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Beomaster 6500 slight overhaul

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tournedos
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tournedos Posted: Sun, Mar 4 2012 11:38 AM

The winter is finally letting go (the snow level has dropped below 0.5 meters, anyway) and I'm again getting interested in actually doing something with electronics.

The first project of the year will be a slight overhaul of my Beomaster 6500, one of my earliest B&O buys from 2007. Back then, I only adjusted the idle current of the power amps, but now it is time to do a bit more.

I spend probably 99% of my time listening to radio, and the tuner has developed a couple of annoyances; first, the antenna socket apparently has a bad contact, and lately one of the stations I listen to most has developed a bad distortion while others are fine. It is at the lowest end of the frequency scale, so this might be some real problem.

I'll also replace some caps in the power supply and the CPU board - the IR control range has gotten worse lately, which is usually a sign of them starting to go bad.

Finally, I'll rewire the transformer to 240V instead of the original 220V so the Beomaster doesn't warm up so much as it does with the current nominal 230V mains voltage.

So, the Ebenholz panther will have to go and step around somewhere else for a while...


--mika

tournedos
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Thank god the plastic only gets yellow on the inside!


--mika

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Easy things first... transformer primary wiring before (top) and after (below). Just two wires to move, and there's even enough length in the existing wires, a refreshing change from normal.

Earlier, the Beomaster stayed warm even in standby. This should help with that, and as a nice side effect, cuts the power consumption by 10%.


--mika

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hemenex replied on Sun, Mar 4 2012 12:32 PM

tournedos:
Finally, I'll rewire the transformer to 240V instead of the original 220V so the Beomaster doesn't warm up so much as it does with the current nominal 230V mains voltage.

That's the best idea IMHO ever since I've lost a BM901 (early version) left channel by forgetting that one :-(

And those dam*ed Motorola BD697/698 are nowhere ever to get except from other 901's. The 901 seems to be at the upper limit of the voltage scale...

They changed the Trans's to other ones that had to be mounted on the other side of the PCB.

 

tournedos
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hemenex:
That's the best idea IMHO ever since I've lost a BM901 (early version) left channel by forgetting that one :-(

Yes, I guess that one has particularly tight speced components... many filter caps in vintage kit are also at the edge of their limits, even at nominal voltage.

On to the tuner then - as I said, that's my most used source, so it will receive some special attention (in addition to being fixed).

Once you remove the correct screws (and only them), the tuner board flips up nicely and locks in the service position. For the other work, it could actually remain like that, but I'll remove it completely to make work easier.

Be careful with this kind of connectors, which are common in B&O kit from the '90s and on. The wires have only a single strand of copper and break easily where they have been pinched by the forks of the connector. They can be reattached if you dismantle the entire connector and cut a few millimeters off, but it is a pain as the wires are usually separate (not a ribbon cable) and non-marked!

--mika

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hemenex replied on Sun, Mar 4 2012 1:49 PM

tournedos:
Be careful with this kind of connectors

Mika, again I have to second that Wink

Had exactly this problem on my BC9500; thank god it was only a 5 pin connector; And I had to find out they were cross-wired so pin5 went to the opposite pin1 and so on.

But those were even worse on the other end Super Angry

As you can see they loosened from the glue and those are pretty complicated to fix as you can't strip them one by one...

That's a BM8000, BTW

  Gunther

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After all connectors are off, the tuner board detaches from its hinge (no need to remove the screws this time either!) and here it is.

There are a few electrolytic caps that are purely on the AF signal path, and I'm going to upgrade them - that brought an audible improvement to FM radio in a Beomaster 5000 I restored one time. These are

  • C201/401 (10 µF) - measured ESR 4 ohms: out of spec, replaced
  • C207/407 (4.7 µF) - measured ESR 11/23 ohms: way out of spec, replaced with MKS foil caps
  • C35 (10 µF) - barely acceptable, replaced anyway as it is on the FM audio path

The circuit boards in this Beomaster are not too good quality IMHO, and the PCB pads come off all too easily even if heated carefully. Therefore I'm going to disturb them as little as possible and replace any other caps only if they measure bad. None of them actually do, so they can stay. I'll just redo any dubious looking solderings and hope that corrects the little problems I had.

That completes the tuner board.

