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 all,
again, my BG8000 is playing up đĄ
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
Sound like an opto fault.Replace the tacho IR sender LED.
Martin
Thanks Martin,
i presume you are talking about the bottom part of the speed sensor ?!
would a OP240C work and if Yes, wouldn’t I have to replace both partnering the Sender LED?
again thank you for your advice
OP240A, if I remember correctly, is what I use.There is only one sender LED. The top one is the receiver and I never saw one of them go bad yet, whereas I have replaced many senders.
Interesting exercise replacing the sender LED in the speed sensor.....but
yes, its a but.......the BG simply won’t shut down.
the moment I plug it in the platter spins madly - I can operate play...the carriage does everything right
arm lowers where it should, activating stop brings it back to its resting position however the platter keeps spinning
and the servo bulb remains on ??
well, back to the drawing board and studying the technical product info.....
does not look like just a break issue but on/off as well đĄ
shall I wish Denmark best of luck in their âŊī¸âŊī¸ encounter against AUS ??
Martin, are you listening ?đ
Hi everyone,
after further investigation the platter still spins out of control after connecting the table to the mains voltage.
activating PLAY and all moves into position etc except the platter, spinning madly - in this case
according to the drive system preamp the gate at TR26 should go positive but shows -9 VDC ?
Going negative means the platter spins too slow .....which is not the case !
that is one issue !!
the other issue is the table is not completely shutting done after STOP is activated ??
servo light remains on at end position and platter keeps spinning anti clockwise ?
reactivate PLAY the arm moves in position, platter spinning anti clockwise.....
i can break down the platter by hand and it starts spinning correctly.....well, until it goes mad again.
am I wrong barking at the Brake Circuit ???
your thoughts ?
Next step in the investigation:
looking at the Brake Circuit again....
at record play-out stop the base of 1TR31 should see a low level...checking 2IC1 Pin 37 voltage at stop
goes from 5V down to 0.7V but the base of 1TR31 never sees that low level...why ??
instead base of 1TR31 goes down to 4.4V and platter spins anti clockwise....great đĄ
back to work....
Seems like everyone is on holidays or at the world cup ?
well, no curther progress I am afraid and it is indeed very hairy to describe a such irratic behaving machine accurately !
my money is still on the drive / brake circuit !
0TR2/3 are new, 1TR29 & 30 tested fine, still under suspicion is 1TR26 and 1TR 27/28/31 all tested fine and 1TR33 is new.
That puts 1TR21 ON/OFF also in the frame as the table does not entirely switches off ?!
i do not neccessarily suspect the uP
as always, comments and ideas are most welcome - don’t be shy đ
If your deck has the extra 4013 IC in the feedback circuit on the piggyback-board in the processor housing, check that IC.
My deck hasn’t got that piggyback- board nor the 4013 IC đ
having a superfast spinning platter is one thing but theother issue is
that the deck does not shut off as well as explained previously
Are you referring to the IC in the processor box ?
if Yes, my deck does not have that piggy-pack board.
if you referring to the sender LED in the speed sensor I did replace that with the OP240C to be on the safe side....!
Check 0TR1 on the subchassis.I have seen it go leaky, not closing the 15V supply completely in standby.
Check with a scope that the signal from the tacho-opto reaches the CPU and that the signal a well defined at a reasonable level.
0TR1 = TIP 32 was indeed gone at hfe=7.
was replaced - new one with hfe=157 !!
photo transistor in the speed sensor assembly was replaced with OP550A.
signal at P6 Pin2 shows a clean straight skirting signal at about 3.1VDC
but ...... the deck still does not turn off ??? Instead when the carriage reached its resting postion the platter starts spinning anti-clockwise ?.
really not idea what else to check đĄđĄ
Usually it's not the phototransistor that fails, but the IR sender LED.How high (voltage) are the low parts of the signal from the opto?They should be fairly close to ground.
