the mounting screws of the preamplifier board to the cabinet I was reminded of a problem (in my opinion) with the design of the connector panel. The RCA jacks are too close together. This is also the case on the Beomaster 4000 receiver. I don't own any audio cables with RCA plugs that can mate with the Beomaster 4000 and 4400 receivers. The only solution will be to make my own and use heat shrink tubing instead of the outer shell that comes with the RCA plugs.

You can see that only the bare RCA plugs can fit the space allotted by the Beomaster connector panel.

I always connect Bang & Olufsen source components to the Beomasters so it isn't a problem for me but it is something to be aware of if you are planning on using your Beomaster 4400 for some non-B&O audio source components. The solution in that case is to get an adapter cable that goes from the RCA plugs to a 5-pin DIN plug.

Anyway, just a pet peeve on my part. Continuing on it is time to see what happens when power is applied to this newly recapped Beomaster 4400.  In the case of the older Beomaster amplifiers I like to use a variac with a dim-bulb tester on the first power up. It is just added protection in case I missed something. 

The Beomaster 4400 powered up fine. That is great so now I checked all of the DC voltages in the Beomaster.

Here is the +15 VDC power check where the regulator 0IC1 attaches to the PC5 board.

Next is the +35 VDC rail voltage at TP3 of PC5.

Then the -35 VDC rail voltage at 5R16 of the PC5 board.

I checked the +24 VDC voltages at the emitters of 5TR3 and 5TR4.  Here is a picture of the 5TR3 emitter. Both measured +24 VDC as they should.

Last I checked the -12 VDC at TP15 of PC5.

Very nice. Everything looks good so far. Tomorrow I will start adjusting the no-load current (idle current) and the source levels. Once that is done I will be able to see how this amplifier performs with audio signals.

Beomaster 8000: Power Testing the Receiver

Time to catch up with the status of the Beomaster 8000 restoration. I left off with the Beomaster reassembled and ready for its initial power up test.

Plugging the Beomaster into the AC power outlet for the first time is always filled with a little nervous excitement but it was all anticlimactic. Nothing visually happened. Mainly there was no red dot on the display board showing that the Beomaster was in standby mode. As I unplugged the Beomaster I did hear one of the power relays click so that was good to hear.

When this sort of thing happens the first thing to investigate is what is going on with the power supply. The 120 VAC, 60 Hz line voltage was there at the transformer (my house is actually 125 VAC). The 5 VDC regulator was measuring 5 volts. The ±15 VDC regulators and the ±55 VDC rail voltages were not present...but that is to be expected on initial start up if the unit never gets past the standby mode.

I opened the lid to the processor board and verified +5 VDC to the processor chips. That wasn't so welcoming of news. It means a problem on the microcomputer board.

I have three spare Beomaster 8000 microcomputer boards for this type of scenario. I swapped in the first one and tried power on the receiver again.

This time the standby LED illuminated.

Now I could start exercising some Beomaster 8000 operations. A recheck of the voltages showed me the ±15 VDC on the +15 and -15 voltage regulators. The large reservoir capacitors for the 55 VDC rails measure ±56 VDC.

During those above tests I also tried to increase the volume level but it was stuck on zero.
The problem with that could be anything from the rotary volume wheel sensor (or cable) and the microcomputer IC.

I tried a second spare microcomputer board with the same result so the problem is most likely the sensor or sensor cable. I have a spare sensor to swap with so I tried it.

There it is. The original rotary volume wheel sensor assembly has a problem. The replacement sensor assembly allows the microcomputer board to adjust the volume level up and down.

That left me with some decisions to make regarding this Beomaster microcomputer board. I have spare boards ready to go but I also have one set of Beomaster 8000 master and slave processor chips. The set is used and I don't know 100% if they are good but I decided I might as well exhaust all of the options I have. I installed the spare processor ICs in the original microcomputer board I took out of this Beomaster and gave it a try.

What do you know, the replacement processors bring the Beomaster into standby mode and then to on mode. The volume control works but now there are missing segments from the display. I know the display board itself is fine as I ran a 24 hour burn-in test on those display modules earlier.  So is the segment problem due to the processor chips or are there additional problems on this microcomputer board?

I decided to reflow the solder joints of the signal paths for the display segment drivers along with trying a couple replacement driver ICs (SN74247) I have for IC1 and IC2. The results were not successful and the problem got worse.

Eventually I got to a point where the microcomputer board would not function again. Not totally surprising as I wasn't confident that the replacement ICs I have available for testing this microcomputer board were good so I decided to go ahead and use one of my spare, working microcomputer boards as a replacement for this project. It is the safest and more reliable direction to go. I considered moving parts from the spare board to the original board out of this Beomaster but that would be an unwise risk. The less handling of the processor chips the better (even with wearing anti-static straps).

Spare board installed...These are much better results.

Moving on I found another problem with the Beomaster.  After the original bench testing of the output amplifier boards where I set the initial no-load idle current, I rechecked the left and right output amplifiers again now that they are re-installed.

The idle current check still measures good so I moved on to the DC offset voltage adjustments (for the left and right channels).  The right channel easily adjusted to the specificied tolerances of the service manual : 0.0 ± 5mVDC.  I am at 0.0 - 0.6mVDC on the right channel.

On the left channel adjustment I can only adjust the DC offset down to around 0.0 ± 50mVDC.

It isn't a high enough value to prevent me from test playing the Beomaster. I have been playing the radio and an ipod connected to TP2 for a few hours now.  However, it is not satisfactory to leave it like this. I will have to pull out the left channel output board and investigate the problem with the offset.