--mika

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Stonk replied on Sun, Mar 4 2012 1:57 PM

tournedos:

Colemans mustard? Why is it you electronic buffs always have to have some kind of sauce to hand?Hmm

If you think nobody cares, try missing a couple of payments.

tournedos
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Stonk:
Colemans mustard? Why is it you electronic buffs always have to have some kind of sauce to hand?Hmm

Big Smile

I keep pens in it. The empty tin can, that is.

We are now working our way up higher on the ladders of annoyance (and I should apparently clean the lens of my phone).

Underneath the now removed tuner board, is the preamp board, and on the corner of it, the speaker muting relay that often gives problems. So did mine in the beginning, but it magically fixed itself after some use, and I'll let it stay.

The preamp board has plenty of electrolytic caps on the signal paths and they could be replaced with fresh caps or upgraded - if you're interested in that, visit Die Bogener's workshop thread on BM6500/7000 in the archived forum.

The caps I'm actually interested in now are on the power supply & power amp board, behind the relay under the plastic fan duct.

The duct will need to get out of the way for any hope of access. There's only one screw and two clips through the circuit board below, you'll need to ease them out with a screwdriver. Then you can flip the cover, which also holds the two main power supply filter caps, and swing it away with the caps still attached in their wiring. You may need to rotate them little by little to free all the length of the wires.

Power amp is between the fan and the cooling fins, and between the cooling fins and the transformer, most of the power supply section. There are four small electrolytics in there, and they'll all be ripe for replacement after all these years of baking in the heat.

But, before you remove the duct Embarrassed , you flip the Beomaster over to remove the bottom plate and gain access to the solder side of the PCBs. Four big screws, three smaller, and a lot of trouble later on aligning the bottom plate properly so that the front panel buttons will still work...

Under the bottom plate, you will find a lot of dust and a duplicate of the type / serial number sticker from the rear panel.

--mika

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Step1 replied on Sun, Mar 4 2012 2:42 PM

Nice work Mika :) I think I am going to have a look at my 5500 soon, mostly to redirect the line out but also to give her a checkup :)

Olly

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No big surprises there - the four small caps C8, C9, C11, C14 were all on their way out, with C11 (22 µF) not even measuring on my ESR meter any more. And this Beomaster still worked!

C10 was fine as were the big filter caps, rarely reason to replace them at this age.

Didn't bother taking pictures at this phase because it wouldn't really add much... just be careful not to mix values up, mind the polarity, don't damage the circuit board, don't drop the Beomaster on your toes while juggling it around.

I also checked the electrolytics on the power amp board. The bigger ones are all fine, C212/213 and their counterparts on the other channel have degraded... but they are still reasonable and don't affect the sound quality, they are in the overload detection circuitry.

C202 and C402 - the audio input couplers - on the other hand surprise me by being really bad, and I'll replace them with MKS2 plastic caps again for good measure.

***

On the old forum, we had a good fight or two over the audible benefits of removing C215/216 and C415/416. Those weren't present in Beomaster 5000, and allegedly not even every later model had them. The are supposed to have something to do with the stability of the power amps. Sometime earlier, I had removed them, but as I conveniently now found the old caps in my tool box, they'll go back. I never was completely convinced I heard any difference, and I suppose my other changes on this time will have a lot more effect anyway.

--mika

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chartz replied on Sun, Mar 4 2012 4:02 PM

Thanks Mika. Now I'll feel guilty not doing mine! Angry

What bottom plate? I don't have a bottom plate on my 5500!

Jacques

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Now, after some espresso and a good piece of Sacher-Torte, I reconsidered the preamp. I'll probably never sell this Beomaster, I listen to it all the time, and the sound goes through all those old electrolytic caps.

I'll just replace the signal caps with MKS2 types while it's now open, although it will deplete my stock of 1 µF MKS2s... there are around 20 of those caps on that board, and still some 2.2 µF and 10 µF caps.

The 6500 has a place for an optional RIAA preamplifier which you see very rarely. It has coupling caps on both inputs and outputs. The output caps (C1/C28) aren't needed when the amp isn't there, so I'm not going to replace them.

C25/26, the phono input coupling caps, were 2.2µ on my Beomaster instead of 1µ as in the service manual schematic.

--mika

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chartz:
What bottom plate? I don't have a bottom plate on my 5500!

