Beomaster 8000 tuner issues.

Hi Guys,

My BM8000 that has been behaving itself for a good while has suddenly decided to act up. 

The tuner is behaving strangely in that none of my presaved selections work (they are still stored) and tuning using the wheel will find them but the display always reverts to 97.1 no matter what station is tuned in and playing. 

I’ve checked the usual connectors and solder joints but it’s not that. I’ve tried changing both of the tuner boards and get the same behaviour. I’ve reseated both processors on the cpu board. The joints between the cpu board and the display board are hard wired....

I’m assuming it must be something on the CPU board but I’m at a loss as to what. 

Please help

Lee

 

If I unplug P84 from the processor board it behaves the same as if it was plugged in (ie same fault)

Hi Lee,

 

there was a similiar or identical failure some years ago

http://archivedforum2.beoworld.org/forums/p/9630/84070.aspx#84070

 

Jaques could make it work again finally.

 

Thanks for that.

I’ll try changing the ICs and see what happens.

Lee

Changed the IC on the little piggy back board... same problem...

Re-flowed all the VIAs and any suspect joints... no change.

Time to change the other IC I guess.

Strangely the tuner picks all the stations up properly and doesn’t jump from one end of the band to the other.

The display just always reverts to 97.1 as soon as a station is tuned in. The station plays fine and you can tune up to the next one but the display again jumps back to 97.1

to be save change the 4013 which is placed on the processor board and check if this helps.

 

There's another thing i stumbled over when studying the Beomaster 8000 Technical Product Information, available here on this side for silver and gold members:

 

It deals with the TMS memory chip used. You didn't change the chip but maybe it shows the same symptoms decribed here:

 

 

 

 

Could I place the new chip over the top of the old one to test? To save me desoldering it?

The new 4013 could be placed on the old one for testing. Atleast it won't damage something but it gives no real result: If it works you got it, if it doesn't you still don't know for sure

 

Lee:

Could I place the new chip over the top of the old one to test? To save me desoldering it?

NO!
If one fails high or low and other goes the other way, you will have a short.
They will never be equally fast either.
Besides, if you have a shorted input or output, you can connect whatever you want across it - it will still not work. The bad component will
pull the good one down.
Diagnose the fault instead of guessing and risk messing things up further;

Do you have proper tuning voltage?
Do you have proper feedback loop from the tuner?
Do you have clean supplies to the processors? 

If the tuner tunes correct frequency but the display shows wrong, the problem is most likely in the feedback loop or the processor count.
Prescaler, divider or so. There is a small and delicate coil in that circuit too. 

Martin

Hi Martin,

thanks for the reply.

the tuning voltage is 3v so that seems fine. 

How do I check the feedback loop? I don’t have an oscilloscope unfortunately  

Ive checked the coil in the circuit and it seems to be fine. 

Do you think the U264B is a likely contender? 

Thanks 

Lee

The tuning voltage should vary as you travel the dial.

A bad U264B wouldn't be a first.
The 4013 divider (if fitted in your Beomaster) also lives a hard life and I have seen more than a few of them go bad.
Bad vias in the CPU board has also caused many a fault.
As has ripple to the 5V supply.

Without the proper instrumentation (plus tools, electronic education and experience), a fault like this could be difficult to diagnose but
the servicemanual shows the schematics, which really tells everything about the way this tuner and its feedback works.

Martin

I will add my 2 cents. I have seen this (or similar) tuner problem on a Beomaster 8000 receiver I worked on. In my case the Beomaster would go to the saved FM station (Px) and begin receiving the station. After a little bit the tuner would suddenly jump away to a different frequency. Like Jacques, replacing the CD4013 (9IC8) fixed the problem. However, any of those things that Martin listed could be a source of this type of problem.

I would like to add a warning to any do-it-yourselfers that changing out 9IC8 is not a piece of cake. Swapping out an integrated circuit always sounds easy but in this case de-soldering the fourteen pins to remove CD4013 can be a bear. Five of the pins are soldered to the microcomputer board ground plane and can require a lot of heat to de-solder. Too much heat can damage the PCB traces which can cause new problems. There are also some jumper wires to various pins in that part of the board you need to be careful of. Also...don't forget to avoid static electricity discharge. Wear a protective wrist band. When I got my CD4013 removed from the board I installed a socket for the new one.

A socket is a good idea. Choose one with round ("tulip"-style) pins.
Removing the old IC with as little risk as possible for the PCB is easiest done by first cutting the old IC off the
PCB from the component side, leaving as much as of the pins left in the PCB as possible.
Then a carefull pull with pliers from the component side while heating the pins solder pad from the other side, one pin at a time.
Finally clear the old solder using wick, or vacuum from one side while heating from the other.

And make sure not to buy a counterfeit IC.
- Yes, they counterfeit these too!

And as John suggests - ESD safe workplace - ALWAYS when dealing with CMOS technology.

Martin

Thanks for the tips guys.

I successfully sorted out the issue today... it was IC5. Luckily I had a spare processor board to steal it off.