Sign in   |  Join   |  Help

Beomaster 8000 frequency problem

rated by 0 users
Not Answered This post has 0 verified answers | 19 Replies | 2 Followers

chartz
Top 25 Contributor
Burgundy, France
3,957 Posts
OFFLINE
Gold Member
chartz posted on Thu, May 9 2013 5:57 PM

For those who did not follow the saga two years ago, I have a problem in which the tuner won't tune at all past 97 MHz, it will go directly to 108 MHz, and I can hear all the available stations very briefly while it goes up there...

The tuner side is okay, I tried a (working) tuner module from another Beomaster.

The power supplies are fine, with new caps, and deliver the intended voltages with no ripple.

I've used the receiver every day since then, and apart from that, it works perfectly.

Old thread from 2011 (archived forum).

Still a bottle of champagne to win.

Jacques

All Replies

Beobuddy
Top 25 Contributor
Utrecht, The Netherlands
3,765 Posts
OFFLINE
Founder

Just a wild guess.

If you donor tuner boards works the same, did you double check your ground leads and it's connections?

The 2 different groundings are joint together through the processorboard. (black wire on the back of the upc board through P76)

If this connections isn't correct, e.g. even the output offset can't be set properly.

I used a desoldering iron to suck the old solder out before putting new one on all the connectors on the upc board. Some cracked joints were hardly visible and only made visible by using a loupe with lamp.

This loupe showed my several cracked or floating joints on many occasions.

chartz
Top 25 Contributor
Burgundy, France
3,957 Posts
OFFLINE
Gold Member
chartz replied on Fri, May 10 2013 8:57 PM

Mmm. Interesting. I do have a later board with no such connections it seems. Can you be a little more specific? I've spent hours inspecting the blasted board you know.

Here is my board: 

http://archivedforum.beoworld.org/forums/t/39090.aspx?PageIndex=2

Jacques

Beobuddy
Top 25 Contributor
Utrecht, The Netherlands
3,765 Posts
OFFLINE
Founder

I had a board with the old fashioned pin sticking out. This pin was wired to the outputstage and to the central grounding placed just above the tunerboards.

 


Beobuddy
Top 25 Contributor
Utrecht, The Netherlands
3,765 Posts
OFFLINE
Founder

didn't see that pin on your board.

 


chartz
Top 25 Contributor
Burgundy, France
3,957 Posts
OFFLINE
Gold Member
chartz replied on Sat, May 11 2013 9:17 AM

Thanks.

I would really like to have the revised PCB layout, possibly not in black and white. There are too many differences - discrepancies? - between what I see and the diagram, not to speak of the PCB, in the service manual I have.

I think it is something stupid I haven't been able to spot so far.

The frequency display is correct all along the scale. After 96 MHz, it continues to count normally. Only the voltage jumps directly to its max value (normally corresponding to 108 MHz) and stays there. I have to go all the way back down to 88 and wait for a few seconds for tuning voltage to go down again.

A ground problem? Yes but where?

Jacques

solderon29
Top 150 Contributor
U.K.West Midlands
728 Posts
OFFLINE
Gold Member

Hello Jaques.I notice from my manual that the upc module could be bought for £89.50,back in the day!!! I remember that we did replace them too,as sometimes problems were considered beyond the general workshop skill set.

B&O were very helpful then,praps they still are?We could send modules back for exchange.Happy day's indeed.

However,to your current problem.Are you saying that the Beomaster will scan the full band,ie 87.5-108Mhz,but only lock on stations up to 97Mhz?

If so,it does suggest tuning voltage range,or more likely as other's have noted,corruption of  the crucial local osc feedback to the computer.

Replacing the tuner panel seems to rule out rf problems such as the result of inexpert twiddling at some stage in the unit's past?

Have you checked tuning voltage range as per the manual.Also the "usual suspect" and it's associates ie,ic5,ic8 and 5volt supply

I have the original training notes for this Beomaster,that go into much more detail on the tuning system operation.May be able to copy,if it will help.

Regards,

Nick

chartz
Top 25 Contributor
Burgundy, France
3,957 Posts
OFFLINE
Gold Member
chartz replied on Sun, May 12 2013 11:35 AM

Hi Nick!

Thanks for taking some time to answer my query.

The "usual suspects" were duly checked on. 

My problem is that the tuning voltage goes to its maximum value all of a sudden after 96. But the minimum and max. values are indeed correct!

