Hi all,

The PhotoResistor on my BG6000 is not operating correctly.

I opened up the assembly, and the installed component appears to be a non-original Motorola substitute part (appears to be 2N5779 PhotoDarlington), as it has 3 leads, but only the Collector and Emitter are being used, and the Base has been cut off.

Cutting off leads is definitely not B&O's style!

In the Service Manual, it is listed as part # 5210005, RPY58, on PC board 8009032.

I couldn't find any datasheets for RPY58 on the net, but I found some spec sheets, which don't help much, other than showing that Philips and RTC made them once long ago.

Is there anyone who can shed some light on this particular RPY58 part, and which of today's current production units are a suitable substitute for it? 

Regards

Menahem Yachad

yachadm:

I opened up the assembly, and the installed component appears to be a non-original Motorola substitute part (appears to be 2N5779 PhotoDarlington), as it has 3 leads, but only the Collector and Emitter are being used, and the Base has been cut off.

Cutting off leads is definitely not B&O's style!

Well, it was the 70s, and the innards weren't always quite as stylish as the outside...

It's common practice to leave the base of photoresistors (or the receiving part of optoisolators) disconnected, if they aren't needed. They are only used if the transistor needs to be biased at a certain point.

According to my books also, RPYwhatever really are photoresistors, not transistors. I'd try with any generic phototransistor, I'm sure the RPY58 will be hard if not impossible to find, and it's possible that it was replaced already during the production.

Thanks Mika!

Can you give me some Manufacturer part numbers to look for? 

Thanks

M Y

I'm at the summer house behind a lousy connection and away from my data books now, but some types that I can remember offhand are TPS622 and SFH 300-3. The latter is in a LED-like case and probably awkward to install in this sideways looking application. You were talking about the sensor at the "ruler" / carriage position encoder, right?

Both are cheap. And I'm pretty sure you will have to modify the lighting and/or the photo signal amplifier stage as well, as you will probably get a stronger signal from a modern phototransistor. I've been thinking about this myself too, since my BG6000 still gets confused at the 45 rpm landing zone maybe every 20th time and decides to end playing. I have a theory that the sensor leaks too much in the dark.

Hi Mika,

Looks like we're on the same "wavelength" here!   Isn't it a bit early yet for summer in Finland?  

You're absolutely correct - it is the sliderule / carriage sensor. 

Like yours, that was a similar problem with mine - the arm would not recognize the 45 position. I did try the normal repair, which is to adjust the incandescent light to a straighter angle, but there was no improvement.

So, I assumed that there is a problem with light quantity. I replaced the weak incandescent light with a bright white LED. It was a very simple mod, with the addition of one resistor only. See picture.

So, the problem of the 45 position was fixed.  

Now, once in a while, when I press START, the arm goes to the edge of the LP, but instead of lowering to the LP, it reverses direction, and returns to rest. This is the only problem remaining.

(I can get around the problem by pressing START, then immediately <, then, when the tonearm is over the LP, press V )

OK, so I've looked at the specs of the TPS622 - looks like I can pull one out of a broken Opti-mouse.

But the datasheet says that it will work optimally with an infra-red LED (probably for a peak sensitivity wavelength of about 800-900nm. I have a bright white LED installed - White light is operative at all wavelengths. What's your opinion? 

If we use an LED light and TPS622 type sensor, would we still need to mod the amplifier stage?

Menahem

yachadm:

Looks like we're on the same "wavelength" here!   Isn't it a bit early yet for summer in Finland?  

The typical holiday season over here is in July, but it was 28°C on Thursday and Friday, so I left work a little early

You're right about TPS622, I forgot it was infrared although it would probably respond to long end of red also. The white LEDs usually have a couple of peak wavelengths and only seem white to the eye, so the TPS might not "see" it.

But, I have an idea - steal the LED from the same mouse! They would obviously work together. This might have the added advantage that the IR system would be more immune to ambient light. TPS622 also has very narrow directional response, so it wouldn't care much about light from other directions. Sacrificing a single poor mouse you'd have optical pairs for fixing four Beograms!  In most modern mice the optoencoders unfortunately are a single component, so they might not work as donors.

I can't remember how the sensor amplifier was constructed, but it might work just as is after you find a suitable current level for the LED.