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Beocenter 9500 some LEDs and buttons not working

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Martin
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Martin posted on Sat, Nov 14 2020 10:19 PM

 

I am restoring a Beocenter 9500 which has a few issues which might be related.

- No dual-LEDs are lit - except the one for "Timer", which works (but only when the system is in standby, is that the correct behaviour?) and the dual "Volume" LEDs flash briefly when going to standby.

- No buttons related to the functions using dual LEDs work.

Everything works when using the remote. Does that mean that the logic ICs are fine or are they just for interpreting the buttons and lighting the LEDs?

Since the dual LEDs are fed 7 Volts, that is my first guess where to start checking.

However, I am a novice in interpreting the service manual schematics, so I am not able to find where to measure this?

 

Where is the best way to probe for the 7V power source?

Any other ideas what could cause this type of problem?

 

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Martin
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Answered (Verified) Martin replied on Fri, Feb 26 2021 5:58 PM
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Problem solved! After disconnecting and reconnecting the connector between the lower keyboard and the system control board (G in service manual), all LEDs were lit! That was the only connector I had not removed before. Circled red in the picture.

The voltage is not at 7V when the lower and upper displays are connected and the system is powered on. The voltage drops about 0.7V for each board connected, showing about 5.6V.

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Martin
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Martin replied on Mon, Nov 16 2020 2:51 PM

It looks like TR19 on board 65 supplies 7 Volts. Not sure it that is the only source?

Picture shows a probe connected to the collector (the middle wire of the ribbon cable that goes to board 60) of TR19.

Do I need to connect the upper and lower display/keyboards before connecting the power cable or will I risk damaging any components if some boards are disconnected?

Guy
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Guy replied on Mon, Nov 16 2020 4:08 PM

Martin:
No dual-LEDs are lit - except the one for "Timer", which works (but only when the system is in standby, is that the correct behaviour?) and the dual "Volume" LEDs flash briefly when going to standby.

The Timer light should also work when the system is on - you should be able to toggle it on/off by pressing the timer button on the lower panel.

The Volume LEDs should not flash when gong into stand-by.

Also, although I am no expert, I am unclear why you suspect the 7v supply to the LEDs. Surely if any of them work then they are receiving the correct 7v?

In the first instance, I would use the 'test mode' as explained in the service manual (page 7-6) - at the very least this will test the displays as well as for RAM/ROM errors.

I would also check connectors between control and display boards.  Do the lower buttons work by touching the sensors gently when the glass panel is removed?

Also is the internal battery OK - if dead it can cause some strange errors/malfunctions.

 

Martin
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Martin replied on Mon, Nov 16 2020 5:37 PM

Thanks for your input!

I actually found now when testing again that there are in fact single LEDs not lighting up as well. REC on the upper panel is off and only the power LED on the lower panel lights up.

Regarding the Timer light - so something is preventing it from working when powered on.

Regarding the volume LEDs - I mean the red dual-LED to the left of the green ones. It briefly lights up, just when pressing the Standby button.

Regarding the 7V supply - you are correct! If they all get the power from the same source, it should be OK!

Regarding the battery - Is there an easy way to test it? It seems difficult to reach without disassembling the entire system...

 

I have tried the Test mode and I notice that only the Power LED to the far right on the lower panel lights up when entering Test mode. See Pic. 1

Pressing the test buttons for the upper panel lights up all LEDs - except REC and all the dual ones. See Pic. 2, 3 and 4

The buttons on the lower panel all work except for the ones below dual-LEDs I believe.

The connectors between the boards have continuity, though I have not yet been able to test the fixed one with blue wires which connects the upper panel to the "mainboard".

 

Martin
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Martin replied on Mon, Nov 16 2020 6:37 PM

Inspecting the Service Manual in more detail, I see that all of the single-LEDs that are not lit are actually driven by 7V.

So there is something fishy going on with the 7V supply - but only when being powered on!

Could it be some type of logic (IC) error since the "Timer" LEDs work when in Standby?

Martin
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Martin replied on Sat, Jan 30 2021 11:27 PM

It seems that the 7V supply only supplies 7V when the system is powered off. When powering the system on, the voltage drops to 1.7V.

It seems that the TR19 transistor supplies the 7V in the schematics below to connector P84, marked yellow.

What could cause voltage drop behaviour? Bad TR19? Bad C10?

 

 

Board 60 is discolored as if it has been subjected to a lot of heat but there are no components on the other side close enough to cause it, unless it is the actual resistors that are the cause.

The transistors on Board 65 behind this one do not align where the discoloring is.

 

Martin
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When disconnecting the lower display/keyboard, the 7V LEDs on the upper panel actually lights up but only dimly unfortunately.

But it is good to know that the LEDs actually work, it is just that they are not supplied enough power (my guess).

So hopefully, there is nothing wrong with the lower display/keyboard it is just that the extra load it brings, makes the already weak 7V rail to not light them up at all when connected.

Next step should be to try to measure the voltage when no displays/keyboards are connected at all.

Martin
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Answered (Verified) Martin replied on Fri, Feb 26 2021 5:58 PM
Verified by Martin

Problem solved! After disconnecting and reconnecting the connector between the lower keyboard and the system control board (G in service manual), all LEDs were lit! That was the only connector I had not removed before. Circled red in the picture.

The voltage is not at 7V when the lower and upper displays are connected and the system is powered on. The voltage drops about 0.7V for each board connected, showing about 5.6V.

Guy
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Guy replied on Sat, Feb 27 2021 10:20 AM

Great news that it is now working fully!  And thanks for letting us know what the problem was.

Enjoy your BC9500Smile

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