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Dead Beocenter 9500

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Mikael
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Mikael posted on Sat, Sep 1 2012 7:45 AM

 

Hi all,

Maybe you have been following my other thread about my Beolab Penta 3 restoration. They came as part of a package which included a non-working Beocenter 9500. The lady who sold it thought it had blown a fuse during a party. The lower glass panel is cracked across. 

I decided to make a quick investigation and opened up the small cover on the back of the mains transformer. The fuses checked out for continuity and negligble resistance. But one was 0.2 Ohm. I figure that could be normal but I will replace it anyway once I buy some fuses.

Hooking up 220v makes a small hum from the transformer. The connectors on the #64 pcb does not show in the service manual so it is hard to see if the voltages check out but something is fishy here. I read 10v Ac on some points but no 12v as in the diagram. I don't really trust my multimeter and will get another one.

Next is opening up the unit more and measuring the rectifier PCB and stabilizers. Any thoughts?

Beocenter Overture | Beolink passive | CX100 | CX50 

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sonavor
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Verified by Jason

Orava:

I did snap ring from old cap and solder it to board to make a bridge.

That's a great solution, thanks !

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Mikael
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Suggested by TimGonser

Ok, so I'm back from measuring the voltages coming out from the PCB #60 (Power supply and output amps). The relay clicks as it should and all voltages seem to check out in comparison. There is a relay on the rectifier board #62 also clicks so this leads me to believe it is trying to get out of stand by mode. Since the relay on the rectifier board seem to also click as it should (and output some of the mixed voltages to the #60 board to be stabilized) I'm thinking that the power supply of the unit should be ok. 

The problem is that the 9500 is dead in every other way. No lights on the upper panel or the lower panel is lit. The only sign of life is the CD mech that do a sort of startup move with the laser and stops when powering up the unit.

This leads me to suspect that there is something wrong with the controller board #40. I've seen some post on the archived forum that states that the standby mode cannot be exited if the backup lithium battery is dead. But would that give the effect that I see (no lights no nothing)?

I've tried to short circuit the TEST MODE connector with no change. Just to be sure, I tried to send some IR traffic with a beolink 1000 remote without any luck.

Next up is checking the voltages on the upper and low display (keyboard) board.


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Mikael
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Since there is very little feedback from the community I will continue this thread as part of my therapy Wink

Anyway I seem to have found the source of the problem! While investigating if the controller PCB #40 was alive I noticed that the !RESET signal is always low on connector P50 pin 4. This signal is generated from the transistor circuit seen below on the power supply PCB #60. If disconnect the connector P50 on the PCB #40 and manually short pin 4 to ground briefly, then the unit goes to stand by and lights the standby indicator diode. Shorting the TEST MODE connector under the glass panel enters the testing routines. I also get the CD door to open (though it needs some TLC, it doesn't move smooth) and the cassette door.  

So I'm going out tomorrow to get some new BC577B (TR15 & TR16) transistors and the C12 (2.2uF). Hopefully that will allow me to fix the problem. 

Stay tuned!

 


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Dillen
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Sounds like a good place to start.
What kind of voltage do you have around TR15 ?

Martin

Mikael
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Hi Martin,

I have done some measurements:

Conditions: connector P85 (containing pin 8 !RESET signal to MCU PCB #40) connected

Measurements:

TR15:

Base 6,75V

Collector 4,97V

Emitter 1,3V (RESET)

IC4:

Pin V1 11,5V

TR16:

Base 158mV

Collector 15,5mV (!RESET)

 

I assume that the circuit should work normally so that while the system voltage is on the rise the TR16 allows current to pass until TR15 becomes saturated? So would you say that the TR16 is the problem (always energized)? I'm a bit rusty in the analogue domain. 

Since the MCU board comes alive when I disconnect the connector from the PSU board and manually ground the !RESET pin briefly I'm thinking the problem should not be there?

Mikael

 

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tournedos
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Mikael:

TR16:

Base 158mV

Collector 15,5mV (!RESET)

Sounds like either TR16 or C12 is shorted.

--mika

Mikael
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Mikael replied on Tue, Sep 4 2012 11:13 AM

Hi,

I'm not so sure it is shorted. There is approx 150kOhm across TR16 collector and emitter when !RESET is connected to the MCU pcb #40. If open connector then i read several MOhms on the same spot.

/Mikael

 

Beocenter Overture | Beolink passive | CX100 | CX50 

RaMaBo
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RaMaBo replied on Tue, Sep 4 2012 11:39 AM

Hi Mikael,

as mika said check TR16 and / or C12. The collector of TR16 should be around 0V only for a short while after power on. Then it should rise to nearly 5 Volts. You said that you get 15,5 mV at the collector that's logical a '0'. The RESET line is low-active due to the line above RESET. and a logical '0' is low. so your processor gets a constant reset signal and cann't start working it's propgramm. If you disconnect the reset line as you done before and connect the RESET line briefly to ground the µP can start as you stated.

Ralph-Marcus

 

Ralph-Marcus

Mikael
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Hi,

I'm leaning towards replacing TR16 and maybe the C12 while at it.

/Mikael

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Dillen
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TR15:

Base 6,75V

Collector 4,97V

Emitter 1,3V (RESET)

 

The TR15 emitter should be held at a constant 5V by the voltage supply.
I suggest you check this.

Martin

Mikael
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Ok, back from my little workshop. I've replaced both TR15 and TR16. That gave no improvement at all. More or less the same voltages as before. The TR16 collector is 50mV now so still a logical zero. 

Then I replaced C12 as well. That also gave no improvement.

Checking R36 and R37 gives resistance according to the schematic. 

Sigh, I am a bit out of ideas right now...

I guess moving on to check the mcu PCB which btw still starts up if I manually reset it.

/Mikael

Beocenter Overture | Beolink passive | CX100 | CX50 

Dillen
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Did you check the 5V supply to TR15 emitter as I suggested ?

Martin

Dillen
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Oh, are you sure, you didn't get the emitter and collector pins mixed up for TR15 ?

Martin

Mikael
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You mean the voltage over TR15 collector and emitter or from IC4 pin VO? I will check both.

About mixing the pins, I will double check. I'm pretty sure that the replacement transistors drops right in without any shift in pins from the old ones since I got a bc557b and a bc547b.

/Mikael

Beocenter Overture | Beolink passive | CX100 | CX50 

Mikael
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Made some more measurements:

TR15

Vce=-3.14v (postive probe on C)

Vbe=1,8V

Ve=4,85v

Vc=1,3V

IC4

Vo to TR15=4,5mv

I was thinking if the Vi voltage of IC4 is only 11,5v compared to the 13v in the schematic. Would that give a too low voltage on the TR15 base?

/Mikael 

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