A Pair of Beomaster 1900 Receivers for Restoration: Unit #1 Power Restored

The first of two Beomaster 1900 units sent for restoration is completed and ready for some testing.
To begin testing a restored Beomaster the work always begins with plugging it in to line power, turning it on and checking the power supply voltages.

With this Beomaster I was not getting any power.

In the previous post I suspected the +15 VDC power supply fuse (a 2A fuse) and the fuse holders that had burned spots on them. I also looked at the Beomaster 1900 mains power switch and found a wire exposed through the insulation.

I fixed the wiring on the main power switch.

The Beomaster 1900 has a nice way of securing the wire to the line voltage. It holds securely but it is easy to open up and work on.

There is a plastic wire holding clip that just slides out to loosen the wire.

I fed more wire into the Beomaster so I could cut off the bad section that had the exposed copper wire.

Then I wired the main power switch back up and put everything back in place.

That looks much better.

Next I changed the fuse holder for the +15VDC supply.

However, there was still no power. I could see now that I was getting proper voltage from the transformer to the bridge rectifier but no DC voltage out of the device. 

The reason I changed the bridge rectifier was because the Beomaster arrived with a pieced together diode bridge and I could see the charred remains of some past event involving power on this receiver.
There is nothing wrong with making a bridge rectifier that way but I wanted to return this Beomaster back to the way it originally was.

Here is the original state of the Beomaster 1900 +15 VDC power supply as I received it.

Here is the Beomaster 1900 with new parts: fuse holder, bridge rectifier and 2200uf smoothing filter capacitor.

There is no way the new bridge rectifier could be bad so I investigated my installation of it again.
Checking continuity of the signal paths on the trace side of the main circuit board I discovered that the solder pads for the bridge rectifier leads had two damaged pads. They didn't reveal their damage when I installed the new bridge rectifier but underneath they were not making contact with the trace on the board.

Here I show what happened when I pulled one of the AC voltage connections to the bridge rectifier.
The +VDC pad was also not making connection even though you could not visually see it.

I reworked the bridge rectifier connections and now it looks like this.

You will note that I also had to place a jumper on one side of the new fuse holder leads on the trace side.
This was required because the original two-pin holder clamp previously makes that jumper.
At first I thought that was the source to my power supply problem but after making that addition I still had no +15 VDC. 
There were still the two bridge rectifier solder pads that required repair.
As often happens in these repairs there can be multiple issues affecting one function. :-)

...and now there is +15VDC power on the Beomaster.
The transformer sends around 18 VRMS to the bridge rectifier whose DC output is around 23 VDC as shown on the meter below as measured across the smoothing capacitor.
That voltage then goes through a +15 VDC regulator.

Now I can finally move on to testing the Beomaster 1900 power supplies and make some service manual adjustments.

A Pair of Beomaster 1900 Receivers for Restoration: Unit #1 Reassembly for Testing and a Power Problem

 The next step before testing the Beomaster 1900 was to reinstall the four output transistors that mount on the rear heatsinks. I had removed the heatsinks and the original thermal insulating paste. On the reassembly I like to use modern SIL-Pad thermal insulators. They do a great job and don't have the mess that thermal paste does.

Here are the parts laid out for reassembly.

I like the way Bang & Olufsen chose to mount the transistors to the heatsinks. They use curved, metal spring clips that press the plastic face of the transistor against the heatsink...sandwiching the thermal insulating material in between.

Here are the output transistors reinstalled.

Everything is installed that is necessary to start testing the Beomaster 1900.

It only took the amount of time for me to connect up the variac and dim bulb tester to try powering up the Beomaster to discover a problem.

The Beomaster 1900's +15 VDC power supply was not turning on. No Standby lamp illuminated.
I exercised the main power switch again to make sure it wasn't dirty but nothing.

I unplugged the power cord and started to check around the +15 VDC power supply.  I could not measure anything across its fuse.  I had noticed the fuse holders were badly tarnished but this unit had powered up prior to starting the restoration. I pulled the fuse and it was okay. I just couldn't get anything through it from the fuse holders.

Here are the fuse holder clips and where I removed them from on the board.

Age has not been kind to these fuse holders. I remember now that the original bridge rectifier had been replaced on this Beomaster and there was a large, charred mark under where the bridge rectifier had been mounted. It is likely some big power event had occurred sometime in the past.

In any case I need to order some of these fuse holders on the +15 VDC power supply line.  If I order them today Mouser will deliver them on Tuesday.

The power supply incident got me thinking about all of the input power to the Beomaster 1900. I had seen a bad power switch on a Beomaster 2400 in the past so I should look at this one more closely.

I am glad I did. The switch actually measures good and I did some cleaning on it with Deoxit.  However, I found a cut in the insulation on one of the main power wires delivering line power to the Beomaster.  It probably wouldn't hurt anything but I don't like bare wires where they are not supposed to be.

I will rework the wiring on the power switch and fix that problem while I am waiting for the fuse holder clips to arrive.

Here is the cleaned up and prepared power switch.

