Inside the VX

What is the main problem around these VX recorders?

 It's pretty simple, it's time and heat. The VX becomes pretty hot during operation, they are now 12-18 years old and B&O used some of the worst caps on this planet. My experience with the black RUBYCON and the blue NICHICON is sooooo bad, i cant tell you...

Take a look at this picture, it's a detail from the CPU board and you know what i'm talking about...

link

 If the board has turned it's colour to dark brown, it was used a lot of time. Usually the board a bright brown, like honey.

Look at the small chip, the acid of the caps was spread all over the board, the pins of the chip are black, there is a black oxide on it's connectors... and the acid conducts currents.

Hmmm, boards like this are scrap, usually they cannot be really repaired. The acid of the caps is spread all over it and is now also under the copper on the solder side. If you try to solder new parts in such a board, it stinks awfully and the copper contacts of the board seperate from the substrate. The copper is black oxidated... 

Some more: Clean the boards. The acid causes short cuts and will be working all the time, causing more and more oxide on the copper and other parts. I clean these boards with hot water and a bath cleaner. Yes, these boards can be washed! But take care that they are dry before using... i let them dry for several days in a warm room. Turn them arounf that no water stays inside steel or cabinet parts.

 

 

 

 

Or should i say HITACHI? Yes, this VX7000 and the older VX5000/5500 were not produced in Denmark, they were produced in Japan. And most of the parts are identical to Hitachi parts, the drive deck, the loading unit and maybe some parts more. You wont find any label inside stating produced by Hitachi... only the service numbers can tell you the story, that these parts have the same number like Hitachi ;)

 

What is what?

 

 

 

The Power Supply

 This is the power supply of the VX7000. It's an evolution of the VX5000/5500 linear regulated supply to a switched power supply. The power consumption especially in standby dropped from around 20W (!) to around 5W, also in operation from 60W to 32W. That's really nice.

And it became more durable, at least a little bit since to less parts and better parts... and less heat.

For a complete rebuild of this power supply you need only 6 caps:

C854, C865 (on the small board) = 10uF 16V standard and miniature or both miniature

C851 = 2200uF 50V

C856 = 3300uF 25V

C853 = 1500uF 35V, diameter 12mm, hight 38mm, RM5, that's something very rare.

C858 = 2200uF 25V, diameter 12mm, hight 38mm, RM5

Note: There are also versions of the VX7000 where C858 is a 2200uF 25V type or a 1500uF 35V. I can confirm this, i have seen now both versions. In this case use the same values again. The 1500uF caps are very, very hard to get, the others are standard 105 degree low esr types. Take a close look at them, sometimes they are still ok.

Note: There is some brown stuff around these caps, this is epoxy or a special type of glue to protect these caps against vibrations. You may think that this brown stuff could be acid, but this is quite normal. But... if you see drops you can wipe off or this typical smell when you solder on it, it could be really a defect cap.

But what you should replace is the blue 10uf Nichicon cap. You will probably see the black acid around his feet... nasty.  

And one WARNING: NEVER RUN THIS POWER SUPPLY WITHOUT LOAD! IT MUST ALWAYS BE CONNECTED TO THE VX! Otherwise 2 zenerdiodes for protection will blow, followed by the other fuses. 

 Here is a provisoric picture of the power supply, my camera got damaged... 

 link

 The power supply can be tested, look "the lower mainboard" 

 

The Upper Mainboard

 

 

 

The Lower Mainboard

This is the lower mainboard. On this board are:

- Power Regulators

- the HiFi Audio Decoder

- Linear Audio

- System Control

- Servo and Motor Control

 

 link

Please note, that there a several different versions of this board. I know of 3 versions, there are some minor changes of the components.  

OK, a lot of parts... but here it is always quite the same problem: caps. B&O ( or should i say: HITACHI? ) used a lot of the worst caps on this planet, the black RUBYCON and the blue NICHICON. They are prone to fail.

This board becomes pretty hot around the power regulators, the heat damages also the CPU board above.

Sorry, it's a lot of work to do here, replace them all. Even if you dont see acid or black feet on the caps, they will fail, sooner or later.

Part List:

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Some interesting part is the fuse QF1601 on this board. It is a chip fuse, looking like a 2-pin transistor. If there is a problem with overload or  overvoltage it will blow... but almost nobody knows about this fuse. The VX will be almost completely dead.

QF1601 is in grid section 2C. Either you use the orignal type ICPN20= 800mA or you use one of the small round standard fuses with RM5.

QF1601 = N20 is specified as a 800mA medium-slow type. You can replace it by a standard MINI MTR 0.8A type. This one here will fit perfectly for this job. It has the same size and the same spec. And it can be socketed in 2 standard pins of a chip socket. Nice and clean, and B&O uses this type of fuse also... so it's almost "original"  ;)

 link

 

Note: There is also a second chip fuse QF901 = N5 = 0.250A, section 3C, right between a large blue and white socket.  On a different board the same fuse is called QF902, next is a print on the board for QF901 which is bridged by a wire. So, here is the proof that B&O used several version of this board. Interesting is also, that neither QF901 nor QF902 are documented in the circuit plans or in the part list... but they are on the boards.

link

 Here is a picture of the other mainboard version from Friedmett.

link

link

 

 Testing the Power Supply and the Power regulators

OK, let's test the power supply. You need access to the lower mainboard, section 2B, there is a 8-pin connector PG1623, the pins are numbered 1-8. It is directly connected to the outputs of the power supply. Since it is not possible to operate the power supply outside the VX, use the connector PG1623 instead. All boards are correctly mounted and connected inside the VX, nothing is missing. You can use the steel cabinet of the VX for ground.

Pin 1: 5,4V regulated

Pin 2 + 4 + 6 + 7= ground (take care... there are several ground connections on the power supply, they split on the lower mainboard to 4)

Pin 3: 13,5V regulated

Pin 5: 50Hz clock signal

Pin 8: 27V unregulated

Check these voltages.

If 27V is missing, the Fuse F853 = 2A or the rectifier D851 is dead.

If 13,5V is missing (probably around 0.4-0,5V), then the zener diode ZD1605 (16,3V, grid 2C) is dead and makes a shortcut. This happens if the power supply failed to overvoltage.

If 5,4V is missing, then the power supply was used outside the VX without load. ZD855=6,2V on the power supply makes a shortcut. 

If these 3 voltages are ok, then the power supply is ok.

The power regulators on the lower mainboard:

There are 6 more tests for the power regulators on the lower mainboard.

Check the fuse QF1601=800mA grid 2c. There must be 13.5V on both pins. (Sometimes there is a glued black rubber block... the text is hard to find)

Check  C1614 grid 1c or the output of Q1603, there must be 9V if the VX powers up.

Check C1603 grid 1d or the output of Q1601, there must be also 9V if not in standby. Used for the tuner.

Check C1607 grid 1D or the output of Q1605, there must be 12V if not in standby.

Check Q1614 grid 2c, there must be 5.4V if not in standby. Used for the tuner.

Check the output of Q1611 grid 2c, there must be 11.3V during operation for the capstan motor

If one of the voltages is missing, the fuse QF1601 is blown or the according transistor is defect or overloaded.

 

 The parts to be checked are marked red.

 

 link

 

 

 

 

The CPU and AV-Switch Board

 

 

 

 

The Modulator

 

 

 

 

The AV Connector