Beomaster 4000 (type 2408) Circuit Differences

39 replies
SO
Offline
sonavor
Bronze
Posted December 18, 2011 at 02:23 GMT
#1761445

Here is another refurbish project on the Beomaster 4000.  As I have been following Søren's (Mexico) project I have been preparing to begin mine.  Part of the preparation was to get a capacitor kit from Dillen which I now have.  My goal is to refurbish my first BM-4000 so that it will be a dependable receiver I can use every day. 

In my case, I have two Beomaster 4000 units that I am wanting to restore.  I bought both of them in the past year - buying just one at first, then getting a second later on a pretty good deal.  Both of the units were working where I could get sound.  The second one has some switch issues and the tuning section appeared to not stay in stereo mode.  The first unit needs the slider switches cleaned and it has the problem where the transformer vibrates.  To make things more interesting, I later bought two more units as repair units.  One of these came without a transformer.  The other one has a transformer but it has a short - and consequently, some burn marks on at least one PCB.  Both of those repair units were dirt cheap so I had to buy them for possible spare parts.  It turns out that they are also useful in comparing the wiring between the four units.

I decided to begin with the BM-4000 that I felt was in the best shape.  That is the one with the vibration in the transformer.  Here is what the wood cover looks like and is another reason why I want to get this one done first.

In looking at the power section I saw the crowded little piece of circuit board that has the two 180 ohm, 1W resistors -

 

The resistors look pretty well aged.  The way that whole assembly looks kind of odd to me but I noticed that Søren's was the same way.  Now for something interesting. In my other Beomaster 4000 unit that I want to refurbish, this same circuit is implemented differently.  The second unit has the same resistor and capacitor components but they are mounted on a nice PCB numbered: 8002135    Here is a picture -

I figured that the difference may be because of a difference in model type.  However, both units are marked as Beomaster 4000 type 2408.  Another difference between the two units is in the main PCB - 8002095.  That PCB has the same 8002095 number on both units but the actual PCB traces are different.  I will show some pictures of those differences a little later.  The other thing that is interesting is that while my two BM-4000 units implement the resistor/capacitor mounting for the above circuit differently, the actual circuit and component values are the same.  However, that actual circuit is not the same as the schematic that is included with each unit.  I will post those differences as well.

-sonavor

 

SO
Offline
sonavor
Bronze
Posted December 18, 2011 at 02:41 GMT
#1761446

The first differences I want to show is in the schematics

Here is my redraw of the circuitry in the original schematic drawings included with the BM-4000

Now here is the schematic as I traced out of my first BM-4000 (the one with the small piece of PCB material like Søren's) -

 The first thing to notice here is that the 8.2k ohm resistors are replaced with different values.  Not only that - the original schematic has the center node between two 8.2k ohm resistors connecting to a node between two diodes.  The actual circuitry on this small resistor board and the 2002095 PCB separates the nodes between the diodes.  On the actual 2002095 board in my BM-4000, I can see that a board rework was done (during manufacturing I guess) that separates the connection between the two diodes.  In my second BM-4000, the 2002095 PCB is layed out differently and the diodes are separated in printed circuit.  Here is the same circuit for my second BM-4000.  The difference between this and my first unit is that the resistor/capacitor components are shown on the undocumented 8002135 PCB -

 

 

 

SO
Offline
sonavor
Bronze
Posted December 18, 2011 at 03:08 GMT
#1761447

Here is a picture of my first BM-4000 unit small resistor/capacitor board that connects to the power capacitors and the 8002095 PCB -

Now here is the same circuit from my second BM-4000 that has this circuit placed on the PCB designated 8002135

 

SO
Offline
sonavor
Bronze
Posted December 18, 2011 at 03:33 GMT
#1761448

Here is the original schematic PCB layout for 8002095.  The two pairs of diodes (579 and 582, 489 and 492) are highlighted.  Notice that the connection node for each pair shows them connected per the schematic drawing -

 Looking at the node between 582 and 579 on my first BM-4000 unit, here is that picture -

 You can see that the connection trace has been cut.  I believe this must have been a mod to this 8002095 PCB either at the factory or by a B&O authorized repair shop. 

This next picture is the same point on the 8002095 PCB for my second BM-4000.  This is the one that has a new 8002095 PCB layout -

 In the BM-4000 units I have with the 8002135 resistor board and the updated 8002095 layout, the connection wires between the 8002095 board and the resistor board are different colors on the following: The green wire is equivalent to the black/white wire. 

 

 

SO
Offline
sonavor
Bronze
Posted December 18, 2011 at 04:03 GMT
#1761449

Here are the component sides of my two BM-4000 (type 2408) unit's 8002095 PCB -

My first unit's 8002095 PCB -

 

 My second unit's 8002095 PCB -

The first thing I noticed was that this second unit's 8002095 PCB has an additional two trim pots in the bottom, center of the board.

The original BM-4000 schematic that comes with each unit shows just two trim pots.  That, along with the fact that my first BM-4000 unit has the mod to separate the two pairs of diodes seems to indicate my first BM-4000 was an earlier model than my second BM-4000.  Plus, my second unit has the updated 8002135 board for the power supply resistors.

My first unit's (serial number?) NO. on the back is 145047.  My second unit's NO. is 876039. 

A confusing thing about those numbers is that on my two "parts" units I bought have NO. 274152 and 1239044.  On those two units, the 274152 circuits are like my 145047.  But the 1239044 are like my 876039.  I'm not sure I trust the internals of those "parts" units though.  It looks like attempts have been made on those before.  So it is possible that they have parts that were changed out.

 

 

P(
Offline
PDH (archived)
Bronze
Posted December 18, 2011 at 06:07 GMT
#1761450

Maby this can help a little

 

Per H

mexking
Offline
mexking
Bronze
Posted December 18, 2011 at 10:10 GMT
#1761451

Per H is faster than I am, but the only update on my BM are the resistors 490,491.

 

Location: Mexico city

Retired
Printing machine technician
Restored various 1960-70 items
Rock and Roll music
Collecting Vinyl
Restored Jukebox Wurlitzer 1050
mexking
Offline
mexking
Bronze
Posted December 18, 2011 at 10:20 GMT
#1761452

Here the update text in English

 

Location: Mexico city

Retired
Printing machine technician
Restored various 1960-70 items
Rock and Roll music
Collecting Vinyl
Restored Jukebox Wurlitzer 1050
S(
Offline
Step1 (archived)
Bronze
Posted December 18, 2011 at 12:31 GMT
#1761453

I would like to know how they setup those extra presets.. Maybe introducing a fault and measuring accordingly? Where's Martin when you need him!

SO
Offline
sonavor
Bronze
Posted December 18, 2011 at 14:00 GMT
#1761454

Okay, so I think I understand it -

Diagram A shows the update from the original BM-4000 type 2406 to the ones I have (which are type 2408). 

Diagram B shows an update of type 2408 for units with serial numbers after 227250.  That update is what I have on my second unit.

Thanks a lot Søren,

sonavor

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