Beogram 4004 Type 5526 - California Project - Completed, Tested and Ready to Ship

This post continues from the last post where the initial power on and start play operations were tested on this Beogram 4004.

Even though most of the functions I tried appeared to work I still needed to finalize moving the new trimmer for the platter sensor circuit to its final position.

Here is the DC voltage check of that platter sensor circuit as measured at the collector of 1TR3.
The new trimmer is adjusted to get 4 VDC at the collector with no platter in place.

That was easy to dial in but when I examined the platter sensor signal with an oscilloscope I could see quite a bit of noise on the signal.  The signal was the expected shape but the noise wasn't expected.

I checked the 21 VDC rail voltage for the circuit and could see noise there as well.

The voltage was good but the noise wasn't.

To remove the unwanted noise on the 21 VDC rail voltage I changed the filtering capacitor I had added to a 10uF value, then remeasured the rail voltage and platter sensor signal.

Much better now.

Even though the sensor circuit appeared to be working correctly, I have seen where noise like I was getting cause strange things with the Beogram control circuit.  

I installed the new Beogram platter speed indicator lamps next.
These are the Beolover LED replacement lamps from the DKaudiolover.com store.

Here are photos of the cleaning and Deoxit treated Beogram control panel contacts.
This Beogram 4004 will be getting the Beolover Remote Commander installed but I want to make sure the manual control button operation is perfect.

This picture shows a couple of contacts cleaned and treated on the left while the other contacts have yet to be cleaned.

...and this picture shows the full set cleaned and treated.

I used the Beolover RPM measurement tool to calibrate the 33.33 and 45 RPM platter speeds of the Beogram 4004.  This Beogram 4004 has a Beolover restored DC platter motor so it must be calibrated to the correct speeds.

Next is the installation of the Beolover Remote Commander (one of my favorite additions to any Beogram 4002 and 4004 turntable).

The installation of the Remote Commander to a Beogram 4004 is slightly different from a Beogram 4002 as the Beogram 4004 has a basic, no-frills remote control circuit that must be tied in to.

A drawback of the built in Beogram 4004 remote control circuit is that it is only functional when the Beogram 4004 is paired with a Beomaster 2400 receiver.  And...the remote control of the Beogram is just play, pause and stop.  The Remote Commander provides all of the Beogram 4004 control panel functions.

Now the Beogram 4004 is ready to be reassembled and some records played on it.

The final step of this restoration project was to replace the original dust cover with a brand new one from DKSoundParts along with a new aluminum trim piece.

The first step is to center the new trim piece and mount the trim onto the top portion of the new dust cover.  The two ends that bend down over the left and right sides are left straight at this point so the dust cover can be mounted onto the metal hinge assembly.

Here is one side of the metal hinge assembly and dust cover attachment screws.

After the dust cover is attached to the metal hinge assembly, the left and right sides of the new aluminum trim can be bent into place.

Note:  This attachment of the trim can be a little tricky. I found that I had to clamp the top and sides in place to make sure the double-sided tape bonded the trim securely (without pulling away).

The new dust cover assembly is now ready for installation on the Beogram 4004 frame.

There are two of these spring loaded mounting clamps that screw down on the dust cover assembly.

I am leaving the protective plastic wrap on the dust cover and Remote Commander remote so the owner of this Beogram can be the first to open them up.

I will listen to a few more records on this Beogram before shipping it back to its owner.

After that, I have another Beogram 4004 to begin restoration on.

Beogram 4004 Type 5526 - California Project - Floating Chassis and Circuit Board Restoration

The previous post for this Beogram 4004 restoration finished up the initial disassembly and cleaning of Beogram.

In this post I finished up the mechanical restoration tasks and the restoration of the circuit boards to the point I was able to test some basic functions of the Beogram 4004.

Power circuitry, tangential arm control and the platter motor are now working.

Here is a photo of the initial start play test.

To get to this point I had to complete the tangential arm assembly restoration.

A lot of that was taken care of in the previous post for this restoration.

Continuing from there I disassembled and cleaned the tonearm lowering damper, then lubricated it with some PMX-200 silicone liquid and replaced the gasket of the piston.

