The Workbench

Re: It Lives !!

richtoy — Thu, 20 Jan 2011 16:40:37 GMT

I fitted a new prescaler and the BM5500 tuner is now fully working

I gave it a complete set of caps whilst it was on the bench and the sound improved quite a lot. Much crisper high notes.

However the audible "pop" when you switch between inputs is still there and it is also there as you tune between FM stations so I guess that means that there is a fault in the muting circuit... Something to be tackled in February.

Re: It Lives !!

Dillen — Wed, 19 Jan 2011 17:02:18 GMT

I never tried that but it looks like a decent replacement.
A bit slower but even 120MHz should still be within limits.

Check the voltage supplied to the IC.

Martin

Re: It Lives !!

richtoy — Wed, 19 Jan 2011 16:48:14 GMT

The tuning problem only affects FM and is caused by a defective SP8629 pre-scaler.

My local shop has DS8629 on stock which are marked as equivalent. Does anyone know if they are really equivalent and will work?

The chip looks like it has been getting hot for a while and the previous owner hinted that the radio did not work before the power surge killed the CPU and display chip. Is there anything else that "as good practice" should be replaced at the same time as the pre-scaler?

Richard

It Lives !!

richtoy — Wed, 19 Jan 2011 12:08:18 GMT

A quick update.

With the two new chips the Beomaster shows signs of life

Using a cassette player as a test source I get the expected output for all remote input sources.

However, when switching between sources there is a noticeable "PLOP". Further investigation required if it still occurs after recapping.

One segment of the left hand 7 segment display is out. Signal appears to be there so it and joints are good so it must be the display.

There is a problem with the radio not locking to a station. I managed to change AM to FM with the Sound option on a Beo4 and I have now made it tune with both the BL1000 and Beo4 but it just tunes straight through the stations without stopping.

Re: BM5500 fault

tournedos — Tue, 18 Jan 2011 17:01:51 GMT

Hopefully it'll spring to life with those new parts... But after damage like that, there's always the possibility that pretty much every semiconductor might be toasted

Anyway the CPU should run after you replaced it, and if it doesn't, there's still the firmware ROM chip... it's a mask ROM but can be replaced with a 27128 EPROM if somebody has the code image to burn on a blank. Might even be still available as an official spare part.

Re: BM5500 fault

richtoy — Tue, 18 Jan 2011 15:22:54 GMT

Thanks for all the replies. There was no ALE so I replaced the CPU (local shop has exact replacements) and the MM5450 will hopefully arrive tomorrow. I have also replaced the small elcos on the PSU, CPU and display boards. All voltages look ok.

It was the BM5500 off markplaats but rather than struck by lightening I just think it may just have been the victim of a power surge.

Once the MM5450 is fitted I should know more...

Re: BM5500 fault

Dillen — Mon, 17 Jan 2011 18:21:43 GMT

I agree with Mika.
And check voltages before replacing components (!)
Don't forget the 8V supply, a BD-something transistor, it's the one closest
to the right end of the cooling fin if I remember correctly.
If it shorts, it will allow a much higher voltage through and that
will kill a lot in the Beomaster.

Note that the service manual gives a wrong output
voltage, stating -13V instead of 13V as the voltage used for the 8V regulator.

Martin

Re: BM5500 fault

Blackrix — Mon, 17 Jan 2011 16:15:55 GMT

Do you know what caused the problem? There has been a defective white BeoMaster 5500 sold in the Netherlands on Marktplaats which was struck by lightning, I hope it is not this one?

Re: BM5500 fault

tournedos — Mon, 17 Jan 2011 05:39:10 GMT

Replace the electrolytics on the CPU board and also the small caps in the power supply. The +5V supplies needs to be stable for the processor to start properly. Resolder the connectors of the board as well.

If this doesn't help, I'd suspect both the chips you mention... the CPU is dead or disabled as the receiver is essentially brain dead, but the MM5450 should also initialise with all outputs off when not controlled.

You can easily check if the processor is running at all by scoping the ALE pin, it should have a stable digital signal of about 1 MHz.

The processor in these is in danger because it has very little protection from power surges and ESD spikes from the various Datalink buses.

I'm not sure about the relay click... my BM5000 did click with a dead CPU but it is actually quite different in the brain department.

BM5500 fault

richtoy — Mon, 17 Jan 2011 04:45:04 GMT

I have just brought my first Beomaster from the BM5000, 5500, 6500, 7000 series.

It was brought defective but it is in white which means it matches much of my other B&O.

When you apply power, many of the LEDs on the front panel illuminate together with one segment of the frequency display (always the same ones). There are no sounds from any relay (should there be?) and the fan moves very breifly (1/10 second), just enough to notice.

The unit dows not respond to either a remote control or either of the front panel buttons.

All standby voltages are present and no fuse has blown.

The battery on the CPU board has been replaced in the past and measures OK.

My guess is either the MM54500 display chip or the 8031 CPU (available in my local shop for 4,65 !!)

Can anyone recommend any check to further narrow down the problem?

Richard