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Beogram 8000 main drive issues

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ALF
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ALF posted on Mon, Jun 18 2018 2:30 AM

greetings all,

again, my BG8000 is playing up ๐Ÿ˜ก

it started with a sudden dramatic platter speed increase basically out of control and so far ended with a reverse spinning platter after the turn-off ??

the drive behaves irratic - like stuttering -  when start is activated!

would it be fair to suspect a fault in the brake circuit ?

help/advice urgently needed

thank you

ALF

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Lonnie
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Lonnie replied on Wed, Jul 18 2018 12:30 AM

Hi ALF,

I would've been very surprised if you did have a current probe.

It's still an interesting measurement. I presume the light blue trace is P4-2, anyway it shows that the brake is being activated.

Regards

Lonnie

sonavor
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Yes that is interesting to see the waveforms at the two connector pins. I am still puzzled by your test where you lifted 1R108 to disconnect the microcomputer pin 37. You reported

"...deck does not power-off (servo light bulb still on) and the platter motor still shows some very gentle stuttering clockwise".

I would have expected the Beogram to start up in Standby mode and stay there. I wonder if this is another symptom of what is wrong with your Beogram. Again, sorry I can't try the same test here to compare but maybe Lonnie is in a position to test it on his. 

ALF
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sorry, but every little bit is as described Erm..

here are two better pics of P4-1 / P4-2 - blue line = pin2. yellow line = pin 1

first pic is during PLAY mode, second pic is at STBY/STOP


ALF
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this is the second pic STBY/STOP mode


ALF
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ALF replied on Wed, Jul 18 2018 8:07 AM

Hi Lonnie,

perhaps a side issue, but measuring 0S1 in open position should not deliver a finite ohm reading but should rather show OL on the DMM ?

i do not understand why this is not showing !

ALF

sonavor
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Measuring across the open switch in this case is measuring into the Beogram. The impedance is whatever the attached circuit is where you are measuring. It won't necessarily be OL as you would get with the DMM leads measuring across an open switch no connected to a circuit.

Lonnie
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Lonnie replied on Wed, Jul 18 2018 8:58 AM

Hi ALF,

John's explanation is correct, you'd have to take the switch out of circuit and re-measure it to see an open reading.

You previously gave readings at P6-10 to confirm the voltage when the switch was open and when it was closed. Those voltages were fine so the switch is operating as it should.

I'd be interested for you to measure the voltages around 1TR6 which controls the LED in the tonearm. What are CBE voltages during Stby and Play? I'd like to know if the uC is biasing 1TR6 on the whole time.

My daughter has custody of the TT in her room and she loves it! However, I'll try and pry it away from her and take some further measurements over the week-end.

Regards

Lonnie

ALF
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ALF replied on Wed, Jul 18 2018 9:36 AM

Yes, of course, John is absolutely right !...I should have known that....just brainless fishing for a cheap answer or desperation ? ๐Ÿ™„

i will take the measurements around/at TR6 and report back.

good luck with the daughter......’s TT I mean ๐Ÿ˜

ALF

ALF
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ALF replied on Wed, Jul 18 2018 10:03 AM

Hi Lonnie,

did measure at TR6:

                      C                             B                   E

STBY.    45mV to 595mV.          5.05 V.          5.07 V

PLAY.    10mV to 695mV.          4.98 V.            5 V

what was interesting is both modes at C the voltage steadily climbed up to a max and fell again?!

ALF

Dillen
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Dillen replied on Wed, Jul 18 2018 12:02 PM

These voltages should see the LED off in both stby and play.
I lean more and more towards a broken PCB track, perhaps a missing ground somewhere.
When you measure these voltages, where are your ground lead connected?

Martin

Lonnie
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Lonnie replied on Wed, Jul 18 2018 12:15 PM

Hi ALF,

Was the LED in the tonearm on during both measurements?

Assuming it is, then 1TR6 is not being biased on properly and the only way for the LED to be on is for 1TR6 to be faulty. I'd pull it and test it.

Regards

Lonnie

ALF
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ALF replied on Wed, Jul 18 2018 1:48 PM

Are we talking about the transport indicator arm LED ?

if YES, this LED only comes on at << or >> or 2xPlay flashing.....not during this particular meaurment !

i measured twice with ground from chassis and ground at minus of C27......in both cases the outcome is the same.

ALF

ALF
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ALF replied on Wed, Jul 18 2018 1:53 PM

Hi Lonnie,

just answerd that....if we are talking about the transport indicator LED then the answer is no in both modes!

what is however on all the time is the bulb in the photo control part as power won’t be properly turned off.

i will test TR6 tomorrow, its getting late ๐Ÿ˜ด

ALF

Dillen
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Dillen replied on Wed, Jul 18 2018 5:05 PM

TR6 is fine.

Martin

Lonnie
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Lonnie replied on Wed, Jul 18 2018 11:15 PM

Hi ALF, 

Sorry, I thought you were indicating that the LED in the arm was on all the time. Re-reading you post you clearly say servo bulb.

As Dillen indicated 1TR6 is fine so no need to remove and check.

Regards

Lonnie

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