While the floating chassis was still out of the cabinet by itself, I like to do as many of the mechanical adjustments and electrical tasks that are possible in that state.

The following photo shows the replacement of the platter detection sensor lamp with the DKaudiolover.com LED lamp assembly.  The photo also shows the adjustment of the arm to arm distance (7.7 mm) and the new locking nut on the tonearm counter-weight.

I was also able to check and adjust the Beogram 4004 vertical tracking angle (VTA).
That is the angle that the stylus contacts the record groove.
With the Beogram 4004 turntables, that angle is defined in the service manual as the adjustment of the top surface of the sensor arm to the top surface of the platter.
That distance is to be set at 23 mm.

On the Beogram 4004 turntables, the platter to arm height for the VTA is adjustable because the platter height can be moved.

The Beogram 4004 platter assembly sits on a platter bearing.
The platter bearing has threads and a locking nut so the platter bearing can raise or lower the Beogram 4004 platter.  Thus altering the VTA.

Also of note, there are three adjustment screws on the platter bearing assembly that affect the tilt of the platter.

Ideally none of these require adjusting but they can be re-adjusted if necessary.

In the case of this Beogram 4004 the 23 mm platter to arm distance was good.

Next, I adjusted the arm lowering limit and the tracking weight calibration.
I adjusted the tracking weight at the zero position with the counter-weight screw.
Then checked and set the tracking weight for 1.2 grams.

For the electrical restoration of PCB 1 (main board) and PCB 8 (output board) I replaced the electrolytic and tantalum capacitors with new capacitors.  On capacitors with values of 4.7uF and less, I switched to non-polarized WIMA MKS capacitor types.  On values greater that 4.7uF I used new electrolytic capacitors.

Here is PCB 1 after replacing the capacitors.

PCB 1 contains the motor control, sensor detection and control logic (done with analog circuitry).

For the platter sensor reliability we always change the fixed resistor 1R26 to a trimmer resistor so the platter sensing signal can be dialed in better during calibration.  We also check the 1TR3 gain to see if it is at a high enough value (typically greater than 500).  In this case, the gain was below 400 so I installed a new transistor for 1TR3.  It has a gain of around 700.

I mounted the new trimmer for resistor 1R26 on the trace side of the board.
That is just temporary so I can easily set the value before moving it permanently to the component side of PCB 1.

I also changed out the two speed adjustment trimmers (one for 33.33 RPM and one for 45 RPM) to multi-turn type trimmers as well as replacing the speed select relay to a DKaudiolover.com relay assembly.

I changed the two Darlington pair, power transistors, IC1 and IC4, to new transistors (TIP102 and TIP107 respectively).
IC1 requires an added filter capacitor to lower the ripple current on the 21 VDC supply.
If there is too much ripple on this 21 VDC supply voltage, the control logic of the Beogram 4004 can behave unreliably.  I will check what the 21 VDC voltage looks like on the oscilloscope later.

Last, I replaced the capacitors, audio muting relay (another DKaudiolover.com relay) and added a grounding switch to the output board, PCB 8.

Because phono audio signals can sometimes produce a hum in the signal due to different types of phono amplifiers the Beogram is connected to, the grounding switch allows a quick option to connect or disconnect the Beogram's signal ground from chassis ground on the phone cable connection.

At this point the restored Beogram 4004 parts were ready to be assembled together to check the restoration progress.

It was time to put the floating chassis back into the cabinet.

Here again, is the cleaned up cabinet base.  It is all clean but the outline of stain from whatever the spilled liquid was in the Beogram is still visible.

The three mounting and chassis locks for the Beogram have to be installed first.

The Beogram floating chassis contains the platter and the tonearm assembly so those components move together if there is any vibration or bump against the cabinet while playing a record.

To prevent the chassis from floating during transport, Bang & Olufsen engineers created a locking mechanism that tightens down and prevents the chassis from moving.

The way it works is the Beogram chassis is suspended on three leaf springs so the chassis is isolated from the cabinet base.