You really should get one - it's this ridiculously heavy steel thing that does wonders preventing accidental short circuits and electric shocks Big Smile

I did this almost same thing with my 5500 a couple of years ago, and I'm pretty sure the casework was mostly identical...? Hmm

--mika

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So, after a quite a while of tinkering, every electrolytic cap in the signal path of the preamp is now either Nichicon audio grade electrolytic (10µ) or Wima MKS2 (smaller values):

And no matter how careful I was, I managed to lift a couple of traces off the PCB Angry

Definitely no business going here without a temperature controlled soldering iron! Better check for continuity right after soldering, troubleshooting will be a lot more annoying after you have wrapped things up...

Oddly, the solder side of my preamp board had no silk print, which made things a bit slower.

All the old caps were electrically fine, so if you don't believe in "audiophile" recaps, these could've been left alone. Therefore, I also didn't replace C61/62/66 which have nothing directly to do with audio reproduction.

Next up, the front panel circut board which will have some filter caps related to IR traffic replaced, and the most risky business, the CPU module...

--mika

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Behind the front panel on the top, there are three screws. You loosen them (the middle one needs to be removed to disconnect a grounding cable) and then the front panel flips forward and out.

You will need to disconnect the headphone socket cable from the muting relay board, the IR signal cable from the CPU module (brown 5-pin connector, lift the CPU module up enough to get it free) and then the black multiwire data connector coming from the CPU module. Yes, it's one of those delicate connectors.

Wiggle the cables out and you can remove the front panel completely. On the circuit board side, there is one screw in the middle. Remove it and you can slide the PCB to one side and it can be separated from the front panel hardware.

Clean the four transmitter LEDs - they will be dusty or, horrors, covered in cigarette tar - this alone will increase the two-way IR response range. Do the same for the receiver photodiode (small black component on a tiny daughterboard on one end, right in this picture), not forgetting the rears of the corresponding windows on the front panel!

There are three electrolytic caps on this board - the blue Philips type was practically dead and the golden Roedersteins not far from it. All replaced.

In the past, I have repaired some bad solder joints on these boards; I guess they flex a bit when the front panel buttons are operated. Might just as well re-heat all of them, there aren't that many.

This is a good quality fibre glass circuit board, but you still don't want to crack it around the opening in the middle.

--mika

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henrik replied on Sun, Mar 4 2012 6:46 PM

Well done!

My Beomaster 7000 really needs an overhaul like this. As mentioned in the old forum, I recently realised that most of my disappointment with my Pentas (which i bought last year) has to do with my bm7000 - when I connect my Pentas to my bc9500 the sound is much brighter sp there is definitely something wrong with my 7000. I wish I had your skills!.

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Yes, I read that thread, Henrik... you're right there is probably something wrong in your Beomaster. If you can't find anybody to look at it locally, I guess it wouldn't be enormously expensive to ship it to Dillen for example? Smile

***

Now, the CPU. When I said "risky" earlier, I mean ESD aka static electricity. Even though accidentally zapping something in this Beomaster isn't quite as final as for example in a Beomaster 5000 (the processor etc for that are nowhere to be found any longer), it still contains some quite sensitive chips. It should only be worked on in a controlled environment and with proper precautions.

Having said that, this is my own Beomaster and I have more than 20 years of experience with this kind of work, so I believe I know what I'm doing and take some risk on my kitchen table instead of driving to the office where I have a proper workplace. You have been warned, though!

The CPU module is sandwiched in the chassis behind the front panel and is a bit difficult to wiggle out. You have to detach some wiring looms from their holders to pull the module up far enough to disconnect the remaining connectors. These are both of the ugly type - resist the temptation to put any force on the wires. Pry them out little by little working from the ends with a small screwdriver; in these connectors, the socket part surrounds the plug from three sides. Once they are off, you can remove the module completely.

All the heavy business part is inside the shielding metal box. The covers of it can be pried off on both sides. This is the top side of the module.

The warning on the lithium battery is no joke. If you solder on them directly, they will pop off in your face!

The battery is the round cell on top right. If you need to replace it (mine is still OK), only replace with a type with solder tags, or solder in a socket for a regular button cell.

