I have already replaced the idle current trimpots and reset them correctly (and yes, those controversial silly power stage caps are still there ).

Still I feel this amp is running hotter than it should be, at least compared to my BM6500. With the covers on, after it has been playing radio a while at volume 30 into passive Pentas, the cooling fins are hot to the touch (probably around 50°C, maybe more). Another thing is that this receiver seems to have notably shorter remote control range (both in and out) than my BM6500. Before I start measuring around, are there any other common problems that might cause these issues?

BTW, how hot do these receivers actually have to get for the cooling fan to kick in? I've never been able to do that...

Hi,

yes, there are other problems with the BM5500-7000.  You can see that the amp section is on the left side, the power supply on the right side. There are some power regulators and there are also some red 10uF caps... replace them.

Inside the CPU board is a cap, C1=47uf. This cap sometimes explodes... literally, causing high current and sometime the small 1A fuse blows. Check also wether C1 has a stable 5V power supply. Sometimes it's higher than 5V...

It is also very common that the 80C32 cpu dies, runs hot and the ir control becomes worse. This happened already several times, especially in link systems.

Martin 

Thanks! I actually tried to load the amp more by connecting another pair of speakers (S80.2) and ran it at vol 40. The problem(?) definitely seems to be in the power amp side - that end of the cooling fin got hot enough that I had to take my fingers off of it after a while. This seems abnormal although the amp sounded fine and never shut off.

I'll measure/scope the PSU voltages and check the caps. I believe this receiver spent all its former life stuffed inside a cabinet (who would want to do that..?) and it may have more heat related problems than the age would otherwise suggest.

You have checked the "no load current" of the amps? This should be the problem... maybe somebody deactivated the heat protection.

Die_Bogener:

You have checked the "no load current" of the amps? This should be the problem... maybe somebody deactivated the heat protection.

Yes and replaced the trimpots, as I said in the first post... I'm beginning to suspect the test points don't quite tell the truth about the actual current, so maybe I'll also start checking for bad connections and solder joints. I already fixed some in the front panel which caused the mute relay to rattle and other various funky things when the front was touched...

I had now time to work on this a little more. I did the following:

• resoldered the front panel in its entirety
• replaced the four small caps in the power supply: C8, C9, C14 and C22 - all of them were bad according to my ESR meter
• replaced C35 (47u) and C57 (100u) in the CPU module - both were bad, the latter almost completely dead

I also checked the 5V supply, it was a little high at 5.17V but still within specs so I left it there. Now the remote control range is much better and more reliable (maybe even better than my BM6500, which might need similar work sooner or later...) and the amp doesn't seem to heat up nearly as much.

Thanks for the help Martin

Hi,

I've got a similar problem.  Since a few day my BM7000 started humming and running hot (in my impression).

I changed the C8, C9 and C14 in the power supply, but without result.

Any suggestions?  Is the a near death of my BM? :-(

Kind regards

Joost

Hello,

Now, I also changed the C22 in the powersupply and the heatproduction seems to have diminished, but the hum is still present.

So, I guess I'll have to have a look at the idle current trim pots.

I have the service manual and there's a section on 5-1 on adjusting the No-load current.  I guess this is the thing I have to do?

Is this hard or 'dangerous' to do?  The trimpots to be replaced, are that the 2R226 and 2R426?  Can some give me a clue where I can buy those kind of things online (conrad, RS-components,...)?

Kind regards

Joost

Yes, you should do that. I can't remember the component designations, but they are 100 ohm trimmers near the "end" of the power amps and you can't miss them by looking at the "no-load" section of the service manual. Do them one at a time and preset the new trimmer to the approximate value / position of the old trimmer first - this should give you enough time to get the setting right before the amp heats too much. Remember to disconnect speakers and turn the volume to 00 before checking the adjustments!

I suggest cermet type of trimmers (i.e not the cheapest ones - it will still only be a couple of euros). All the typical horizontal trimmers you can buy nowadays should have the correct footprint.

I dunno if this will get rid of the hum, but it is definitely the first thing to check for overheating problems.

