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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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beo3000
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Not sure it's unusual I have come across it twice and have only 5 first time I think it was something to do with the switches on switch PCB on the arm I can't remember exactly (is the light on the arm lighting up?), the next time I don't have an image to hand but you should see a bear copper wire going close to the dampened arm lower mech it had bent down a little and was shorting I added some heat shrink to avoid further problems in the future Good luck 

Dillen
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Dillen replied on Fri, Apr 14 2017 1:49 PM

Badly adjusted contacts
Heavily oxidated contacts
Broken wires.
Bad power resistor
Weak voltage regulator circuit.
Any combination of the above.

Martin

ALF
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ALF replied on Sat, Apr 15 2017 11:49 AM

Hi Martin,

thanks for the pointers.

would you care to be a bit more specific ? Which voltage regulator circuit and power resistor am I looking at in particular ?

I did check the wiring- so far nothing suspicious has been discovered as well as the muting and current limiter contacts.

that would leave the spring-leave contacts of the control board and the nipple-switch contacts the get activated by the carriage moving over them....

or do I see that the wrong way ?

thanks - ALF

 

ALF
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ALF replied on Sat, Apr 15 2017 11:49 AM

Hi Martin,

thanks for the pointers.

would you care to be a bit more specific ? Which voltage regulator circuit and power resistor am I looking at in particular ?

I did check the wiring- so far nothing suspicious has been discovered as well as the muting and current limiter contacts.

that would leave the spring-leave contacts of the control board and the nipple-switch contacts the get activated by the carriage moving over them....

or do I see that the wrong way ?

thanks - ALF

 

Dillen
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Dillen replied on Sat, Apr 15 2017 11:56 AM

ALF:

would you care to be a bit more specific ? Which voltage regulator circuit and power resistor am I looking at in particular ?

There's only one of each with relation to the soleniod circuit.

Martin

ALF
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ALF replied on Thu, May 25 2017 12:52 PM

Power resistor - I assume it is the 1W 8.2ohm resistor - is fine!

all brass contacts and springs have been clean-sanded, they work as they should!

current limiter contact has been adjusted and the Tip41A has been replaced.

the rattling seem to have disappeared 😁

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 !

looking at the fault finding chart I get to " is SI missing low IMP " can someone please explain the meaning ?

IMP=impluse ?

SI missing = 0V ?

thank you for clarifying that for me

ALF

chartz
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chartz replied on Thu, May 25 2017 2:58 PM
Hi,

I had the rattle at some point too. Same symptoms, different cure. There was a bad contact and I had to replace a brass blade to restore normal operation. Can't find the post or the photos, sorry. Sad

This is Rudy's picture. One of those anyway, the upper one perhaps.

Jacques

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

 

ALF
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ALF replied on Sun, Jun 4 2017 1:13 PM

What happened in the meantime:

I took out the nipple-switches carrying PCB and again - only this time perhaps more throrough - cleaned all brass parts underneath.

the same procedure I did with the control panel switches......very fiddly indeed.

the platter now starts spinning at '33', the carriage moves now right accross with arm raised all the way and returns to its resting position

after ES has been activated.

I would expect that in case there's no record on the platter but not with a record present ?!

in other words, i can not lower the arm nor does the carriage stop at the 30cm mark when a record is present ?

so far I got through the first 7 steps of the fault flow chart......but having replaced OTR4, TR10 and TR11 already,  it is getting "dark" in relation

to the non-lowering arm/non functioning solanoid.

the pcb1 and pcb 2 received a full recap job and 2D5 had been changed to what is actually listed in the parts list of the SM.

One of the things still is not quite clear is "is SI missing low IMP" ??

i will keep digging !

cheers

ALF

ALF
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ALF replied on Sun, Jun 4 2017 1:21 PM

It is important to add:

when the arm was lowering way before the 30cm mark the DBT lit up the moment the solanoid had been activated 

and the table switched off !

that included a chattering solanoid !

sometimes after several tries it would eventually lower the arm...but let's not dwell any longer on that !

it is now performing as described in my previous post, only a correct  carriage stop and arm lowering

Has not yet been achieved.

ALF

ALF
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ALF replied on Tue, Jun 6 2017 3:04 AM

Hi John,

based on your great posts on the BG4000 and the most interesting exchange we had I did go back to an old conversation we had about

another one of my BG4000 tables:

i again studied your fantasticly colour modified logic board, showing various voltages etc.

i also followed various branches of the SM fault- flow chart.

what is still not quite clear is the definition of Low and High at different in or outputs signals ?

you once stated the "logical high" as being about 6V and the "logical low" as being around 0V ? In oposition to the latter

you also stated that ES, DS and OFF needed to be not lower than 0.5V for Q1 to .......do you get my drift ? There seems to be a "grey area" of what is

considered high or low - i am referring to the fault flow chart ! It obviously determines which branch to follow and what fix to implement.

as you explained, that combination of electric and mechanical switching can be tricky - yes, indeed.

I followed your suggestion in operating those nipple switches manually......pressing the 25/30 or 17 nipple has no impact, but I can see

Both make contact - ES and OFF work fine.

following different branches of the fault flow chart led to replacements of 1TR12, 13, 20 & 21 as well as 3IC7 & 3IC4 and3C1.

if I could perhaps get a better understanding of those low or high voltages it could lead me to the correct fault chart branch ??

i do value your reply very much 🤗

cheers

ALF

 

 

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

ALF
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ALF replied on Tue, Jun 6 2017 9:49 AM

hi John,

thank you for replying - no, I actually thought about that diagram on the bottom half of your 2nd link !

however, the cause of action I will follow now is trying to basically replicate your top-half spreadsheet from your 1st link

and see what voltages I can measure and take it from there.

that should hopefully present a much clearer picture for me.

So, give me some time to do my "homework".

cheers

ALF

 

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