Under it, the chip with the sticker is an EPROM which holds the software of the Beomaster. Mine is version 1.5 as it seems. The big chip is an 8-bit microcontroller, a 8032 - a member of the venerable Intel MCS-51 family whose derivatives have been manufactured by the billions over several decades.

Other than that, not much special - this type of module has only two electrolytic caps and they are both all but dead. This would've resulted in startup problems or other malfunctioning sooner or later.

This is the solder side. This module has one logic chip that has been added later - I've never seen this before. It works though, so I don't care either Big Smile

The caps are a bit hard to unsolder. The circuit board has a very heavy ground plane which conducts heat away from the solder joint. This is really bad in a BM5000 where the hand-drawn PCB has no... urm... lightening (as it is called in Finnish) around the solder pads. You'd need to heat up half the board before they melt through, so in a 5000 I won't even bother trying - I snip off the old caps, leaving enough wire stubs to solder the new caps on them.

One of the cap legs (I forget which) is soldered on both sides - remember to redo it like that as well as this board apparently is not through-plated.

After the job is done, replace the metal covers, and the exciting part is getting closer...

--mika

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As always, the assembly is the reverse of the disassembly, although with lots and lots of small problems getting everything to fit.

The cables and wiring looms will need to be routed exactly as they were, or the CPU module won't fit or the cables will get pinched when you try to refit the covers, and so on. The tuner board has quite a few connectors and you can't forget any.

Before the tuner, though, It's best to refit the bottom plate - see, Jacques! Big Smile

Check and double check that everything is connected and there aren't any stray screwdrivers rolling inside... and we can turn the Beomaster upright.

Mains plug in - a relay clicks and the standby dot illuminates *phew*

I pick up a remote and press RADIO... yes! I try with an MCP that the remote control works both ways - and from afar! - and fetch some headphones. Radio 1 of the Finnish Broadcasting Company (the former culprit) locks in without any antenna connected, and comes on the headphones loud & clear on both channels.

So far, this is a success but there's still a bit to be done.

--mika

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...and that is checking & adjusting the idle, or no-load current setting of the power amps. For this, the fan duct needs to get out of the way again.

A couple of tiny spring hooks for the multimeter are invaluable. I took the risk and didn't replace the trimmers as they were fine 4½ years ago, and they have held their setting until now as can be seen - the factory adjustment value is 11 mV across the emitter resistors, but I like to err on the smaller side, so the were adjusted to 10 mV where they still are.

--mika

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So, the work is all but done. I will of course first need to test all other sources and recording as well before screwing everything down and calling it a day, because I messed with the preamp board...

But in any case, it is time to raise a glass of red to all these old caps, who gave their life in providing the original owner and me with 20 years of quality entertainment Smile

Edit: of the tuner board attachment screws, one is bright (non-anodized?). It belongs to the spot that has no solder mask on the PCB, to provide a chassis ground connection for the board.

--mika

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chartz replied on Sun, Mar 4 2012 8:48 PM

Cheers Mika!

Now I'll have to order a kit from Martin!

Jacques

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tournedos replied on Sun, Mar 4 2012 10:07 PM

I connected the Beomaster back in the stack, turned it on... a slight problem. The Beolabs don't turn on.

I tried mute on & off, reboot, everything. Then I realized it's the stupid switch in the headphone socket stuck again, forcing mute on! It was probably less than a month ago when I adviced somebody else on this on the forum, and now I forgot to take care of it myself when I had the Beomaster apart! What an idiot I am... Big Smile

I managed to get it working again by wiggling a plug in the socket, but I think I'll really fix it this time as I still have at least the top cover off. Other stuff seems to work, but I won't say anything about the sound quality until it's daytime again and I can use some volume.

--mika

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tournedos:
and now I forgot to take care of it myself when I had the Beomaster apart! What an idiot I am...

Don't feel bad... I fired off 2 frames yesterday with the lens cap on...

Nice thread, Mika.

  • One B&o bottle opener
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tournedos replied on Sun, Mar 4 2012 11:26 PM

ɓʋɾɑɳɫɘɮ:
Don't feel bad... I fired off 2 frames yesterday with the lens cap on...

Like you'd know the difference with those sunglasses! Big Smile

Just went to feel the cooling fins after an hour of being in standby. I don't feel any heat at all, while earlier they stayed clearly warm all the time. In addition, the Beomaster doesn't say "growllll..." any more when I first turn it on.