Beomaster 4400 Type 2419: Reassembly and testing again (UPDATED)

I am pretty sure this has been one of the most difficult Bang & Olufsen restorations I have encountered.  Cleaning, recapping and adjusting a Beomaster 4400 receiver is not usually this difficult. The reason for that is I never had to dive in and disassemble the front panel. Unfortunately the power on/off switch on this one made it necessary for this project.

One big lesson I am taking from this project does involve the front panel and all of its related components. I started on the front panel by removing the minimal amount of things to get to the switch. That sounded good at the time but in hindsight the better approach (and the one I will use from now on) is to bite the bullet and disassemble everything from the front panel. Unobstructed access to the parts are the most important thing.

Had I done that from the outset I probably wouldn't have run into this situation...

It was time to re-install the rebuilt power on/off switch to the Beomaster 4400 switching rail.
The mounting tabs for the switch on the original switching rail were all but gone.
The tab on an unused switch mount is shown in the green circle. That is what the tab should look like.

I gave it a go anyway to see what it would take to mount the switch on the original switch panel.
NOT SO GOOD.  Obviously this is not Beolovely and unacceptable.

I had another switching rail from a spare parts Beomaster 4400 that the replacement power on/off switch came out of.  It still had serviceable mounting tabs.

Here is what I mean about complete disassembly of the front panel.
The switch panel assembly is removed in the photo above but for full access and working room in remounting the power on/off switch, the circuit board (and flexible circuit assemblies) should be removed.

With the switch remounted I reinstalled the circuit board (PCB6). Note that in the photo below I also desoldered the flexible circuit from the FM preset assembly.  This is important to do because the preset assembly is bulky and heavy. Leaving it attached makes it very risky to cause the flex circuit to crack and break. I have seen cases of that. So play it safe and just desolder the flex circuit from the preset assembly.

While PCB6 and the flex circuit were separated I took the opportunity to replace the 6R1 2.5KΩ trimmer. If the trimmer needed to be replaced later I would have to completely disassemble all of this again and I really want to avoid that. So to be safe I replaced it with a new Bourns trimmer.

Another thing to take care of for future insurance is the small, red FM Stereo indicator lamp. It is an LED that has been glued to the Beomaster 4400 front panel.

I investigated removing it but I couldn't figure out how without breaking the LED.

So I reconnected wires to the lamp with a small, two-pin connector for ease in removing the front panel. I also tested the LED.

That appeared to work but when working on the front panel reassembly one of the LED wires broke off again.

I reworked the wire attachments to be more secure and used a dab of epoxy on each wire to fix it to the panel as a strain relief for the leads to the LED.

In the process I didn't notice that I got the wire colors reversed where they attach to the LED. Luckily I have the 2-pin connector I had added earlier so I can just take care of the polarity there.

Continuing on with the front panel reassembly I reconnected the components.
I didn't break out the individual steps in photos (sorry) but I did find that mounting the switch rail to the toggle switch actuators and front panel is really, really difficult to do if the actuator assembly is already attached to the front panel.

I was successful by first attaching the actuator assembly to the switching rail. This allowed me to properly set the position of the actuators.

After that mini-assembly I was able to fit the switching rail with the actuators pretty easily into the front panel.

Next up was the task of resoldering all of the wires I had to remove as part of the disassembly.

Here are a couple of photos of the reattachment of the flexible circuit to the FM Preset assembly and the remounting of the main FM tuning dial.

Finally the new power on/off switch can be hooked up to the Beomaster 4400 and I could try another power test.

I applied power with my variac and dim bulb tester in the circuit for safety.
The first thing I checked was the +15 VDC regulator as that was part of the earlier repair where there were burned up ground traces on PCB5.
I also still have the FM boards removed from the Beomaster. Because they were involved with the burned ground traces I need to check them out separately before putting them back into this Beomaster.

Another quick check was made on the idle current for both channels in the output amplifiers.  They did require some adjustment so I performed those and the Beomaster 4400 was ready for a listening test.

Like before I used a pair of headphones and an iPod Nano connected to the Tape 1 input.

Success finally.  The new power switch operates perfectly and I have nice music playing through the Tape 1 source.

With this Beomaster 4400 unit though, it would not be in character for everything to work perfectly.

A new issue has popped up. I had to use the Linear switch to get sound in both channels. With the Linear switch deselected the left channel drops out.

The Linear switch is an option to bypass the Treble and Bass tone control section of the Beomaster 4400 preamp. So either the left channel is not making it through the tone controls or there is a problem with the Linear switch.

I was hoping it is just a wire that isn't mating well (maybe broke off during the front panel reassembly)

Sure enough, a broken wire to the switch.

I resoldered the broken wire and now the normal stereo selection works.

Now that problem is solved and I can return to the FM boards on this unit.

Beomaster 4400 Type 2419: Power on/off switch rebuild completed

I had some time tonight to finish preparing the rebuilt Beomaster 4400 power on/off switch for re-installation into the receiver.

My method of wiring the switch this time was to cut and fit the bus bars first. Then I attached the relative wire pieces to the bus bars before attaching everything to the switch contacts.

When I did attach the mini-assemblies to the switch contacts I used some solder shield clamps to prevent any heat from reaching the plastic switch housing.

