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MCP5500 not working!

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hoangduongo
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hoangduongo posted on Fri, Jun 1 2018 6:22 AM

Hello,

I've recently purchased a MCP 5500 for my Beomaster 5500. It worked well for a while initially but then quickly showed various signs of malfunction like show No contact or wrong indication whenever I push a button. Replacing the batteries couldn't help.

Now the MCP stays in a steady state where it doesn't contact with my BM5500 at all (I checked with another Beolink1000 to make sure the BM5500 is working normally). It (the MCP) keeps showing "Standby" and "Set clock" and won't turn off unless I remove the power, pressing whatever button does nothing.

Following are several attempts I've tried (mostly following the hints in BM6500 service manual):

- Replace batteries with 6VDC from my bench supply, the consumption is approx. 80mA steady.

- 4.75V line: I've checked and readjusted R117 to make sure it's 4.75V

- 12TP3: Since the MCP stays on, I thought it has smth to do with TP3. Its voltage is measured 30mV, checking pin B of TR41 (which serves to active TP3) is 0.56V. It seems TR41 has no problem but likely the CPU keeps sending "Supply constant on" signal.

- 12TP4: the display did flash when I checked this test point (shorted to neg. supply). Power consumption jumped between 60 and 80mA (probably due to the display flashing). The MCP stayed on that state (flashing) whatever I do unless remove the power.

- 12TP1: the MCP did transmit a 200uS/3.1mS pulse/pause signal (measured across D3 of PCB 13/14 with my oscilloscope) following the test BUT did not stop when I push a (whatever) button.

- 12TP2: I didn't check since the display kept stay on anyway.

- Volume wheel: removing the connectors from Volume wheel (in case there's something wrong there) didn't help at all.

Now I'm stuck and clueless. Any suggestion is welcomed.

Thanks,

Duong

Answered (Verified) Verified Answer

Dillen
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Copenhagen / Denmark
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Verified by Peter

Check for stuck buttons.

Martin

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Dillen
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Copenhagen / Denmark
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Verified by Peter

Check for stuck buttons.

Martin

hoangduongo
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It' quite embarrassing to admit that I didn't think of this!!!

Just checked all the button and found one (Stop) show considerably lower resistance (but not shorted) than the others. Poking around the plastic tape that hold the contacts solved the problem.

Thanks a lot for your promptly yet helpful hints, Martin.

 

Peter
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Peter replied on Fri, Jun 1 2018 9:06 PM

I think it is fair to say that is the case of vintage B&O, the best answer to any query is to ask Martin!

Peter

hoangduongo
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Hello,

After fixing the stuck button, now I have another problem with the same MCP.

The can control my Beomaster 5500 without issue, however it won't shutdown after that, i.e. the indicators stayed blinking.

If I remove the power then apply again, the LEDs won't light up but the controller still consumes approx. 60mA from my bench PSU. If there is any other indicator, the consumption increase accordingly.

Now need your suggestions again.

Thanks alot.

Adn
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Adn replied on Thu, Jul 16 2020 8:48 PM

Hello, sorry I know this is a very old post but you are probably still around here. Did you by any chance managed to fix the problem of your mcp5500? I'm having the exact same problem where the display is constantly flashing and won't shut down, no matter if I put in a set of new fresh Duracell batteries or my lab power supply. I've already done all the tests included in the service manual and everything seems ok. Any help is appreciated.

 

Has anyone managed to solve this problem that seems common in this unit?

Thanks. 

Adrian.

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