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Beogram 4000 solenoid rattling

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ALF
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ALF posted on Fri, Apr 14 2017 1:24 PM

hi all,

the other day I encountered an unusual problem with one of my Beogram 4000 table:

a rattling - or perhaps bettter juddering - solenoid, preventing the arm from lowering ?!!!

the table eventually switches itself off.

Beolover has a short video that demonstrates this issue:

 http://beolover.blogspot.com/2015/08/beogram-4000-arrives-from-uk-solenoid-oscillation.html

in his case it was a detached wire - not in my case !

could some of our BG4000 experts give me a clue what else might cause that problem ??

yes, I checked the SM, circuit diagram and fault flow chart but........???

thank you if you have an idea, suggestion etc

cheers

ALF

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sonavor
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ALF:

what is however interesting is the fact that the arm is now lowering way before the 30cm record mark,

meaning the carriage springs do not even get to the "nipple switches" plus the table starts with 45rpm and not 33rpm ??

I can manually change the speed to 33, no problem but it is not correct !

What I normally do in this case is test the turntable without the plate containing the contact springs for the "nipple switches". With those exposed I can operate them manually to verify they do what they are supposed to. If the switches can be operated manually then the problem is in the contact spring alignment. That alignment is tricky as you have to set the position on the slide as well as make sure the contact surface of all the springs are on the same plane. I had one not working due to one contact spring being very slightly higher (or lower) than the others. 

If manually operating the switches doesn't result in correct operation then you could have a faulty switch or some other electrical problem. For me the problem has always ended up being a mechanical position problem.

Regards,
John

 

sonavor
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Hi Alf,

You are referring to this diagram, right?

That diagram shows the name of an event across the top. An event is a user pressing a control button or a sensor caused signal.
The vertical part of the diagram is the signal name in the service manual and the pin I made the measurement on.
The voltages in the table cells are what I actually measured.
The Beogram 4000 #1 was the good working unit in that diagram. 

A lot of the logic signals have a logic low signal of around 0.5 VDC and a logic high of around 6 VDC. However, some signals are close to 2 VDC when active and 0.7 VDC when inactive.

If pressing the nipple switch is expected to cause an event to happen and it doesn't, then either the switch is bad (probably unlikely...though possible) or, more likely, there is another signal in the logic that is overriding the event.

On the diagram you can see there are some key signals, like DR and DS (plus a few others), that are constant during the operation. If those signals are in a different state than shown then they could be overriding some event you are expecting. Remember that in many cases it is a combination of the states of several signals that allow some event to happen ... as the AND/NAND gates of this diagram show.

Regards,
John

Dillen
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As I mentioned earlier, the voltage regulator circuit is a bit on the weak side, often resulting in vibrating solenoids, simply due to lack of power.
Adding a series "dim-bulb tester" doesn't really help this in any way.
Use a proper variac instead - I would recommend you get one with current monitoring.

Martin

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ALF
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ALF replied on Tue, Jun 6 2017 9:50 AM

thanks Martin,

I will look into that !

ALF

ALF
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ALF replied on Fri, Jun 16 2017 8:16 AM

Hi John,

i finally got around to check a few things further.

i focused on your  spreadsheet, looking at the measurements of your working BG4000 in the first 2 events

control panel ON,  sensor panel 25/30cm switch

this is where trouble showed up:

33 :  control panel ON. 1.95V instead of 0.48v........25/30cm switch 1.95V instead of 0.48V

Qo:  25/30cm switch. 0.8V instead of 6.3V

Q1:  25/30cm switch  6.0V instead of 0.2V

Wo : control panel ON  1.65V  instead of 6.3V

my question is: what is the message here ?

all nipple switches can be operated perfectly fine and make correct contact !

i did not get any reaction from pressing lower or raise arm when operating the control panel, therefore nothing to measure!

the solanoid simply gets no trigger and perhaps as you suggested that trigger impulse might get overwritten by one of the logic chips ??

yes, i did replace a number of transistors, replaced all caps on board 1 and 2  incl the power reservoir caps.

where from here ?👿

regards

ALF

 

 

sonavor
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Hi Alf,

Are you saying that if you manually press the 25/30cm switch that the event does show up on the control logic board?  Or do you never get a signal to lower the tonearm?

The Wo signal not being at 6V is a problem. It is a derived signal at 3IC7. On my Beogram 4000 Wo switches from two states: 6V and 0.5V.
If you are measuring 1.95V it sounds like you might have a power problem. The voltage at IC1 pin 5 to ground should normally be around 6V and momentarily go to 0.5V when it reacts to the event pulse for lowering the arm. 
Check the power pins of the ICs on the board (Pin 7) to ground and see what those voltages are doing. While you did get 6V for the Ǭ₁ signal, that signal has a pull-up to 6V so that is probably why it gets there.