Had another look at the signal coming in at P6 Pin 2:
bottom is about 80mV, top about 3.1V
if that is what you were referring to ?!
still spinning in reverse after carriage final stop?
Check if the reverse running comes as a command from the CPU on one or both of the brake outputs.Did you replace any diodes in this deck?You have the platter on - right?
No diodes have been changed but testedthe ones involved in the drive and break circuit.
however I noticed 1D40 was a 4004 type instead of a SFD184 or 1N 4148 type as the SM listed?!
it made no difference running the deck with or without the main platter, both spin anticlockwise after STOP is activated.
when STOP is activated I should see a voltage change at P6 Pin10 but the voltage temains steady at around 65mV ??
i am having difficulty identifying the break outputs here.....are we looking at P4-2 and P4-1 ?
Four lines control the platter rotation; Fast up, Fast down, Slow up and Slow down..
‘Fast Down’ should apply a low level to the base of TR31 - checking P6-5 I get around 5VDC when platter is spinning at 33rpm clockwise.
the moment stop is reached the voltage drops down briefly to about 0.7VDC but quickly oscillates then between 0.7 and 4.9VDC ?
checking P6-7 ‘Fast Up’ at 33 rpm spinning clockwise is around 130mV, at stop oscillating up to 5VDC.
checking P6-6. ‘Slow Up’ at 33 rpm spinning clockwise is oscillating between 200 - 280 mV, at stop around almost steady on 140mV
checking P6-8. ‘Slow Down’ at 33 rpm spinning clockwise is about 4.8VDC, at stop about 4.9VDC steady.
the platter is not always spinning fast anti clockwise after STOP but can also almost stop spinning with a visible stuttter clockwise after STOP ?
sorry, got lost here.....?!
Does the 15V supply (the transistor you replaced on the subchassis) close properly in standby?
These are the voltages I an getting at 0TR1:
platter spinning at 33rpm
E = 23.5 V. C = 15.1V. B = 22.8 V
STOP / Standby
E = 23.4 V. C = 15.1 V. B = 22.6 V
meaning nothing changes after STOP / Standby ??
So it doesn't close.Check the power on/off circuit.Start at the CPU pin 38.
Ok,
Pin38 on/off. Checking P6-4:
spinning at 33rpm clockwise voltage is oscillating between -1.6 to -1.8
STOP is reached voltage goes down very briefly to -0.6V but quickly back to to previous level.
checking 1TR19 collector voltage is -17.9 V , it should be -15V
checking 1IC3 pin5 voltage stays at around 1.6V
checking 1TR21:
with platter spinning clockwise
C = between -0.6 and -2.5V jumping
B = between 1.3 and -1.7V jumping
E = -10mV steady
SOP is reached
C = between -0.6 and -2.1 V jumping
B = between -0.5 and -1.6 V jumping
E = -3 mV steady
this is as far as I got .......do I miss the trees in the forrest ?
ALF: checking 1TR21: with platter spinning clockwise C = between -0.6 and -2.5V jumping B = between 1.3 and -1.7V jumping E = -10mV steady
More than about 0.6-0.7V on the base of a NPN transistor that has its emitter at ground, points to either a bad transistor or a wrong ground reference.
It's not uncommon to see copper traces break on these boards and it can be very difficult to spot, even using a microscope.Check all traces around 1TR21.
Did you replace the CPU socket or merely reflow its solder joints?
My apologies, Base values should read between -1.3 and - 1.7 V jumping and not +1.3V !!
again I tested 1TR21 and can not find anything wrong with it.
in the meantime checked the processor socket which turned out to be still the old white socket - that has now been replaced with
the gold plated contacts tulip style socket.
sadly that did not change things as they are đĄ
somewhere I red that kind of deck is easy to repair........đ
not entirely convinced though.
I shall re-visit and check all traces around 1TR21 again and perform some ohm-measurements to make sure
TR 21 is connected correctly.
I would like to rule out a fault in the SO switch as the carriage stops properly at its resting position
and exclude the TR21 itself as well.
