Beogram4000 carriage issues

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ALF Posted: Mon, Jan 18 2021 12:12 PM

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Hi All,

i hit a roadblock working on a BG4000 where the carriage doesn't move at all incl the automatic slide transport in !?

the platter spins when ON is activated

the OM2 motor is fine, SI is present, ES, OFF, Q1, R, FF and L are all high at 3 IC9 and 3IC0.

3C12 and 13 both show about 47nF instead of 33nF.

i was unable to reproduce the 0V across the OM2 when ON and Lift is activated as per circuit diagram but get about 500mV on both sides.

i also checked all brass contact switches - all were carefully sanded to avoid mal-contact due to corrosion.

where to from here ?

a helping hand would be greatly aporeciated - thank you

alf

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Spassmaker replied on Mon, Jan 18 2021 1:48 PM

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Hi Alf

My suggestion would be to not search on the Terminal PCB.

The last BG 4000 which was not moving the tonearm at all had trouble in the motor drivers bridge.

have a closer look to:

TR 25 to TR 29 and

TR 30 to TR 34

Often one of them is shot. Best way is to take them out because they are connected as a darlington.

Good luck and best regards

Christian

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ALF replied on Mon, Jan 18 2021 2:55 PM

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hi Christian,

thanks for taking the time to reply......yes, the motor-control section was indeed my next step!

however, I was hoping to bypass that one as those can-transistors are hard to come by - I had my fair share of chinese fakes !

i am with you in almost ruling out the keypad boards as these logic ICs are fairly reliable and unlikely to fail ?!

looks like the work for tomorrow is mapped out for me and I shall get back with the findings.

regards

alf

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Spassmaker replied on Mon, Jan 18 2021 6:38 PM

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BC 141 and BC 161 will work as well as the originals.

I bought them in the big auction house...

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Spassmaker replied on Mon, Jan 18 2021 6:38 PM

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doublepost

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ALF replied on Tue, Jan 19 2021 1:20 AM

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Ok, that's good to know - taken on board !

on the menue: testing this morning 😁

alf

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ALF replied on Tue, Jan 19 2021 3:52 AM

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Hi christian and all interested guys,

good news, after testing all 10 transistors from the motor control circuit off-board I had to replace 3 almost-dead ones.

the carriage with all its functions works fine again 🤙🤗

regards

alf

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Spassmaker replied on Tue, Jan 19 2021 6:53 AM

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Hi Alf

Congrats to your success. Enjoy the music

Kind regards

Christian