With Wo in a limbo state your Ǭ₁ never goes low to allow the arm to lower.

regards,
John

ALF
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ALF replied on Sat, Jun 17 2017 7:46 AM

hi John,

thank you for your reply - very much appreciated.

I did check all ICs on the logic board - all show around 6.3V at Pin7 with the exception of IC9 where Pin7 has no visible connection to a 6V source, instead Pin 8 shows about 6.3V.

operating the 25/30 nipple switch manually causes a short voltage drop to about 0.55V at IC8 Pin10, the Wo signal however shows no reaction at IC1 Pin5

operating from the control panel the lower or raise function shows no reaction at all.

at the solenoide /coil  I get about 36V.

I remember we previously discussed the possibility of one of the FCH chips being faulty........but what else could cause the Wo not reacting ?

do I get the feeling here that the problem is not on the logic board but perhaps on the main board ?

another side issue is the speed adjustment of the carriage, which is odd to say the least, after replacing the old trimmers VR4 &6.

VR4 needs to be right down to not influence the ES signal - if set too high it will over-write the VR6 (return) and the carriage edges slowly forward ??

I can not imagine that this would be related to the original arm-lowering issue ??

regards

ALF

 

sonavor
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ALF:

operating the 25/30 nipple switch manually causes a short voltage drop to about 0.55V at IC8 Pin10, the Wo signal however shows no reaction at IC1 Pin5

operating from the control panel the lower or raise function shows no reaction at all.

regards

ALF

Hi Alf,

With the 25/30 cm switch operated manually and you seeing the pulse from the switch at 3IC8-10 then you at least know that the switch is working and the connection to the logic board input is there.

Now you can see what is going on with the logic board managing W0.  When you operate the 25/30 cm switch manually you should next verify it results in a low logic voltage to high logic voltage momentarily at 3IC7-3. That logic high pulse should be the last piece on those inputs to drive the output (3IC7-8) low momentarily. That is W0. From what you have reported so far, that appears to not be happening. So first verify the 25/30 cm pulse is getting to 3IC7-3 (I suspect it is). Then check 3IC7 pins 2, 4, 5 and 6 to see if (which) one is a logic low voltage. If one of those is a low logic state then 3IC7-8 will not be able to pulse low on the 25/30 cm signal.

Hopefully one of those other input signals will be exposed as the culprit and you can pursue it.

If you discover that 3IC8-1 doesn't follow its pin 10 input pulse (with an opposite state pulse) then you will need to check the path for the 17cm switch to make sure it isn't blocking. If 3IC8-8 is stuck in a low logic level state then it would block the 25/30 cm switch signal.

Regards,
John

ALF
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ALF replied on Sat, Jun 17 2017 8:40 AM

Thanks John,

will follow that up !

BTW: ignore the adjustment of slow forward etc. I looked at the FF and FR switch and the tongue does not always goes back to ground...very very tricky and hard so actually see - have to striaghten that out somehow.

with the rest I will report back - just allowing myself a break and a cup of tea 🍩

Cheers

ALF

ALF
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ALF replied on Sun, Jun 18 2017 11:28 AM

Hello John,

many thanks again for taking the time to support.....🤗

Checked 3IC7 pins as suggested.....pin4 and 6 were low - not sure where pin4 would have left me, pin6 pointed to the BS signal and 3 D1 !??

3IC8-pin1 and 10 were doing the right thing!

while checking 3D1&3 I must have slipped with the probe and the solenoid came to life....! Both diodes tested fine off board!

off to have another look at 3IC7,  took it out as it was on a socket and noticed that pin8 was bent......replaced that chip and for now

All seems fine again.

i have to get around to re-adjust the FF and FR contact springs though to reset the VR4&6 trimmer / voltages.

many many thanks again - you are truly an inspiration with loads of patience  .... let's have a big one 🥃

Will post some pics from the recap 

Talk again soon

ALF

 

 

ALF
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hi all,

just some pics of the recent re-cap work.....now completed !

Big thanks again to John of all his guidance through troubled waters :-)

enjoy

ALF

The Power Reservoir Caps - all new 


ALF
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the power supply board - all new caps incl a new D5 rectifier diode according to SM spec


ALF
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and of course the main board, fully recapped :-)


ALF
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ALF replied on Mon, Jun 19 2017 7:00 AM

off to the next job,

waiting in the wings is the re-adjustment of the voltage for the slow FF & FR....VR4&6

wish me luck !

ALF

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