There is always the uP.....but lets not paint a dooms-day scenario đ
why the 0TR1 is not closing is still unclear ?
will report back....in the meantime further comments are welcome at any time
Big thank you
It could still be a connection problem somewhere.If you are trying to troubleshoot with the Beogram components in the cabinet I recommend removing them as it is easier to get to measurement points. Check the black wire from the microcomputer board to P1-1 on the uC Control sub-board PC7 (8005060) that mounts to the main PCB. That jumper often breaks or is on the brink of breaking. Also check the main PCB connector that the Beogram control panel plugs into.
Here is my typical Beogram 800x test setup.
Thanks John,
that is how I have don it in the past - however my deck does not come with the PC7 board ?!
the SM listed 1IC1 as MLM324P, my board shows a LM324N instead....it has never been replaced!
i guess it is an early model in that production run....I have just checked all joints at the connectors again....no adverse findings here.
the uP socket as mentioned has been upgraded.
TR21 is properly connected to its surrounding components, but as Martin pointed out: if you can not see broken tracks even
with a microscope.....well ??
the question is whether I would have to fit that PC7 board ? But the deck has performed ok before without it until.....đĸ
right now this looks pretty dark.
I see. I agree, the Beogram should perform without that board then since that is how it originally came off the assembly line and, as you say, it was working earlier.This type of problem doesn't happen too often but I did have one of my Beogram 8002 turntables work great for a year then began acting up with intermittent behavior. I spent a couple of weeks trying to catch the problem but after determining the problem was somewhere on the main board I finally just swapped the board with a spare. No problems after that and I do intend to revisit the problem board one of these days. Too many projects to mess with it right now though.
From your earlier posts do I understand you correctly that as soon as you plug the Beogram into the wall outlet the platter begins turning? Is the display showing the Beogram in Standby mode when this happens?
If that is the case then I would start at the signal that drives the motor and trace back to its origin. I'm sure you already know this but just to remind you...You can unplug P4 from the main board to keep the platter motor from getting a drive signal while you check other functions of the Beogram. You could then trace from the P4 board connector and investigate why it is trying to turn the platter. The behaviour kind of sounds like the Turn button is stuck on. Do the 33 and 45 buttons work when this is going on?
Quick recap:
the moment The deck gets connected to the wall outlet the platter starts spinning anticlockwise and the Standby dot is shown on the display.
sub-platter in place, activating PLAY moves the carriage right across ( unless interrupted with << or >> ) but does not stop at the drop down point
to lower the arm , (that happens without the top platter !! But with the top platter on I can understand that as there is no record to detect)
while the platter is still spinning anticlockwise.
I can brake the platter by hand and it will spin clockwise at the correct speed shown on the display.
if the TURN mode is constantly active the uP then obviously does not get a reset to get back on default mode,
but does that explain the anti clockwise fast spinning ?? It simply does not power-off even with the carriage at its resting position.
I shall check what is going on at P4 with P4 unplugged ?
Interesting. I vaguely remember that condition on one Beogram 8002 I had a few years ago but the issue went away once the restoration was complete. I know that doesn't help solve your problem but I can confirm I have seen that before...so I believe what your are reporting .To expand on that start up with the reverse spinning....If you brake it by hand and stop the reverse turning, does it stay stopped when you remove your hand brake?
Also, you did say after hand braking that the platter will start turning in the correct direction, right?
Other than the tangential arm assembly not detecting the set down point does it successfully detect the limit of its travel and return to the standby position?
