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 wrote:

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