Beocenter 9300 No Life - almost

19 replies
filip_kbh
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filip_kbh
Bronze
Posted April 12, 2024 at 12:58 GMT
#1664066
After changing the three diodes on the standby board plus fixing the trace on the processor board, the tape motor now spins but that is all. I still don't know why I have 24V on pin 7 when it should be 7.8V. My measurements in red below. I am also missing a 15V supply.

Location: Copenhagen

filip_kbh
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filip_kbh
Bronze
Posted April 12, 2024 at 13:18 GMT
#1664068
When the motor is spinning, pin 3 gives 15V - but it is not every time the plug is plugged in that the motor will start.

Location: Copenhagen

filip_kbh
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filip_kbh
Bronze
Posted April 12, 2024 at 19:13 GMT
#1664078
I think there’s still an issue with the micro processor board. I realise I made a mistake repairing the dead track but now that it’s fixed to the right points, there is no relay clicking. I did experience that some of the panels lit up but I don’t know what I touched prior to that. Argh.

Location: Copenhagen

filip_kbh
Offline
filip_kbh
Bronze
Posted April 12, 2024 at 22:02 GMT
#1664082
Can someone please upload a clear, zoomed in picture of the cpu board front and back? The service manual scan is not very clear.

Location: Copenhagen

filip_kbh
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filip_kbh
Bronze
Posted April 14, 2024 at 21:45 GMT
Edited April 14, 2024 at 21:45 GMT
#1664130
Hmm - these three legs are shorted. Am I right in assuming that they shouldn't be? It's pcb3. When the board is not connected, the BeoCenter starts up with two relays and the tape motor kicks in. The chip is right under the battery damage on the other side, so who knows what's underneath of great surprises.

 

Location: Copenhagen

filip_kbh
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filip_kbh
Bronze
Posted April 15, 2024 at 22:40 GMT
#1664167
Turns out the three pins get the same signal but there was a broken trace under the IC.

Location: Copenhagen

Ninni
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Ninni
Bronze
Posted April 16, 2024 at 13:46 GMT
#1664182
The 7400 is a quad NAND gate. Connecting three pins together isn't uncommon. You do it when you use one gate as an inverter.
filip_kbh
Offline
filip_kbh
Bronze
Posted April 16, 2024 at 20:47 GMT
Edited April 16, 2024 at 20:48 GMT
#1664192
Yes - thank you.

I have now turned my attention to board 10. Since I am getting 24V on P74-1 (and it should be much less - 7.8V unregulated), I am looking at TR36, and it is not working properly, so I will have to replace that.

However, it puzzles me that there is seemingly a short on the board. TR31  measured a short, so I took it off but even without the component, I still measure a short :(

 

Location: Copenhagen

filip_kbh
Offline
filip_kbh
Bronze
Posted May 9, 2024 at 18:20 GMT
#1664445
I changed Tr31 and Tr36 but the unit is still dead. A relay clicks and the tape motor runs but that’s it.

Location: Copenhagen

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