Have you checked the signals around the first opamp with a scope ?
It could be interesting to see if the faulty tuning was actually commanded by the CPU.

Martin

Thank you both.

TR1 and IC1 have been replaced. I find it funny that the voltage at the output of IC1 jumps to 13.7 V when the fault occurs.

TR7 and D4 are new, as well as TR5 and D3.

I'm going to get the scope and see what happens there. Back in 10 minutes!

The pulses are normal at each turn up to 96.3 ( about 0.5 V ptp, TR7 collector), then it remains stuck at 0.5 V. The other way round, same thing, but I get the wheel signal back at about 90 MHz.

If I revert to my programmed station at 94.4 there is a pulse (square wave) continuous signal and it remains like that. But if I select the inferior 89.6 programme, it locks instantly onto it.

When a station is locked, there is of course no signal at all.

(edited)

Disconnecting AFT doesn't change anything.

Disconnecting the prescaler makes voltage go down to 4.7 V (PIN 7 IC1) which is the normal 108 MHz value, then it jumps to 13 V!

At 87.5 the voltage is always correct at 7.5 V.

I think replacing the processor(s) will be next.

Martin

Dillen:

I think replacing the processor(s) will be next.

Martin

Got that Martin.

I think I won't ever be able to find a good spare PC9... Mine had already been opened (and badly re-soldered)

Hi everyone!

I am currently waiting for a set of borrowed tuner boards (thanks XXX!!)...

But if they didn't solve my problem, would anyone here have a spare processor board? (I'd even be ready to buy one if I could, see my desperation).

Thank you!

I'll report about it of course, when the tuner boards arrive!

Hi everyone.

Just to out of curiosity, I opened all the caps I replaced in this Beomaster.

The red ROE caps were dry, save one which had all its electrolyte inside!

The other axial ROE (silver yellow) looked fine inside, as well as the blue Philips ones which had some electrolyte left inside.

None were shorted, leaky or cracked though.

Funny thing, I dismantled an old Grundig VCR which also had the red ROE caps, in very critical parts of the circuit! They were full of electrolyte after 20 years. They must have been very good when new I guess.

I noticed that two caps on the filters/volume board had their polarities printed the wrong way around!

Hello everyone,

Replacing the tuner boards with known good ones didn't change the tuner behaviour.

I'll try to explain the fault again:

- everything works as it should below 96-97 MHz: tuning up and down, memorized stations below this frequency,

- manual mode: the frequency display goes all the way up to 108, but from about 96.3 you can hear all the stations pass very briefly until the max voltage is attained. The voltmeter shows precisely this, and this is also visible at the integrator input, where the perfectly normal (up or down) signal goes mad after this frequency,

- auto mode: the dial won't go past 96.3, unless you really insist by spinning the wheel very fast! Then the same symptoms appear.

- after the fault (i.e. when I go above 96.3) hitting the P2 (94.4) button does nothing. I have to select something below 90 to get the control back, or manually go to that value.

The rest of the Beomaster behaves normally and is stable. I can listen to 94.4 or 95.9 for a whole day, no problem at all.

Now the last thing that could be done would be a processor board swap. I was wondering whether this fault could be identified more accurately within this circuit in the perspective of repairing it. 

A bottle of Champagne to whom finds the fault!

Hi,

I admit to being a pain, but would anyone here have a spare BM8000 processor board please?

Also looking for the Beolab Terminal that a certain Adam snipped, and left orphan my Beomaster!

Hi,

A new problem appeared: crackles and pops (and some buzzing) after two minutes on the left channel. Then silence, back to normal.

A quick monitoring showed offset to be unsteady until the amp temperature was stabilized. The cracks were related to a massive increase in voltage (>200mV) and back to 3mV or so immediately after the last pop!

Our good friend Martin suggested bad trimmers/caps/solder joints... but I knew caps and trimmers were replaced (no dust, looking shiny new!).

Ah yes, the left amp board... What a pain to take out! Not for the faint-hearted, this! You have to remove so many screws, the alu bonnet, dear me, and once done, getting the PCB out is olympic gymnastics I can tell you! I admire Fredrik's job even more after that!

Murphy's law amendment: the defective board will be the most difficult one to extract!

