I have here a Beomaster 5000, which doesn't react to anything. When I plug it in, the relay on the preamp board activates, and deactivates shortly after I plug the receiver off. Other than that, it doesn't even light the standby dot.

I measured the +5V to the CPU board, and it is there and seems stable. Any generic faults to check next?

Well I dug further into this and the problem seems to be (at least) the reset circuit of the CPU. C59 was pretty much dead and I replaced it. The diodes (D2/D3) measured OK, but still I seem not to get a clean reset signal to the CPU; when looking at it on an oscilloscope, it oscillates fast between 1-2V which probably means the 8051 won't start up. Any ideas now?

Replace capacitors in the power supply area, especially the smaller ones, 10uF and up.
Also all the electrolytic caps on the processor module.

Martin

Done. C10 / 1uF  from the +5V power supply (similar axial ROE...) was dead as well, replaced by a Wima MKS. C8 (+34V) replaced.

C68, C65 and C59 from the CPU board replaced. All voltages that should be there on standby seem present, still no life at all. Argh. 

Edit: one  more thing: TR6 (BD138) on the CPU board - the IR transmitter power stage - gets really hot if P22 is connected No change in function otherwise, as far as I understand disconnecting P22 only disables the IR tx & rx...

- Is the transmitter LED's transmitting (lit) permanently (use a digital camera/phone camera to see the light) ?
- Is the 13V (P23 pin2/3) correct and clean ?
- Is the CPU module correctly grounded ?
- Do you have another CPU modulde to swap-test ?

Martin

• Yes, it's transmitting continuously - which seems about right, since pin 37 of IC1 is constantly low... (perhaps normally, since the CPU isn't running at all and doesn't initialize it?).
• 13V is 13.8V with ~500mV of ripple with P22 disconnected, around 1 volt of ripple with it connected.
• The grounding lug was indeed disconnected since I had the module flipped out - I added a separate wire, with no change.

Unfortunately I don't have an extra module, would've tried it already. The problem is that I've never seen this unit power up, so it might be lightning damage, or anything else for all I know... too bad this is from the era of bugless software and they used a mask ROM version of the CPU - I would've had 8031's laying around to try

For maybe half of a second after plugging the unit to the mains, I see the ALE pin (30) of the processor oscillating like it's actually writing data to the I/O chip, so there might be hope...

OK, after some further investigation I'm now pretty sure that to make this fancy doorstop something useable, I need either a complete working CPU module (PCB no. 4) or perhaps just the processor itself (4IC2, 8051).

Please PM me with offers, if you have an otherwise trashed BM5000 lying around, or have parted out one sometime in the past... this is externally too nice to the skip.