I can't look at the service manuals now to see how the voltage / fuse ratings go, but could this be a possible problem?

Martin,

 

I am merely an enthusiast not a technician; however a friend who gives me pointers and is aware of your efforts to help me has suggested the following:

 

“I was puzzled by the tonearm action at the mid point of the record.  This midpoint is close to where a 45 rpm 7 inch record would be and that position is represented by a pattern on the strip in 4002's at least designating where the tonearm would drop for the smaller record.  That strikes me as a logic problem of sorts as unlike the 8000; there is no circuitry or logic that counts the rotation of the servomotor to adjust the position of the tonearm, so the pattern would seem to make a difference.  Perhaps at look at the transistors at this pattern sequencing or recognition.” 

 

This friend is in California and has never seen a Beogram 4000, but he repairs 4002’s, 4004’s, and 8000’s as a hobby.

 

I have NO idea if what he mentions has any merit in regard to a BG 4000, but I put it forward simply as a possibility.

 

Mika, I and fairly certain that the 250ma 250v fuse is the correct one.

 

Jeff

 

Martin,

 

Has your “thinking cap” produced any new insights? I sure hope so as this sad non-functioning Beogram 4000 really needs your help!

 

Thanks.

 

Jeff

It's one of the cases that I'd wish I had here. If I had room and time that is. I've had a rush-in of repairs the last couple of days/weeks. Currently no less than 8 tangentials are in for repairs; 4002, 4004, 6006 etc. but none of them 4000's so I have no way of comparing measurements.

There's a couple of different things you can try to (maybe) further circle in the problem.

Is the problem related to an amount of time powered on or a specific event (arm lowering, tracking etc.) ? This would indicate either a general overload problem (power supply) or a problem related to a specific function.

Try the Beogram without a record and see what happens. You can also try to move the arms a bit using the arrows right after start and let it hover above the platter (or record) for a couple of minutes to see if that makes the fuse blow.

Martin

Martin,

 

The first time the fuse blew the Beogram 4000 was playing a record and was at the mid-way point. Everything just stopped and the arm lifted off the record.

 

With the fuse replaced, I can press play the 4000 functions normally, the arm moves to the correct position over the record and begins to drop, but that is as far as it gets. Once the tonearm begins to drop there is a VERY strange drift to the right and the fuse blows. It all happens in a few seconds.

 

The previous owner reported have a fuse issue that eventually forced him to sell the 4000 to me, after the problem was ostensibly repaired. I can only imagine that it was as I had 10 months of regular service from this 4000 before this issue occurred.

 

I tried your suggestion of playing the 4000 without a record and the 4000 went to the correct play position and dropped the arm in spite of the fact that there was no record. Then the arm did the previously mentioned drift to the right, and the fuse blew.

 

However, this maybe noteworthy, in the past three attempts to use this 4000 it was always been the right fuse to blow. This time the left fuse blew. Does this tell you anything, so are things just getting worse?

 

Jeff

Martin,

 

Correction, I was mistaken. In my haste I forgot to install the belt. With the belt in place the turntable plays indefinitely without blowing its fuse. Left and right functions work properly…. everything works properly so long as there is no record and the arm does not drop.

 

Please forgive this stupid error.

 

Jeff

Addendum: I have left this Beogram 4000 rotating its platter for well over an hour, with no problem. Turning the turntable on and off repeatedly raises no issues. The left and right controls are now working correctly, with their contacts recently cleaned. The only thing I note that is amiss is that the 4000 does not change speed to 45 rpm’s at the appropriate spot (7”). It will do so manually, but at the 7” mark it should do so automatically, but it doesn’t.

 

I thought this had potential to be relevant.

 

Jeff

Check the contact activated by the lift/lower solenoid. It has a function to switch the solenoid current from a strong "Activate" when the arm is to be lowered to a milder "Hold"  to merely hold it down. It's on the left side of the tonearm carriage.

Martin

Hi Martin,

I know where the problem lies but not how to fix it.

