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Master Control Panel 5500 Knob and Sensor

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Keri
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Keri Posted: Sun, Oct 25 2020 10:13 PM

Hello

My latest project is a Beomaster 5500 with the Master Control Panel 5500.

The MCP5500 uses a rotating knob to adjust things like Volume, Balance, etc.  The knob has a printed black and white pattern around the perimeter to indicate movement which is read by a reflective optical sensor. The direction of rotation is read by a momentary contact SPDT switch triggered by an arm which slides against the backside of the rotating knob.

On my example, everything possible was wrong with the knob. The plastic knob itself is cracked, the 16005 ball bearing on which the knob rotates was clogged with dirt and would not rotate and the reflective optical sensor, a Siemens SFH900-2 no longer functioned. At least the printed black and white strip didn't fall off, and was the only thing holding the knob together.

 

First thing was to restore function to the optical sensor. The Siemens SFH900 is no longer available, but is merely an infrared LED and a phototransistor combined into one compact part with the LED's cathode and the phototransistor's emitter tied together to a common pin. 

Many modern generic reflective optical senors are available. I chose a generic RPR-220  as the width is about correct and the leads are laid out so that if the cathode and emitter are joined together on one side, the anode and collector are available on the other side. A little creative bending of leads and it fits in place of the SFH900-2.  At first it refused to work, but positioning it 1mm further away from the knob coaxed it to life.

 

Next, removing and cleaning the 16005 bearing made it useable once more. I also obtained a spare bearing, having glued the original knob to the original bearing.

Next, out with some calipers and Fusion 360.  A few minutes later, I designed a new knob and 3D printed it. After a few tries I got a good one.  Then I arranged a series of black 9mm x 8mm rectangles into a strip and printed it onto a DYMO adhesive label, and attached it to the new knob.

 

 

 

And it all works!  Checking the electrolytic capacitors revealed correct capacitance on all but one, which I replaced.  The MCP 5500 is now working correctly and controls the Beomaster as expected. Now on to the Beomaster! And the Beocord... and the Beogram CD....

¡No entiendo Español!

NEIN! Nicht Versteh!

Я немного говорю по-русскии но не очень хорошо... и

I'm not very good at English either! Maybe someday I'll find a language I'm good at?

TWG
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TWG replied on Tue, Oct 27 2020 9:05 AM

Well done!

Dillen
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Dillen replied on Tue, Oct 27 2020 1:17 PM

Nice job, though the red ring looks out of place in my opinion.
I take it, you will be fitting a black one?

Perhaps not the best time to tell, that I have new original opto components in the drawer...

Martin

Keri
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Keri replied on Tue, Oct 27 2020 4:38 PM

Haha... now you tell me! About the optical sensor that is.

I have a black knob fitted now, but am altering the dimensions slightly to make the printing process more consistent.

 I am experimenting with different plastics and colors... so far my favorite is black PETG and the pictured

Prusa orange PETG .  I think PETG is the best choice so far. Maybe I’ll try clear next. I also have ABS and Polycarbonate in white, black and yellow.

 

 

too small for my 3D printer are the little plastic hinge gear things for the MCP lower cover. I successfully salvaged a set from my MCP5000.

 

can send out some knobs for evaluation if you’d like

 

Keri

¡No entiendo Español!

NEIN! Nicht Versteh!

Я немного говорю по-русскии но не очень хорошо... и

I'm not very good at English either! Maybe someday I'll find a language I'm good at?

Dillen
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Dillen replied on Tue, Oct 27 2020 5:27 PM

Thanks, that's very kind of you, but I don't need any knobs.

Martin

davidosborne436
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Nice job. I like the red!

I have one of these. Question. The microswitch is ok but when i turn the volume circle nothing lights up. If i hit the status button all lights come on so I know they work. I'm assuming that leads to a questionable optical reader?

Dillen
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Dillen replied on Mon, Feb 22 2021 6:47 PM

Either a bad switch contact or a dead opto component.

The opto can be found here.

Martin 

davidosborne436
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Thanks. This is from the web site you linked me to...

If the MCP fails to light up when the wheel is rotated, the problem is often dirty switch contacts at the wheel (or bad batteries).

I have new batteries and when I check the microswitch it seems ok....uuum


Keri
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Keri replied on Tue, Feb 23 2021 4:10 AM

This knob is now on Thingiverse!

https://www.thingiverse.com/thing:4772637

¡No entiendo Español!

NEIN! Nicht Versteh!

Я немного говорю по-русскии но не очень хорошо... и

I'm not very good at English either! Maybe someday I'll find a language I'm good at?

Dillen
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Dillen replied on Tue, Feb 23 2021 9:54 AM

Did you check the switch contacts with an ohmmeter?

Martin

davidosborne436
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i did. they seem fine. Any ideas would be greatly appreciated...

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