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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
I did read that blog 🙄 before.....not much point trying that as my platter already spins anticlockwise in Standby 😕
are you implying that 1TR31 somehow may has its base connected to ground ?!?
again i had a look at P4-1,2 and 5:
P4-1 = 13.4VAC, supplied from P7-5and remains the same in StBy/Play
P4-2 = 26VAC, supplied from P7-12 / 4C1 and remsins the same in StBy/Play, which is also at 1D40 cathode,
while the anode side of D40=32VAC, influenced from P7-11 via TR31 ?!?
P4-5 = 0.040VAC in StBy
ALF
I am implying that the symptoms you have match what Beolover was doing intentionally. Beogram is in standby mode and the platter drives in reverse. That can occur due to the brake circuit. It could also occur with a microcomputer problem if the problem was that the microcomputer had the Beogram in standby mode and was sending a brake circuit command at the same time. I believe you checked that and that is not the case. So in order for the Beogram to operate in reverse I think the problem has to exist in that brake circuit. With the Beogram in standby start checking at the motor and see what voltages are there. Trace back from there to what is causing the problem. Have you gone through the transformer connections and the 39uF capacitor there?
A quick check of the microcomputer's role in the problem would be to disconnect the 2IC1 pin 37 connection at 1R108. That is where the brake stop command comes from. If the Beogram platter still drives in reverse then that will eliminate the microcomputer having a role in the problem.
Here is what happened after disconnecting the uP from the brake circuit (disconnecting 1R108):
In StBy mode after connecting deck to mains platter does not spin anti-colockwise, however deck does not power-off (servo light bulb still on)
and the platter motor still shows some very gentle stuttering clockwise !
after reconnecting R108 to the brake circuit checking voltage at P6-5:
in StBy mode P6-5 = 0.72V
in Play mode (after hand-brake, platter spinning clockwise) P6-5 = 4.95V.... back to STOP/StBy voltage drops to 0.72V
can we still exclude the uP from the problem ???
from memory: didn’t you check/question the voltages (transformer) at P7 in one of your posts or am I wrong here ?
I replaced 4C1 (39uF, 55V) as it showed 57uF !! with a 47uF 100V cap, which actually shows 42uF, close enough.
the original value is nowhere to be found 😕
If the emitter of TR33 gets AC current from P7-11 I should measure VAC at that point ?!
the same would then apply to its base and collector.....if so, how can I get basically the same readings at E, B and C ?
or am I sitting on my brain ?
ALF: Here is what happened after disconnecting the uP from the brake circuit (disconnecting 1R108): In StBy mode after connecting deck to mains platter does not spin anti-colockwise, however deck does not power-off (servo light bulb still on) and the platter motor still shows some very gentle stuttering clockwise ! after reconnecting R108 to the brake circuit checking voltage at P6-5: in StBy mode P6-5 = 0.72V in Play mode (after hand-brake, platter spinning clockwise) P6-5 = 4.95V.... back to STOP/StBy voltage drops to 0.72V can we still exclude the uP from the problem ??? from memory: didn’t you check/question the voltages (transformer) at P7 in one of your posts or am I wrong here ? I replaced 4C1 (39uF, 55V) as it showed 57uF !! with a 47uF 100V cap, which actually shows 42uF, close enough. the original value is nowhere to be found 😕 ALF
Interesting results. The voltage measurements here would be better if they were with an oscilloscope so we could see the phase of the AC voltages at P4-1 and P4-2. I am curious to look at one of my Beogram 800x units the chance I get (maybe in September). Several years ago I tried making some measurements of the Beogram 8002 transformer outputs but that was on my first Beogram 800x restoration and the results aren't useful here. Your 4C1 capacitor should be okay except I would have tried for a DC voltage rating closer to 55V. You made sure to use a non-polar capacitor, right?
I will try to replicate those with the scope....and YES, 4C1 is a non-polar cap where I tried to find a lower DC voltage rating !
lets see what the scope provides us with ?
The signals at P4-1 and P4-2 in StBy/Stop mode are in phase !
I tried to upload the scope picture but won’t allow as it does not have the right extension.....
i will try the digi camera and hope to upload this way....
Hi ALF,
The current will under go the phase change not the voltage so unless you have a current probe for your oscilloscope you won't be able to measure the phase change.
Regards
Lonnie
well, I do not have current probes for the scope
so this lousy shot with the digi camera shows the VAC signals in STBY/STOP mode at
P4-1 and P4-2 respectively:
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.
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.
sorry, but every little bit is as described
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
this is the second pic STBY/STOP mode
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 !
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.
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.
Yes, of course, John is absolutely right !...I should have known that....just brainless fishing for a cheap answer or desperation ? 🙄
i will take the measurements around/at TR6 and report back.
good luck with the daughter......’s TT I mean 😁
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?!
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
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.
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.
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 😴
TR6 is fine.
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.
So it sounds like this Beogram can go into a pseudo standby mode where the microcomputer thinks it is off, the standby LED is on but some things are actually still being powered - the servo light and the brake circuit. Maybe the microcomputer being in standby is causing it to ignore any platter rotation information coming in. The brake circuit is trying to brake without any feedback so it just keeps going and the platter is driven in reverse.
Check the ±15 V supply lines when the Beogram is in standby and when in play.