However, the IR receiving sensitivity seems after all actually worse than when I started, while transmission is great. I'll go back to the front panel PCB to see if I missed something, I'll need to remove it anyway to look at the headphone socket.

--mika

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chartz replied on Mon, Mar 5 2012 12:31 PM

Mika, same here. With the Beolink 1000 remote sensitivity is great, even far, far away from the set.

However, the MCP 5500 will return a no contact indication from time to time. I have replaced the caps in the remote control circuit of the BM, but not inside the MCP. I think I should open it and do something about it. What do you think?

What was that growling noise you got?

Not any heat at all? Really? Mine remains lukewarm (I'd say 25-30C). I did set it on 240V when I first got it. 

 

Jacques

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chartz:

Mika, same here. With the Beolink 1000 remote sensitivity is great, even far, far away from the set.

However, the MCP 5500 will return a no contact indication from time to time. I have replaced the caps in the remote control circuit of the BM, but not inside the MCP. I think I should open it and do something about it. What do you think?

That's actually the opposite of what I have now. I only noticed it after I had installed the BM back in the stack, and it wouldn't respond to commands from the MCP which sat on a side table in the same position it used to be.

The status updates from the BM to the Beolink 7000, however, work great with no direct line of sight. So the Beomaster transmits strongly now but isn't too sensitive receiving.

I suspect bad solders on the front panel or the CPU card; the IR cable connector was really tight coming off. Perhaps the IR receiver needs adjusting as well, I'll bring the oscilloscope home tonight.

I've never done anything to the MCP - perhaps you could try cleaning the optical parts? I believe Ville once showed me some popped caps inside an MCP as well, which is quite odd for a low power battery operated device...

chartz:
What was that growling noise you got?

From the transformer I guess; it complained for a second after startup. That is gone now.

The fins feel like room temp on standby. I can feel some warmth coming up from the circuit board side in the rear corner, though.

--mika

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Awesome thread! Really interesting stuff. My BM7000 is still going strong (remote range -problem), thanks again, Mika, for replacing the caps on the CPU card! Yes

Interested to hear how the overhaul has affected the sound quality!

Looking at my photos I see that my BM7000 was factory-made for 240V. Would have done the change after seeing this thread, it it wasn't already correct!

I have noticed that the MCP gets easily "confused" if you try do too many things with it quickly (like scrolling volume up and down very quickly). I guess that if the link between the units isn't too good the devices will try sending data back and forth and at some point it gets timed out.

Btw; what's the function of the golden coloured cap in the third picture? The one next to the transformer. Looks somehow part of the powersupply thingy, could it affect the heat business if leaky?

 

tournedos:

I've never done anything to the MCP - perhaps you could try cleaning the optical parts? I believe Ville once showed me some popped caps inside an MCP as well, which is quite odd for a low power battery operated device...

Indeed. I bought two MCP6500 from eBay, both had at least one blown cap. I think the MCPs did work, can't remember if the range was affected. There is one trimmer inside the MCP. I looked at the service manual (Beomaster 6500, it has the MCP at the end) but couldn't see any mention of it's function). In my MCP it looked a bit tired, perhaps worth looking?

 


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chartz replied on Mon, Mar 5 2012 5:44 PM

Well I dismantled my MCP with the firm intention to unsolder something, but the caps were perfect (unlike those above, oh dear, just like the one I found in the IR circuit of my 5500!), with very low ESR.

Then I noticed the inside part of the windows were very dusty. The rest of the innards was very clean, like new. Trouble is, static electricity caused by wiping off draws all the dust towards the IR windows. 

Anyway, problem solved, now the MCP works admirably!

Thanks for the tip Mika!  Drinks

Jacques

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Good to hear your 7000 is still going strong - and a nice one with the MCP, Jacques! Smile

lausvi:

I have noticed that the MCP gets easily "confused" if you try do too many things with it quickly (like scrolling volume up and down very quickly). I guess that if the link between the units isn't too good the devices will try sending data back and forth and at some point it gets timed out.

I believe that's because at some point, the Beomaster will be sending replies to the MCP, and depending on what you have been doing meanwhile, those might get sent at the same time the MCP is sending the next command, resulting in mid-air collision so to speak. Then the frames get corrupted or lost; the devices can't send and receive simultaneously because their own transmission overloads the receiver. The Beomaster actually has a circuit which "mutes" the IR receiver automatically while the transmitter is sending.

