Beomaster 8000 Type 1903 - Arizona Restoration Project - A Couple More PCB Restoration Tasks

After the previous post I couldn't stop thinking about the Beomaster 8000 frequency response results.  The output was a little beyond the expected -0.5 dB at the two ends of the 20Hz to 20,000Hz frequency range.  Since the preamplifier board and volume control/filters board of this Beomaster had never been restored, I decided to go ahead and update those two PCBs.

Here is the before and after restoration of the Beomaster 8000 Preamplifier PCB.
The op amp devices and electrolytic capacitors on this board are all in the audio signal path.

I replaced the electrolytic and tantalum capacitors with nonpolarized audio capacitors.  
The op amps were replaced with TI OPA2134 op amps. They are more expensive than the original TL072 and LF353 op amps but the OPA2134 op amp has a very good reputation for usage in audio applications.

The Beomaster 8000 audio signal path leaves the Preamp PCB and goes to the Volume Control/Filters PCB.  The Volume Control circuit is first and the Filters circuit is second.  However, in the Beomaster 8000, the audio filtering (including Bass and Treble) is bypassed by default.  The Filters button inside the metal control panel lid engages and disengages the filtering.

The performance measurements I have been making have been with the filters bypassed.

Here are the before and after photos of the Beomaster 8000 Volume Control and Filters board.

Here is the Beomaster 8000 Volume Control and Filters board after being restored.
Like the op amps in the signal path of the Preamplifier PCB, I used the TI OPA2134 op amps here as well.

Now for the frequency response measurements again.

Quite surprising to me, there doesn't appear to be much improvement.  I was expecting a more noticeable result.

At 20Hz the signal is down just over 0.5 dB.  At 20,000Hz the signal is down about  0.8 dB on the Left Channel and just over 0.5 dB on the Right Channel.

As and FYI, I did adjust the Tape 1 input pots to make sure the Left and Right channel test signals are as identical as possible.

I decided that I needed to look at the frequency response measure at different points in the signal path.

First, just the preamplifier section.
I still kept the input signal source on the Beomaster 8000 Tape 1 source input.
For the output measurement though, I pulled the jumper bars between the Beomaster 8000 External Filter input and output RCA jacks.  This would show me the audio test signal only at the preamplifier stage.

My test cables picked up some noise from the line 60Hz but the frequency response is still very flat.
The output at 20Hz is only down about 0.02 dB and the output at 20,000Hz is only down about 0.04dB.

Next is the Beomaster 8000 Output Amplifier.
I used the Output Amplifier P39 connector for the audio input signal and I measured the output across the 8 ohm, dummy speaker loads.

My test setup encountered much less noise with this measurement.

The Output Amplifier frequency response measurement was also nice and flat.
At 20Hz the output is only down about 0.2dB while at 20,000Hz the output is only down about 0.05dB.

The Preamplifier and Output Amplifier boards checked out very flat as I would expect.

That means the Volume Control and Filters board must be the affecting the frequency response measurement I get with the end to end test.

Here is the Left Channel frequency response with the audio input at P27 of the Volume Control and Filters PCB and the output measured at P24.

Again, my test setup picks up the line 60Hz but you can see how much different the shape of the frequency response is.

I hadn't looked at just measuring the Volume Control and Filters board by itself before so I spent a little extra time.  Because the capacitors and op amps are all new and known good components, I wondered about the AD7110 (logdac) IC device itself which performs the Beomaster 8000 volume control functions.

Instead of jumping in and replacing the volume control devices (there is an AD7110 IC for each channel), I decided to take advantage of having a couple of spare Volume Control and Filter boards available.

Both of my other (restored) Volume Control and Filter boards yielded very similar frequency response waveforms.  It would appear that is a characteristic of this volume control design...but I will need to measure more Beomaster 8000 units to confirm or refute that.

For now, this as far as I will take this experiment.  The frequency response results I am getting are very close to the -0.5dB range specified in the Beomaster 8000 technical data sheet.  More importantly, the music output of this Beomaster 8000 sounds very good as things currently stand.  So I will start putting components back into place inside the Beomaster 8000 cabinet and do some final listening tests before shipping this receiver back.  

I have several more Beomaster 8000 units to restore so I will definitely be repeating these measurements for comparison.

Beomaster 8000 Type 1903 - Arizona Restoration Project - Finalizing The Repairs

This Beomaster 8000 project is almost ready to wrap up. 

I left off with this Beomaster functionally working.  To continue that, I did some music listening with the Beomaster 8000 connected to an FM antenna, an iPod (in Tape 1 and Tape 2 source inputs) and with the speaker 1 and 2 outputs connected to my workshop Beovox S-55 and MC-120.2 speakers.

