Hi all,

I have got back an old beomaster 6000 (type 2251) and I have checked it.

First, in the amplifier part, some capacitors which are C201, C202, C215 have melted and a resistor R221  is cut. I think it's due to a problem of overloading or bad capacitors and I will fixe that later since the other problem is more boring.

Then, the second problem is that the beomaster doesn't want to switch on when I pressed a FM preset button and so on...I have just three points which are lighted, on the screen used to indicate the FM tuning or the hour, and the lamps used for the balance: IL3 are slightly lighted and IL4 very well lighted.

I have the schematic diagram and I have checked if TR16 for instance for the preset P1 has the information when P1 was pressed and it's the case. And I have also noticed that on the card16, at the collector of TR4, I don't have 5Vpp but far less although I have 1Vpp on its basis. And I have replace TR4 but the same thing occurs!

So I don't know if there is a problem with the µcomputer (I hope it's still OK) or others components. 

Can someone help me?

Thanks in advance. 

Regards, 

Mathieu

The capacitors on the power supply module 16 will probably be bad. The reset circuit for the CPU will need checking, if my memory serves me rigth there's a trimmer that goes bad. Finally a complete overhaul of the amplifier module, new caps and new trimmers for idle current and DC offset (plus of course a new adjustment of these) Burned resistors should be investigated further. Check also for cracked solders on module 14, it's very common to see, especially at the connectors.

The Beomaster won't power up if the amplifier is at fault (for safety reasons) but it should come into standby (one red dot) with mains connected.

Martin

Hi

Check that you have all the voltages on module 16. On my unit the 6.5v was out of spec and it's controlled by the trimmer R4. Also check the uC-supply on module 6 - it will feed the microcontroller with 5v at pin 40 (ic4 on mod 2). This auxillary supply is fed from the 15v of mod16. You will not get any 5v p-p on collector of tr4 mod16 if the microcontroller doesn't have 5v.

/Fredrik

Hi,

Thanks Fredrik for these advises, I will check them tomorrow, but now the µC works fine thanks to Martin.

Thanks Martin, now I can switch on or off the beomaster, I can adjust the hour...But the LED display in FM tuning mode only show 74.8 and when I change the frequency, it doesn't modify the display.

Then , I will check the amp module but what are the value of idle currents (10mA like on a beocenter 7000 or more...). 

Thanks again for your help Martin and Fredrik!

Regards,

Mathieu

The factory specs are all stated in the service manual which also gives the correct measuring points. Replace the trimmers before adjusting, the old ones will be bad and could be the reason for the Beomaster not working. There are four trimmers in total on the amp board.

The 74.8 FM readout is the typical symptom of a dead prescaler IC. This part has been obsolete for years but I still have a few in stock, not the cheapest IC though but of course worth it if you get the rest of the Beomaster going.

Martin

Hi Mathieu 

Nice work - it's starting to wake up

I'm curious of what had happened to the output amplifier. Please tell me when you find out. Maybe some photos of the damage?

/Fredrik

The idle current of the output amplifier is 50mA or 22mV across the resistors R143,R144 (Rch) and R243,244 (Lch)

/Fredrik

Hi,

 Thanks Fredrik for this information, I will check the amp module in few minutes and I think it was a problem of overloading... I have also some pictures of it, but I don't know how I can add them?

I have checked UC264B and I have a DC signal at its input and not an AC one. So it could be the cause of the 74.8 FM readout on the LED display.

Regards,

Mathieu

Hi

To attach a picture - select reply, on top of "the old message" select the options tag and select Add/Update. There is a limit of file size at 100kB.

/Fredrik

Martin, do you supply a full overhaul kit for the Beomaster 6000.

Mine is working ok, or it was last time I tried it, but I'd like to replace all the electrolytics, tants and anything else that should be done.

I also rember you said something about adding a heatsink to the display driver or was it the fm decoder chip.

There's a capacitor kit available and I also have the U8 prescaler IC (original mfg. new part) plus diverse used parts, boards etc..

There's a large transistor near the U8 that gets hot when operating. I usually try to bend it slightly away from U8, it won't go far, though. Not that I have been able to confirm that the heat is what actually kills the chip, probably more likely to be a bad batch of IC's.

Martin

Hi all,

I'm come back and sorry for my delay. I have attached 2 pictures of the beomaster 6000. Since the last time I have noticed that I have a DC signal at the imput of the IC prescaler U264B and perhaps it could be the reason of the 74.8FM readout on the LED display? What do you think? Then I have a short-circuit in the amplifier module (for the -50v supply)

Do you have any idea for the problem of burned capacitors and for the short circuit although I will check the MOSFET?

Regards,

Mathieu 

And the second picture,

Mathieu

The Beomaster won't power up with the amplifier looking like this, a capacitor kit alone won't cure it, I'm afraid.

I'm sure that the 74.8 frequency readout is caused by the prescaler.

Martin

Wow. What a meltdown.

You should check every component on that board and the output transistors to track down this fault. As Martin says a cap kit won't repair it but you will probably change a lot of components on that board, so a kit is "good to have" anyway. I can understand why the cap c215 and the resistor r221 is damaged for example if there is a short in tr210, tr211 and/or the output devices. But I can't figure out what can cause c201 and c202 to melt. It would be interesting to see what reason you will find out when you measure the components of that board. Please report any progress here.

The damage to the chassis can be repaired with "chemical metal" or anything equal.

Good luck and keep us updated!!!

/Fredrik