Hi Dillen and friends:

I have a BG 4002 that has developed a new problem.

When I press play, the arm will move to the play position, lower and then a few seconds later it will pop back up and return to rest position.

This appears to be an intermittent problem but now is happening much more frequently than before.

The turntable won't play from begining to end now. Sometimes it will play for several minutes and then all of a sudden the arm will pop up and return to rest.

Any ideas where/which part of the circuitry to examine for the fault? The sensor on the sliding ruler appears to be working as it is able to sense the pulses from patters. The switch on the one the sled sensing when the tone arm has lowered was also cleaned and is working.

Also do you know where I can get BC142 transistors? NTE has a cross but they are rather expensive.

Thanks,

Derek

Derek,

Check the power supply.
When it's playing, is the carriage tracking fine ?

I've seen tantals in these decks start to fail more frequent recently, so a cap fault can't be ruled out.

BC142 - use BC141 instead, it's commonly available. Or at least I have some
if everything else fails.

Martin

Pretty much similar to what my BG6000 did when I got it. At first the stops were seemingly random.

Then I replaced all electrolytic (including tantals) caps from the control circuitry, and the stops got much more regular: either right after start, or when the arm reached the 45 rpm landing zone (wide black stripe) while playing.

I never found the real reason, but got away of the problem after I modified the position sensor circuitry so that it needed more pulse energy to detect an edge on the ruler (one cap and one resistor, can't remember the details...). My theory was that the light sensor was somehow defective, and started to see non-existent light when it was actually in the dark. The rest of the circuitry was working just as it was supposed to; because of the random pulses from the sensor, it accumulated the "run-off" signal and presumed the record was over...

Hi Martin:

Thanks for the quick reply. Let me replace the tantalums. I've replaced all of the electrolytics a while back as you may recall.

What about the flim capacitors? Are they stable?

The power supply seems fine.

Now that the problem has been come more regular I do notice some tracking error which is audible to my ears. Is the mistracking related to the Power Supply?

Thanks you,

Derek

Hi Derek,

I never had a problem with the film caps. But, ALL tantalums and electrolytics on mine were replaced as a matter of first-course.

Because most of them were 4.7uF and lower, I used Wima MKS2 film caps, instead of electrolytics.

Also, check the 1N400x on the underside of the board next to the solenoid - it may be failing at full current. I replaced mine with a UF4007. 

I also replaced the 6 potentiometers on the right side of the PCB with Piher 10mm units.

Never had any problems return after these changes.

Menahem

As always, Thanks Menahem.

Hope you are well.

Derek

Dillen:

Mistracking problem is fixed. It was a seperate and unrelated problem to the arm popping up. One of the drive transistors was weak. After replacement the deck plays fine now.

The problem still remains with the arm popping up at the beginning and around the 45 record diameter location. I've changed all the tantalum capacitors as well as well as checking the transistors in the circuitry.

How likely is it that the photo sensor is going bad? It appears to be a standard photo resistor. Do you know the specs on it, perhaps I can try a replacement?

Thanks,

Derek

Hi:

If anyone has been following this thread with interst, I've found a solution to this problem.

After consulting with Menahem and Mika, who have both delt with variations of the same problem we've determined that the cause is sensor failure. (For further information read in archives a similar thread between Mika and Menahem).

RPY 58 is the photo resistor that has degraded. It appears to see spurious light even in darkness.  This part is difficult to find but I have an elegant solution that requires no parts at all.

The original part was manufactured by Valvo of Hamburg, a division then of Phillips.

Unlike CDS photo resistors available today, RPY 58 has photo sensitive material on both sides. The solution then is to take apart the sensor assembly and flip the cell around (ie back now faces light source).

I've been running the deck several times during the long weekend here in the US and the arm has performed flawlessly.

Thanks again to all who contributed advice and responded to this thread.

Derek

Now that was clever!

I'll need to try the same trick on mine when I have the deck open the next time.

Derek is our premier outside-of-the-box thinker.

Absolutely well done!

I never saw this sensor fault myself but I'll definitely keep this clever fix in mind.

Martin

auric:

. The solution then is to take apart the sensor assembly and flip the cell around (ie back now faces light source).

Genius!