At first I thought the sound was okay.  Thinking back, that itself was a little odd.  Usually I am more impressed during the first listen.  Something seemed off with this Beomaster 8000 sound so I connected up my audio testing equipment.

Here is my test setup.
I mainly wanted to view the frequency response of the Beomaster at various output levels.
For that, I used a QuantAsylum QA-403 Analyzer and my two, bench dummy speaker loads (8 ohms).

The frequency response testing showed that the output amplifier had quite a drop off in output between 20 Hz and 100 Hz (the low end).

Here is a QA-403 frequency response test output with the Beomaster 8000 at its maximum rated output, 100 Watts into 8 ohms. 

A Beomaster 8000 should output its audio signals between 20 Hz to 20,000 Hz with only a ± 0.5 dB difference.

As you can see, at 20 Hz, the output levels are around -4 dB down from where the output is at 1000 Hz!

Looking at the left and right channel Output Amplifier modules (Module 5) I spotted a problem.
These Output Amplifier modules had already been re-capped previously by an electronics shop somewhere.  They did pretty good work but on the 100uF, 16V electrolytic capacitors (there are two per Output Amplifier PCB), the technician transposed the numbers for the capacitor.  Instead of grabbing 100uF, 16V capacitors, he (or she) selected 10uF, 160V capacitors.

One of those capacitors is for the Beomaster 8000 Output Amplifier feedback.  
The gain on the feedback is especially sensitive to the value of that capacitor and the 10uF capacitor results in the impedance of the capacitor at 20 Hz to be around 795 ohms instead of 79 ohms of a 100uF capacitor.
That really knocked down the gain of the amplifier output at the lower frequencies.

Here is a photo of the Output Amplifier boards as they were with the incorrect capacitor values.

The accidental selecting of the wrong capacitor values there didn't cause any catastrophic problem to the Beomaster but it did rob the Beomaster of its low frequency performance.  That is the problem I was hearing during my first listening tests.

Here are the boards now with the correct capacitor values installed.

Remeasuring the Beomaster 8000 frequency response at 100 Watts output across the 8 ohm dummy loads show a much improved low end.

The low frequency output is now very close to the -0.5 dB limit specified in the service manual.

The high frequency output is a little off from 0.5 dB at 20,000 Hz but for now, that isn't something I am going to address.

Listening to music on this Beomaster 8000 is now noticeably improved over what I was hearing before.

That problem and fix was an unexpected detour task on this Beomaster.  I had planned to fix the FM display segment problem and the broken lid lever problem discovered earlier in the initial assessment of the project.

Here is the broken lid lever problem.
 

The plastic lever had broken in half but the lid damper also had a couple of problems.
Highlighted in red, above...A plastic hook on the lid damper frame was also broken.
Plus, the damper was leaking damping grease.

One thing to note though, the damper and lever are for slowing down the opening of the lid, not the closing.

The Beomaster 8000 lid is sprung so that it pops open and remains open until someone manually closes it.

It turned out, this Beomaster 8000 lid had another problem besides the damper and damper lever.
The lid assembly itself, had a broken cover for the spring that raises the lid.

Here is a photo of the broken lid and the replacement (spare) lid that I have to replace it with.

I think that I can (later) design a fix for the broken lid assembly but for this project, this Beomaster gets a replacement lid.

For the lid damper fix I also provided a replacement damper from my collection of spare parts and a new, replacement lever that I got from DKSoundParts.

For the lid damper damping grease, I tried two different types.  I have used these two types before.
The Nye Lubricants PG-44A is the thickest damping grease I have come across.  Its high viscosity is really good on Beogram 800x turntable lids.  The Rocol Kilopoise is supposed to be what B&O originally used on these dampers.  Its viscosity feels about half the viscosity as the PG-44A.

However, I ended up going with the Kilopoise filled damper on this Beomaster.  I felt the higher viscosity PG-44A put too much pressure on the plastic lid lever and I didn't want it to break again.

Next was the FM display segment problem.

In my earlier testing of the Beomaster 8000 I noted that one LED segment and the LED period were not illuminating on the FM display.  I have highlighted those in the picture below.

On this project, the plan was to only fix the broken display segments, not go to the expense of replacing the whole set.

That being the case, I took a fully functioning FM display module from one of my spare Display boards.

I tested the faulty FM display and the replacement FM display on a test fixture I designed for these B&O LED display modules.

With my bench power supply I was able to increase the current and voltage to get the missing LED period to illuminate on the faulty display.  That took more voltage and current than it should and the display got a little warm.  Also...There is still the same missing LED segment.

The picture below shows both the old and new displays on the test fixture.

Here is the Beomaster 8000 with the replaced FM display module installed on the Display Board.
I tested it out as I also tested listening to the Beomaster FM tuner.  Both worked perfectly.

Now to carefully reassembly the Beomaster 8000 and do some more functional testing before returning it to its owner.  