OK, Thanks.

I'll give it a try.

While I'm in the BM, I'll also want to change the capacitors on the CPU-board, that you mention.

It seems that that PCB is dual layer.  Is it difficult to solder, or are there soldercontacts on front and back of the PCB?

kind regards

Joost

joostdeclercq:

It seems that that PCB is dual layer.  Is it difficult to solder, or are there soldercontacts on front and back of the PCB?

It was pretty hard. It has a lot of copper and the pads seem pure round without "unweighting" or whatever it should be in English... which means that the heat runs away from the pads and you end up getting even the nearby components uncomfortably hot before the solders melt through.

The good news is that all the electrolytic caps you'd like to replace are axial, which means you can just snap them off with cutters and do one lead at a time, or just let the old wire ends stay on the PCB and solder your new caps to them. I actually used miniature radial caps on mine, there's just enough space that you can install them lying down. Be careful not to create shorts to the metal shields, though.

Hi,

Thanks for the tips. 

I ordered some new trimpots for the no-load current, but they were the wrong size :-(.  I checked the existing trimpots and the current was almost 11mV, as required.  I additional adjusted them, to match exactly the 11mV.

But the hum stays present.  I additional checked the 5V Power-supply as stated in the service manual.  I measured 7,3V between pin 2 and 5 in P14, where it should be 5,1V.  So, I guess there's a problem.

The servicemanual states that the current should be adjusted by disconnecting or shortcircuiting 2J38 and 2J38, but I don't exactly know what they mean by that.

Can anybody help me?

Kind regards

Joost

Joost,

Please don't get me wrong but unless you are an educated tech guy I suggest you
leave servicing of stereo equipment to someone who is.
You not understanding the instructions given in the service manual and not knowing
how to solder a multilayer PCB points in the same direction.
In my opinion, a Beomaster 7000 is not the one to practice on.

You don't state where the humming is coming from. Is it from the Beomaster physically
or from one or both speaker(s) ?
- If from the Beomaster physically, you can replace everything inside the Beomaster
without getting rid of the humming.
- If from the speakers, something more drastic is wrong with the Beomaster, which
should be attended only by a prof repairshop. If you feel ready for the
task, put an oscilloscope to the signal path. Do some stops along the path,
like the source selector, tonecontrol and volume IC's, the preamp etc. and let
us know your findings, that will help us help you.

Also let us know if the humming is present on all sources and if it's a
50Hz or 100Hz hum. An essential thing to know if we are to guess at a reason.

A readout of the Beomasters main power consumption in idle would also be good.
This will tell us if something inside is drawing too much current.

You can also put a distortion meter to the output and a signal generator to
an input and let us know the results.
This can help us determine if f.e. a transistor in the output stage is defective.

Martin

Yesterday, I just finished replacing every electrolytic capacitor (plus a couple of film caps) and every single trimpot on a customer's treasured BeoMaster 5000 - close enough to the BeoMaster 7000.

Exactly 2 trimpots and 3 capacitors did NOT need to be replaced.....

So, all were done anyway - no need to be cheap here, and I'm certainly not cutting corners.

Point is, that sooner or later, on this entire range of BM's (5000 thru 7000), the work is going to have be done properly. Just changing a cap here, or a trimpot there, is not going to solve anything.

Here's what came out of the BM5000.

Most of the original caps were made by Marcon - the forerunner of today's United ChemiCon, and of course the gold and blue ROE caps which are still around today under the Vishay banner - Roederstein and BC Components.

I chose to use Wima MKS2, Panasonic FM, and FC in the signal and audio paths, and Nichicon PW in the power section, and of course, my favorite Vishay BC 138 for the axials.

For the trimpots, I used Bourns 3352E Cermet units.

I haven't got all the parts for it yet - I'm waiting for Martin Dillen's package to arrive, but shortly, I'll put a full thread up on the overhaul of this, a BeoCord 5000, and 2 S55 Speakers.

http://forum.beoworld.org/forums/t/28475.aspx

Menahem