Hi John,
i checked all +15 V / -15 V points
STBY/STOP PLAY
TR19-C -17V Around -15V
P2 - 9 15 V 15V
TR15-E 15V 15V
P4-8/R46. 15V 15V
C8. 15V. 15V
TR30-C. 15V. 15V
TR29-C -17V. -16.5V
TR1/TR3-C. 15V. 15V
What about P3-4 ?
Sorry John, I missed that one:
P3-4: StBy/Play = 14.9V 😕
That is the power for the servo sensor lamp. That should be off when in Standby. Tonight I opened the little black lid in the tonearm compartment of the Beogram 8002 in my office. The servo lamp is off when the Beogram is in Standby mode (which is how you would think it should function). If I press Turn or Play the servo lamp comes on. Pressing Stop returns to Standby and the servo lamp goes off.
Some signal(s) in your Beogram have the microcomputer and logic confused where part of the Beogram is in Standby mode and other parts are not.
John
I really hate to see this Beogram is getting a power-off handswitch plus a handbrake job to start the play mode......
such a great TT when it works !!
almost beyond believe this should end up as a non-repairable unit ...... but what else can I possibly check ????
Finding broken tracks that even a microscope can not pick up ? Missing/faulty ground ?
These things do take time but now you know why the original symptoms you reported are that way they are. Lonnie had you in the right area earlier, the 1TR21 transistor On/Off switch. Check the paths it is supposed to turn off. Check the grounds of the related components. Recheck 1TR21 and measure the collector when the switch is supposed to be off. I think when you measured it a while back you said it was oscillating.
Well, it has been a most interesting journey so far 😳
and its time to thank everyone who participated with good advice and suggestions 🤗
I will dive back in that muddy water of brakes and power-off devices and report back 🙏
I think the (non)brake issue is a byproduct of the standby switch problem. To me it appears that the Beogram microcomputer detects the tonearm is back in the parked position (via the 0S1 switch). The microcomputer generates an "Off" command and instructs the display to show the Standby dot. As far as the microcomputer is concerned the Beogram is off. Meanwhile, the 1TR21 switch is not successful in executing the off command (either directly or due to some other component in the path).
That is my updated guess
Solving it will still be a tough task but check why the servo lamp still has power and trace that back to where it should have been turned off.
All sounds quite plausible 🙄
I revisited TR21 and its surroundings, checked all components in its path up to 0TR1 incl TR1 itself:
no adverse findings, all ground connections of TR21, 20 and 18 are fine.
No damaged tracks from TR21 up to 0TR1, verfied via ohm measurements.
what is the reference voltage going out from the uP pin38 for power ON/OFF ?
there is definitely a clean path from P6-4 to ghe base of TR21 ! So this transistor must receive the uP signal, provided it is the correct signal?!
I really develop an “ uneasy feel” towards the uP ?!?
As there are constant +15VDC on at 0TR1 the servo bulb can not be turned off.
yes John, you are sbsolutely right: tough task ☹️
Perhaos another option could be getting the uP box from a working deck, connect that and see what happens.....but this only if the uP is at fault??
What is the collector to emitter (ground in this case) voltage measurement on 1TR21 ?
I still think the microcomputer is doing its job. It correctly has the Beogram in standby mode when it is supposed to. Once it generates the "off" signal the transistor circuit is supposed to take care of shutting things down. If you had a spare microcomputer IC then I wouldn't be opposed to trying it but another thing you could try is removing 1TR21 and installing a manual switch (just temporarily) to test.
Also, when you check the grounds how are you doing that? Are you checking them against more than one ground elsewhere on the Beogram board?
ALF: Well, it has been a most interesting journey so far 😳 and its time to thank everyone who participated with good advice and suggestions 🤗 I will dive back in that muddy water of brakes and power-off devices and report back 🙏 ALF
Following, keep on going Alf
Collecting Vintage B&O is not a hobby, its a lifestyle.
Thanks Søren,
will do...at least for a while longer 😁
The C-E voltage on TR21 is not steady - in STBy between 1.6 to 1.9V, in PLAY 1.5 to 1.8V
as for the ground measurements I do ohm measurements to make sure no broken tracks.
TR18/20/21 share the same ground points, same measurements. i have not verified connections to other ground pads
not sure whether I quite follow that switch idea instead of having TR21 ?
Do you want to isolate TR21 from P6 pin4 (uP and TR21) and using a simple on/off switch between ground and D26/E of TR20 ??
As I said before, I cannot check an actual Beogram 800x unit right now. However, putting the Beogram 800x on/off circuit in Multisim I am able to run a simulation. What I get with the simulator circuit is around 0.6 VDC at 1TR21-C to ground when the Beogram is "On". That allows the +15 VDC voltage at the 0TR1 collector and -15 VDC at the 1TR19 collector.
When I switch the Beomaster "Off", the voltage at 1TR21-C to ground goes to about 50mVDC and the ±15 VDC supplies are almost 0 volts.
If my simulator circuit is correct then your results at 1TR21 are not good. When I get one of my Beogram 800x units back on the bench I will check these voltages with the simulator circuit. I think it is correct. Just for fun I removed 1TR21 in my simulation and replaced it with a switch that is open or ground. Using that I get the same result.
I know other people have asked before but are you sure you have the pinouts correctly mapped on your 1TR21 (BC547B) transistor?
For example if you had the TR21 base going to ground instead of the emitter then TR21 would behave as you are seeing it behave.