[Martin Lundholm]

Aha. But it really seems like everything else is working when switching on the unit by pressing a button. I have a BM 6000 with a dead CPU, and that unit is really dead.

Anyways I’ve put it on a shelf and will probably sell it for parts. I has been fun to troubleshoot though.

[Martin Lundholm]

Yesterday I focused on the 455 kHz band-pass filter. If I disconnect the IR reciever, there is no 50 Hz disturbance. So it *could* be the band-pass filter, which is broken. Not very likely, but I’m running out of likely causes. The only 455 kHz band-pass filter available in my local shop is CFUCF455KB4X, which is surface mounted. So I bought a small adapter board for a SO8 to DIL8 and soldered the SMD filter on that. And then I replaced the original filter with this one. But still no “luck” with getting the Beomaster to respond on remote control signals. I will continue another day to make certain the new band-pass filter is connected correctly. But it may very well be that the new filter is not suitable for the Beomaster. I think I’m getting closer to give up (putting it on a shelf for another year) on the BM6500.

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[Martin Lundholm]

A small progress was made today. On the BM5500 CPU board there is no 50 or 100 Hz in the IR reciever signal, as far as I can see. So I checked 5Va and that is stable, but on the other side of R45 which feeds the IR receiver, I can clearly see voltage fluctuate at 100 Hz (double 50Hz). Not a lot but it gets amplified of course. I replaced a few capacitors, although it feels stupid to replace ceramic capacitors in a low voltage circuit. I’ll replace the rest and all the diodes in the IR receiver circuit another day. If that is not doing anything I have to try to check the ground plane I guess  (I’m not sure how I can do that). The fact that the BM5500 CPU board works in the BM6500 should mean that there is no problem with the power supply, but the 50/100Hz disturbance signal sure is pointing at the power supply as the culprit.

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[Martin Lundholm]

I tried putting the CPU board from BM5500 in the BM6500 (with the BM6500 front PCB), and that works fine. I also tried to replace all the transistors in the IR receiver path, but no “luck”. So either it’s the 455 kHz (ceramic?) filter or any of the small capacitors, or something completely different. Really puzzling.

I was a bit surprised that the first transistors after the 455 kHz filter has such high voltage rating (65V). Does voltage build up due to the filter? There seems to be no apparent risk of external electric shock. It does not seems so easy to find a replacement for the 455 kHz filter. At least not in Sweden, but I’ve found a SMD which I can try to add leaders on.

[Martin Lundholm]

So tested to put the BM6500 CPU board (4) into the BM5500. I found that there is one difference on the CPU boards and that’s P17, which is unmounted on BM6500. It seems to be a loopback from the IR tranceiver to the receiver to avoid receiving what is sent out. But there’s already a transistor to do that job, so I guess they found P17 to be unnecessary. Anyways  the BM6500 CPU board didn’t wake up on IR receiver input in the BM5500. Now I at least knows it is not the photodiode or the LC-circuit of the IR-receiver which is broken.

The BM5500 is now reassembled and working again. Perhaps I’ll open it up again to take photos of the oscilloscope at different stages of the IR receiver circuit, to compare with the BM6500. Or I’ll just replace the rest of the transistors on the IR receiver circuit. The only replacement for the BF240 would be my BF494, but I’m not sure it’s a good replacement so I’d leave it for last. For the 455 kHz filter I have not clue. I’ll google… Perhaps I should also check the 50/60 Hz signal coming on the board. Actually I should have put the BM5500 CPU board into the BM6500 also, just to rule out that there’s anything fishy with the BM6500 power supply board.

[Martin Lundholm]

Since nobody objected, I put board 9 from the BM6500 in the BM5500, and this combo works fine 🙂 So that’s a relief at least.  Also the CPU boards (4) looks exactly identical so I will try switching in the one from BM6500 next. The SW may be a bit different, but switching between inputs should be the same.

[Martin Lundholm]

Thank you for your suggestion! But I have already a project plan for a long winter (or two) which is to replace the Mostek 3870 CPU in a BM6000 with an atmega-1284p 😊

[Martin Lundholm]

I put the BM6500 on hold for a while, but yesterday I started to troubleshoot it again. It’s not a lot of transistors in the IR receiver and I tried to replace a few. But with no positive result. When testing the BF240 I got an extra diode in the test screen which I haven’t seen before (see the attached file). I think the transistor is fine, as the other BF240 showed an identical image. I put them back as they seemed fine. Anyone who knows what the extra diode means?

I’m not even sure where the 100Hz is I see on the final IR input signal coming from. The only LC-circuit I see is the IR receiver and that sure (I think at least) doesn’t produce 100Hz.

Anyhow, I have a working BM5500. By looking at the schematics I could try to replace the front PCB with the one from BM5500. Actually the schematics for the 5500 and the 6500 are confusingly identical. I got even unsure if I actually had the right schematics, but it seems so. If I can replace the PCB, I can also check the signal from start to end and compare. That should give me a clue of what is wrong, or if it’s actually something else.

Does anyone know for certain if the IR receiver/transceiver boards are identical for the BM5500 and the BM6500? I wouldn’t like to end up with two broken Beomasters…

 

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[Martin Lundholm]

I kept power down and up with 30-60s in power down, and eventually it responded to the remotes! The idle square wave actually looks a bit different now. It’s  ~50 Hz and the duty cycle looks rather different from the two previous photos and is more steady. So I guess I have to investigate what is driving the idle square wave. I have had a glance at the circuit of course, but there are mainly BCnnn transistors which rarely fails from my experience. But it would be a rather quick thing to change them, if I have them at home. Well, there’s a BF240 and I don’t have any BFnnn transistors. Will check if I can replace it.

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[Martin Lundholm]

Thank you for your reply! No, unfortunately it didn’t help. I can see the IR receiver signal in the oscilloscope, but the Beomaster is still cranky.

I have a Beomaster 5500 which responds to both the MCP and the BL1000 so I know the remotes are working. Well, I had to replace to opto sensor in the MCP to be able to control the volume…

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