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Beogram 4000 carriage control issues

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ALF
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ALF Posted: Mon, Mar 29 2021 10:33 AM

Hi All,

i am sitting over my Beogram 4000 trying to figure out the carriage control issues:

just replaced all TO93 transistors in the H-bridge of the motor control circuit - all had issues and the carriage wasn't moving at all.

Just wondering how critical it actually is to perfectly match those transistors TR31/30/29/28 ??

transistor TR29 should be a BC144 as per SM, however I only had a BC142 at hand ?!

the carriage moves again but is showing some strange behaviour.

When it is moving out to its resting position the BG turns off but the carriage immediately moves back, travelling in, just enough to turn on the BG again ??

In other words, as it stands I can only turn off the BG by unplugging it from the mains. It almost appears as it would get another Start-up Impulse ?? But how ?

Could someone explain or provide me with a pointer ??

thank you kindly

ALF

ALF
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ALF replied on Tue, Mar 30 2021 7:20 AM

Ok,

As one should in a next step, I tried to verify the 6V and 24V supplies are present !

on the main board #1 I have 6V present but the 24V are infact 32V, depending on status ON, arm not lowered or OFF ??

the 24V supply is nowhere to be found: not at C of 2TR7, not at E of 0TR1, not at the SO switch on board and not at 2MS1 (reed relay) on board 2 ???

but isn't 0TR1 generating the 24V for the reed relays ? If so, either 0D1 or 0TR1 must be faulty ?

does that sound correct ?

thank you once again for your inputs

ALF

ALF
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ALF replied on Wed, Mar 31 2021 1:28 PM

Well, another session with testing components:

0TR1 tested fine and so did all the other transistors from the Power supply board #2

the carriage goes back to its ES but : the BG does not completely turn off - 3IL3/4 are still on !!!

as described earlier, when the carriage reaches ES it immediately travels back in a very short distance (about 1cm)

there should also be a 24V point at one of the Reed relays ? I measured their coil resistance, showing about 293 ohm.

i haven't checked their glass-tubes yet, however the outer glass tube from 2MS1 showed a constant 'OL' when I measured continuity,

meaning its contacts are open.

so, a couple more issues to further investigate......

anyone in a position to help ?

thanks, ALF

 

Dillen
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Dillen replied on Wed, Mar 31 2021 2:17 PM

A shorted Reed-relay element?

Martin

ALF
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ALF replied on Fri, Apr 2 2021 2:58 AM

Yes, thank you Martin - that's a possibility !

I ordered a set of the reed glasstube switches as the ohm measurements in ON/Off state are inconclusive.

Good lead to follow up.

ALF

ALF
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ALF replied on Fri, Apr 16 2021 10:11 AM

Hi All,

apologies for the long delay but thanks to the corona crisis postal services are slower than a snail's pace.

the new glass reed switches finally arrived and were installed in one of the reed relays. That itself wasn't a big issues, however during

the "surgery" one of the micro-thin coil wires detached itself from its post 😡

so, after micro-surgery I managed to reattach that wire, checked the coil resistance to be sure contact had been established...yes !

time for a test run: nothing....dead !

after checking the fuse box it turned out firstly two wrongly rated fuses were installed and one fuse died - easy fix, fitting the correct fuses and.....

turned on the Beogram and all seem to work again 🙏🤩

the carriage moves in and out, the arm lowers at the drop down point and carriage moves out to its resting point and unlike before the Beogram

Now switched off again.

isn't it nice when everything works again, be it only for a while 😁 until the next drama unfolds.

Interested parties will know how complex that table is and the serious headaches it can inflict.

i am signing off for now - thank you Martin and all other interested followers.

ALF

PS: don't damage those reed relays !!

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