The lock for the chassis is a screw with two sections.  The upper section and lower section are threaded in opposite directions so when the screw turns, the locking nuts close together (for locking) or open up (for unlocking).

This picture shows the two sections of the transport lock screw and the two different locking nuts.
The top and bottom nuts are threaded differently so they must be installed to their respective ends.

The washers for the chassis locking mechanism are convex on one side.  I have noted in the photos their orientation.

Here are the stages of installing the Beogram 4004 floating chassis beginning (upper left photo)
with the underside of the floating chassis lock assembly in place and ready for the Beogram floating chassis to be installed.

That is followed by the installation of the floating chassis and then the topside of the lock assembly.

Also part of the cabinet reassembly was the 4000uF reservoir capacitor for the AC power for the Beogram.

For that component I used the new DKaudiolover.com Beogram 4002/4 capacitor assembly.
Very nice.

I then soldered the arm lowering solenoid and DKaudiolover.com tracking sensor lamp assembly to their respective solder pads.

The last restored components I installed were the tangential arm spindle, pulley for driving the tonearm assembly.

That brings me back to the first photo in this post showing the first start play test of this Beogram 4004.

I am very pleased with the restoration so far.

The next step is to calibrate and move the platter detection circuit 1TR26 trimmer to its permanent position on the component side of PCB1 and calibrate the record tracking sensor.
I will also measure voltages and signals with the oscilloscope.

Beogram 4002 (5501): Return of an Old Friend from Australia - Dead Solenoid Transistor and a Carriage Motor with a Corroded Lead

Sadly, recently I received a well-worn Beolover Beogram shipping container from Australia. Contents: A Beogram 4002 (5501) that I restored in 2016. Type 5501 Beograms are special since they represent a briefly made transitional version when B&O went from Beogram 4000 to 4002. While the 5501 already has the analog control system characteristic of the 4002 series (the 4000 had a more advanced hard wired digital logic system, which was unfortunately (IMO) downgraded for the 4002), it still has mechanical carriage position switches like the 4000. It also has an exciting rotary encoder for the detection of the end groove. You see the Beolover is a bit love with the 5501, but seeing it for a third time caused a bit of a heart ache...;-).

Anyway, the reason it needed to visit my bench again was that it stopped working. The indication was that upon plugging it in the solenoid immediately became activated, while the deck was unresponsive to any keypad entry except 33/45 RPM changes.

So I removed the hood and the aluminum panels to have a look:

After a bit of poking around I found that the TIP41 that drives the solenoid had a short circuit:

After replacing it with a new one, the solenoid started working properly and it again responded to pressing the arm lowering key. This shows the new type implemented:

I also replaced the browned 8.2 Ohms solenoid resistor (4R1)

With a modern 2W rated unit:

This shows the voltages measured across the activated solenoid

and the resistor:

This means that the resistor runs at about 1.2W. The original types are rated 1W, i.e. a bit too low.

After this repair, the deck still did not respond to any of the 4 keys that control the carriage motion. After checking some of the transistors in the electronic switch it finally occurred to me that the carriage motor itself did not work anymore. I extracted it and opened it up. I found that one of the flimsy wires had disconnected from its tab on the motor due to corrosion. The other wire also came right off when I moved it slightly:

I cleaned the terminals and soldered 22AWG wires to them. I also replaced the completely deteriorated sound proofing with a cut to size self-adhesive piece of neoprene rubber:

Then I installed the motor again:

and everything was fine. At this point the deck's functions had been restored. I decided to do some preventative maintenance since I learned since 2016 that the AC motor driver transistors (found underneath the main PCB) often have issues in the AC motor type Beograms. This shows the original transistors 0TR2 and 0TR3:

I also found a hood attachment bolt spring near the transistors (which explained the absence of said spring when I removed the hood..;-). This shows one of the original transistors, the PNP TIP32 (0TR3, on the right):

I replaced it with a modern BD438. Note the reversed emitter and base leads on these types:

I also replaced the NPN TIP31 with a complementary BD437 (also with reversed wiring). This shows both new transistors installed:

I will now test this Beogram for a while, and if nothing else comes up it will travel back across the big pond to Australia!