Beogram4000 behaving erratically

[alf]

Hi All,

this one is going to be a bit tricky to explain: the erratic behaviour of my BG4000.

So far I have observed the following issues:

activate ON, the arm moves in one cm or two, stops and nothing else is happening ?

activate ON, the arm moves in about the same distance and lowers way before the dropdown point.

activate ON, the arm moves to to dropdown point, stops but nothing else. I I “finger-activate” the solenoid everything works on as normal.

activate ON, everything works normal as it should…and that can go on like this for half a dozen records without a glitch and then out of the blue is playing up again ???

in all those scenarios the main platter spins.

i am sorry, but I can not find any meaningful  explanation for that behaviour or simply put don’t know where to start.

those brass contacts which may potentially be the source have been cleaned multiple times.

Perhaps one of you guys can make sense out of this – I would be very grateful indeed.

ALF

 

[hcraig244]

Alf

When you say you have cleaned the “those brass contacts” are you talking about the carriage transport switches?

I have had similar strange behaviour on a BG4000 deck that was eating my lunch for days….intermittent faults. Finally traced it to the transport switches (one in particular) and it turned out that the actuating plastic nipple that operated the brass leaf switch was sticking every so often….I had thought i would lubricate these switches with silicone grease to keep them moving freely…..mistake! cleaned all the lubrication off them and everything was fine…..just a thought.

[alf]

That is a interesting point – I actually used silicone spray for those plastic nipples not just at the carriage switches but on the keyboard switches as well….but I never had that trouble with other Bg4000 tables ??!

ALF

[chartz]

I’d say an erratic bulb perhaps? When it’s on its way out the deck will have the strangest behaviours…

[alf]

Well, two ways to interprete:

on its way out = about to die

on its way out (in) = approaching the drop down point, drop and play a record.

just today I played about 6 or 7 record sides in succession over the course of the day

and the BG hasn’t missed a beat…….?!

which means precisely nothing as it is just as likely to fail at the 8th records.

that is exactly the issue here.

of course I can keep taking transistors off the board and checking, cleaning switches but i do not believe that will cure it. Simply put: some component isn’t playing ball !

all I wish for is a consistent fault.

ALF

[solderon29]

Is it a silly question,but is the carriage drive belt in good condition?

Silicon anywhere near those switch contacts is bad new’s too!

Nick

[alf]

No silly Q at all Nick, yes the servo belt is fine. I am just questioning the mentioned issues caused by silicon spray ??

i have never observed any issues with it like sticking on plastics etc.?? What I will do is getting all the plastic nipples out and wash them including their holders.

the reason I am sceptic is the BG works fine for a number of records and then all of a sudden something is happening and I wish I’d know what ?

ALF

[hcraig244]

It may well be something entirely different, however it only takes one switch to be out of step to create havoc with the logic controls. I do suspect the old timer design engineers decided to create the most complicated deck ever built, integrating complicated logic gates simply because they could…..logic gates that are still in lots of modern day control systems (albeit in sotware format these days)…bear in mind the only thing that opens the switch is the quite light pressure of the leaf spring contact….take a look i nothing else other than to eliminate them from your enquiries

[solderon29]

This type of problem is of course tricky to trace as it’s so intermittant,but I suspect a power supply problem.

Have you refurbished the machine Klaus?

Those reed switches that route the supplies,can cause all sorts of problems.The 6 volt regulator is a known troublemaker too.

If you can connect a meter,then when the problem occur’s again,check if anything is missing?

Could temperature have some bearing?Do you leave the machine in standby,or disconnect when not using?

Freezer spray might provoke the gremlin?Try around the power supply board.

Nick

[hcraig244]

Martin recommends moving the voltage regulator 2TR6 from the 2 PCB and mounting it away due to heat issues…..I cant recall exactly but I have a feel ing the logic switches state around 0.5 to 2.5vdc and its the IC that supplies the power to “wet” the switch contacts I have a feeling that it all goes tits up if you dont have 4vdc min……

[alf]

Hi Nick,

thank you for replying. The BG is plugged into mains constantly. The main board has been recapped as far as I remember but will double check. Most morning I just activate play and it works but as said: most times, not all the time.

I got some reed switches and may consider replacing the existing ones if that indeed could cause those issues.

just drives me mad, every time I put the alu decking back on it is playing up….meaning

the BG has its “bonnet” open at all times for now.

i shall report back once I found something fishy. The last post quoted Martin, having suggested to move the voltage regulator (2TR6)  from board 2 because of heat issues?!

ALF

[hcraig244]

Yes…..Martin recommends doing this as the transistor does run quite hot, I did this on one of my units that I was having an issue with, didnt solve the problem as that turned out to be a contact issue as previously discussed

[alf]

Many thanks for the picture – I will do that.

the unit’s most prominent issue seem to be that the carriage is moving in after ON is activated, stops at the drop down point but nothing is happening.

in that case I can “finger-operate” the solenoid and everything is fine. The lowering can’t be blocked as the solenoid would otherwise not click in.
Does that mean the 24VDC is not getting to the solenoid when the automatic lowering (drop down) should occur ?

ALF

[hcraig244]

Couple of things here….firstly take out OTR4 and check it, if this is good you need to look at the power limiting part of the circuit….the set of contacts (those leaf spring contacts again) that need to be closed, thus shorting 7R1 to ground,  when the solenoid is initially activated allowing max current to pull in the solenoid coil before opening up when the armature moves to drop the tone arm…..its possible you dont have a good connection at these contacts..

Craig

[alf]

I will have another check at those set of contacts (as I have done before).

the BC119 transistor is on order, heatsink I got – that should not be too hard, only takes time until it arrives.

fairly confident the 0TR4 = Tip41 is ok. I had another good run, basically no problems

until the sequence came to an end with the carriage moving in, stops -as described- but no lowering…..

ALF

[alf]

Ok,

transistor 2TR6 has been relocated as recommended. Sorry, I would have posted a picture but I do not have the appropriate photo software compatible with this forum.

my ipad takes excellent photos but they are all too big for uploading.

The erratic issue seemed to have been related to the switch next to the solenoid.

as mentioned, the contact must have been insufficient between the pin and the leaf spring (closest to the spindle) so I adjusted the pin.

so far the Beogram hasn’t missed a beat and I begin to feel cautiously optimistic it may have fixed the erratic behaviour ???

ALF

 

 

[chartz]

Good!

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