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Beogram 4002 servo issues

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ALF
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ALF posted on Mon, Sep 13 2021 1:43 PM

Hi,

just working on a BG4002 and noticed the servo does not engage when the tonearm is lowered.

all other carriage functions work well though.

with the tonearm lowered there is no reaction from the carriage motor when I move the arm “by hand”.

the bulb of the servo opto is ok, which would suggest either the LDR (0R1) is faulty or 1D26 ?

what kind of voltage range should I see at P4 pin 8 ?

if indeed the LDR is faulty could anyone suggest a replacement ??

very much appreciate your input.

thanks, ALF

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Mark
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Mark replied on Mon, Sep 13 2021 4:47 PM

I don’t have a source for the LDR, but since the bulb is fine, have you confirmed that the shutter is not way out. I have run into this in the past where the bracket has been physically shifted to the point where the shutter never engages.

avensis18
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Hi, i had the same problem also check if the shutter is not broken.

avensis18
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Hi, i had the same problem also check if the shutter is not broken.

ALF
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ALF replied on Tue, Sep 14 2021 2:48 AM

Hi Mark / Alensis18

thank you for replying - the shutter works as it should, no trouble there.

i still want to check 1D26 to make sure it is not blocking any “supply” for 1TR19 / 20 in the H-bridge.

if it turns out to be a faulty LDR in the servo opto than I am really stuck, unless……

i may have to contact Martin to see if he has a replacement ???!

regards

ALF

ALF
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ALF replied on Tue, Sep 14 2021 2:48 AM

Hi Mark / Alensis18

thank you for replying - the shutter works as it should, no trouble there.

i still want to check 1D26 to make sure it is not blocking any “supply” for 1TR19 / 20 in the H-bridge.

if it turns out to be a faulty LDR in the servo opto than I am really stuck, unless……

i may have to contact Martin to see if he has a replacement ???!

regards

ALF

Mark
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Mark replied on Tue, Sep 14 2021 8:37 PM

This is like the speed selection relay or the control pots. Best to replace both of them with a relay pcb kit from eBay and 5k 10-turn pots. 

ALF
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ALF replied on Wed, Sep 15 2021 2:08 AM

Hello Jordan48,

unfortunately your problem is not related to my issue but for your main platter drive and not the carriage drive !

but i see you had already some good pointers to help with your issue.

regards

ALF

ALF
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ALF replied on Wed, Sep 15 2021 1:30 PM

Hi All,,

good news at last after a bumpy ride:

the servo engages again 🙏🏼

intermittent fault of the lightbulb (happened unnoticed) pointed the finger to the LDR.

rechecked the LDR and its resistance at no and strong light showed about 0.6 MOhm and 5-6 kOhm…so, it was working.

next changed the bulb and the carriage was racing…..that pointed to alignment of the shutter, which was way out…..realigned…..all working 👍

thanks for your interest - good outcome

ALF

 

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