Beogram 4002 - No Detector Or Solenoid Function

jacope

Gold

64 posts

Posted June 24, 2025 at 22:05 GMT

Hi all, I have a BG4002 (5523) that has two major issues:

The detector arm does not function. I have confirmed the bulb works but does not turn on when pressing START. It is not being sent more than a few mv from the mainboard.
The solenoid does not trigger with the up/down button (not sure if it would trigger from the detector arm). I have confirmed the switches are clean and are making contact. Lift/drop mechanism has been cleaned and lubricated, and solenoid triggers when I short IC4.

I have been pouring over the schematics but I don't have a good enough idea on what I'm looking at to solve. I have tested a few relevant resistors and transistors including IC4, but I don't want to keep prodding at random things. I've also reflowed most of the solder points looking for broken joints, and I have not been able to find any cracked leads. Any help would be incredibly helpful. Thanks!

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Mark-sf

Bronze

592 posts

Posted June 25, 2025 at 05:25 GMT

#715399

You may have an issue with the 22v DC supply that feeds both circuits. Lowering the arm with the cuing control does not need the lamp working. Check that you have 22.8V on the high side of 1R42 and 12v on the collector of 1TR11 when the table is on and the arm is stopped before the record. If this table has not had a capacitor replacement, it is long overdue and where I would start. You can get a service kit for your model

jacope

Gold

64 posts

Posted June 25, 2025 at 20:06 GMT

#715412

I have replaced the caps, sorry for not mentioning. No difference after replacing. On R42 I am getting 18.57v on one end, and 18.31v on the other. On Tr11 C I am only getting 0.643v dc. I have a working BG4004 to test against and the readings for R42 and TR11 are very similar.

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jacope

Gold

64 posts

Posted June 25, 2025 at 20:53 GMT

#715415

One area i have noticed a difference between the two is working my way back from the detector arm. 1R36 should have 21v on the high end and 9v on the low end. This is true for the working 4004, but on the 4002 I'm getting 21 on the high and 20 on the low. I checked TR5 and it seems to be good.

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Mark-sf

Bronze

592 posts

Posted June 25, 2025 at 21:48 GMT

#715417

First, if you are only getting 18v then there is still a power supply problem. I would work backwards to see where the voltage drop is occurring. You could still have a bad cap or transistor. As to 1R36, you may have a bad Zener diode, 1D17.

jacope

Gold

64 posts

Posted June 26, 2025 at 16:25 GMT

#715435

Found the culprit - a bad 1D16 diode. Both the detector arm and solenoid are now functioning correctly. Would you mind telling me how this diode affects both circuits?

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Mark-sf

Bronze

592 posts

Posted June 26, 2025 at 21:36 GMT

#715440

1D16 is a Zener diode that is supposed to set the base voltage of 1TR5 which turns on the lamp in the detector arm. If it shorts it not only will not keep the lamp off but will pull down the 22V rail that will impact other circuits such as the solenoid driver. Glad you got it working again.

jacope

Gold

64 posts

Posted June 27, 2025 at 16:34 GMT

#715446

That makes sense! Of course one more problem found - the up/down button will lower the tonearm, but will not raise it. Pressing any of the other buttons will raise it if it is down, but not the up/down button. Back to the schematics

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jacope

Gold

64 posts

Posted July 4, 2025 at 16:31 GMT

#715495

No luck so far, my working one reads 17v momentarily when arm is manually lifted at 1R64 (as per service manual), but the not working unit does not receive this pulse. Still playing with it but any input would be great!

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Mark-sf

Bronze

592 posts

Posted July 6, 2025 at 01:03 GMT

#715514

I would focus on the components around the 1TR14 portion of the electronic switch and I would also reflow solder connections in that area.

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