Hello,

So I got myself a Beomaster 4400 which was advertised as mint but faulty.

Mint? Yes it certainly was but due to careless packing it arrived with both sides of the alu panel damaged and a crack in the cabinet. Good start!

This in spite of my alarmed warnings to the seller...

Now the faults: a defective preamp 24V supply, two blown BC237B transistors. Not too difficult. Regulated 35V down, I replaced the BC142.

After a chat with Martin, here are a few pointers. The amp trimmers and capacitors are new. The tuner section works normally.

1) there is +33V at the speaker output of the left channel (the right channel works), with +32V instead of -1.1V at IC102.

    +1.1V at IC101 as it should. +/- 35V rails are fine.

2) the protection circuit doesn't trigger, in spite of the fault (no voltage at the relay, possibly bad darlington, but why?),

3) the overload beacon stays lit at all times, even with the left channel unlugged (again, why?),

4) the right channel (the one that actually works) hums a bit, and when the left channel is unplugged, it shows reduced power (but no hum),

5) I'm unable to find the faulty component, the transistor junctions measure correctly and I find identical values on the working channel. I couldn't find any copper tracks discontinuities.

Thanks for any clues, before replacing everything!

Did you buy it on eBay and pay with Paypal????

Hi, 

Ebay, yes. Paypal, well our German friends don't indulge... but the parcel was fully insured. 

So why are you messing about with it??? If it wasn't received  mint, get a claim in!

joeyboygolf:

So why are you messing about with it??? If it wasn't received  mint, get a claim in!

Done, I should get my money back, but I'm still willing to get it working! Since I also have a Beomaster 6000 and an 8000 I see it as a lab experiment!

This sounds fun Jacques :) I would forget about the overload atm, as I think maybe tr11 is being biased by tr113, which in turn is being driven by the +33v output.

I would possibly take the chance to check the fault switch, then before sorting out work on the amp. I am sure this will be a s/c / leaky or open transistor somewhere but finding the little sod might be fun :)

*I should say Grahams advice is certainly best really, I know they are not overly common but there will be other oppertunities I am sure!

Step1:

 I am sure this will be a s/c / leaky or open transistor somewhere but finding the little sod might be fun :)

Yep, that's what it is. Fun? What's fun?

Found the little rascal!

The more I read the diagram, the more I inspected the positive rail (yes, I woke up very alert today!).

It turns out to be the MPSA06. Shorted collector-emitter junction. I'll have to wait for the component because there is no satisfactory replacement at hand... unless a BC546 for instance does it.

Any advice from there?

should be ok to test imo but I think you need to work on the fault circuit while waiting for the replacement!

Well, I've tested with a MPS3904 and it works!

The overload beacon remains unlit and I get sound on both channels! Voltages OK.

Now time to repair the protection circuit, if someone could come up with an idea please... given that the relay works.

I reckon it is either tr16 or ic3. Have you taken any measurements? try shorting C+E of tr16 see what happens...

Done that... Smoke (very fugitive, I couldn't see where it came from!) was the result.

The preamp hum came from a defective BC142.

I've tested the Beomaster for some time now and everything just works! I'm awaiting a cap kit from Martin, plus an MPSA06 and the protection darlington, BC516.

Pity about the alu dents, because the set is very, very nice and the transformer is completely silent! As our friend Martin suggested, I'll try to file out the "excess" of metal.

I repaired the wood damage and it is not visible! Yeah! Pictures will follow...

Have a look! You can see one side damage on pictures 2 and 3. I filed the excess. Hmm, doesn't look too good, but definitely better, almost acceptable!

Hi,

I want to make it clear that I'd done the short Olly talked about before he actually advised doing it!

I have now soldered the proper MPSA06 and changed all the caps, bare the one which is soldered underneath the power switch...

Photos will follow!

Note the horrible solution I came up with for the impossible-to-get-at solders.

Nice one Jacques :) So how does she sound?

Hi Olly!

See Søren's post, where I give my first impressions!

Hope she "lives long and prospers" for you. 

Well done, Jacques!

What's she driving?

Rich:

Hope she "lives long and prospers" for you. 

Well done, Jacques!

What's she driving?

Thanks. Driving a pair of MC120-2!

I'd like to find a pair of mint MS100 though!

I have now repaired the protection circuit. I didn't want to know, I just replaced the unavailable darlington with a BC516 (thanks Martin) and both BC548s with BC172s. 

I've let it on playing for hours. Checked the quiescent current again, and adjusted it to 14 mV finally, as per Martin's advice. The only detail I'd like to solve is that there's a fugitive hissing noise when I switch the unit off on one channel. It goes Ffffft for half a second. That's it. No humming, no hissing. Even the transformer keeps quiet which, as I understand it, is not that common!

The received really sounds great, if possible better that both BM 6000 and 8000... That came as a surprise, and it's rapidly growing on me!

Where's the remote though?

Wow, Looking good!

I left the two under the power switch

Søren Hammer:

I left the two under the power switch

So you'll never know what the receiver is capable of! I'm sure these are precisely the ones that affect sound quality the most!

chartz:

Søren Hammer:

I left the two under the power switch

So you'll never know what the receiver is capable of! I'm sure these are precisely the ones that affect sound quality the most!

I thougt just the same, but I was not in the mood for playing with free-style solutions! Doing the caps if cleaning the faders need cleaning, as the fascia has to come off when doing it

Beware, those tiny volume and tuning wheels have à tendency to go to funny places... I spent some time looking for one in my workshop!

The two middle screws seem impossible to access, but B&O techs left some space to insert à screwdriver from the bottom, between the different layers of circuits!

And the tuning slider is glued to the string!