I am not able to put one of my Beogram 800x turntables on the bench to make some comparison measurements for you right now as my work benches are currently full. The next time I get a chance I will measure the P4 signals connected and disconnected on a working Beogram 800x. Don't hold your breath though...I have at least a month's backlog on the workbench right now before I can check a Beogram 800x turntable.
the detection and returning carriage issue was the failing opto at the spindle end - that is now solved....arm lowers at drop point and carriage returns
at record end to its resting position after the IR sender and photo transistors in the opto had been replaced.......one win đđ
when STOP is reached the platter spins keeps spinning fast anti-clockwise and even the “handbrake” attempt fails.
when PLAY is activated the carriage moves correctly, platter spins anti- clockwise but spins clockwise at the correct speed after a “handbrake” attempt.
i must stress again that the deck does not shut down completely with the servo bulb still on and platter spinning in the wrong direction !!!
that is where the deck stands right now.......đĄ
now that the carriage issues been rectified I will revisit P4 - plugged in and unplugged - ti see what is going on there.
You said earlier that you verified the SO switch was working. If that is the case and the Beogram is not recognizing that then that is a key thing to investigate. You need to determine why the "Stop" is not working.
Looking at the circuit diagram,
0S1 should have a close to zero ohm reading when closed, and should show OL on the DMM when its open, or did I get this wrong?
fact is, when its closed it shows about 0.8Ohm, and open it shows about 475Ohm....happy to check again, but that is what The ohm measurement
between P2-1 and P2-3 is !
Those sound reasonable. I haven't measured the open switch resistance but you will be measuring whatever it is looking into the Beogram at that point. For the closed switch measurement you can get 0.8 ohms depending on how good the contact with the DMM probes are. The SO switch is read by the uC (2IC1 on pin 32). You monitored what the value of that input is for both positions of the SO switch, right? The Beogram either has the tonearm parked in the off position where the platter should not be turning (unless you press the Turn button) or it is in Play mode where the platter should always be turning (at either 33 or 45 RPM). So your problem must be somewhere in the bottom section of the schematic which is the Tangential Drive circuitry (including the Brake) and the control lines from the uC (2IC1) that are inputs to 1IC3 (Slow Down, Slow up, Fast Up, Fast Down). There are also voltages from the transformer involved including the 39uF bi-polar capacitor. Something in those areas must be causing the problem.
In the lower part of the CD - power on/off, driver and brake - I have practically tested all suspecious components....all ok !
looking at the voltages that come from the transformer i can see all but no clear signals on the scope âšī¸
Having checked the AC voltages supplied via tabs b, c and d on the transformer tabs !
i wonder if those were bad enough to cause the problem with only one decent clear sine wave signal at tab d if I recall correctly ?!
testing all involved transistors and diodes on the main board leaves not a lot options đĸ
It's too hard to accurately diagnose a problem remotely but I would still say if the controls put the Beogram in Standby and the processor thinks it is off (the red standby dot shows on the display) but the turntable still has a signal driving it then there has to be a voltage in the motor drive circuitry that is telling it to turn. Individual components may test okay but when in the circuit there could still be a problem. Often in this type of situation though, I eventually find a connection problem. Anything from a missing solder joint, broken solder joint or connector problem. I have had a couple of tough ones where I had looked at the board over and over and never noticed the problem. But it was there.
Regarding the 2IC1 uC though...Have you monitored and checked the Turntable Regulation table and verified the values. I think they should all be at 0 when the Beogram is in StandBy (and Turn is not pressed). Have you checked the 1IC3 OpAmp?
Call me overcautious, but when I desolder components I always try to replace those with new or better ones because of the heat stress.
with that in mind I have replaced 1TR21, 26, 27, 28, 33 a well as 1IC3.
further 0TR1, 2 & 3.
tested D31, 32, 33, 34, 35, 36, 37, 38, 39&40.
perhaps I am sitting on my brain, but I can not figure out how to interprete that regulation table in the SM 1-3 ?
certainly can measure Pin 34, 35, 36 and 37 but they all change depending on the deck’s action.
My understanding is when
Fast Speed Up occurs that is either a speed change from 33rpm to 45rpm or simply activate Play from the Stop position
Fast Speed Down when 45rpm to 33rpm or from play to Stop
Slow Speed up/down when the deck is correcting speed fluctuations ??
am I wrong here ?