The cap on the transformer is in series with the primary, in parallel with the two diodes. I believe the circuit is some kind of a mains interference suppressor. The diodes might overheat if the cap dies, but I don't think it affects much of anything on the secondary side.

***

Today, I started with the headphone socket. It has two on-on switches, and in this model it is used so that the switches make when a plug is inserted, which commands the muting circuit to switch off the #1 speakers.

It indeed got somehow stuck when I inserted a plug again, with both switches "on" both ways. Unfortunately the socket seems impossible to take apart, so I gave it a dash of contact spray (it smells good, if nothing else) and a good session of the ol' in-out thing. The switches began to work seemingly reliably, and I reinstalled the socket.

Then I resoldered all of my front panel, and the connectors on the CPU card. The damn IR receiver coil is impossible to adjust! You need two hands to hold the PCB while it's connected so it doesn't short anywhere, a third hand to keep a remote button down, and a fourth hand to tweak the coil, which is located so that your hand shadows the IR receiver differently with every movement. Nevertheless, I tried, and I believe I got a slightly better 455 kHz carrier amplitude after the IR preamp.

I made an interim test on the kitchen table and was quite happy with the IR reception - it worked well bouncing off one or two walls. I put the pieces together and reinstalled the BM in the stack... bad again. Must be something odd, perhaps the interconnect cable.

That's just about all the time I have to spend on this today, so proper listening tests will unfortunately have to wait. That area is definitely not worse than before I started, though!

--mika

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lausvi replied on Mon, Mar 5 2012 7:13 PM

tournedos:

so I gave it a dash of contact spray (it smells good, if nothing else) and a good session of the ol' in-out thing. 

And I always thought I was the only weird one liking that smell! Big Smile PRF 7-78? Just having a plenty of that smell here (was about to send my Beomaster 5000 tuner to service as it was humming loudly, now I tried again and it's working perfectly! Had to give the switches a great deal of cleaning, though).

Good luck with the IR-thingy!

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lausvi:
And I always thought I was the only weird one liking that smell! Big Smile PRF 7-78?

Exactly! Big SmileBig SmileBig Smile

I don't use it if there's any better way, but now it did the trick.

--mika

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Rich replied on Mon, Mar 5 2012 7:35 PM

Nice thread and great work, Mika!  Hope the listening goes well!


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Another day and time to continue. I finally realized how the IR receiver should be tuned - disconnect the front panel entirely, power it up from an external 5V supply and reprogram my home made "STB controller" to continuously send the B&O "volume down" command. Two hands are now quite enough and I managed the adjustment. Oddly, the most sensitive setting is completely to one side of the coil so I'm not sure if either the coil or the cap inside the coil tank are somehow a little bit off value now.

I believe tweaking the coil would've been unnecessary from the start - the adjustment is far from sensitive.

I also added one 4.7µ tantalum supply bypass cap for the IR preamp in case it would benefit something. Not much else I can do to the front panel, so after checking the cables I assemble it.

I also soldered a couple of lead wires to the detector part of the IR receiver, which is on the end of the CPU module, so that I can scope the signal at one intermediate point and the final logic level signal that goes to the CPU, even while the CPU module is installed. At the same time, I resoldered that area completely to make sure it doesn't have cracks - it unavoidably got bent back and forth when working with that tight IR connector.

After firing up the Beomaster again, I immediately note a lot of traffic on the IR signal going to the CPU. It's at clean logic levels, but those pulses are obviously originally just random noise. I've never had to look at this signal before, so I'm not sure if it should be like that - I suspect no. The real commands get through anyway with decent sensitivity, so I decide to once again try the Beomaster at the normal location.

Surprisingly, it works well over there; perhaps not perfect, but at least as good as before I started. The MCP works very well in its old place, so does the BL7000 which is located essentially behind the back of the Beomaster. I'll just let it be like this now, I'm getting bored with this step and the functioning is now completely acceptable.

***

In summary:

  1. The voltage change was a success
  2. The tuner works well now
  3. IR sensitivity is at least as good as originally
  4. Sound?