I had found that the arm driveshaft was bent and straightened it as per Derek’s suggestion. The shaft is now perfectly straight.

However something I did in removing it for repair has disturbed something alignment-wise and now the arm switch comes perilously close to the driveshaft, perhaps even touching it. I tried adjusting the driveshaft angle but that didn’t seem to help.

The whole driveshaft assembly is quite loose and moves about, but I see no place to tighten anything.

I thought that just maybe I had everything just right and fried fuse number 4, pressed ON, the 4000 sprang to life, the platter turned and the tonearm went into position, dropped to the record and began to play. I sensed victory, but then the fuse blew.

I have no doubt that the BG 4000 will continue to rotate the platter and the arms can go back and forth with no problem, but I can not have the arm drop or the fuse immediately fails.

As such I don’t believe that this is a motherboard problem at all, but something electro-mechanical in regard to the arm.

I found nothing wrong with anything associated with the arm.

I don’t know exactly what to look for in regard to the solenoid, but everything there looks fine.

Befogged as ever.

Jeff

Martin,

A learned friend as suggested the following and I put to forward simply becuase I do not know what to do next:

"The design of these tangent tables include safety engineering with the pickup arm lift/setdown function. The safety issue is that if there is a line voltage interruption the pickup will be immediately raised off the play surface. Thus the design calls for the opposite of what might be suspected in the use of the pickup solenoid. The solenoid is ENERGIZED during the setdown function and remains so throughout the entire play function so power failure will raise the pickup. My first suspicion is that you have a solenoid drawing too much current. All it would take is a mere two turns of the windings touching one another to create an opposing EMF showing the power supply a short. I would check for a failing solenoid and/or associated boost capacitors, (some of those large jobs lying in the chassis bay). Any or all those suspects if faulty will cause an excess surge in current draw and pop the fuse."

If it is a failing solenoid or boost capacitors, how do I check for them?

Jeff

Yes, a too high current will disturb the system but the Beogram is nowhere near as intelligent as your friend suggests. It's correct that the arm is raised if the power fails as a safety precaution but the electronics don't take reverse EMF into account.

Check the switch contacts, check that it actually drops the current to the solenoid when the tonearm has lowered. You can put an amperemeter in series with the solenoid if you want to watch the current flow. Your Fluke will have a 2A or even 20A range.

Of course no contacts, solder lugs or whatever is allowed to touch the threaded spindle, the underside of the platter or anything else.

Martin

Hi Martin,

 

You have already dedicated a good deal of time to my problem, for which I am most appreciative.

 

However, could you possibly be a bit more specific in regard to your instructions, “Check the switch contacts, check that it actually drops the current to the solenoid when the tonearm has lowered.”

 

I am sorry, but being quiet new to the world of B&O repair, I don’t quite understand what I am checking for.

 

Thank you Martin for your patience with my lengthy learning curve.

 

Jeff

Hi Jeff,

No problem. Servicing "per remote" is always a challenge. 

Don't mind the red circle, check the switch in the green circle. You can see that it is activated by an arm running from the solenoid. This switch is activated when the tonearm solenoid has completed it's travel to change the solenoid current from a fairly high current (in order to activate things) to a much lower current (to simply hold it there). If this switch is bent, missing or otherwise disabled, the current is always at max. This will eventually blow the fuse and/or destroy the solenoid (sadly a very common fault).

Martin

Thank you Martin, I think I have it.

 

The switch in question, in green, is not missing, and I don’t remember it being bent in any particular way. I will, however, verify this carefully.

 

One way or the other, the problem HAS to be something to do with this solenoid or its associated switches because as long as the Beogram 4000 is not permitted to drop the tonearm, it functions normally.

 

I turned the 4000 on and off repeatedly in fairly quick succession with no problem whatsoever. Ditto moving the arms left and right again and again. No problems.

 

However, within seconds of the tonearm dropping to the record, the fuse blows.

 

I can well imagine the difficulty and frustration in attempting to repair one of these turntables remotely. You must have the patience of Job.

