Beomaster 5000 very soft sound?

19 replies
A(
Offline
AlexB (archived)
Bronze
Posted September 22, 2007 at 04:51 GMT
#1751768

Excuse my ignorance, and I appreciate that I am talking to people far more electronically gifted than myself... but could it possibly be a short in the external circuitry (eg either chewed cables, a stray wire strand at speaker terminals, or internal within speaker)? That would cause the clip circuit to remain "on" would it not?

Very best of luck, Philippe!

Alex

DI
Offline
Dillen
BronzeModeratorFounder
Posted September 22, 2007 at 07:57 GMT
#1751769

Interesting case and definitely one I would have enjoyed having on the bench, if for nothing else than curiosity and the challenge.  ❓

The 20V supply is essential. Check that this is present and clean at the preamp board. There's a 5V and 28V as well, they also need to be present at the board.

Martin

SO
Offline
solderon29
Gold
Posted September 23, 2007 at 13:03 GMT
#1751770

Your tenacity is admirable,but this is getting to be a real puzzle!

Alex has a point about shorted speaker wires,but this would not affect both channels surely?

I assume that voltages around the power output stage are correct?

I'm still suspicious of the pre-amp/volume control stage,particularly as you have no volume control pulses?

I'll break out the ice bag and study the circuit for further inspiration.

Nick

CR
Offline
crm114
Bronze
Posted September 24, 2007 at 08:41 GMT
#1751771
Hello Nick, Martin and Alex
thank you for your words of encouragment.

I still have a few things to try, like being more systematic with
the power supply measurements, so far I've concentrated with the pre-amp as
this seems to be where the symptoms are, but they may be only the victims of
some other failure. (hard to imagine, as all the supply levels to the IC's
read 20volts?).

Also, as I've mentioned above, we've had a few 'brow outs' lately, maybe the BM was damaged then. I'll have a look around the 'standby' circuit, and see if anything is amiss there.

I've also ordered a TDA 1028 and 1029, as these look like they deal with the
signal also. Lots of IC's to interact.

I'll try a few more things in the next few days and post further on the
board.

Thanks for the encouragement.

Philippe



SO
Offline
solderon29
Gold
Posted September 25, 2007 at 13:11 GMT
#1751772

It might be significant that you have had power interuptions.There may be damage to the pcb which explains why you have 20volt seemingly everywhere on the preamp panel?

The preamp/control section has single ground return to the power supply.Connector P11,pin9 on the preamp panel should connect to connector P9,pin 6 on the power supply panel.P9,pin 6 of the power supply panel,should then connect to the common ground,ie the junction between C6/C7(the two large capacitors that clip into the plastic moulding)

There is a section of print that can rupture in case of flashover,it could be the cause of all these problems?

Good luck

Nick

SO
Offline
solderon29
Gold
Posted September 25, 2007 at 13:20 GMT
#1751773

Check that there is continuity between P11,pin9 on the preamp panel,and the junction between 2C6 and 2C7.These are the two large capacitors that clip into the plastic moulding over the output stage.It should read zero ohms,as it's the ground return for the preamp.If not it may mean that the print is ruptured somewhere,due to flashover and could explain why the preamp voltages are odd?

Nick

CR
Offline
crm114
Bronze
Posted October 1, 2007 at 01:28 GMT
#1751774
OK, I'm still waiting for the TDA 1028/9 to arrive, so I've been looking around some more.

All voltages into the IC are correct, so 20 volts supply seems OK.
I replaced IC1 in the power supply, but this made no change. Amp still distorts.

One last thing I've just discovered, and may be related (How?).

On the tuner board TR34 is too hot to touch.


I see this is a large transistor, BD533, with a metal tag, but it does not seem right to me.

Now how this relates to anything, or maybe it's OK?

I'll update as I find more.

Chers

Philippe
CR
Offline
crm114
Bronze
Posted October 29, 2007 at 07:22 GMT
#1751775
OK

it's finally fixed!

In the end it was something trivial:
a 330nf cap on the IC u741 in the power supply section.

I think it has something to do with the MUTE function, but not very clear how..anyway it works and that is all that matters.


Thank you to all that contributed, especially Martin and Nick.

I thought I would get back to let you know.

(It took a while as Mouser took a long time to send me TDA1074, but that turned out to be a dead end anyway). I reverted to heat gun and freeze spray in the end - brutal but effective 😁

Cheers

Philippe
DI
Offline
Dillen
BronzeModeratorFounder
Posted October 29, 2007 at 08:51 GMT
#1751776

Philippe,

Thanks for the feedback, always nice to hear what was actually wrong.

Power supply caps can cause the strangest faults.

Martin

or
BeoWorld Gold Membership card
Join BeoWorld

Register to access the forums, reference material, and exclusive member benefits — including our monthly prize draw.

Become a Member

December 2026 Prize Draw

Gold Members Only

As a Gold member you're automatically entered into our exclusive prize draw — your chance to win iconic Bang & Olufsen products. A unique benefit of BeoWorld Gold membership, every draw brings a new opportunity to win something special.

View Prize Go For Gold