I had the confirmation that trimmers and capacitors were indeed changed, as well as the driver transistors, which came as a surprise! 

Anyway, there were three bad solder joints.

Everything back together... sweat on forehead... Problem solved!

'Still have the tuner issue though...

Well done !

If you lift up and take off the left side control panel and take out the metal bottom tray in the connector bay,
you will have enough access to the left amp board to flip it sideways up to vertical and do most repairs.

Martin

Yes.
You only need to undo the left screw for the large aluminum lid because it holds
a small metal bracket that locks the connector bay tray.

Martin

Hi everyone,

I am now proud to tell you that the Beomaster 8000 no longer has any original electrolytic in it! I have just replaced the last caps in the PSU board. Didn't make much of a difference, but I can now sleep on both ears! And to convince myself it was a good thing to do it anyway, there were a couple of very doubtful solders joints there too.

I am left with the odd tuner issue.

I feel a little abandoned right now... (sigh)

chartz:

I feel a little abandoned right now... (sigh)

Well, if only I had a spare processor. It looks as if that's what you need.

Martin

Hi everyone!

My Beomaster has worked for three months now. Almost always on, and never more than lukewarm at most!

I have tried very hard, but I haven't found any solutions for the tuner problem. I know the tuner boards are good for sure, since Martin kindly sent me spare ones (now back to Denmark of course).

Processor board anyone?

Or some lead to fixing mine?

Finally, a small video to illustrate the problem... (Am I being thick or what?)

After 97.3 the tuner is ordered to go directly to 108 and it obeys: this is what you can hear. I'm sure that if there were a radio station there I could hear it (the last one is at 107.7).

By the way, I can continue all the way to 108 manually and the display is correct... but the tuner has already arrived there, long before me!

See it on the second small video.

I'm sure this is fixable. Everything is, isn't it?

Hi,

The story goes on, and I am more and more puzzled!

I finally changed the 7805 regulator (along with caps and the bridge rectifier), because it reacted strangely under strain. Now I am almost sure there's nothing wrong with the processor module, because now I can dial up to 102.5 MHz before the system collapses. Voltage (5V) remains dead stable.

Help!

The 5V supply was always very sensitive in the BM8000 and it should be held within maximum +/- 0.1V or so.
I've seen many strange issues based on instability or wrong voltage but never a tuning fault like this.
Anyway, I suppose you already replaced the cap(s) on the regulators ?
If you have a 10uF or 22uF cap directly across the 5V regulator, you can add a 100nF across it.
If you don't have the 10uF or 22uF, I suggest you add one.

Martin

Thanks Martin.

Yes I did fit a 22µF cap across the new 7805 (out), and a ceramic 100nF (in). 

All the other caps have been replaced with brand new ones.

I now have three Beomasters, the 80's 6000, the 8000 and the 5500. To my ears, the absolute best is undoubtedly the 8000, it is more detailed and has more depth. The runner-up will be the 6000 (undefeatable tone controls?), with the 5500 being last: less detailed, less interesting to listen to, although it is not bad! This is surprising because these are all based on the older 4400!

So it is a shame I can't say it's fully working! The bottle of champagne still holds for anyone who leads me to fixing it (yes there will be another one for me too).

In the meantime, cheers!

chartz:

Yes I did fit a 22µF cap across the new 7805 (out), and a ceramic 100nF (in). 

According to general knowledge on the 78xx regulators (with no specific experience on the BM8000, and I'm not going to argue with Martin if he tells you otherwise for this application), these regulators are prone to oscillation if you have (only) an electrolytic directly on the output. I would replace it with a 100n ceramic, or at least add one there as well.

tournedos:

chartz:

Yes I did fit a 22µF cap across the new 7805 (out), and a ceramic 100nF (in). 

According to general knowledge on the 78xx regulators (with no specific experience on the BM8000, and I'm not going to argue with Martin if he tells you otherwise for this application), these regulators are prone to oscillation if you have (only) an electrolytic directly on the output. I would replace it with a 100n ceramic, or at least add one there as well.

I know. I've used them for 30 years and I always put a 100nF mylar at the output as safe practice. Why did B&O didn't do it in the BM8000 I wonder. They did put a 330nF before though. Let's see what it does!

No difference, I tried mylar and ceramic. Still stuck at 102.