I still need to connect up actual Beosystem 8000 components to verify that the remote control functions all work.  

Beomaster 8000 Type 1903 - Arizona Restoration Project - Replaced Microcomputer Board Testing

I decided to go with my already restored, early serial number Beomaster 8000 09 Microcomputer module in this Beomaster 8000 receiver.  I re-installed the original unit's metal shielding box on the replacement 09 PCB.

After working with this early serial number Microcomputer PCB, although the shielding box is a pain to work with, I should have removed it by focusing my de-soldering work on just the tabs that were soldering onto the shield box lids.

Reinstalling the box is much easier than removing it.

Here is a picture of the new Microcomputer PCB at the corner where the original board had broken traces.
Everything is good with this 09 module.

Here is the new Microcomputer board reinstalled in the Beomaster 8000 cabinet.

I went through all of the control panel functions both with the control panel buttons and the remote control buttons.

Everything worked as it should except that the FM station display has the two missing LEDs.

I can deal with the display LEDs later.

Right now I wanted to try out this Beomaster 8000 and see how it sounds.

Before doing that though, I needed to check the No-Load Current and DC Offset of the Beomaster 8000 Output Amplifier boards per the service manual.

Both the No-Load Current and DC Offset values needed adjusting.  

Here is the No-Load Current check after I adjusted the TR226 trimmer on both channels.

Note: These checks and adjustments are made with no speakers connected and the volume at zero.

No-Load Current

DC Offset

Those service manual adjustments encountered no problems so I moved on to some real listening tests.

I connected up an FM antenna and an iPod Nano to Tape 1.
I connected a pair of Beovox MC 120.2 speakers to Speaker 1 outputs of the Beomaster.

I will leave the Beomaster 8000 playing for several hours with the volume level at a low volume level (2.4).

Beomaster 8000 Type 1903 - Arizona Restoration Project - Microcomputer Board

Having determined the Microcomputer PCB (Module 09) has a problem in this Beomaster 8000 receiver, I removed it to examine it more closely.

I am not fond of these Microcomputer (uC) PCB modules from the early serial number Beomaster 8000 units.

B&O decided to solder the top and bottom (metal) lids of the uC assembly to the PCB. On later serial numbers, B&O changed the PCB shielding to be a metal frame around the PCB with snap-on lids.

To remove the metal lids on this uC PCB, the board connections have to be de-soldered.
It is safest here to use solder wick on the six mounting spots.

Here is the 09 PCB with the metal lids removed.

Right away I could see some breaks in the 09 PCB traces near connectors P75 and P76.

I verified the open trace connections with my DMM then set about repairing them.
Of course I hoped this would be the single source of the 09 Module problems and could move forward.

Here is the PCB 09 with the breaks in the traces bridged.  On the wider traces I decided to use some copper strips.  On the two thin traces I just used some signal wire.

Note that while I had the 09 PCB on the soldering station, I reflowed the solder joints on all of the 09 PCB connectors.

I tested the connections again with my DMM, then re-installed the 09 PCB in the Beomaster to try powering it on again.

This time I do get the Standby LED with this original 09 PCB.

The control panel buttons do not consistently operate the Beomaster 8000 though.
I double-checked source selection, volume control and FM tuning using a Beomaster 8000 remote control.

That worked so there is an issue with the control panel buttons connected to this original 09 PCB.

With the remote control though, I checked out some of the Beomaster 8000 functions.

I could select all of the sources but the FM tuning did not work.  The lack of FM tuning was a reason the owner sent me the Beomaster 8000 so at least the reason for that problem makes sense.

This picture shows the selection of FM presets P1 and P8.  You can see that the FM tuning indicator is not correct.  The tuning control couldn't do anything that made sense on the display either.

This photo shows source selections for phono and tape 1.  I also checked tape 2.  Those all select fine except that I had to do the selections from the remote control.

My next test was to uninstall this original 09 PCB and replace it with one of my Workshop Beomaster 8000 09 PCB modules again.  This time, however, I grabbed my Workshop 09 PCB from an early serial number Beomaster 8000.  That is a better match than the late serial number 09 PCB I tested with earlier.

Here is my Workshop 09 PCB next to the fault 09 PCB from this Beomaster unit.

They look identical except that my Workshop 09 PCB has a new 22uF capacitor and 1uF capacitor.
It also has new oscillators.

With my Workshop 09 PCB installed, the Beomaster 8000 source selections, volume adjustment, balance adjustment and FM tuning all work.  Both from the control panel and the remote control.

I can see that a separate issue with this Beomaster 8000 is on the display segments. 
The FM tuning display is missing one segment and the period for the frequency display.

What I have to do next is figure out what the solution will be for this Beomaster 8000 unit.

This project has budget and time constraints that limit my choices.

