ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
greetings,
I am still working on my BG8002.....not much more left to do except the damn servo won’t engage?
after replacing the dead bulb IL2 - not the easiest job !!! - the bulb is now working again, however the servo still will not engage?l
the adjustment procedure acc to the SM 5-3 brought no change, so the next suspect seems the LDR?
once the arm is lowered I can move it freely left to right and measure 4.8V at P3-1 and
between 540mV - 1.2V at P3-5, depending on how far I move the arm
Are these measurements consistant with would should happen ? If yes then there must be something else
playing up ??
Anyone with any other suggestions ?
ALF
First answer: it was the LDR which caused the problem !
replaced and now I can actually adjust the sensitivity of the servo 🤓
good outcome I thought, notwithstanding the aweful fiddly job 😬
time to play some records !
Well, the pleasure of listening to the good old vinyl was shortened by speed fluctuations.....
I should add there is a metal tacho disc in service !
the keyboard display stays firm at 33.33rpm, does not flicker at all despite those speed variations but I can hear it.
looks like back to the drawing board.
anyone care to comment ?
Checked the speed sensor signal via P4-7 and 1IC1
Checked the speed sensor signal via P4-7 and 1IC1-14 with the osci.
both signals showed the same frequency range of 81-83.8 kHz, oscillation mainly around 82kHz.
that would rule out the speed sensor as the source.
checked the metal tacho disc....looks fine with the naked eye......from memory Martin’s metal disc looked more solid to me !
Does that point to an unstable power supply for the eddy coils/ platter drive ?
By hearing the speed change do you mean you hear the change in pitch in music source (vinyl record) playing or do you mean you hear the Beogram braking trying to adjust the platter's speed?
Run the Beogram with the turntable opened in the service position and the platter off so you can adjust the platter sensor position. See what happens when you vary the sensor position.
Regards,John
A leaking diode in the speed regulator circuit wouldn't be a first.
Martin
Hz of course, not kHz !!!
sorry
Hi John,
Yes, thats correct .... I can hear the pitch change and see the frequency variations via the osci when looking at the speed sensor signal
changing the speed sensor position does not change things worth mentioning.......
Martin suspects a leaking diode in the speed circuit ??!
finding that one will be fun 🙏
Looking at the circuit diagram:
Possible canidates are 1D36, 37 , 39 and 40 ?!
All those 4 diodes have been replaced - no change, still pitch fluctuations!
looking at 0TR2 and 0TR3 :
BD 441 had about hfe 348, BD 442 had about hfe 80 ?
I replaced the one with hfe 80.
according to their spec sheets both should have a typical hfe of around 140 ?!!
Those two should ideally be better matched, shouldn’t they ?!?
Again I checked both signals at 1IC1-12/14 and 1IC3-1 and revisit 1IC3-4/8 !!
So, as it stands I am really no wiser nor has there been any progress 😡
there must be some voltage/current fluctuations caused elsewhere impacting in the drive’s performance???
any suggestions or ideas would be most welcome 🤔
Update:
revisiting 1IC3 - 4/8 delivered
+14.98V and -14.4V............and that’s not right !
the big question: is it the mains transformer , 1IC3 or 1TR26 ?
Next step is checking if the integrator/1IC3 is malfunctioning and/or 1D33 ?!
Following the -15V trail:
the collector of 1TR19 showed about -14.3V, same at the anode side of 1D26.
that is the voltage reading I am getting at 1IC3-p4.
looks to me that 1TR19 has a problem ?!
sadly that is a PU 01 type, no longer available.......substitute a 2SC4135 or BD507 ?!
will keep you posted
ALF: looks to me that 1TR19 has a problem ?!
Why do you conclude that?
92PU01is no longer produced, but that doesn't mean that no more can be found.The two replacements you suggest are two very different transistors.ZTX751 would be a better choice, I think.- But why?
martin,
the conlusion comes from a reading of 1TR19-C of 14.3V, which is exactly what I see at the integrator/1IC3.
as for “my suggestion”:
on july 21, 2008 you replied to a post ‘Beogram 8002 transistors’
suggesting that 92PU01 can be replaced with .......2SC4135 or BD507 ?!
did I misunderstand that ?
as I could not find a suggested replacement elsewhere I took this at face value.
I will test that transistor in question off- board and see what the outcome is - just can not see
where else that voltage breaks down ?
can you ?
Wrong conclusion - 1TR19 is ok
would have been too easy....😫
is it really a leaking diode.... ????
back to the drawing board 😠
suggesetions are still most welcome
Unfortunately, correcting wrong or misleading info in the archived section is not possible.But the info is not THAT wrong, and the two types would possibly work, but the ZTX would be a much closer replacement.
14,3V doesn't sound all wrong,Where do you mean the voltage drops?What are the voltage readings on the three pins of the transistor in question?
A very skillful teaser HE is, sorry.....teacher I meant 🙄
Seems diode 1D33 was the culprit - after 4 records still no further pitch variations......🙏
for anything else is mastercard 🤑
Martin, You are right about that voltage !
can’t remember exactly what the readings were at T19 but from memory around 21.8V and 14.3V.
closed the BG already 😕
just can not explain where the voltage gap occurred, if you want to call it gap ?
acc to the SM 1IC3 - pin 4/8 should have +/- 15V.
Replacement of 1D33 seem to have cured it ! Isn’ that good news 🤗
thanks again for that valuable pointer - much appreciated.