Hello there,

After receiving my remotes from ebay, I started to use my beosystem often and I found that I`ve got a problem with my Beogram CD5500. About an hour after turning it on, it "freezes", all the lights on the front panel start flashing and it stops playing and responding. First I thought that there is something wrong with the power supply and changed the capacitors after the ac/dc diodes, but without a result. Than I thougt it might overheating and put heatsinks on the DAC and chips around it, two transistors near the power caps that get hot (can`t tell their shematic names because the unit is not here) and glued with a termo-band an extra heatsink to the big one at the back, but it`s still the same.

I still think it`s overheating, because when I play it when it`s open, it can play for hours without trouble, but why? The ac/dc diodes get really hot, how normal is that? I`m running out of ideas, so I`ll be very thankfull for any help :)

Tonislav

It might be bad soldering contacts of the connector from the powersupply to the mainboard. They could cause this kind of problem!

Hello Tonislav,

While you play it open, you can heat bit by bit with a hairdryer (cover the back a bit to get more heat and less air out of it, or use a hot-air-gun at low settings) and see what happens. For detail diagnostic, you should have cooling spray. Use this, when the fault shows. Spray each single component a little and see (hear?) what happens. Remember also SMD-components!

Good luck!

Chris

I ll try resoldering today after work and see what happens. Chris, it is good idea but when it freezes I have to  unplug it from the mains, that`s the only way to recover it, so it will be hard to find the problem this way.I`ll try it, of course, and will write back the result.

Thanks for the help, guys, I rely on you!

Tonislav

fagaldi:

it is good idea but when it freezes I have to  unplug it from the mains, that`s the only way to recover it

this sounds as a faulty cpu or things around that, also the data-link section

Yes, I would check the electrolytics in the reset circuits of the microprocessors (both of them). Obviously the +5V supply needs to be stable as well.

I have just changed the both LM7805 (IC1 and IC2), switched the transformer primary coil from 220 to 240V (that`s the voltage in Bulgaria, measured it about 236), resoldered everything on the main PCB (that was the problem with my Terminal 5000), but the problem is still there :( It freezes when I heat by a hairdryer the zone around the DAC and the shielded area and continues playing when heating the power supply zone. So tomorrow I`ll check the caps by desoldering and measuring, hope to find something...

Tonislav

OK, all caps was changed, still nothing. The unit freezes after heating IC6 or IC4 - the both processors. Looks like processor failure, but I always thought that if cpu fails, it wouldn`t work at all, not only when it`s cool for example. And I also noted that when listening, it freezes quicker without the metal shield arround the chips.

So do you have other suggestions? It would be great to fix my 5500, it sounds great and i love it, would be sad to throw it away, because now it is useless.

Check the main board itself. The front corners in particular.
I've seen a couple of cases where the copper traces had
broken due to vibrations in transport/moving around.
The soft spots seem to be apprx 3-4 cm from the physical board corners.
One case, a recent repair from the UK, had the front
right corner of the main board broken clean off in shipping, taking
a handful of copper traces with it.
Both that and the original fault was repairable.

Look for light streaks in the main board in the front corners.
Check continuity of the copper traces that runs close to the corners.
You can also, as already suggested, heat or cool the board a bit.

It could also be a servo board failure but the symptoms are not typical.

Martin

The PCB is OK, I watced it on a microscope. The judgment is, unfortunately, dead IC4-MAB8461 W142 :( The strange thing is that when it freezes, the oscilator stops working. I tried changing the both 6MHz oscilators (the other one is for MAB8441 who seems to be alive), but nothing, both of the them are working fine, looks like internal chip failure. Is that specialized processor or it has to be programmed first? Is there something i can do?

Tonislav

Those are microcontrollers with mask programmed ROM, and since it is the application processor and serves a B&O specific purpose, I'm pretty sure the only source for it will unfortunately be another CD5500. W142 is the manufacturing code for this specific program version. The processor on the decoder board might be more generic and interchangeable with some CD decks of similar design.

But don't throw the deck away if you have space to store it - sooner or later you'll come across with another failed CD5500 that could serve as a mainboard donor with a working CPU. I've waited over six months for a spare part on more than one occasion!

That IC carries embedded data (ROM). I'm almost 100% sure that B&O will not be able
to sell you a new one so you will have to find a replacement from
a donor machine. Either the discrete IC or the whole board, whatever is easiest.
If you buy a new IC, it will be blank and won't work.

My guess is that it shouldn't be too hard to find since most faults to these wonderful
players happen elsewhere.

Martin

Well, I`ll start looking for another one, just sounds too good to be left.

Thanks for your support!

Tonislav

I have had 2 of these with the same problem. I also thought that it was the MAB chip.... then I discovered the cause by accident (as are most good solutions).

The cable connectors between the PCB's are not good-quality, and the internal pincers "cut" the actual copper conductors to "grab" them.

If the cables have been manipulated many times, one or more conductors has fatigued and separated from the pincer inside the plastic connector housing.

To check, pull each conductor gently, and see if it comes out of the connector.

Menahem

Hi Menahem,

Thanks for your post, that`s very useful info, it`s a good idea to check that cables anyway. But in my case the problem is 100% the MAB. I`ve removed it from the PCB, supplied it, put 6MHz quartz on the osc pins and attached osciloscope. The clock starts at the beginning, but then suddenly stops and the chip consuption drops to zero, looks like internal conection interruption.

Anyway, I was lucky enough to find and buy another one, here in Bulgaria those beautiful products are rarity. Now I`m even going to do slight upgrade by changing caps with Sanyo Oscon in the digital part, Panasonic FM in the analogue, Panasonic FC in the power supply, Elna Silmic II as output coupling and changing the 833 opamps with OPA2604. I`ll share the results in new thread.

Regards: Tonislav