That leads me to wanting to just replace the original 09 PCB with my, already restored and working, Workshop 09 PCB.

The time it would take to troubleshoot and rework the broken 09 PCB could be expensive and at the end, it would still be a PCB that had repairs to some broken traces.  I could live with that if this were my own Beomaster 8000 but not when it is a unit that has to be shipped back to an owner.

Another option would be to assemble a new 09 PCB from scratch using a new PCB from Fredrick Adenholm.  He has reproduced the Beomaster 8000 Output Amplifier PCB, Display PCB and uC PCB.

I have all three of those blank, ready to populate boards.  The 09 PCB is pictured above.

However, in the case of this project, doing that to replace the 09 PCB is out of scope.

Beomaster 8000 Type 1903 - Arizona Restoration Project - Power On Troubleshooting

After the initial assessment of the first post on this Beomaster 8000 (Type 1903) restoration, I left off needing to know if this Beomaster unit had a working power supply.

The expected "standby" LED segment (a red dot) was not illuminating on the display so I checked the power supply for the 5 volts the Beomaster 8000 Microcomputer PCB needs to operate.

The incoming DC voltage (about 11 VDC) was present on the reservoir capacitor and the regulator measures a 5 V output.

I didn't check the ±15 volt regulators but I did measure their reservoir capacitors.  They measured as expected.

After double-checking the cables and individual wires from the power supply to the Microcomputer PCB, I tested the Beomaster 8000 power on again.

Same result, the Beomaster 8000 appears dead.

The problem is most likely in the Microcomputer PCB.

One reason I have a Workshop Beomaster 8000 unit is so I have easy access to known good boards from a working Beomaster 8000.

I swapped the Microcomputer PCBs between this restoration unit and my Workshop Beomaster 8000.

The result is the Beomaster 8000 comes to life.

The source selection functions all operate as well as the volume dial and tuning dial.
There are some display segments out but I will sort those later.

The owner of this Beomaster 8000 says that he stopped using the receiver because the FM tuning stopped working.  Since it appears to work with my "good" Workshop Beomaster 8000 Microcomputer PCB, I can say that the Microcomputer PBC of this Beomaster being restored has a problem.

I will start in on that PCB next.

Beomaster 8000 Type 1903 - Arizona Restoration Project - First Look

I have been waiting for a while now to clear out other restoration projects so I could return to some Beomaster 8000 restorations.

The first one is a very nice, one owner Beomaster 8000 from Arizona.

The two, round control wheels operate smoothly and cosmetically, everything looks great on this Beomaster.

I plugged the Beomaster in but no "standby" red dot appeared on the display.

On to looking inside...

The center control bar on the Beomaster 8000 slides to the left in order to unlock the cabinet and access the screws hold the bottom control panel in place.

After removing the control bar, I could see that this Beomaster 8000 has been worked on in the past.
One tell is that two of the three, flat, metal springs for the control bar are missing.
Those springs just lay in place under the control bar and easily fall out when the Beomaster 8000 is opened up for service.  Unfortunately it is more common than not to open up a Beomaster 8000 and discover missing control bar springs.  I guess people lose the springs or forget to put them back.

Here is a photo comparing this unit with one that has the control bar springs.

I will have to see if I can fabricate some spares.

Another issue I quickly discovered was that the metal lid for the filter control panel did not open and close properly.

That lid is supposed to be spring loaded so that it slowly raises by itself with the control bar is pressed.
In this case, the lid has to be lifted manually and it free-falls shut.
That problem is also common though, most likely a broken lid lever.

This Beomaster 8000 unit has the original B&O configuration of the audio input sockets.
The tape RCA input and output jacks are on the TAPE 1 source.  Later, after serial number 2554003, those changed from the TAPE 1 source to the TAPE 2 source.

I lifted the front control panel into the service position next.

That confirmed that this is an early serial number Beomaster 8000.  At least, prior to B&O changing the Microcomputer Board.  This unit has the type of Microcomputer Board where the metal shielding case is soldered closed.  Later serial number units changed to a metal shielding case that snaps together.

I believe that began with serial number 2375027.

Here is a photo of the Microcomputer and Display boards.

Those boards appear to be original and untouched.

To the left side of the cabinet are the Preamplifier, FM, Filter and Left Channel Output boards.

The capacitors on the Preamplifier and FM boards look to all be original.  The Left Channel Output board looks like it has had some electrolytic capacitors replaced before.

I can also see the metal door lid mechanism now.  It does have a broken lever.
The lever can be replaced.

Behind the Microcomputer and Display boards is the Beomaster 8000 power supply and the Right Channel Output board.

The capacitors on those boards have been replaced already.

My next step will be to get out some test leads and trouble-shoot the power problem to see why the Beomaster 8000 standby LED is not coming on.

I will cover that in the next post.