...tomorrow it's time to dig up some CDs from the stacked up boxes where I still have them Big Smile

***
Edit: Hah, something funny going on. If I connect the antenna cable (fed from the central antenna of the building), IR reception goes down the drain again. Restored once I disconnect the cable.

Could probably fix that with a galvanic isolator, but I think I'll just use a room antenna. The FM signal from the central antenna is crap anyway.

--mika

Stonk
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Marlow, Bucks, UK
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Stonk replied on Tue, Mar 6 2012 9:46 PM

tournedos:

Another day and time to continue. I finally realized how the IR receiver should be tuned - disconnect the front panel entirely, power it up from an external 5V supply and reprogram my home made "STB controller" to continuously send the B&O "volume down" command. Two hands are now quite enough and I managed the adjustment. Oddly, the most sensitive setting is completely to one side of the coil so I'm not sure if either the coil or the cap inside the coil tank are somehow a little bit off value now.

I believe tweaking the coil would've been unnecessary from the start - the adjustment is far from sensitive.

 

I also added one 4.7µ tantalum supply bypass cap for the IR preamp in case it would benefit something. Not much else I can do to the front panel, so after checking the cables I assemble it.

I also soldered a couple of lead wires to the detector part of the IR receiver, which is on the end of the CPU module, so that I can scope the signal at one intermediate point and the final logic level signal that goes to the CPU, even while the CPU module is installed. At the same time, I resoldered that area completely to make sure it doesn't have cracks - it unavoidably got bent back and forth when working with that tight IR connector.

After firing up the Beomaster again, I immediately note a lot of traffic on the IR signal going to the CPU. It's at clean logic levels, but those pulses are obviously originally just random .........

I have no idea what you have said above but still mightily impressed. 

If you think nobody cares, try missing a couple of payments.

Søren Mexico
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Mexico City
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Stonk:
I have no idea what you have said above but still mightily impressed. 

Impressed too, but what has the central antenna to do with the remote ??

Collecting Vintage B&O is not a hobby, its a lifestyle.

chartz
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Burgundy, France
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chartz replied on Wed, Mar 7 2012 7:40 AM

Bad ground insulation from the aerial amp phantom PSU? A common problem.

Jacques

tournedos
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Finland
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chartz:
Bad ground insulation from the aerial amp phantom PSU? A common problem.

Close... the thing is that in the same corner, I have an ugly PC that takes care of my TV recordings. A typical computer power supply has two mains suppressor caps connected from each mains line to the protective earth. When they are connected to a non-earthed mains socket (such as I have, this is a 40+ years old building with original electrics), the chassis of the computer ends up floating at around half the mains voltage. The available current is so small that it isn't dangerous, but will pinch your fingers when attaching cables.

Now the PC is connected to the TV socket of the same antenna outlet, and from there the 50 Hz disturbance got to the Beomaster. If I didn't have it there, some neighbour's kit probably would've ensured the antenna ground isn't clean. I'm not sure why it wasn't a problem before (all the ground straps etc are still attached)... the FM antenna signal from the rear panel socket goes to a cable that terminates in a small plug on the tuner board. For some reason, the sleeve of the plug was oxidized black and I cleaned it. Perhaps it just didn't have any ground connection left before this? But the fundamental problem is still somewhere else in the Beomaster. Now that the sun shines on the front panel, it's no good again.

--mika

tournedos
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Finland
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tournedos replied on Wed, Mar 7 2012 10:03 AM

Time to dig up some records. I believe it sounds a tiny bit better than before - more punchy and effortless in the top register, in particular. Was it worth it? Impossible to say. The last time I really paid attention to the sound was in my previous flat, a completely different room and completely different speakers.

I would've expected the bad coupling caps in the power amp inputs to make the most difference, but now I realize that since I have currently Beolab 8000s in the Powerlink outputs, they aren't even used. Wish I had my Pentavoxes up here...

--mika

pimzel
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pimzel replied on Sat, Apr 14 2012 9:05 PM

pimzel posted on 04-14-2012 9:18 AM

Hi all,

I have recently bought a beomaster 6500. It seemed alright but after an hour or so I can hear a relay click, it switches of and  on again resets the volume to default and resumes playing. If I disconnect it from power overnight it will play again for another hour or so.
Any idea's where to start looking ?

 

kind regards pim

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