Here is the power on/off switch fully wired back up and ready for re-installation.

I was very pleased with the wire connection results.  Now to check the switch operation again.

Very nice. I exercised the switch actuator a bunch of times and never had a case of a contact failure.
The contacts in fact remained nice and solid. No movement in them whatsoever.

This switch is ready to be re-installed.

Beomaster 4400 Type 2419: Rebuild 2 of the power on/off switch

Using the various Beomaster 4400 power on/off switch piece parts I selected the best switch components to rebuild a good switch for this project.

I secured the new switch contacts in the top housing using some instant epoxy. It is pin point so I could just place a drop around each contact coming through the housing. That secured the contacts and allowed me to test fit the two switch housing halves to make sure the contacts go into their respective slots.

Here is a picture of the contacts and actuator in the top housing half ready for mating with the lower housing.  I have the contacts that open and close turned around so that I am using the unused sides of the contacts. These refurbished contacts look way better than what switch contacts looked like previously.

So far, so good.

I installed the actuator lever and the lower housing, then checked the switch operation with an ohmmeter multiple times.  The switch operated perfectly each time.

Satisfied with the rebuilt switch I sealed the two housings with a bead of black hot glue.  This type of glue does a great job of hold things together but can easily be peeled off it access to the switch contacts is ever needed again.

The next step will be to carefully connect the switch wiring (including the two wires to my arc suppression device) without overheating the plastic switch housing.

I am also designing how I will re-attach the switch to the Beomaster 4400 switching assembly. I will need to somehow strap it in place.

Beomaster 4400 Type 2419: Rebuilding another power on/off switch

I looked over the three broken Beomaster 4400 power on/off switch components. That included two sets of pretty badly charred contacts. When I first looked at them I figured I would just toss them away. Fortunately I waiting and thought about it more. I also did a little research and confirmed that I can't just go find and purchase replacement contacts. The best thing would to be to try and salvage what I have. Then I remembered one of the most important tools in the workshop...the Dremel.

I used the Dremel and an ultrasonic cleaner to refurbish the damaged switch contacts. The results came out pretty good I think. I finished up the cleanup with a Deoxit treatment on the contacts and here is what they look like now.

Here are the cleaned up switch housings and actuators.

I have a decent selection of parts now to come up with a working Beomaster 4400 power on/off switch.

This set of components looks like my best bet.

The large switch housing piece has the hole in it from a burned contact but the rest of it looks pretty decent. After I re-install the contacts I can fill that hole with some epoxy.

For mating the two switch housing halves I can use a bead of hot glue again but I am thinking about drilling and tapping three M2 screw holes where the wide part of the housings (where the old mating tabs are). If I go that route I will use nylon M2 screws to join the parts.

Once I have the stationary switch contacts pressed back into the smaller housing I will solder on some connection wires to use when I place the switch back into the Beomaster.  I will make sure I protect the plastic switch housing when doing that soldering this time around.

Beomaster 4400 Type 2419: Power On/Off Switch Woes

This Beomaster 4400 would be ready to resume testing again if only its power on/off switch would work properly.

If you remember the original power on/off switch caught fire and had badly burned contacts.

For the replacement power on/off switch I pulled a switch out of a spare parts, donor Beomaster 4400 unit. I had no idea of the condition of that unit and when I opened up the power switch it had some pitting but overall wasn't too bad. A little cleaning and it was ready to install and that should have been the end of it.  It wasn't of course :-).

While the replacement switch initially measure a nice 0.1 ohm to 0.2 ohm "On" resistance when it was installed and in use the switch became unreliable and needed some fiddling with the buttons to get the Beomaster to turn on. Something mechanical was not right.

My next plan was to grab a second replacement, donor power on/off switch from another parts unit. The switch didn't look too bad until I checked it out with an ohmmeter. Off measured fine but the "On" resistance jumped around in the 100 to 300 ohm range. Not a good reading.

So I opened up this third Beomaster 4400 power on/off switch and it was about as badly burned as the first one.

Here is the third switch (second replacement candidate).

Very ugly and very disappointing to say the least.

I don't even want to try to clean that up.

When I reopened my first replacement candidate switch its contacts still looked pretty good but the switch contacts had shifted position so good contact was not being made. That explained the mechanical inconsistency.

I had to stop and think about my options.  I could really go for a nice 3D printed replacement switch about now.  Unfortunately that doesn't exist (yet).

My best chance here is to select my best contacts and my best plastic housing components to put together a solid working power on/off switch.

I think my first replacement switch attempt failed because I soldered too many connections to the outer terminals.  They heated up and then shifted internally which caused the poor switching performance.

This time I will make sure to make the other connections away from the switch and just attach two wires to the switch contacts. In addition I will use some heat protection while the contacts are soldered.

Here are my collection of Beomaster 4400 power on/off switch contacts.

If I turn the best set of contacts around I will have fresh new surfaces to mate for the power on switching. I will clean up the switch housing on the lower right to use in the new switch assembly attempt as it is the most structurally sound.

Another problem involving the power on/off switch that I will have to solve is remounting the switch on the switching assembly.  There are damaged mounting tabs so I will have to construct something to secure the switch when I mount it.