 

I will report back when I have properly checked the switch in the green indicated circle.

 

Thank you, as always, for all the help!

 

Jeff

Hi Martin,

 

The switch that you had circled in green engages first then the other two switches are activated in a delayed fashion. As such, it appears to me that all switches are working properly.

 

I managed to get the arm to drop repeatedly in order to check the switches, carefully raising the arm within a second or so and the fuse did not blow. On the one attempt that I was a bit slow in my reaction, the flue did blow.

 

If you agree, I assume the problem would appear to be the solenoid and if this is the case, can you sell me a proper replacement?

 

Jeff

Hi Jeff,

Yes, we are definitely closing in now. The solenoid could be the problem but it could also still be an electronic fault so that the switching to a lower current doesn't take place. Only a measurement of the solenoid current will answer this.

Currently I don't have any solenoids for the BG4000.

Martin

Martin,

 

I hope that you will forgive yet another question, but how do I measure the solenoid current?

 

Jeff

Unsolder one lead off the ones coming from the solenoid and put your amperemeter in between, one pin to the solenoid lead that is now not connected to anything and the other lead to the point where it was connected. In series with the solenoid.

Martin

Hi Martin,

Will do.

What sort of numbers do you expect from this test, that is what would be normal and what would be out of range, or a definite sige of a problem?

Jeff

Hi Martin,

The results are in.

With the lead disconnected and the multimeter in place I got a reading of -.34 amps. A second test had a reading of -.33 amps. After each test within a second or two the fuse blew.

Is this the result you were looking for?

Assuming that I need a replacement solenoid, could you kindly supply the part number? I have searched the Service Manual cover to cover, twice, and I can not find it. Every other part in the 4000, but not the solenoid.

Thanks!

Jeff

Yes, that's a bit high. It does match with what I'd expect for the "engage" current though but should switch to a lower current when the solenoid arm activates the switch. I think I would concentrate on this circuit first rather than the solenoid itself. The switch is a break type, normally closed, opened when hit by the arm. It shorts a resistor at the emitter of the solenoid driver transistor.

Please do two voltage checks across the switch poles. One while the tonearm is lowered (should be 0 volts), the other when the tonearm is fully lowered (should be a couple of volts or so).

One more thing you can try is to solder off one of the wires to the switch, maybe you need to help the solenoid engage the mechs initially but it should hold fine by itself afterwards and the fuse should stop blowing. If you get this result, the solenoid is probably fine.

The solenoid part number is 6810001 reading from the schematics but check the other things first.

Martin

Martin,

 

Thank you for all the information.

 

However, there is a problem. The tonearm only once made it to the record before the fuse blew out of 6 tests. Thus I can not test the voltage after the tonearm is fully down because it doesn’t make it that far before blowing the fuse.

 

I can test the voltage at the switch to see if it is at 0 as you mentioned, but I can not test beyond that.

 

Also a note of curiosity, one of the two switches (circled in red in your photo) has no wires going to it, so I don’t see how it can effect anything.

 

Jeff

The other switches are controlling other things (starts the tracking system and unmutes the signal). The switch of our interest is the one on the green circle.

Did you try soldering off one of the switch's leads ?

Martin

Martin,

 

Sorry for the confusion with the multiple switches.

 

No I did not try soldering off one of the switch leads, but I most certainly will if this is what you want me to do.

 

However, I thought the purpose of the switch was to lower the voltage once the tonearm reached the record. As such wouldn’t defeating the switch guarantee the fuse would blow?

 

Anyway, if you want me to solder off one of the switch leads than that is what I will try next. My above question was just to make sure that I understand you correctly.

 

Jeff

Normally, it would. 

The switch is a break-type. It's normally closed (switched on) to bypass a resistor. When the solenoid arm activates it, it breaks it's connection (switches off).

Soldering off one of its leads will force all current through the resistor and thereby lower the current at all times.

The voltage readings I also suggested will provide more info.

Martin