I have the manual too. I 'scoped everything as per manual but I don't understand what triggers the sudden shift. How do I check that the loop is correct? I tried but then all if a sudden voltage the processor signal drifts and I can't measure any further.

I can listen to a radio station for hours and the tuner is dead stable.

Jacques

solderon29
Top 150 Contributor
U.K.West Midlands
728 Posts
OFFLINE
Gold Member

Do you have a frequency generator Jacques?The training notes I have,go into some detail about testing the tuning loop,but I suspect it will only lead you back to the computer as "prime suspect".I'll try and copy the relevant part.

Nick

chartz
Top 25 Contributor
Burgundy, France
3,957 Posts
OFFLINE
Gold Member
chartz replied on Sun, May 12 2013 5:50 PM

No infortunately I have no HF generator.

Jacques

Beobuddy
Top 25 Contributor
Utrecht, The Netherlands
3,765 Posts
OFFLINE
Founder

You probably (double) checked, but just for the purpose to eleminate.

- what kind of aerialsystem do you use, just a single wire in the air or the analog stations from the cable supplier?

(cable providers often use a part of the range of frequencies)

Are the cables you use not strongly bend and proper shielded if you use the cable provider?

- No damaged or bend hf-cable or loose connector in the socketpanel?

Just a minor hings for us fellow members to get the complete picture.

chartz
Top 25 Contributor
Burgundy, France
3,957 Posts
OFFLINE
Gold Member
chartz replied on Mon, May 13 2013 7:35 AM

Hi,

I use a real dipole under the roof, and my other tuners work fine.

I live in the country so no cable, barely any broadband for that matter...

Everything is cabled and grounded properly.

Thanks for your thoughts!

Jacques

RaMaBo
Top 150 Contributor
near Munich
588 Posts
OFFLINE
Gold Member
RaMaBo replied on Mon, May 13 2013 3:59 PM

Hi Jaques,

 

in the old thread  ( 5. Jun.11 9:39 ) you wrote that when you revert to 94,4 you get pulses. Does the tuning voltage go down if you come from 108,0 MHz or something like that or does the voltage get stuck at max level?

I think you got an oscilloscope, so do you get a constant sweeping frequency at IC4/Pin21 if you turn from 87,5 MHz up to 108,0 MHz and back down to 87,5 MHz. The frequency at this pin of the processor is between 383,6 and 463,7 kHz, so a constant variation should be be visible.  The readout of the Beomaster is given by the processor of the beomaster and not the measured frequency (kind of 'should be' and not of 'it is').

How much is your 5V Voltage at the emitter of T5 (near the µ264) and how much is the voltage at Pin 8 and Pin 1 of µ264 ? Maybe the 2,2 Ohm resistor is getting old? According to the service manual there should be 5 V at the emitter of TR5 and 4,85V at Pin 8 of µ264 and 3,3V at Pin 1. In the old thread you wrote that your 5V was 4,93 with µp inserted after a new 7805 Voltage regulator, so your voltage should be a bit lower.

 

Just a few thoughts about your problem with the beomaster.

 

Ralph-Marcus

 

Ralph-Marcus

chartz
Top 25 Contributor
Burgundy, France
3,957 Posts
OFFLINE
Gold Member
chartz replied on Mon, May 13 2013 4:15 PM

Hi Ralph, and thanks for bothering!

Yes the tuning voltage stays stuck as well as the pulses monitored - which are correct at both extremes.

Whatever happens after 96-97 I do not understand. 

I have to turn the wheel down to about 90-91 now to get the pulses back and for the tuning voltage to drop down. I don't get constant sweeping, no.

About the 5V rail I eventually replaced the regulator and it now delivers 5V, and the other values are now spot-on.

 

Jacques

RaMaBo
Top 150 Contributor
near Munich
588 Posts
OFFLINE
Gold Member
RaMaBo replied on Mon, May 13 2013 5:11 PM

Hi,

So if the tuning voltage is stuck at the maximum after 96-97 MHz and no pulses are coming from the processor it can be the prescaler or the processor itself. If you tune down the same applies until 90-91 MHz.

There might be a problem with the prescaler or the supply of this part of the ciruit. That's why i asked for the continuity of the divided freq. at Pin 21 of the processor when sweeping from min. tuning voltage to max. tuning voltage.

Do you have a scope? This could help to see the sweep of the divided frequency going into the processor.

 

 

Ralph-Marcus

Page 1 of 2 (20 items) 1 2 Next > | RSS
Beoworld Security Certificate

SSL